Vertical Pathway Inhibition Overcomes Adaptive Feedback Resistance to KRASG12C Inhibition

In the paper

“BRAF inhibition in BRAFV600 mutant cancers leads to loss of negative feedback signals regulated by the MAPK pathway, leading to receptor tyrosine kinase (RTK)-mediated reactivation of MAPK signaling through wild type RAS and RAF, particularly in specific tumor types, such as colorectal cancer (9–12).”

What the sources say

• Partly supported

  The Abstract Results report rapid recovery of phospho-ERK signaling after BRAF inhibition in melanoma cells. The Discussion suggests that pathway blockade may relieve feedback inhibition and cites prior work on signaling shifting from BRAF to CRAF. It does not establish RTK-mediated reactivation through wild-type RAS and RAF or a particular effect in colorectal cancer; those mechanisms and the broader tumor-type claim go beyond this paper. (LLM, conf=0.88)

  cites [9] Paraiso, 2010, Recovery of phospho-ERK activity allows melanoma cells to escape from BRAF inhibitor therapy, Br J Cancer sourceExperimental — accuracy not yet measured
• Supported

  The Results describe increased RAS activity after RAF inhibition in BRAF-mutant thyroid cells, consistent with relief of upstream negative feedback. The Discussion links pathway rebound to RTK activation and signaling through wild-type RAF proteins; the Abstract and Discussion also report transient MAPK inhibition and EGFR-linked resistance in colorectal cancer cells. The paper’s direct mechanistic experiments concern thyroid cells, while its colorectal point is reported from other work. (LLM, conf=0.86)

  cites [10] Montero-Conde, 2013, Relief of feedback inhibition of HER3 transcription by RAF and MEK inhibitors attenuates their antitumor effects in BRAF-mutant thyroid carcinomas, Cancer Discov sourceExperimental — accuracy not yet measured
• Partly supported

  The Results and Discussion (page unavailable) support EGFR-mediated reactivation of RAS, CRAF and MAPK signaling after vemurafenib treatment in BRAF-mutant colorectal cancer. The citing sentence also presents loss of MAPK-regulated negative feedback as the cause; the Discussion offers that mechanism as a possibility and says further study is needed to establish it. The paper does not explicitly establish that the RAS and RAF involved are wild type. (LLM, conf=0.87)

  cites [11] Corcoran, 2012, EGFR-mediated re-activation of MAPK signaling contributes to insensitivity of BRAF mutant colorectal cancers to RAF inhibition with vemurafenib, Cancer Discov sourceExperimental — accuracy not yet measured
• Partly supported

  The ‘feedback activation of EGFR’ section reports that BRAF inhibition activates EGFR in BRAF-mutant colorectal cancer cells, and that adding an EGFR inhibitor produces more complete MEK and ERK inhibition. It describes feedback involving MEK, ERK and CDC25C, but does not establish that MAPK signaling is reactivated through wild-type RAS and RAF. (LLM, conf=0.86)

  cites [12] Prahallad, 2012, Unresponsiveness of colon cancer to BRAF(V600E) inhibition through feedback activation of EGFR, Nature sourceExperimental — accuracy not yet measured

In the paper

“These inhibitors undergo an irreversible reaction with the mutant cysteine present only in G12C mutant KRAS, making them highly selective for KRASG12C versus wild type KRAS or other RAS isoforms.”

What the sources say

• ?Not checked — no full text of the sourcecites [3] Patricelli, 2016, Selective inhibition of oncogenic KRAS output with small molecules targeting the inactive state, Cancer Discov source
• Supported

  The Results report that ARS-1620’s activity was selective for KRASG12C rather than wild-type KRAS or other tested KRAS alleles, and attribute that specificity to covalent modification of Cys-12. The Introduction and Discussion also describe this inhibitor class as covalent and mutant-allele-specific, supporting the citing sentence’s account of its selectivity. (LLM, conf=0.88)

  cites [4] Janes, 2018, Targeting KRAS mutant cancers with a covalent G12C-specific inhibitor, Cell source
• Partly supported

  The passage labeled Abstract (page unavailable) reports that compound 13 was inactive in two wild-type KRAS cell lines and one KRAS-G12D cell line, supporting selectivity for KRAS-G12C over those comparators. It does not report testing against other RAS isoforms, so that part of the claim is not established by this paper. (LLM, conf=0.85)

  cites [5] Fell, 2018, Discovery of tetrahydropyridopyrimidines as irreversible covalent inhibitors of KRAS-G12C with in vivo activity, ACS Med Chem Lett sourceExperimental — accuracy not yet measured

In the paper

“in KRAS mutant cancers, MEK inhibitor treatment leads to adaptive feedback activation of RAS signaling, often through EGFR or other human epidermal growth factor receptor (HER) family members or FGFR, limiting efficacy (13,14).”

What the sources say

• Partly supported

  The “FGFR1 mediates adaptive drug resistance” section reports that trametinib increased FGFR1 signaling and RAS-GTP in KRAS-mutant lung cancer cells, supporting feedback activation that limits treatment efficacy. But the “FGFR1 inhibition enhances trametinib effects” section reports no increase in EGFR in the tested cells and only limited combinatorial activity for an EGFR/ERBB2 inhibitor. The paper therefore does not support the claim that EGFR or other HER family members are often the route of this response across KRAS-mutant cancers. Page numbers are not provided in our copy. (LLM, conf=0.86)

  cites [13] Manchado, 2016, A combinatorial strategy for treating KRAS-mutant lung cancer, Nature sourceExperimental — accuracy not yet measured
• Partly supported

  The Results and Discussion report that MEK inhibition triggers feedback activation of ERBB3 or FGFR1 signaling in different subsets of KRAS-mutant lung cancer, reactivating MAPK/ERK signaling and contributing to resistance. The claim extends this finding to KRAS-mutant cancers generally and names EGFR as a route; this paper’s EGFR feedback example concerns BRAF-inhibited colorectal cancer, not MEK-inhibited KRAS-mutant cancer. The paper primarily demonstrates reactivation of downstream MAPK/ERK signaling rather than RAS signaling itself. (LLM, conf=0.86)

  cites [14] Kitai, 2016, Epithelial-to-mesenchymal transition defines feedback activation of receptor tyrosine kinase signaling induced by MEK inhibition in KRAS-mutant lung cancer, Cancer Discov sourceExperimental — accuracy not yet measured

In the paper

“early preclinical studies with KRASG12C inhibitors, such as ARS-1620, have suggested a potential role for adaptive feedback as a mechanism of resistance (7) (15).”

What the sources say

• Partly supported

  The paper’s indexed text (section labeled Abstract; page unavailable) reports that feedback-related RTK activation attenuated the inhibitory effect of ARS853 and suggests ways resistance to this class of drugs might emerge. It studies ARS853, not the cited example ARS-1620, so it does not directly support the claim for that compound. (LLM, conf=0.86)

  cites [7] Lito, 2016, Allele-specific inhibitors inactivate mutant KRAS G12C by a trapping mechanism, Science sourceExperimental — accuracy not yet measured
• ?Not checked — no full text of the sourcecites [15] Misale, 2019, KRAS G12C NSCLC models are sensitive to direct targeting of KRAS in combination with PI3K inhibition, Clin Cancer Res source

In the paper

“However, preclinical and clinical data have demonstrated that other RTKs can drive feedback in an EGFR-independent manner”

What the sources say

• Supported

  The Discussion (page not supplied) reports EGFR-independent MAPK reactivation in patient biopsies and identifies CRC cell lines in which RTKs other than EGFR, such as MET, drive reactivation and resistance. It concludes that both EGFR-dependent and EGFR-independent feedback signals need to be inhibited in BRAF V600E-mutant colorectal cancer. (LLM, conf=0.93)

  cites [34] Corcoran, 2018, Combined BRAF, EGFR, and MEK inhibition in patients with BRAFV600E-mutant colorectal cancer, Cancer Discov source

In the paper

“This finding is consistent with prior studies identifying HER family and FGFR signaling as key mediators of adaptive feedback to RAS-MAPK pathway inhibitors (10–14,21,22) and recent functional genomic screens(40).”

What the sources say

• Partly supported

  The Results and Discussion (page unavailable) identify HER2/HER3 signaling as a mediator of rebound signaling and reduced response to RAF or MEK inhibitors in BRAF-mutant thyroid cancer cells. Our copy does not identify FGFR signaling as a mediator; searches for “FGFR” and “fibroblast growth factor” found no supporting passage. The paper also emphasizes that the relevant reactivated receptors vary by cell type. (LLM, conf=0.90)

  cites [10] Montero-Conde, 2013, Relief of feedback inhibition of HER3 transcription by RAF and MEK inhibitors attenuates their antitumor effects in BRAF-mutant thyroid carcinomas, Cancer Discov sourceExperimental — accuracy not yet measured
• Partly supported

  The Results (page not provided) identify EGFR, a HER-family receptor, as the predominant mediator of MAPK reactivation after RAF inhibition in BRAF-mutant colorectal cancer cells. The Discussion (page not provided) describes a possible feedback mechanism but says it remains unproven. Our copy does not establish FGFR signaling as a mediator, so it supports only the EGFR portion of the broader claim. (LLM, conf=0.88)

  cites [11] Corcoran, 2012, EGFR-mediated re-activation of MAPK signaling contributes to insensitivity of BRAF mutant colorectal cancers to RAF inhibition with vemurafenib, Cancer Discov sourceExperimental — accuracy not yet measured
• Partly supported

  The “feedback activation of EGFR” section reports that BRAF or MEK inhibition activates EGFR, a HER-family receptor, in BRAF-mutant colorectal cancer cells. It does not establish FGFR signaling as a mediator, and its findings are narrower than a general claim about HER-family and FGFR responses to RAS–MAPK inhibitors. (LLM, conf=0.87)

  cites [12] Prahallad, 2012, Unresponsiveness of colon cancer to BRAF(V600E) inhibition through feedback activation of EGFR, Nature sourceExperimental — accuracy not yet measured
• Partly supported

  The Discussion identifies FGFR1 feedback activation as a prominent mechanism of resistance to the MEK inhibitor trametinib in KRAS-mutant lung cancer. The “FGFR1 inhibition enhances trametinib effects” section reports some combinatorial activity for an EGFR/ERBB2 inhibitor, but does not establish HER-family signaling as a key mediator in this setting. The claim also generalizes beyond the specific inhibitor and cancer contexts examined. (LLM, conf=0.87)

  cites [13] Manchado, 2016, A combinatorial strategy for treating KRAS-mutant lung cancer, Nature sourceExperimental — accuracy not yet measured
• Supported

  The Introduction reports that MEK inhibition activates ERBB3 signaling in epithelial-like KRAS-mutant lung cancer cells and FGFR1 signaling in mesenchymal-like cells. The Discussion identifies these as distinct feedback mechanisms that reactivate MAPK signaling. This supports the cited paper as an example of HER-family and FGFR-mediated adaptive feedback to a RAS–MAPK pathway inhibitor. (LLM, conf=0.90)

  cites [14] Kitai, 2016, Epithelial-to-mesenchymal transition defines feedback activation of receptor tyrosine kinase signaling induced by MEK inhibition in KRAS-mutant lung cancer, Cancer Discov source
• Partly supported

  The Discussion (page not provided) reports that MEK inhibition upregulates ERBB2 and ERBB3, forming active HER-family complexes that sustain downstream signaling. This supports the HER-family part of the claim in KRAS-mutant lung and colon cancer, but our copy does not identify FGFR signaling as a mediator of this feedback. (LLM, conf=0.86)

  cites [21] Sun, 2014, Intrinsic resistance to MEK inhibition in KRAS mutant lung and colon cancer through transcriptional induction of ERBB3, Cell Rep sourceExperimental — accuracy not yet measured
• Partly supported

  Clinical-Translational Advances (page unavailable) describes receptor tyrosine kinase upregulation as an adaptive response to MEK inhibition, and Concluding Remarks gives a HER-family-targeting combination as an example. The copy does not identify FGFR signaling as a mediator of that feedback, so it supports only part of the attributed claim. (LLM, conf=0.86)

  cites [22] Johnson, 2014, Molecular pathways: adaptive kinome reprogramming in response to targeted inhibition of the BRAF-MEK-ERK pathway in cancer, Clin Cancer Res sourceExperimental — accuracy not yet measured
• Supported

  The citation is attached specifically to “recent functional genomic screens,” and this paper reports genome-scale CRISPRi screens in KRASG12C-inhibited NSCLC and PDAC cells (Results, “Genome-scale CRISPRi screens nominate KRASG12C collateral dependent genes”; page unavailable). Its Results also identify EGFR and FGFR1 as cell-specific dependencies in those models. The citation therefore supports the cited example of a functional genomic screen, rather than a claim that both pathways mediate feedback in every RAS–MAPK inhibitor setting. (LLM, conf=0.90)

  cites [40] Lou, 2019, KRAS(G12C) inhibition produces a driver-limited state revealing collateral dependencies, Sci Signal source

In the paper

“First, as described by Lito et al, increased RTK activity may lead to increased cycling of KRASG12C to its active GTP-bound form that hinders the binding of most KRASG12C inhibitors, which bind specifically to the inactive GDP-bound form (7).”

What the sources say

• Partly supported

  In the supplied copy (section labeled Abstract; no page given), Lito et al. report that RTK-mediated nucleotide exchange affects inhibition and that increased exchange lowers the GDP-bound KRASG12C available for ARS853 binding. This supports the proposed mechanism for ARS853, but the paper does not establish that most KRASG12C inhibitors bind specifically to the GDP-bound form. (LLM, conf=0.88)

  cites [7] Lito, 2016, Allele-specific inhibitors inactivate mutant KRAS G12C by a trapping mechanism, Science sourceExperimental — accuracy not yet measured

In the paper

“SHP2 acts to dephosphorylate and activate multiple nodes of RAS signaling downstream of RTKs, enhancing signaling through the RAS-RAF-MEK-ERK cascade (25–28).”

What the sources say

• Partly supported

  The Introduction describes SHP2 as a phosphatase and scaffold downstream of RTKs that promotes RAS activation. The Results and Discussion link SHP2 to RAS-GTP loading and downstream RAS/MAPK signaling through adaptor-protein interactions and membrane recruitment. They do not establish that SHP2 dephosphorylates and activates multiple RAS-signaling nodes, so that specific mechanism is unsupported. (LLM, conf=0.86)

  cites [25] Nichols, 2018, RAS nucleotide cycling underlies the SHP2 phosphatase dependence of mutant BRAF-, NF1- and RAS-driven cancers, Nat Cell Biol sourceExperimental — accuracy not yet measured
• Partly supported

  In “SHP2 Is a Bona Fide Oncoprotein” (page not available), the paper says SHP2 is required for full Ras/ERK1/2 activation and describes several sites whose dephosphorylation can promote that signaling, including Ras itself. But it presents the mechanisms involving several sites as current models and says they remain under investigation; the claim states them as established and specifies RAF and MEK, which the cited passage does not discuss. (LLM, conf=0.84)

  cites [26] Frankson, 2017, Therapeutic targeting of oncogenic tyrosine phosphatases, Cancer Res sourceExperimental — accuracy not yet measured
• Partly supported

  The main text (lines 35–37 and 58–60; page not provided) describes SHP2 as linking RTK signaling to the RAS-RAF-MEK-ERK pathway and says increased RTK signaling activates that pathway through SHP2. It does not say that SHP2 dephosphorylates and activates multiple nodes of RAS signaling; that specific mechanism is unsupported by the cited passages. (LLM, conf=0.85)

  cites [27] Mainardi, 2018, SHP2 is required for growth of KRAS-mutant non-small-cell lung cancer in vivo, Nat Med sourceExperimental — accuracy not yet measured
• Partly supported

  The introduction (lines 37–40, 63–64; page not specified) describes SHP2 as a phosphatase involved in signaling downstream of receptors and says it promotes RAS–RAF–MEK–ERK signaling. The results (lines 168–175; page not specified) show that SHP2 phosphatase activity is required to restore MAPK signaling after MEK inhibition. Our copy does not identify multiple RAS-signaling nodes that SHP2 dephosphorylates and activates. (LLM, conf=0.86)

  cites [28] Ruess, 2018, Mutant KRAS-driven cancers depend on PTPN11/SHP2 phosphatase, Nat Med sourceExperimental — accuracy not yet measured

In the paper

“Indeed, in BRAFV600 colorectal cancer, targeting EGFR—the RTK thought to be the primary driver of feedback reactivation from preclinical studies—in combination with BRAF inhibition, has led to an improvement in clinical efficacy (34–39).”

What the sources say

• Supported

  The Discussion (page not provided) reports modest clinical activity with BRAF plus EGFR inhibition compared with BRAF inhibitor monotherapy. The Results (page not provided) give a 10% confirmed response rate for that combination, while the Introduction reports 5% for vemurafenib alone. The paper also describes EGFR as a proposed driver of feedback reactivation, while noting that other mechanisms can contribute. (LLM, conf=0.92)

  cites [34] Corcoran, 2018, Combined BRAF, EGFR, and MEK inhibition in patients with BRAFV600E-mutant colorectal cancer, Cancer Discov source
• Supported

  The Discussion states that BRAF or EGFR inhibitors alone had limited activity in BRAF-mutant metastatic colorectal cancer, whereas clinical studies of combinations showed improved efficacy. The Introduction also describes EGFR-mediated pathway reactivation as a reason for poor response to BRAF inhibition. Page numbers are not supplied in our copy. (LLM, conf=0.93)

  cites [35] van Geel, 2017, A phase Ib dose-escalation study of encorafenib and cetuximab with or without alpelisib in metastatic BRAF-mutant colorectal cancer, Cancer Discov source
• Partly supported

  The Discussion reports enhanced activity for combined BRAF and EGFR inhibition compared with historical data for vemurafenib alone. But the study was small and had no vemurafenib-only control arm, so it does not establish the clinical improvement as firmly as the citing sentence implies. (LLM, conf=0.83)

  cites [36] Yaeger, 2015, Pilot trial of combined BRAF and EGFR inhibition in BRAF-mutant metastatic colorectal cancer patients, Clin Cancer Res sourceExperimental — accuracy not yet measured
• ?Not checked — no full text of the sourcecites [37] Kopetz, 2017, Randomized trial of irinotecan and cetuximab with or without vemurafenib in BRAF-mutant metastatic colorectal cancer (SWOG S1406), J Clin Oncol source
• Supported

  The Introduction (page not provided) states that BRAF inhibition triggers EGFR feedback activation in BRAF V600E–mutant colorectal cancer cells. It also reports that clinical studies confirmed improved activity when EGFR-targeted therapy was added to BRAF inhibition. (LLM, conf=0.94)

  cites [38] Cutsem, 2019, Binimetinib, encorafenib, and cetuximab triplet therapy for patients with BRAF V600E–mutant metastatic colorectal cancer: safety lead-in results from the phase III BEACON Colorectal Cancer Study, J Clin Oncol source
• Partly supported

  The Results > Efficacy section reports one response with vemurafenib plus cetuximab in BRAF V600–mutated colorectal cancer, versus none with vemurafenib alone. It does not establish an overall improvement in clinical efficacy: median progression-free and overall survival were shorter in the combination cohort, and the Discussion describes its clinical activity as modest. Page numbers were not available in our copy. (LLM, conf=0.85)

  cites [39] Hyman, 2015, Vemurafenib in multiple nonmelanoma cancers with BRAF V600 mutations, N Engl J Med sourceExperimental — accuracy not yet measured

In the paper

“supporting previous findings that SHP2 perhaps plays a more important role in KRASG12C-driven tumor growth in vivo (27,28).”

What the sources say

• Supported

  In the in-vivo tumor-growth results (Fig. 3f; lines 125–131), SHP2 inhibition severely inhibited growth of tumors driven by KRAS G12C. The paper also reports little effect under standard cell-culture conditions (opening summary; lines 38–44), supporting the suggested greater importance in vivo. The result is not unique to G12C: KRAS G12V tumors were also inhibited. (LLM, conf=0.88)

  cites [27] Mainardi, 2018, SHP2 is required for growth of KRAS-mutant non-small-cell lung cancer in vivo, Nat Med sourceExperimental — accuracy not yet measured
• Partly supported

  The tumor-maintenance results (lines 140–153) report slower in vivo tumor growth after SHP2 loss in KRASG12D models and in xenografts bearing KRASG12D or KRASG12V. The paper supports a role for SHP2 in mutant-KRAS tumor growth, but the passages do not establish that its role is greater in KRASG12C-driven tumors. (LLM, conf=0.85)

  cites [28] Ruess, 2018, Mutant KRAS-driven cancers depend on PTPN11/SHP2 phosphatase, Nat Med sourceExperimental — accuracy not yet measured

In the paper

“The inhibitors function by locking KRASG12C in an inactive GDP bound state, exploiting the unique property of KRASG12C to cycle between the GDP- and GTP-bound states (6,7).”

What the sources say

• ?Not checked — no full text of the sourcecites [6] Ostrem, 2016, Direct small-molecule inhibitors of KRAS: from structural insights to mechanism-based design, Nat Rev Drug Discov source
• Supported

  The paper’s Abstract states that drug-bound KRASG12C is trapped in its inactive state because it is insusceptible to nucleotide exchange factors. It also says the inhibitor binds KRASG12C-GDP and that KRASG12C undergoes nucleotide cycling in cancer cells, supporting both parts of the attributed claim. (LLM, conf=0.94)

  cites [7] Lito, 2016, Allele-specific inhibitors inactivate mutant KRAS G12C by a trapping mechanism, Science source

In the paper

“and that the combination of BRAF and EGFR only suppresses signaling in a subset of patients (34).”

What the sources say

• Supported

  The Discussion states that combined BRAF and EGFR inhibition (D+P) produced MAPK suppression in on-treatment tumor biopsies in only a subset of patients with BRAF V600E-mutant colorectal cancer. This directly supports the attributed claim in the population studied. (LLM, conf=0.95)

  cites [34] Corcoran, 2018, Combined BRAF, EGFR, and MEK inhibition in patients with BRAFV600E-mutant colorectal cancer, Cancer Discov source

In the paper

“For example, RTK-driven feedback reactivation of RAS-MAPK signaling has been identified as a key driver of resistance in BRAFV600E cancers treated with BRAF inhibitors (colorectal cancer in particular) and in KRAS-mutant cancers treated with MEK inhibitors (11,12,32).”

What the sources say

• Partly supported

  The Results and Discussion (page not provided) identify EGFR-driven RAS–MAPK reactivation as a mechanism of reduced sensitivity to vemurafenib in BRAF-mutant colorectal cancer. Our copy does not support the separate claim about RTK-driven resistance to MEK inhibitors in KRAS-mutant cancers. (LLM, conf=0.88)

  cites [11] Corcoran, 2012, EGFR-mediated re-activation of MAPK signaling contributes to insensitivity of BRAF mutant colorectal cancers to RAF inhibition with vemurafenib, Cancer Discov sourceExperimental — accuracy not yet measured
• Partly supported

  Split into 2 atoms — 0 confirmed, 2 partially supported, 0 disputed, 0 misattributed, 0 unverifiable. Expand the claim to see per-atom verdicts.

  cites [12] Prahallad, 2012, Unresponsiveness of colon cancer to BRAF(V600E) inhibition through feedback activation of EGFR, Nature sourceExperimental — accuracy not yet measured
• Partly supported

  The main text (p. 5) says that feedback activation of EGFR causes resistance to BRAF inhibition in BRAF-mutant colon cancer, supporting the colorectal-cancer part of the claim. The paper studies BRAF-mutant melanoma as well, but the passages found do not establish the claimed mechanism in KRAS-mutant cancers treated with MEK inhibitors. (LLM, conf=0.85)

  cites [32] Sun, 2014, Reversible and adaptive resistance to BRAF(V600E) inhibition in melanoma, Nature sourceExperimental — accuracy not yet measured

In the paper

“However, adaptive feedback resistance has been a key limitation in prior clinical efforts to target the RAS-MAPK pathway.”

What the sources say

• Partly supported

  The Discussion (page unavailable) links the poor response of BRAF-mutant colorectal cancers to vemurafenib with EGFR-mediated reactivation of MAPK signaling, supporting feedback resistance as a limitation in that setting. The paper does not establish that it was a key limitation across prior clinical efforts to target the RAS–MAPK pathway more broadly; its mechanistic evidence comes from cell and xenograft studies. (LLM, conf=0.84)

  cites [11] Corcoran, 2012, EGFR-mediated re-activation of MAPK signaling contributes to insensitivity of BRAF mutant colorectal cancers to RAF inhibition with vemurafenib, Cancer Discov sourceExperimental — accuracy not yet measured
• Partly supported

  The 'feedback activation of EGFR' section links feedback after BRAF inhibition to the poor clinical response of BRAF V600E-mutant colon cancer to vemurafenib monotherapy (page not provided). That supports a specific example of feedback resistance, but not the broader claim that it has been a key limitation across prior clinical efforts to target the RAS-MAPK pathway. (LLM, conf=0.85)

  cites [12] Prahallad, 2012, Unresponsiveness of colon cancer to BRAF(V600E) inhibition through feedback activation of EGFR, Nature sourceExperimental — accuracy not yet measured
• Partly supported

  The main text (p. 4) says BRAF and MEK inhibitors produced strong initial responses in patients with BRAF-mutant melanoma, but resistance developed rapidly. It also discusses feedback activation of EGFR in BRAF-mutant colorectal cancer (p. 5). These passages support resistance as a limitation for specific pathway-targeting treatments, but do not establish that adaptive feedback resistance was a key limitation across prior clinical efforts to target the RAS–MAPK pathway generally. (LLM, conf=0.82)

  cites [32] Sun, 2014, Reversible and adaptive resistance to BRAF(V600E) inhibition in melanoma, Nature sourceExperimental — accuracy not yet measured

In the paper

“Indeed, SHP2 inhibition alone was shown to have anti-tumor effects in vitro and in vivo (25).”

What the sources say

• Supported

  The Results section reports that RMC-4550 treatment inhibited proliferation in KRASG12C cell lines in vitro. In the section on in vivo tumor growth, the authors report dose-dependent tumor growth inhibition in NF1-deficient and KRASG12C xenograft models, including regression in one model. These findings support the claim that SHP2 inhibition alone had anti-tumor effects in both settings. (LLM, conf=0.93)

  cites [25] Nichols, 2018, RAS nucleotide cycling underlies the SHP2 phosphatase dependence of mutant BRAF-, NF1- and RAS-driven cancers, Nat Cell Biol source

In the paper

“Furthermore, SHP2 inhibition was also demonstrated to have single-agent efficacy in preclinical KRASG12C models by reducing cycling to the active GTP-bound state, offering an additional advantage as a potential combination partner (25).”

What the sources say

• Supported

  The Results section (‘Certain KRASG12 mutant oncoproteins are dependent on SHP2 for activation’) reports that RMC-4550 alone inhibited proliferation and RAS-GTP levels in two KRASG12C cell lines. It also explains that SHP2 promotes GTP-loading of nucleotide-cycling KRAS. The paper notes that not every KRASG12C cell line was growth-sensitive, but the claim does not say efficacy was universal. (LLM, conf=0.92)

  cites [25] Nichols, 2018, RAS nucleotide cycling underlies the SHP2 phosphatase dependence of mutant BRAF-, NF1- and RAS-driven cancers, Nat Cell Biol source

In the paper

“Still, in all cases, combination therapies to suppress adaptive feedback proved key to optimizing the frequency and durability of response in each tumor type (34,50,51).”

What the sources say

• Partly supported

  The Abstract and Discussion report that targeting adaptive feedback improved response rates in BRAF V600E–mutant colorectal cancer. But the Discussion says response duration remained poor and further optimization was needed. This study therefore does not establish that the combination optimized durability, or outcomes in every tumor type. (LLM, conf=0.87)

  cites [34] Corcoran, 2018, Combined BRAF, EGFR, and MEK inhibition in patients with BRAFV600E-mutant colorectal cancer, Cancer Discov sourceExperimental — accuracy not yet measured
• Partly supported

  The Results and Discussion report frequent, durable responses to dabrafenib plus trametinib in previously treated BRAF V600E–mutant NSCLC, with higher response and progression-free survival than an indirect comparison with dabrafenib alone. But the Discussion says whether the proposed resistance mechanisms occur in these NSCLC patients is unknown. This trial therefore does not establish that suppressing adaptive feedback was the reason combination therapy improved responses, or that this was proved across tumor types. No page number is available in our copy. (LLM, conf=0.87)

  cites [50] Planchard, 2016, Dabrafenib plus trametinib in patients with previously treated BRAF(V600E)-mutant metastatic non-small cell lung cancer: an open-label, multicentre phase 2 trial, Lancet Oncol sourceExperimental — accuracy not yet measured
• Partly supported

  The Results (page unavailable) report that adding IGF1R and mTOR inhibitors to a KRAS-G12C inhibitor produced durable regression in lung-cancer xenografts where inhibitor treatment alone led to progression. The Discussion (page unavailable) describes suppressing compensatory feedback, but cautions that resistance may still evolve. These preclinical lung-cancer findings do not establish that combination therapy proved key to response frequency and durability in every tumor type. (LLM, conf=0.88)

  cites [51] Molina-Arcas, 2019, Development of combination therapies to maximize the impact of KRAS-G12C inhibitors in lung cancer, Sci Transl Med sourceExperimental — accuracy not yet measured

In the paper

“in most cell lines, increases in the levels of the active GTP-bound forms of the wild type RAS isoforms (NRAS-GTP, HRAS-GTP) were noted by 48 hours in a dose dependent manner”

In the paper

“no clear rebound in KRAS-GTP levels was noted between 4 and 48 h of treatment at any inhibitor concentration”

In the paper

“SHP2 inhibition was effective in suppressing adaptive resistance to KRASG12C inhibition across all cell lines.”

In the paper

“in each cell line, inhibition of a specific RTK in combination with ARS-1620 led to a marked decrease in cell viability relative to ARS-1620 alone.”

In the paper

“ARS-1620 effectively suppressed KRAS-GTP levels as measured by a RAF-RAS binding domain (RBD) pulldown assay in all cell lines in a dose-dependent manner”

In the paper

“RAS-MAPK pathway activity, as assessed by phospho-ERK levels, rebounded on average to ~75% of baseline levels by just 72 hours.”

In the paper

“co-inhibition of SHP2, which mediates signaling from multiple RTKs to RAS, abrogated feedback reactivation more universally”

• Also stated in: § INTRODUCTION · plain

  “co-targeting of SHP2 (17,18), a key phosphatase that mediates signaling from multiple RTKs to RAS, is able to abrogate feedback reactivation of RAS signaling following KRASG12C inhibition across all models”

In the paper

“on average we observed a 4 to 5-fold increase in NRAS-GTP and HRAS-GTP levels by 48 hours following treatment with the highest concentrations of ARS-1620 across all models.”

In the paper

“We observed high basal levels of several phosphorylated RTKs, including phospho-EGFR in most cell lines.”

In the paper

“The reduction in KRAS-GTP and RAS-GTP levels translated to further suppression of the MAPK pathway downstream of RAS by 48 hours.”

In the paper

“while neither reached statistical significance, a clear trend toward enhanced efficacy relative to ARS-1620 alone was observed with a specific RTK combination in each model”

In the paper

“though strong induction of RAS activity was observed with these combinations”

In the paper

“we found that the SHP2 inhibitor SHP099 led to incomplete suppression of KRAS-GTP levels as a single agent (Fig. 3A).”

In the paper

“we found that SHP2 inhibition could enhance suppression of active RAS in combination with ARS-1620 across both models”

In the paper

“combined KRASG12C and SHP2 inhibition led to a statistically significant reduction in cell number relative to either agent alone in all KRASG12C models”

In the paper

“we observed modest and incomplete suppression of ERK-dependent transcripts, such as DUSP6 after 4 days of treatment with either ARS-1620 or SHP099 alone (Figs. 4E,F and Supplementary Fig. S9).”

In the paper

“Second, in this study we see clear evidence of RTK-driven induction of wild type RAS (NRAS or HRAS) activity following KRASG12C inhibitor treatment, which can reactivate signaling in a KRASG12C-independent manner.”

In the paper

“with a reduction noted in some cell lines (SW1463, MIA PaCa-2, NCIH23, NCIH358) and unaffected or increased levels noted in other cell lines”

In the paper

“and MIA PaCa-2 more dependent on FGFR signaling”

In the paper

“However, combined treatment with ARS-1620 and SHP099 maintained a greater decrease after 4 days of treatment compared to each inhibitor alone.”

In the paper

“while having no effect in the KRASG12D Ls174T model (Fig. 3D, Supplementary Fig. S7, S8).”

In the paper

“and abrogated the adaptive increase in activated NRAS-GTP levels by 48 hours induced by ARS-1620 in some models”

In the paper

“While some models (NCIH358, Calu-1) demonstrated marked suppression of viability with ARS-1620 alone”

In the paper

“and that the pattern of RTK-dependence is highly variable between KRASG12C mutant cancers.”

In the paper

“strong feedback reactivation of MAPK signaling downstream of RAS is observed following KRASG12C inhibition”

In the paper

“the combination of ARS-1620 and SHP099 showed a statistically significant increase in anti-tumor efficacy compared to each agent alone”

In the paper

“multiple RTKs can contribute to adaptive feedback resistance to KRASG12C inhibition”

In the paper

“the predominant RTK dependency of each model differed”

In the paper

“While a reduction in tumor growth relative to vehicle control was observed in both SW837 and MIA PaCa-2 xenograft models with single agent ARS-1620 or SHP099”

In the paper

“SHP099 also reduced NRAS-GTP levels in several cell lines”

In the paper

“We observe that feedback reactivation is driven by multiple RTKs”

In the paper

“and that the pattern of RTK-dependence is highly heterogeneous across KRASG12C models.”

In the paper

“we also assessed potential combinations of KRASG12C inhibition with MEK and ERK inhibitors, which also displayed potential cooperativity across the panel of KRASG12C models”

In the paper

“in all cell lines, concurrent ARS-1620 and SHP099 treatment led to more complete suppression of both KRAS-GTP and total RAS-GTP levels when compared to either agent alone at 48 hours (Fig. 3A).”

In the paper

“Similarly, we note that multiple RTKs appear to be involved in feedback reactivation following KRASG12C inhibition”

In the paper

“Interestingly, the effects of combined KRASG12C and SHP2 inhibition on cell viability were more pronounced in long-term viability assays.”

In the paper

“we find consistent evidence of rapid feedback reactivation of RAS pathway signaling in KRASG12C cancer models following treatment with KRASG12C inhibitors.”

In the paper

“The efficacy of SHP099 monotherapy in vivo was more striking than seen in our in vitro experiments”

In the paper

“and led to tumor regressions in the majority of tumors in each model (Figs. 4A, B; Supplemental Fig. S9).”

In the paper

“ARS-1620 demonstrated modest efficacy as a single agent in both the SW837 and MIA PaCa-2 xenograft models”

In the paper

“with the SW837 model more dependent on HER signaling”

In the paper

“we found that adaptive feedback reactivation in the setting of KRASG12C inhibition exhibited a similarly variable RTK dependence in each model for maintaining both KRAS-GTP and total RAS-GTP levels”

In the paper

“the effects of KRASG12C or SHP2 inhibition on PI3K/AKT signaling, as measured by phospho-AKT, was highly variable across cell lines”

In the paper

“our data do indicate that some RTK inhibitors—in particular the pan-HER inhibitor afatinib and the FGFR inhibitor BGJ398—are effective in combination with KRASG12C inhibitors in many models”

In the paper

“Although some models showed the greatest sensitivity to KRASG12C inhibition in combination with a specific RTK inhibitor”

In the paper

“Moreover, we observed that SHP2 inhibition could consistently block the adaptive increase in wild type RAS (HRAS, NRAS) activation observed after KRASG12C inhibition in many models (Fig. 3A).”

In the paper

“and RTK combinations showed differential effects across in vivo models (Fig. 2C)”

In the paper

“the RTK associated phosphatase SHP2 may represent a common node through which to inhibit feedback reactivation of RAS signaling by multiple RTKs”

In the paper

“these data suggest that adaptive feedback reactivation of pathway signaling following KRASG12C inhibition corresponds with a rebound in RAS activity, in particular an increase in wild-type RAS activity”

In the paper

“Early clinical data with the KRASG12C inhibitor AMG510 was recently reported, showing an initial overall response rate of 24% (13/55) in patients with KRASG12C mutant cancers”

What the sources say

• ?Not checked — no full text of the sourcecites [16] Govindan, 2019, 446PDPhase I study of AMG 510, a novel molecule targeting KRAS G12C mutant solid tumours, Ann Oncol source

In the paper

“highlight the potential importance of vertical inhibition strategies to enhance the clinical efficacy of KRASG12C inhibitors.”

In the paper

“These data identify feedback reactivation of wild type RAS as a key mechanism of adaptive resistance to KRASG12C inhibitors”

In the paper

“previous efforts to target the RAS-RAF-MEK pathway have been hindered by adaptive feedback reactivation of pathway signaling as a major mode of therapeutic resistance.”

In the paper

“These results support that multiple RTKs can contribute to adaptive feedback resistance to KRASG12C inhibition”

In the paper

“these data suggest that blocking adaptive feedback signals driving pathway may be necessary to enhance the efficacy of KRASG12C inhibitors.”

In the paper

“suggesting that multiple RTKs may play a role in adaptive feedback to KRASG12C inhibition.”

In the paper

“this mechanism of action is unlikely to be effective against the second mechanism of adaptive feedback (RTK-driven activation of wild type RAS) (33).”

What the sources say

• ?Not checked — no full text of the sourcecites [33] Young, 2013, Oncogenic and wild-type Ras play divergent roles in the regulation of mitogen-activated protein kinase signaling, Cancer Discov source

In the paper

“co-targeting of SHP2 (17,18), a key phosphatase that mediates signaling from multiple RTKs to RAS”

What the sources say

• ?Not checked — no full text of the sourcecites [17] Agazie, 2003, Molecular mechanism for a role of SHP2 in epidermal growth factor receptor signaling, Mol Cell Biol source
• ?Not checked — no full text of the sourcecites [18] Dance, 2008, The molecular functions of Shp2 in the Ras/Mitogen-activated protein kinase (ERK1/2) pathway, Cell Signal source

In the paper

“Because KRASG12C actively cycles between its GDP-bound inactive state and its GTP-bound active state, KRASG12C may be uniquely dependent on some level of basal upstream activation from RTKs to maintain activity.”

In the paper

“these data support the potential for vertical inhibition strategies to suppress adaptive feedback resistance to KRASG12C inhibition”

In the paper

“supporting the potential for SHP2 as a common downstream node through which to inhibit signaling from multiple RTKs”

In the paper

“but also suggest that co-inhibition of individual RTKs may not be broadly effective across KRASG12C cancers”

In the paper

“While our data suggest that SHP2 inhibitors could be a promising combination partner for KRASG12C inhibitors”

In the paper

“Thus, our results suggest that SHP2 inhibition can mitigate the induction of wild type RAS activity that drives adaptive feedback reactivation of RAS and MAPK pathway signaling in response to KRASG12C inhibition.”

In the paper

“Thus, this prior experience predicts that adaptive resistance may pose a key obstacle for KRASG12C inhibitors, as well”

In the paper

“Together, these data support the potential of vertical pathway inhibition strategies to overcome adaptive resistance to KRASG12C inhibition.”

In the paper

“combined inhibition of RTKs or SHP2 and KRASG12C could represent a more effective therapeutic strategy to overcome resistance and improve efficacy in KRAS G12C-mutant tumors”

In the paper

“our data suggest that interrupting the adaptive feedback loop following KRASG12C inhibition may be critical to overcoming adaptive resistance.”

In the paper

“RTK-driven feedback may contribute to RAS reactivation through two mechanisms.”

In the paper

“Thus, inhibition of SHP2 has the potential to block the ability of multiple RTKs to activate RAS.”

In the paper

“Taken together, our data suggest that adaptive feedback is likely to play a key role in resistance to KRASG12C inhibitors”

In the paper

“suggesting that co-targeting a single RTK is unlikely to be universally effective.”

In the paper

“Interestingly, this pattern of tumor type-specific difference in response is highly consistent with prior examples of adaptive resistance.”

In the paper

“supporting its potential as a more universal approach.”

In the paper

“Conversely, targeting SHP2 provides the potential opportunity to intercept a common signaling node linking multiple RTKs to RAS signaling.”

In the paper

“Similarly, our data suggest that therapeutic combinations will be key to overcoming adaptive resistance and enhancing clinical benefit of KRASG12C inhibitors.”