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Cited by 280Protein Degradation and InhibitorsTelomeres, Telomerase, and SenescenceCell death mechanisms and regulation

Using proteolysis-targeting chimera technology to reduce navitoclax platelet toxicity and improve its senolytic activity

Open access
He, Yonghan, Zhang, Xuan, Chang, Jianhui, Kim, Ha-Neui, Zhang, Peiyi, Wang, Yingying, Khan, Sajid, Liu, Xingui +14 more·2020·Nature Communications
DOI 10.1038/s41467-020-15838-0PMC PMC7181703
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Abstract

Small molecules that selectively kill senescent cells (SCs), termed senolytics, have the potential to prevent and treat various age-related diseases and extend healthspan. The use of Bcl-xl inhibitors as senolytics is largely limited by their on-target and dose-limiting platelet toxicity. Here, we report the use of proteolysis-targeting chimera (PROTAC) technology to reduce the platelet toxicity of navitoclax (also known as ABT263), a Bcl-2 and Bcl-xl dual inhibitor, by converting it into PZ15227 (PZ), a Bcl-xl PROTAC, which targets Bcl-xl to the cereblon (CRBN) E3 ligase for degradation. Compared to ABT263, PZ is less toxic to platelets, but equally or slightly more potent against SCs because CRBN is poorly expressed in platelets. PZ effectively clears SCs and rejuvenates tissue stem and progenitor cells in naturally aged mice without causing severe thrombocytopenia. With further improvement, Bcl-xl PROTACs have the potential to become safer and more potent senolytic agents than Bcl-xl inhibitors.

AI snapshot

Written from the paper’s full text.

TL;DR

Converting navitoclax (ABT263) into the Bcl-xl PROTAC PZ15227 (PZ) reduced platelet toxicity while preserving or slightly improving senolytic activity in vitro and in aged mice. PZ cleared senescent cells and improved tissue stem/progenitor function without causing severe thrombocytopenia.

Key findings

  • PZ selectively degraded Bcl-xl via CRBN and the proteasome, with DC50 = 46 nM and Dmax = 96.2% in WI38 non-senescent cells; it did not significantly degrade Bcl-2 or Bcl-w, and its effects were blocked by CRBN knockout, MG132, excess ABT263/pomalidomide, or the inactive analog Bcl-xl-NP.
  • PZ was less toxic to platelets but equally or slightly more potent against senescent cells: it had minimal effect on platelet viability even at 3 µM and produced a more than 37-fold increase in platelet toxicity index (EC50-PTLs/EC50-IR-SCs) versus ABT263; improved senolytic activity was seen in IR-SCs, RE-SCs, REC, and PAC, but not in Ras-SCs or IMR90 IR-SCs.
  • In naturally aged mice, IP PZ at 41 μmol/kg every 3 days for 7 injections reduced splenic Cdkn2a, Cdkn1a, Il6, Cxcl12, Mmp3, and Tnfsf11 mRNA and reduced Cdkn2a in liver, lung, kidney, and fat; it caused less severe thrombocytopenia than ABT263 and improved osteoprogenitor mineralization, reduced adipogenesis, decreased osteoclastogenesis, attenuated myeloid skewing, reduced SA-β-gal+ LSK cells, and increased HSC clonogenicity.
  • PZ has high molecular weight (1484.13 vs. 974.61 for ABT263), low aqueous solubility, favorable PK by IP or IV but not oral administration, and stability in plasma and liver microsomal assays.

Methods

  • In vitro studies used human WI38, IMR90, REC, and PAC cells; senescence was induced by ionizing radiation, extensive replication, or ectopic Ras. Assays included western blotting, flow-cytometry viability, platelet isolation/viability, AlphaLISA binding, apoptosis analysis, CRISPR/Cas9 CRBN knockout, qPCR, and ubiquitination assays.
  • In vivo studies used naturally aged 20-month-old p16-3MR mice randomized to vehicle, ABT263 (41 μmol/kg or 40 mg/kg, q3d, 7 injections), or PZ (41 μmol/kg or 61 mg/kg, q3d, 7 injections), plus total-body-irradiated mice. Outcomes included blood platelet counts/CBCs, qPCR for senescence/SASP markers, SA-β-gal staining, BM stromal differentiation assays, flow cytometry, HSC colony-forming assays, and competitive repopulation.
  • Statistical analyses used GraphPad Prism 7: two-tailed Student’s t-test, one-way ANOVA with Tukey’s or Dunnett’s post-hoc tests, Kruskal–Wallis with Dunn’s post-hoc test, and two-way ANOVA with Tukey’s post-hoc test for Fig. 2h–j; P < 0.05 was significant.

Limitations

  • The paper states that PZ is unlikely to be totally devoid of platelet toxicity because it retains high Bcl-xl binding affinity (Ki = 1.90 nM for PZ vs. 1.53 nM for ABT263), and that it is highly lipophilic, has high molecular weight and low aqueous solubility, lacks oral bioavailability, and will require formulation/modification; senolytic effectiveness also appears tissue-dependent, and further linker/linkage optimization or use of another E3 ligase such as VHL may be needed.
  • Evident from the text: all findings are preclinical (cell culture and mouse models), with no human clinical data; some in vitro experiments were repeated in only two independent experiments, and aged-mouse groups were small (n = 6–8 per group), limiting generalizability and precision.

Model-written summary. Check it against the paper before relying on it.

Integrity signals

Registry

Crossref · 10.1038/s41467-020-15838-0

Cites

51 of 51 references verified0 citation errors · 0 not checkable

Statistics

Nothing to recompute.

Claims the paper makes

0 of 106 cited sources checked · 0 supported · 0 flagged

  • Findingown data

    PZ has no effect on the levels of Bcl-xl in human platelets.

    “More importantly, PZ had similar potency in degrading Bcl-xl in WI38 SCs induced by ionizing radiation (IR-SCs) (Fig. 1f, left panel) as in WI38 NCs (Fig. 1c), but had no effect on the levels of Bcl-xl in human platelets (Fig. 1f, middle panel).”
    Quote in the paperSubstantial claim
  • Findingown data

    PZ has significantly reduced binding to Bcl-2 and Bcl-w.

    “However, it had no significant effect on Bcl-2 and Bcl-w protein levels, probably due to a significantly reduced binding to Bcl-2 and Bcl-w (Fig. 1c and Supplementary Fig. 1a, c, d); nor did it affect the expression of Bcl2l1 (Bcl-xl) mRNA in WI38 NCs (Supplementary Fig. 1e).”
    Quote in the paperSubstantial claim
  • Findingreasoning

    Compared to ABT263, PZ is equally or slightly more potent against senescent cells.

    “Compared to ABT263, PZ is less toxic to platelets, but equally or slightly more potent against SCs because CRBN is poorly expressed in platelets.”
    Quote in the paperSubstantial claim
  • Findingnone given

    PZ15227 (PZ) is a Bcl-xl PROTAC that targets Bcl-xl to the cereblon (CRBN) E3 ligase for degradation.

    “Here, we report the use of proteolysis-targeting chimera (PROTAC) technology to reduce the platelet toxicity of navitoclax (also known as ABT263), a Bcl-2 and Bcl-xl dual inhibitor, by converting it into PZ15227 (PZ), a Bcl-xl PROTAC, which targets Bcl-xl to the cereblon (CRBN) E3 ligase for degradation.”
    Quote in the paperSubstantial claim
  • Findingown data

    PZ potently induces Bcl-xl degradation in WI38 non-senescent cells with DC50 at 46 nM and Dmax of 96.2%.

    “Among these Bcl-xl-Ps, PZ was selected as a lead for further evaluation because it has high Bcl-xl binding affinity (Supplementary Fig. 1a) and could potently induce Bcl-xl degradation in WI38 non-senescent cells (NCs) with the half-maximal degradation concentration (DC50) at 46 nM and maximum degradation (Dmax) of 96.2% (Fig. 1c and Supplementary Fig. 1b).”
    Quote in the paperSubstantial claim
  • May combine two claims. 45
  • Classified as probably not a substantial claim. 19

  • May combine two claims.

    Findingown data

    PZ-induced Bcl-xl degradation is rapid and long lasting.

    “The induction of Bcl-xl degradation by PZ was rapid (Fig. 1d) and long lasting (Fig. 1e).”
    Quote in the paperNot a substantial claim

  • May combine two claims.

    Findingown data

    PZ selectively induces Bcl-xl but not Bcl-2 poly-ubiquitination.

    “This is further supported by the observations that PZ could selectively induce Bcl-xl but not Bcl-2 poly-ubiquitination and had no significant effect on the expression of the CRBN native substrate, glutamine synthetase (GS)36, and its neosubstrates recruited by thalidomide and its analogues including CK1α37, IKZF1, and IKZF3 (ref. 38) (Supplementary Fig. 1 f, g).”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Findingreasoning

    PZ effectively clears senescent cells and rejuvenates tissue stem and progenitor cells in naturally aged mice without causing severe thrombocytopenia.

    “PZ effectively clears SCs and rejuvenates tissue stem and progenitor cells in naturally aged mice without causing severe thrombocytopenia.”
    Quote in the paperSubstantial claim

  • Probably not a substantial claim: may not pass S4 (based).

    Findingnone given

    CRBN is poorly expressed in platelets.

    “because CRBN is poorly expressed in platelets.”
    Quote in the paperNot a substantial claim

  • May combine two claims.

    Findingown data

    PZ is more potent against IR-SCs but less toxic to WI38 non-senescent cells and human platelets than ABT263.

    “PZ is more potent against IR-SCs but less toxic to WI38 non-senescent cells (NCs) and human PLTs than ABT263.”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Findingcitation

    PZ is a Bcl-xl specific PROTAC that targets Bcl-xl to the E3 ligase cereblon (CRBN), which is poorly expressed in platelets.

    “Here, we report the use of PROTAC technology to reduce ABT263 on-target toxicity by converting ABT263 into PZ15227 (PZ), a Bcl-xl specific PROTAC (Bcl-xl-P), which targets Bcl-xl to the E3 ligase cereblon (CRBN) that is poorly expressed in platelets34,35.”
    Quote in the paperSubstantial claim0 of 2 sources checked
    • cites [34] Bray, P. F. et al. The complex transcriptional landscape of the anucleate human platelet. BMC Genomics 14, 1 (2013). source

      Not checked in the free run.

    • cites [35] Kissopoulou, A., Jonasson, J., Lindahl, T. L. & Osman, A. Next generation sequencing analysis of human platelet PolyA+ mRNAs and rRNA-depleted total RNA. PLoS ONE 8, e81809 (2013). source

      Not checked in the free run.

  • May combine two claims.

    Findingown data

    PZ is less toxic to platelets but equally or slightly more potent against senescent cells compared with ABT263.

    “We find that PZ is less toxic to platelets but equally or slightly more potent against SCs compared with ABT263.”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Findingown data

    Severe thrombocytopenia induced by ABT263 was also observed 1 day after the 7th injection of ABT263, whereas mice that received seven injections of PZ had just a mild reduction in blood platelet counts compared with vehicle-treated mice.

    “Moreover, the severe thrombocytopenia induced by ABT263 was also observed 1 day after they received the 7th injection of ABT263, whereas the mice that received seven injections of PZ had just a mild reduction in blood platelet counts compared with vehicle-treated mice (Fig. 3d and Supplementary Table 1).”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Findingown data

    Both PZ and ABT263 treatment decreased the osteoclastogenic potential of BM macrophages derived from BM myeloid cells.

    “In addition, both PZ and ABT263 treatment decreased the osteoclastogenic potential of BM macrophages derived from BM myeloid cells (Fig. 4l, m).”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Findingown data

    PZ has favorable pharmacokinetic properties and bioavailability by intraperitoneal injection or intravenous injection, but not by oral administration.

    “Moreover, PZ has shown favorable pharmacokinetic (PK) properties and bioavailability by intraperitoneal injection (IP) or intravenous (IV) injection, but not by oral administration (PO) (Supplementary Fig. 6b, c).”
    Quote in the paperNot a substantial claim

  • May combine two claims.

    Findingown data

    Pomalidomide alone was not cytotoxic to WI38 non-senescent cells or IR-SCs, nor did it have any additive or synergistic effect on WI38 IR-SC viability when combined with ABT263.

    “In addition, the senolytic activity of PZ depended on its PROTAC activity because pomalidomide alone was not cytotoxic to WI38 NCs (Fig. 2g, left panel) or IR-SCs (Fig. 2g, right panel), nor did it have any additive or synergistic effect on WI38 IR-SC viability when combined with ABT263 (Fig. 2g, right panel).”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Findingown data

    ABT263 treatment was effective as PZ in reducing the expression of Cdkn2a, Cdkn1a, Cxcl12, and Tnfsf11 mRNA but had no significant effect on the expression of Il6 and Mmp3 mRNA in the spleen.

    “ABT263 treatment was effective as PZ in reducing the expression of Cdkn2a, Cdkn1a, Cxcl12, and Tnfsf11 mRNA but had no significant effect on the expression of Il6 and Mmp3 mRNA in the spleen (Fig. 3e–j).”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Findingown data

    ABT263, pomalidomide, or their combination did not affect Bcl-xl levels in WI38 non-senescent cells and IR-SCs.

    “None of these treatments affected Bcl-xl levels, suggesting that the effect of PZ on Bcl-xl is likely mediated through its PROTAC activity rather than the simple combination of ABT263 and pomalidomide (Fig. 2a).”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Findingown data

    PZ reduced the expression of Cdkn2a mRNA in the liver, lung, kidney, and fat in naturally aged mice, whereas ABT263 was less effective than PZ in reducing Cdkn2a mRNA expression in these organs.

    “Moreover, PZ reduced the expression of Cdkn2a mRNA in the liver, lung, kidney, and fat in naturally aged mice, whereas ABT263 was less effective than PZ in reducing Cdkn2a mRNA expression in these organs (Fig. 3k–n).”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Findingown data

    One day after the first dose of ABT263 (41 μmol/kg or 40 mg/kg), severe thrombocytopenia occurred as expected, while injection of an equivalent dose (41 μmol/kg or 61 mg/kg) of PZ had less effect on blood platelet counts.

    “One day after the first dose of ABT263 (41 μmol/kg or 40 mg/kg), severe thrombocytopenia occurred as expected, while injection of an equivalent dose (41 μmol/kg or 61 mg/kg) of PZ had less effect on blood platelet counts (Fig. 3c).”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Findingcitation

    ABT263 is highly toxic to both WI38 IR-SCs and platelets.

    “As reported, ABT263 was highly toxic to both WI38 IR-SCs (Fig. 1g, middle panel) and platelets16–18,24–27 (Fig. 1g, right panel; Supplementary Fig. 2).”
    Quote in the paperSubstantial claim0 of 7 sources checked
    • cites [16] Chang, J. et al. Clearance of senescent cells by ABT263 rejuvenates aged hematopoietic stem cells in mice. Nat. Med. 22, 78–83 (2016). source

      Not checked in the free run.

    • cites [17] Yosef, R. et al. Directed elimination of senescent cells by inhibition of BCL-W and BCL-XL. Nat. Commun. 7, 11190 (2016). source

      Not checked in the free run.

    • cites [18] Zhu, Y. et al. Identification of a novel senolytic agent, navitoclax, targeting the Bcl-2 family of anti-apoptotic factors. Aging Cell 15, 428–435 (2016). source

      Not checked in the free run.

    • cites [24] Ashkenazi, A., Fairbrother, W. J., Leverson, J. D. & Souers, A. J. From basic apoptosis discoveries to advanced selective BCL-2 family inhibitors. Nat. Rev. Drug Discov. 16, 273–284 (2017). source

      Not checked in the free run.

    • cites [25] Leverson, J. D. et al. Exploiting selective BCL-2 family inhibitors to dissect cell survival dependencies and define improved strategies for cancer therapy. Sci. Transl. Med. 7, 279ra40 (2015). source

      Not checked in the free run.

    • cites [26] Gandhi, L. et al. Phase I study of Navitoclax (ABT-263), a novel Bcl-2 family inhibitor, in patients with small-cell lung cancer and other solid tumors. J. Clin. Oncol. 29, 909–916 (2011). source

      Not checked in the free run.

    • cites [27] Souers, A. J. et al. ABT-199, a potent and selective BCL-2 inhibitor, achieves antitumor activity while sparing platelets. Nat. Med. 19, 202–208 (2013). source

      Not checked in the free run.

  • May combine two claims.

    Findingown data

    IP injection of PZ was slightly more effective than ABT263 in reducing the mRNA levels of Cdkn1a, Cxcl12, Mmp13, and Tnfsf11 in BM-derived osteoblast progenitor cell culture, but the expression of Il1a mRNA was reduced equally by PZ and ABT263 treatment.

    “IP injection of PZ was slightly more effective than ABT263 in reducing the mRNA levels of Cdkn1a (Fig. 4a), Cxcl12 (Fig. 4b), Mmp13 (Fig. 4c), and Tnfsf11 (Fig. 4d) in BM-derived osteoblast progenitor cell culture, but the expression of Il1a mRNA was reduced equally by PZ and ABT263 treatment (Fig. 4e).”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Findingown data

    PZ has a high molecular weight (MW = 1484.13 compared with 974.61 for ABT263) and low aqueous solubility.

    “Although PZ has a high molecular weight (MW = 1484.13 compared with 974.61 for ABT263) and low aqueous solubility, it is highly stable in plasma and in mouse and human liver microsomal stability assays (Supplementary Fig. 6a).”
    Quote in the paperNot a substantial claim

  • May combine two claims.

    Findingown data

    PZ is highly stable in plasma and in mouse and human liver microsomal stability assays.

    “Although PZ has a high molecular weight (MW = 1484.13 compared with 974.61 for ABT263) and low aqueous solubility, it is highly stable in plasma and in mouse and human liver microsomal stability assays (Supplementary Fig. 6a).”
    Quote in the paperNot a substantial claim

  • May combine two claims.

    Findingown data

    PZ treatment attenuated age-associated myeloid skewing and expansion of phenotypic HSCs, but had minimal effects on various hematopoietic progenitor cell populations that were not significantly affected by aging.

    “PZ treatment attenuated age-associated myeloid skewing (Fig. 5a, b) and expansion of phenotypic HSCs (Fig. 6a–f), but had minimal effects on various hematopoietic progenitor cell populations that were not significantly affected by aging (Fig. 6g–j).”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Findingown data

    BM stromal cells from PZ-treated mice formed significantly higher amounts of mineralized matrix and lower numbers of adipocytes than the cells from vehicle- or ABT263-treated mice.

    “We found that BM stromal cells from PZ-treated mice formed significantly higher amounts of mineralized matrix (Fig. 4h, i) and lower numbers of adipocytes than the cells from vehicle- or ABT263-treated mice (Fig. 4j, k).”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Findingown data

    Mouse platelets express low levels of CRBN and are insensitive to PZ-induced Bcl-xl degradation similar to human platelets.

    “In addition, PZ was less toxic to platelets in mice than ABT263 after a single IP injection (Fig. 3a and Supplementary Fig. 6d) because mouse platelets also express low levels of CRBN and are insensitive to PZ-induced Bcl-xl degradation similar to human platelets (Supplementary Fig. 6e, f).”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Findingown data

    PZ-induced significant reduction in SA-β-gal positive cells in HSC-enriched LSK cells in naturally aged mice, which was associated with a significant increase in HSC clonogenicity and a slightly improvement in HSC long-term engraftment.

    “PZ-induced significant reduction in SA-β-gal positive cells in HSC-enriched LSK (lineage negative and Sca1 and cKit positive) cells in naturally aged mice (Fig. 6k), which was associated with a significant increase in HSC clonogenicity (Fig. 6l) and a slightly improvement in HSC long-term engraftment (Supplementary Fig. 9).”
    Quote in the paperSubstantial claim

  • Probably not a substantial claim: may not pass S3 (load-bearing), S4 (based).

    Findingnone given

    PZ is highly lipophilic.

    “In addition, PZ is highly lipophilic and will require proper formulation and/or modifications to improve its drug-like properties as a senolytic agent to treat age-related diseases.”
    Quote in the paperNot a substantial claim

  • May combine two claims.

    Findingown data

    PZ effectively cleared senescent cells in naturally aged mice without causing severe thrombocytopenia.

    “More importantly, we found that PZ effectively cleared SCs in naturally aged mice without causing severe thrombocytopenia.”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Findingreasoning

    After ABT263 is converted into PZ, the PROTAC becomes more specific to Bcl-xl and is incapable of inducing Bcl-2 and Bcl-w degradation.

    “Interestingly, after ABT263 is converted into PZ, the PROTAC becomes more specific to Bcl-xl and is incapable of inducing Bcl-2 and Bcl-w degradation.”
    Quote in the paperSubstantial claim

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Premisecitation

    Senolytics, small molecules that selectively kill senescent cells, have the potential to prevent and treat various age-related diseases and extend healthspan.

    “Small molecules that can selectively kill SCs, termed senolytics, have the potential to prevent and treat a growing number of age-related diseases and extend healthspan2–4.”
    Quote in the paperNot a substantial claim0 of 3 sources checked
    • cites [2] Childs, B. G. et al. Senescent cells: an emerging target for diseases of ageing. Nat. Rev. Drug Discov. 16, 718–735 (2017). source

      Not checked in the free run.

    • cites [3] Kirkland, J. L. & Tchkonia, T. Cellular senescence: a translational perspective. EBioMedicine 21, 21–28 (2017). source

      Not checked in the free run.

    • cites [4] Niedernhofer, L. J. & Robbins, P. D. Senotherapeutics for healthy ageing. Nat. Rev. Drug Discov. 17, 377 (2018). source

      Not checked in the free run.

  • Classified as probably not a substantial claim.

    Premisecitation

    PROTACs are bivalent small molecules containing a ligand that recognizes a target protein linked to another ligand that recruits a specific E3 ubiquitin ligase.

    “PROTACs are bivalent small molecules containing a ligand that recognizes a target protein linked to another ligand that recruits a specific E3 ubiquitin ligase29,30.”
    Quote in the paperSubstantial claim0 of 2 sources checked
    • cites [29] Toure, M. & Crews, C. M. Small-Molecule PROTACS: new approaches to protein degradation. Angew. Chem. Int. Ed. Engl. 55, 1966–1973 (2016). source

      Not checked in the free run.

    • cites [30] Lai, A. C. & Crews, C. M. Induced protein degradation: an emerging drug discovery paradigm. Nat. Rev. Drug Discov. 16, 101–114 (2017). source

      Not checked in the free run.

  • May combine two claims.

    Premisecitation

    Bcl-xl inhibition with ABT263 and other small molecular inhibitors induces platelet apoptosis and results in severe thrombocytopenia, which prevents the use of ABT263 and other Bcl-xl specific inhibitors in the clinic even for cancer patients because platelets solely depend on Bcl-xl for survival.

    “Bcl-xl inhibition with ABT263 and other small molecular inhibitors induces platelet apoptosis and results in severe thrombocytopenia, which prevents the use of ABT263 and other Bcl-xl specific inhibitors in the clinic—even for cancer patients—because platelets solely depend on Bcl-xl for survival24–27.”
    Quote in the paperSubstantial claim0 of 4 sources checked
    • cites [24] Ashkenazi, A., Fairbrother, W. J., Leverson, J. D. & Souers, A. J. From basic apoptosis discoveries to advanced selective BCL-2 family inhibitors. Nat. Rev. Drug Discov. 16, 273–284 (2017). source

      Not checked in the free run.

    • cites [25] Leverson, J. D. et al. Exploiting selective BCL-2 family inhibitors to dissect cell survival dependencies and define improved strategies for cancer therapy. Sci. Transl. Med. 7, 279ra40 (2015). source

      Not checked in the free run.

    • cites [26] Gandhi, L. et al. Phase I study of Navitoclax (ABT-263), a novel Bcl-2 family inhibitor, in patients with small-cell lung cancer and other solid tumors. J. Clin. Oncol. 29, 909–916 (2011). source

      Not checked in the free run.

    • cites [27] Souers, A. J. et al. ABT-199, a potent and selective BCL-2 inhibitor, achieves antitumor activity while sparing platelets. Nat. Med. 19, 202–208 (2013). source

      Not checked in the free run.

  • Classified as probably not a substantial claim.

    Premisecitation

    Senescent cells accumulate with age and as a result of exposure to a variety of stressors including radiation.

    “SCs accumulate with age and as a result of the exposure to a variety of stressors including radiation.”
    Quote in the paperSubstantial claim0 of 7 sources checked
    • cites [1] Childs, B. G., Durik, M., Baker, D. J. & van Deursen, J. M. Cellular senescence in aging and age-related disease: from mechanisms to therapy. Nat. Med. 21, 1424–1435 (2015). source

      Not checked in the free run.

    • cites [2] Childs, B. G. et al. Senescent cells: an emerging target for diseases of ageing. Nat. Rev. Drug Discov. 16, 718–735 (2017). source

      Not checked in the free run.

    • cites [3] Kirkland, J. L. & Tchkonia, T. Cellular senescence: a translational perspective. EBioMedicine 21, 21–28 (2017). source

      Not checked in the free run.

    • cites [4] Niedernhofer, L. J. & Robbins, P. D. Senotherapeutics for healthy ageing. Nat. Rev. Drug Discov. 17, 377 (2018). source

      Not checked in the free run.

    • cites [5] Ovadya, Y. & Krizhanovsky, V. Strategies targeting cellular senescence. J. Clin. Invest. 128, 1247–1254 (2018). source

      Not checked in the free run.

    • cites [6] Muñoz-Espín, D. & Serrano, M. Cellular senescence: from physiology to pathology. Nat. Rev. Mol. Cell Biol. 15, 482–496 (2014). source

      Not checked in the free run.

    • cites [7] McHugh, D. & Gil, J. Senescence and aging: causes, consequences, and therapeutic avenues. J. Cell Biol. 217, 65–77 (2018). source

      Not checked in the free run.

  • May combine two claims.

    Premisecitation

    Most natural senolytics have low toxicity but are usually less potent than targeted senolytics and must be combined with other agents to be effective in clearing senescent cells.

    “While most natural senolytics have the advantages of low toxicity, they are usually less potent than targeted senolytics and must be combined with other agents to be effective in clearing SCs8.”
    Quote in the paperNot a substantial claim0 of 1 sources checked
    • cites [8] Zhu, Y. et al. The Achilles’ heel of senescent cells: from transcriptome to senolytic drugs. Aging Cell 14, 644–658 (2015). source

      Not checked in the free run.

  • Classified as probably not a substantial claim.

    Premisereasoning

    PROTACs act catalytically to induce protein degradation in a sub-stoichiometric manner.

    “Thus, PROTACs act catalytically to induce protein degradation in a sub-stoichiometric manner.”
    Quote in the paperSubstantial claim0 of 2 sources checked
    • cites [29] Toure, M. & Crews, C. M. Small-Molecule PROTACS: new approaches to protein degradation. Angew. Chem. Int. Ed. Engl. 55, 1966–1973 (2016). source

      Not checked in the free run.

    • cites [30] Lai, A. C. & Crews, C. M. Induced protein degradation: an emerging drug discovery paradigm. Nat. Rev. Drug Discov. 16, 101–114 (2017). source

      Not checked in the free run.

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Premisecitation

    Almost all targeted senolytics are repurposed anticancer agents except the FOXO4-p53 interfering peptide.

    “By contrast, almost all the targeted senolytics are repurposed anticancer agents except the FOXO4-p53 interfering peptide2–4.”
    Quote in the paperNot a substantial claim0 of 3 sources checked
    • cites [2] Childs, B. G. et al. Senescent cells: an emerging target for diseases of ageing. Nat. Rev. Drug Discov. 16, 718–735 (2017). source

      Not checked in the free run.

    • cites [3] Kirkland, J. L. & Tchkonia, T. Cellular senescence: a translational perspective. EBioMedicine 21, 21–28 (2017). source

      Not checked in the free run.

    • cites [4] Niedernhofer, L. J. & Robbins, P. D. Senotherapeutics for healthy ageing. Nat. Rev. Drug Discov. 17, 377 (2018). source

      Not checked in the free run.

  • Classified as probably not a substantial claim. May combine two claims.

    Premisecitation

    PROTAC binding induces proximity-induced ubiquitination of the target protein and its subsequent degradation by proteasomes.

    “PROTAC binding induces proximity-induced ubiquitination of the target protein and its subsequent degradation by proteasomes.”
    Quote in the paperSubstantial claim0 of 2 sources checked
    • cites [29] Toure, M. & Crews, C. M. Small-Molecule PROTACS: new approaches to protein degradation. Angew. Chem. Int. Ed. Engl. 55, 1966–1973 (2016). source

      Not checked in the free run.

    • cites [30] Lai, A. C. & Crews, C. M. Induced protein degradation: an emerging drug discovery paradigm. Nat. Rev. Drug Discov. 16, 101–114 (2017). source

      Not checked in the free run.

  • May combine two claims.

    Interpretationown data

    Both PZ and ABT263 can reduce the effects of aging on bone cells via clearance of senescent cells, however, PZ is slightly more effective than ABT263.

    “These findings indicate that both PZ and ABT263 can reduce the effects of aging on bone cells via clearance of SCs, however, PZ is slightly more effective than ABT263.”
    Quote in the paperSubstantial claim
    • Rests on an assumption: Senescence of bone marrow stromal cells contributes to the increase in bone marrow adipogenesis that occurs with age.

  • May combine two claims.

    Interpretationown data

    PZ acts as a PROTAC that depends on the CRBN E3 ligase and proteasome to degrade Bcl-xl and selectively induce IR-SC apoptosis.

    “Collectively, these data confirm that PZ acts as a PROTAC that depends on the CRBN E3 ligase and proteasome to degrade Bcl-xl and selectively induce IR-SC apoptosis.”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Premisecitation

    Senescent cells play an important role in skeletal aging in part by decreasing osteoprogenitor cell number and the generation of osteoblasts that produce the bone matrix, and by stimulating osteoclastogenesis to resorb the bone.

    “Recent studies by us and others have shown that SCs play an important role in skeletal aging in part by decreasing osteoprogenitor cell number and the generation of osteoblasts that produce the bone matrix; stimulate osteoclastogenesis to resorb the bone42,43.”
    Quote in the paperSubstantial claim0 of 2 sources checked
    • cites [42] Kim, H.-N. et al. DNA damage and senescence in osteoprogenitors expressing Osx1 may cause their decrease with age. Aging Cell 16, 693–703 (2017). source

      Not checked in the free run.

    • cites [43] Farr, J. N. et al. Targeting cellular senescence prevents age-related bone loss in mice. Nat. Med. 23, 1072–1079 (2017). source

      Not checked in the free run.

  • May combine two claims.

    Premisereasoning

    PROTACs usually have a longer-lasting effect and require less systemic drug exposure to be effective than their corresponding payloads.

    “These results are in agreement with the unique mechanism of action of PROTACs, that usually have a longer-lasting effect and require less systemic drug exposure to be effective than their corresponding “payloads”.”
    Quote in the paperSubstantial claim0 of 2 sources checked
    • cites [32] Neklesa, T. K., Winkler, J. D. & Crews, C. M. Targeted protein degradation by PROTACs. Pharmacol. Ther. 174, 138–144 (2017). source

      Not checked in the free run.

    • cites [39] Lu, J. et al. Hijacking the E3 ubiquitin ligase cereblon to efficiently target BRD4. Chem. Biol. 22, 755–763 (2015). source

      Not checked in the free run.

  • May combine two claims.

    Interpretationcitation

    PZ might be more effective than ABT263 in rejuvenating aged HSCs under this less intensive treatment regimen because previous study showed ABT263 was more effective in rejuvenating aged HSCs under a more intensive treatment schedule.

    “Again, these findings suggest that PZ might be more effective than ABT263 in rejuvenating aged HSCs under this less intensive treatment regimen because our previous study showed that ABT263 was more effective in rejuvenating aged HSCs under a more intensive treatment schedule16.”
    Quote in the paperSubstantial claim0 of 1 sources checked
    • cites [16] Chang, J. et al. Clearance of senescent cells by ABT263 rejuvenates aged hematopoietic stem cells in mice. Nat. Med. 22, 78–83 (2016). source

      Not checked in the free run.

  • May combine two claims.

    Interpretationcitation

    PZ might be slightly more effective than ABT263 in clearance of senescent BM osteoblast progenitors in naturally aged mice because these progenitors undergo senescence in a p21-dependent, but p16-independent, manner.

    “This result suggests that PZ might be slightly more effective than ABT263 in clearance of senescent BM osteoblast progenitors in naturally aged mice because these progenitors undergo senescence in a p21-dependent, but p16-independent, manner42.”
    Quote in the paperSubstantial claim0 of 1 sources checked
    • cites [42] Kim, H.-N. et al. DNA damage and senescence in osteoprogenitors expressing Osx1 may cause their decrease with age. Aging Cell 16, 693–703 (2017). source

      Not checked in the free run.

  • May combine two claims.

    Interpretationown data

    PZ is a potent broad-spectrum senolytic agent that has slightly improved senolytic activity against the majority of senescent cells studied, yet low toxicity to platelets and non-senescent cells compared with ABT263.

    “These findings confirm that PZ is a potent broad-spectrum senolytic agent that has a slightly improved senolytic activity against the majority of SCs studied, yet low toxicity to platelets and NCs compared with ABT263.”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Premisecitation

    PROTACs act catalytically to induce protein degradation in a sub-stoichiometric manner and their effect is not limited by equilibrium occupancy.

    “This is because PROTACs act catalytically to induce protein degradation in a sub-stoichiometric manner and their effect is not limited by equilibrium occupancy32,39.”
    Quote in the paperSubstantial claim0 of 2 sources checked
    • cites [32] Neklesa, T. K., Winkler, J. D. & Crews, C. M. Targeted protein degradation by PROTACs. Pharmacol. Ther. 174, 138–144 (2017). source

      Not checked in the free run.

    • cites [39] Lu, J. et al. Hijacking the E3 ubiquitin ligase cereblon to efficiently target BRD4. Chem. Biol. 22, 755–763 (2015). source

      Not checked in the free run.

  • May combine two claims.

    Interpretationcitation

    PZ selectively induced Bcl-xl degradation in non-senescent cells and senescent cells, but not platelets, because it targeted Bcl-xl to the CRBN E3 ligase that is poorly expressed in platelets but abundantly expressed in other cells.

    “The resulting Bcl-xl-specific PROTAC lead compound, PZ, selectively induced Bcl-xl degradation in NCs and SCs, but not platelets, because it targeted Bcl-xl to the CRBN E3 ligase that is poorly expressed in platelets but abundantly expressed in other cells34,35.”
    Quote in the paperSubstantial claim0 of 2 sources checked
    • cites [34] Bray, P. F. et al. The complex transcriptional landscape of the anucleate human platelet. BMC Genomics 14, 1 (2013). source

      Not checked in the free run.

    • cites [35] Kissopoulou, A., Jonasson, J., Lindahl, T. L. & Osman, A. Next generation sequencing analysis of human platelet PolyA+ mRNAs and rRNA-depleted total RNA. PLoS ONE 8, e81809 (2013). source

      Not checked in the free run.

    • Rests on an assumption: It is possible to achieve cell/tissue selectivity with PROTACs even when the target proteins are ubiquitously expressed as long as they target the proteins to an E3 ligase that is cell- or tissue-specific.

  • Classified as probably not a substantial claim.

    Study design and conductcitation

    Senescent cells were induced and validated as previously described.

    “SCs were induced and validated as previously described13,14,16.”
    Quote in the paperSubstantial claim0 of 3 sources checked
    • cites [13] Wang, Y. et al. Discovery of piperlongumine as a potential novel lead for the development of senolytic agents. Aging 8, 2915–2926 (2016). source

      Not checked in the free run.

    • cites [14] Li, W., He, Y., Zhang, R., Zheng, G. & Zhou, D. The curcumin analog EF24 is a novel senolytic agent. Aging 11, 771–782 (2019). source

      Not checked in the free run.

    • cites [16] Chang, J. et al. Clearance of senescent cells by ABT263 rejuvenates aged hematopoietic stem cells in mice. Nat. Med. 22, 78–83 (2016). source

      Not checked in the free run.

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Study design and conductnone given

    All western blots shown in the figures were repeated in at least two independent experiments.

    “All western blots showed in the figures were repeated in at least two independent experiments.”
    Quote in the paperNot a substantial claim

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Study design and conductnone given

    Mice with tumors and/or leukemia were excluded from experiments and analyses.

    “Mice with tumors and/or leukemia were excluded from experiments and analyses.”
    Quote in the paperNot a substantial claim

  • May combine two claims.

    Interpretationcitation

    The inability of PZ to efficiently induce Bcl-2 degradation may provide additional advantages for using PROTAC technology to reduce ABT263 on-target toxicity because Bcl-2 inhibition with a high dose or an intensive treatment regimen of ABT263 can lead to neutropenia and lymphocytopenia.

    “The inability of PZ to efficiently induce Bcl-2 degradation may provide additional advantages for using PROTAC technology to reduce ABT263 on-target toxicity because Bcl-2 inhibition with a high dose or an intensive treatment regimen of ABT263 can lead to neutropenia and lymphocytopenia25.”
    Quote in the paperSubstantial claim0 of 1 sources checked
    • cites [25] Leverson, J. D. et al. Exploiting selective BCL-2 family inhibitors to dissect cell survival dependencies and define improved strategies for cancer therapy. Sci. Transl. Med. 7, 279ra40 (2015). source

      Not checked in the free run.

  • May combine two claims.

    Interpretationreasoning

    This unique property of PROTACs can potentially reduce off-target toxicities of ABT263 by lowering systemic concentration and duration of exposure, thus making Bcl-xl-Ps better senolytics than ABT263 or other Bcl-xl inhibitors.

    “This unique property of PROTACs can potentially reduce off-target toxicities of ABT263 by lowering systemic concentration and duration of exposure, thus making Bcl-xl-Ps better senolytics than ABT263 or other Bcl-xl inhibitors.”
    Quote in the paperSubstantial claim
    • Rests on an assumption: PROTACs result in less drug exposure and reduced toxicity compared with traditional inhibitors because their effect is not limited by equilibrium occupancy.

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Premisecitation

    Different senescent cells can use different anti-apoptotic pathways (SCAPs) to resist apoptosis.

    “This observation is in agreement with the suggestion that different SCs can use different anti-apoptotic pathways (SCAPs) to resist apoptosis2–5.”
    Quote in the paperNot a substantial claim0 of 4 sources checked
    • cites [2] Childs, B. G. et al. Senescent cells: an emerging target for diseases of ageing. Nat. Rev. Drug Discov. 16, 718–735 (2017). source

      Not checked in the free run.

    • cites [3] Kirkland, J. L. & Tchkonia, T. Cellular senescence: a translational perspective. EBioMedicine 21, 21–28 (2017). source

      Not checked in the free run.

    • cites [4] Niedernhofer, L. J. & Robbins, P. D. Senotherapeutics for healthy ageing. Nat. Rev. Drug Discov. 17, 377 (2018). source

      Not checked in the free run.

    • cites [5] Ovadya, Y. & Krizhanovsky, V. Strategies targeting cellular senescence. J. Clin. Invest. 128, 1247–1254 (2018). source

      Not checked in the free run.

  • May combine two claims.

    Interpretationcitation

    This increase is likely due to PROTACs' catalytical action to induce protein degradation in a sub-stoichiometric manner, and that their effect is not limited by equilibrium occupancy as are conventional inhibitors such as ABT263.

    “This increase is likely due to PROTACs’ catalytical action to induce protein degradation in a sub-stoichiometric manner, and that their effect is not limited by equilibrium occupancy as are conventional inhibitors such as ABT263 (refs. 29,30).”
    Quote in the paperSubstantial claim0 of 2 sources checked
    • cites [29] Toure, M. & Crews, C. M. Small-Molecule PROTACS: new approaches to protein degradation. Angew. Chem. Int. Ed. Engl. 55, 1966–1973 (2016). source

      Not checked in the free run.

    • cites [30] Lai, A. C. & Crews, C. M. Induced protein degradation: an emerging drug discovery paradigm. Nat. Rev. Drug Discov. 16, 101–114 (2017). source

      Not checked in the free run.

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Study design and conductnone given

    For all assays, cells were plated in triplicate.

    “For all assays, cells were plated in triplicate.”
    Quote in the paperNot a substantial claim

  • May combine two claims.

    Interpretationnone given

    Both PZ and ABT263 can be considered broad-spectrum senolytic agents.

    “Although both PZ and ABT263 can be considered broad-spectrum senolytic agents, their effectiveness in clearing SCs in naturally aged mice appears to be tissue dependent.”
    Quote in the paperNot a substantial claim

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Study design and conductnone given

    Extra cautions were taken during the platelet viability assay to avoid platelet activation, aggregation, and spontaneous apoptosis.

    “Through the whole process of the platelet viability assay, extra cautions such as room temperature storage/incubation, centrifuge without break, gently pipetting and mixing, and rotating platelets during incubation were taken to avoid platelet activation, aggregation, and spontaneous apoptosis.”
    Quote in the paperNot a substantial claim

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Study design and conductown data

    All qPCR reactions were run in duplicate.

    “All reactions were run in duplicate on an ABI StepOnePlus Real-Time PCR System (Applied Biosystems, Foster City, CA, USA).”
    Quote in the paperNot a substantial claim

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Premisecitation

    A promiscuous ligand for about 50 kinases could induce only a subset of its targets for degradation when converted into a PROTAC.

    “In addition, Bondeson et al. showed that a promiscuous ligand for about 50 kinases could induce only a subset of its targets for degradation when converted into a PROTAC45.”
    Quote in the paperNot a substantial claim0 of 1 sources checked
    • cites [45] Bondeson, D. P. et al. Lessons in PROTAC design from selective degradation with a promiscuous warhead. Cell Chem. Biol. 25, 78–87.e5 (2018). source

      Not checked in the free run.

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Premisecitation

    The pan-bromodomain and extra-terminal (BET) inhibitor JQ1, which binds and inhibits the BET proteins BRD2, BRD3, and BRD4, could be converted into a selective BRD4 PROTAC.

    “For example, the pan-bromodomain and extra-terminal (BET) inhibitor JQ1, which binds and inhibits the BET proteins BRD2, BRD3, and BRD4, could be converted into a selective BRD4 PROTAC44.”
    Quote in the paperNot a substantial claim0 of 1 sources checked
    • cites [44] Zengerle, M., Chan, K.-H. & Ciulli, A. Selective small molecule induced degradation of the BET bromodomain protein BRD4. ACS Chem. Biol. 10, 1770–1777 (2015). source

      Not checked in the free run.

  • May combine two claims.

    Premisecitation

    Bcl-2 has fewer lysines than Bcl-xl, which may render Bcl-2 less sensitive than Bcl-xl to PZ-induced degradation.

    “In addition, Bcl-2 has fewer lysines than Bcl-xl, which may render Bcl-2 less sensitive than Bcl-xl to PZ-induced degradation46.”
    Quote in the paperNot a substantial claim0 of 1 sources checked
    • cites [46] Petros, A. M., Olejniczak, E. T. & Fesik, S. W. Structural biology of the Bcl-2 family of proteins. Biochim. Biophys. Acta 1644, 83–94 (2004). source

      Not checked in the free run.

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Study design and conductnone given

    20-month-old male and female mice were randomly assigned to treatment groups.

    “20-month-old male and female mice were randomly assigned to one of the treatment groups”
    Quote in the paperNot a substantial claim

  • May combine two claims.

    Interpretationreasoning

    It is unlikely that PZ will be totally devoid of platelet toxicity, because it retains a high binding affinity to Bcl-xl (Ki = 1.90 nM for PZ vs. Ki = 1.53 nM for ABT263), and thus can still function as a Bcl-xl inhibitor that could potentially induce thrombocytopenia if the concentrations of PZ reach a high level in blood.

    “However, it is unlikely that PZ will be totally devoid of platelet toxicity, because it retains a high binding affinity to Bcl-xl (Ki = 1.90 nM for PZ vs. Ki = 1.53 nM for ABT263), and thus can still function as a Bcl-xl inhibitor that could potentially induce thrombocytopenia if the concentrations of PZ reach a high level in blood.”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Interpretationcitation

    PZ can selectively induce apoptosis in senescent cells, but not platelets, which are dependent on Bcl-xl for survival while having minimal toxicity to non-senescent cells that are less sensitive to Bcl-xl inhibition than senescent cells.

    “Therefore, PZ can selectively induce apoptosis in SCs, but not platelets, which are dependent on Bcl-xl for survival while having minimal toxicity to NCs that are less sensitive to Bcl-xl inhibition than SCs16–18,24–27.”
    Quote in the paperSubstantial claim0 of 7 sources checked
    • cites [16] Chang, J. et al. Clearance of senescent cells by ABT263 rejuvenates aged hematopoietic stem cells in mice. Nat. Med. 22, 78–83 (2016). source

      Not checked in the free run.

    • cites [17] Yosef, R. et al. Directed elimination of senescent cells by inhibition of BCL-W and BCL-XL. Nat. Commun. 7, 11190 (2016). source

      Not checked in the free run.

    • cites [18] Zhu, Y. et al. Identification of a novel senolytic agent, navitoclax, targeting the Bcl-2 family of anti-apoptotic factors. Aging Cell 15, 428–435 (2016). source

      Not checked in the free run.

    • cites [24] Ashkenazi, A., Fairbrother, W. J., Leverson, J. D. & Souers, A. J. From basic apoptosis discoveries to advanced selective BCL-2 family inhibitors. Nat. Rev. Drug Discov. 16, 273–284 (2017). source

      Not checked in the free run.

    • cites [25] Leverson, J. D. et al. Exploiting selective BCL-2 family inhibitors to dissect cell survival dependencies and define improved strategies for cancer therapy. Sci. Transl. Med. 7, 279ra40 (2015). source

      Not checked in the free run.

    • cites [26] Gandhi, L. et al. Phase I study of Navitoclax (ABT-263), a novel Bcl-2 family inhibitor, in patients with small-cell lung cancer and other solid tumors. J. Clin. Oncol. 29, 909–916 (2011). source

      Not checked in the free run.

    • cites [27] Souers, A. J. et al. ABT-199, a potent and selective BCL-2 inhibitor, achieves antitumor activity while sparing platelets. Nat. Med. 19, 202–208 (2013). source

      Not checked in the free run.

  • Probably not a substantial claim: may not pass S3 (load-bearing). May combine two claims.

    Interpretationreasoning

    Alternatively, the lack of efficient degradation of Bcl-2 and Bcl-w by PZ could be due to consequences of under-optimization of the linker and linkage site, which could reduce its ability to form a stable target protein-PROTAC-E3 ligase ternary complex that is required for induction of target protein ubiquitination and degradation.

    “Alternatively, it could be due to consequences of under-optimization of the linker and linkage site, which could reduce its ability to form a stable target protein-PROTAC-E3 ligase ternary complex that is required for induction of target protein ubiquitination and degradation.”
    Quote in the paperNot a substantial claim

  • May combine two claims.

    Premisecitation

    Bcl-xl-specific inhibitors such as A-1331852 and A-1155463 can selectively kill a variety of senescent cells, whereas the Bcl-2 specific inhibitor ABT199 and Mcl-1 specific inhibitor A-1210477 had no such effect.

    “This suggestion is in agreement with previous findings that Bcl-xl-specific inhibitors such as A-1331852 and A-1155463 can selectively kill a variety of SCs11, whereas the Bcl-2 specific inhibitor ABT199 and Mcl-1 specific inhibitor A-1210477 had no such effect.”
    Quote in the paperSubstantial claim0 of 1 sources checked
    • cites [11] Zhu, Y. et al. New agents that target senescent cells: the flavone, fisetin, and the BCL-XL inhibitors, A1331852 and A1155463. Aging 9, 955–963 (2017). source

      Not checked in the free run.

62 of 62

  • The paper relies on this without support.

    The mechanisms of action of most natural senolytics are not well defined nor have their molecular targets been identified and characterized.

    “In addition, the mechanisms of action of most natural senolytics are not well defined nor have their molecular targets been identified and characterized, making it difficult to rationally modify them to improve their senolytic activity.”

  • The paper relies on this without support.

    Repurposed senolytics usually have on-target and/or off-target toxicities.

    “The repurposed senolytics usually have on-target and/or off-target toxicities.”

  • The paper relies on this without support.

    These toxicities limit clinical use as anti-aging agents because older people are more susceptible to adverse drug effects than younger individuals and less tolerant to cancer drug toxicity.

    “These toxicities limit their clinical use as anti-aging agents because older people are more susceptible to adverse drug effects than younger individuals and less tolerant to cancer drug toxicity.”

  • The paper relies on this without support.

    PROTACs result in less drug exposure and reduced toxicity compared with traditional inhibitors because their effect is not limited by equilibrium occupancy.

    “Since their effect is not limited by equilibrium occupancy, it results in less drug exposure and reduced toxicity compared with traditional inhibitors.”

  • The paper relies on this without support.

    It is possible to achieve cell/tissue selectivity with PROTACs even when the target proteins are ubiquitously expressed as long as they target the proteins to an E3 ligase that is cell- or tissue-specific.

    “Importantly, because PROTACs rely on E3 ligases to induce protein degradation, it is possible to achieve cell/tissue selectivity, even when the target proteins are ubiquitously expressed as long as they target the proteins to an E3 ligase that is cell- or tissue-specific.”

  • The paper relies on this without support.

    Senescence of bone marrow stromal cells contributes to the increase in bone marrow adipogenesis that occurs with age.

    “Senescence of bone marrow (BM) stromal cells also contributes to the increase in BM adipogenesis that occurs with age.”
6 of 6

Claims other papers make about this one

Each is checked against this paper’s own text: does it say what the citing paper says it does?

  • PZ15527 (201) efficiently degrades Bcl-xL protein in non-senescent cells, reduces platelet toxicity, and causes minimal thrombocytopenia.

    “Zhou’s team also designed PZ15527 (201), which efficiently degraded Bcl-xL protein in non-senescent cells, reduced platelet toxicity, and caused minimal thrombocytopenia (Table 4).493”

    From Recent advances in targeting the “undruggable” proteins: from drug discovery to clinical trials (2023) · cites this paper as [493]

  • Bcl-xL degraders recruiting CRBN or IAPs showed significantly reduced cytotoxicity against platelets but improved killing of various tumor cells and senescent cells due to differential expression of these E3 ligases.

    “These Bcl-xL degraders showed significantly reduced cytotoxicity against platelets but improved killing of various tumor cells and senescent cells due to differential expression of these E3 ligases”

    From Proteolysis targeting chimeras (PROTACs) are emerging therapeutics for hematologic malignancies (2020) · cites this paper as [60]

  • Only a few PROTACs are tumor-selective to avoid normal tissue toxicity, including platelet sparing Bcl-xL PROTACs reported by us recently by taking advantage of E3 ligases that are barely expressed in platelets.

    “Although numerous PROTACs have been generated in the past few years, only a few of them are tumor-selective to avoid normal tissue toxicity, including platelet sparing Bcl-xL PROTACs reported by us recently by taking advantage of the E3 ligases that are barely expressed in platelets [4, 60–63].”

    From Proteolysis targeting chimeras (PROTACs) are emerging therapeutics for hematologic malignancies (2020) · cites this paper as [60]

Self-check

Percentages, sums and reported differences re-computed from the paper’s own numbers.

Each contradiction between two passages listed here was confirmed by an independent check.

  • Figure 4 assigns panel f to two different analyses

    Minor

    The caption includes panel f in its range for mRNA-expression measurements, then identifies f as a senescence-staining analysis.

1 of 1

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Authors
He, Y., Zhang, X., Chang, J., Kim, H.-N., Zhang, P., Wang, Y., Khan, S., Liu, X., Zhang, X., Lv, D., Song, L., Li, W., Thummuri, D., Yuan, Y., Wiegand, J. S., Ortiz, Y. T., Budamagunta, V., Elisseeff, J. H., Campisi, J., Almeida, M., Zheng, G., & Zhou, D.
Affiliations
  • University of Florida (US)
  • University of Arkansas for Medical Sciences (US)
  • Johns Hopkins University (US)
  • Buck Institute for Research on Aging (US)
Corresponding author
  • Zheng, Guangrong
  • Zhou, Daohong
ORCID
Venue
Nature Communications
Publisher
Springer Science and Business Media LLC
Published
2020-04-24
Volume
11
Issue
1
Pages
1996-1996
ISSN
2041-1723 (ISSN-L)
DOI
10.1038/s41467-020-15838-0
PMC
PMC7181703
OpenAlex
W3019334729
Semantic Scholar
204b79f558d98d0585db7c89458327676b4e2f64
Cited by
280
References
51
Citations by year
2026: 40 · 2025: 40 · 2024: 42 · 2023: 40 · 2022: 46 · 2021: 49 · 2020: 23
FWCI
12.80
Type
journal article
Language
en
Open access
Licence
Locations
  • Nature Communications (publishedVersion, cc-by)
  • PubMed Central (publishedVersion, cc-by)
  • PubMed (publishedVersion)
  • RePEc: Research Papers in Economics (submittedVersion)
  • DOAJ (DOAJ: Directory of Open Access Journals) (submittedVersion, cc-by-sa)
  • eScholarship (California Digital Library) (submittedVersion)
  • eScholarship (California Digital Library) (submittedVersion, cc-by)
Funders
NIH
Topics
  • Life Sciences › Biochemistry, Genetics and Molecular Biology › Molecular Biology › Protein Degradation and Inhibitors
  • Health Sciences › Medicine › Physiology › Telomeres, Telomerase, and Senescence
  • Life Sciences › Biochemistry, Genetics and Molecular Biology › Molecular Biology › Cell death mechanisms and regulation
Keywords
senolytics, navitoclax, Bcl-xL, PROTACs, platelet toxicity, senescent cell clearance, thrombocytopenia, age-related diseases, healthspan
MeSH terms
Aging, Aniline Compounds, Animals, Blood Platelets, Cell Line, Female, Humans, Male, Mice, Transgenic, Sulfonamides, Cellular Senescence, Models, Animal, Ubiquitin-Protein Ligases, Adaptor Proteins, Signal Transducing, bcl-X Protein, Mice, Proteolysis, Primary Cell Culture

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Registry, retraction, Cites and statistics results are computed, not judged, with one exception: a printed reference that no index lists is read once by a model before it counts as a citation error. Claims are extracted by a model and kept only when their quote appears verbatim in the text; each cited source is then checked, with a model’s help, for whether it says what the claim relies on. Those verdicts can be wrong — read the claim’s quote and the cited source before relying on one.

Claims read by deepseek-v4.1-flash under definition version 3 (extract-v3) on 2026-10-06.

Classified by jev-1.13-20260917 (gold-guideline-v0.2) on 2026-10-06.

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