RAS G12C Inhibitors: Three Birds with One Stone.

SUMMARY: In this issue, Rubinson, Tanaka, and colleagues demonstrate that differences among G12C inhibitors rely on their ability to covalently bind not only G12C mutant KRAS but also NRAS and HRAS, proposing sotorasib as a potent NRAS G12C inhibitor. See related article by Rubinson et al., p. 727 (6).

Combined RAF and MEK Inhibition to Treat Activated Non-V600 BRAF-Altered Advanced Cancers.

BACKGROUND: Cancers with non-V600 BRAF-activating alterations have no matched therapy. Preclinical data suggest that these tumors depend on ERK signaling; however, clinical response to MEK/ERK inhibitors has overall been low. We hypothesized that a narrow therapeutic index, driven by ERK inhibition in healthy (wild-type) tissues, limits the efficacy of these inhibitors. As these mutants signal as activated dimers, we further hypothesized that RAF inhibitors given concurrently would improve the therapeutic index by opposing ERK inhibition in normal tissues and not activate ERK in the already activated tumor. MATERIALS AND METHODS: Using cell lines and patient-derived xenografts, we evaluated the effect of RAF inhibition, alone and in combination with MEK/ERK inhibitors. We then undertook a phase I/II clinical trial of a higher dose of the MEK inhibitor binimetinib combined with the RAF inhibitor encorafenib in patients with advanced cancer with activating non-V600 BRAF alterations. RESULTS: RAF inhibition led to modest inhibition of signaling and growth in activated non-V600 BRAF preclinical models and allowed higher dose of MEK/ERK inhibitors in vivo for more profound tumor regression. Fifteen patients received binimetinib 60 mg twice daily plus encorafenib 450 mg daily (6 gastrointestinal primaries, 6 genitourinary primaries, 3 melanoma, and 2 lung cancer; 7 BRAF mutations and 8 BRAF fusions). Treatment was well tolerated without dose-limiting toxicities. One patient had a confirmed partial response, 8 had stable disease, and 6 had radiographic or clinical progression as best response. On-treatment biopsies revealed incomplete ERK pathway inhibition. CONCLUSION: Combined RAF and MEK inhibition does not sufficiently inhibit activated non-V600 BRAF-mutant tumors in patients.

Molecular Characterization of Acquired Resistance to KRASG12C-EGFR Inhibition in Colorectal Cancer.

With the combination of KRASG12C and EGFR inhibitors, KRAS is becoming a druggable target in colorectal cancer. However, secondary resistance limits its efficacy. Using cell lines, patient-derived xenografts, and patient samples, we detected a heterogeneous pattern of putative resistance alterations expected primarily to prevent inhibition of ERK signaling by drugs at progression. Serial analysis of patient blood samples on treatment demonstrates that most of these alterations are detected at a low frequency except for KRASG12C amplification, a recurrent resistance mechanism that rises in step with clinical progression. Upon drug withdrawal, resistant cells with KRASG12C amplification undergo oncogene-induced senescence, and progressing patients experience a rapid fall in levels of this alteration in circulating DNA. In this new state, drug resumption is ineffective as mTOR signaling is elevated. However, our work exposes a potential therapeutic vulnerability, whereby therapies that target the senescence response may overcome acquired resistance. SIGNIFICANCE: Clinical resistance to KRASG12C-EGFR inhibition primarily prevents suppression of ERK signaling. Most resistance mechanisms are subclonal, whereas KRASG12C amplification rises over time to drive a higher portion of resistance. This recurrent resistance mechanism leads to oncogene-induced senescence upon drug withdrawal and creates a potential vulnerability to senolytic approaches. This article is highlighted in the In This Issue feature, p. 1.

Anatomic position determines oncogenic specificity in melanoma.

Oncogenic alterations to DNA are not transforming in all cellular contexts1,2. This may be due to pre-existing transcriptional programmes in the cell of origin. Here we define anatomic position as a major determinant of why cells respond to specific oncogenes. Cutaneous melanoma arises throughout the body, whereas the acral subtype arises on the palms of the hands, soles of the feet or under the nails3. We sequenced the DNA of cutaneous and acral melanomas from a large cohort of human patients and found a specific enrichment for BRAF mutations in cutaneous melanoma and enrichment for CRKL amplifications in acral melanoma. We modelled these changes in transgenic zebrafish models and found that CRKL-driven tumours formed predominantly in the fins of the fish. The fins are the evolutionary precursors to tetrapod limbs, indicating that melanocytes in these acral locations may be uniquely susceptible to CRKL. RNA profiling of these fin and limb melanocytes, when compared with body melanocytes, revealed a positional identity gene programme typified by posterior HOX13 genes. This positional gene programme synergized with CRKL to amplify insulin-like growth factor (IGF) signalling and drive tumours at acral sites. Abrogation of this CRKL-driven programme eliminated the anatomic specificity of acral melanoma. These data suggest that the anatomic position of the cell of origin endows it with a unique transcriptional state that makes it susceptible to only certain oncogenic insults.

Expanding the Reach of Precision Oncology by Drugging All KRAS Mutants.

KRAS is the most frequently mutated oncogene, harboring mutations in approximately one in seven cancers. Allele-specific KRASG12C inhibitors are currently changing the treatment paradigm for patients with KRASG12C-mutated non-small cell lung cancer and colorectal cancer. The success of addressing a previously elusive KRAS allele has fueled drug discovery efforts for all KRAS mutants. Pan-KRAS drugs have the potential to address broad patient populations, including KRASG12D-, KRASG12V-, KRASG13D-, KRASG12R-, and KRASG12A-mutant or KRAS wild-type-amplified cancers, as well as cancers with acquired resistance to KRASG12C inhibitors. Here, we review actively pursued allele-specific and pan-KRAS inhibition strategies and their potential utility. SIGNIFICANCE: Mutant-selective KRASG12C inhibitors target a fraction (approximately 13.6%) of all KRAS-driven cancers. A broad arsenal of KRAS drugs is needed to comprehensively conquer KRAS-driven cancers. Conceptually, we foresee two future classes of KRAS medicines: mutant-selective KRAS drugs targeting individual variant alleles and pan-KRAS therapeutics targeting a broad range of KRAS alterations.

KRAS G12C Mutation Is Associated with Increased Risk of Recurrence in Surgically Resected Lung Adenocarcinoma.

PURPOSE: KRAS G12C is the most common KRAS mutation in primary lung adenocarcinoma. Phase I clinical trials have demonstrated encouraging clinical activity of KRAS G12C inhibitors in the metastatic setting. We investigated disease-free survival (DFS) and tumor genomic features in patients with surgically resected KRAS G12C-mutant lung adenocarcinoma. EXPERIMENTAL DESIGN: Patients who underwent resection of stage I-III lung adenocarcinoma and next-generation sequencing (NGS) were evaluated. Exclusion criteria were receipt of induction therapy, incomplete resection, and low-quality NGS. Mutations were classified as KRAS wild-type (KRAS wt), G12C (KRAS G12C), or non-G12C (KRAS other). DFS was compared between groups using the log-rank test; factors associated with DFS were assessed using Cox regression. Mutual exclusivity and cooccurrence, tumor clonality, and mutational signatures were assessed. RESULTS: In total, 604 patients were included: 374 KRAS wt (62%), 95 KRAS G12C (16%), and 135 KRAS other (22%). Three-year DFS was not different between KRAS-mutant and KRAS wt tumors. However, 3-year DFS was worse in patients with KRAS G12C than KRAS other tumors (log-rank P = 0.029). KRAS G12C tumors had more lymphovascular invasion (51% vs. 37%; P = 0.032) and higher tumor mutation burden [median (interquartile range), 7.0 (5.3-10.8) vs. 6.1 (3.5-9.7); P = 0.021], compared with KRAS other tumors. KRAS G12C mutation was independently associated with worse DFS on multivariable analysis. Our DFS findings were externally validated in an independent The Cancer Genome Atlas cohort. CONCLUSIONS: KRAS G12C mutations are associated with worse DFS after complete resection of stage I-III lung adenocarcinoma. These tumors harbor more aggressive clinicopathologic and genomic features than other KRAS-mutant tumors. We identified a high-risk group for whom KRAS G12C inhibitors may be investigated to improve survival.

TRK xDFG Mutations Trigger a Sensitivity Switch from Type I to II Kinase Inhibitors.

On-target resistance to next-generation TRK inhibitors in TRK fusion-positive cancers is largely uncharacterized. In patients with these tumors, we found that TRK xDFG mutations confer resistance to type I next-generation TRK inhibitors designed to maintain potency against several kinase domain mutations. Computational modeling and biochemical assays showed that TRKAG667 and TRKCG696 xDFG substitutions reduce drug binding by generating steric hindrance. Concurrently, these mutations stabilize the inactive (DFG-out) conformations of the kinases, thus sensitizing these kinases to type II TRK inhibitors. Consistently, type II inhibitors impede the growth and TRK-mediated signaling of xDFG-mutant isogenic and patient-derived models. Collectively, these data demonstrate that adaptive conformational resistance can be abrogated by shifting kinase engagement modes. Given the prior identification of paralogous xDFG resistance mutations in other oncogene-addicted cancers, these findings provide insights into rational type II drug design by leveraging inhibitor class affinity switching to address recalcitrant resistant alterations. SIGNIFICANCE: In TRK fusion-positive cancers, TRK xDFG substitutions represent a shared liability for type I TRK inhibitors. In contrast, they represent a potential biomarker of type II TRK inhibitor activity. As all currently available type II agents are multikinase inhibitors, rational drug design should focus on selective type II inhibitor creation.This article is highlighted in the In This Issue feature, p. 1.

EGFR Blockade Reverts Resistance to KRASG12C Inhibition in Colorectal Cancer.

Most patients with KRAS G12C-mutant non-small cell lung cancer (NSCLC) experience clinical benefit from selective KRASG12C inhibition, whereas patients with colorectal cancer bearing the same mutation rarely respond. To investigate the cause of the limited efficacy of KRASG12C inhibitors in colorectal cancer, we examined the effects of AMG510 in KRAS G12C colorectal cancer cell lines. Unlike NSCLC cell lines, KRAS G12C colorectal cancer models have high basal receptor tyrosine kinase (RTK) activation and are responsive to growth factor stimulation. In colorectal cancer lines, KRASG12C inhibition induces higher phospho-ERK rebound than in NSCLC cells. Although upstream activation of several RTKs interferes with KRASG12C blockade, we identify EGFR signaling as the dominant mechanism of colorectal cancer resistance to KRASG12C inhibitors. The combinatorial targeting of EGFR and KRASG12C is highly effective in colorectal cancer cells and patient-derived organoids and xenografts, suggesting a novel therapeutic strategy to treat patients with KRAS G12C colorectal cancer. SIGNIFICANCE: The efficacy of KRASG12C inhibitors in NSCLC and colorectal cancer is lineage-specific. RTK dependency and signaling rebound kinetics are responsible for sensitivity or resistance to KRASG12C inhibition in colorectal cancer. EGFR and KRASG12C should be concomitantly inhibited to overcome resistance to KRASG12C blockade in colorectal tumors.See related commentary by Koleilat and Kwong, p. 1094.This article is highlighted in the In This Issue feature, p. 1079.

HER2-Mediated Internalization of Cytotoxic Agents in ERBB2 Amplified or Mutant Lung Cancers.

Amplification of and oncogenic mutations in ERBB2, the gene encoding the HER2 receptor tyrosine kinase, promote receptor hyperactivation and tumor growth. Here we demonstrate that HER2 ubiquitination and internalization, rather than its overexpression, are key mechanisms underlying endocytosis and consequent efficacy of the anti-HER2 antibody-drug conjugates (ADC) ado-trastuzumab emtansine (T-DM1) and trastuzumab deruxtecan (T-DXd) in lung cancer cell lines and patient-derived xenograft models. These data translated into a 51% response rate in a clinical trial of T-DM1 in 49 patients with ERBB2-amplified or -mutant lung cancers. We show that cotreatment with irreversible pan-HER inhibitors enhances receptor ubiquitination and consequent ADC internalization and efficacy. We also demonstrate that ADC switching to T-DXd, which harbors a different cytotoxic payload, achieves durable responses in a patient with lung cancer and corresponding xenograft model developing resistance to T-DM1. Our findings may help guide future clinical trials and expand the field of ADC as cancer therapy. SIGNIFICANCE: T-DM1 is clinically effective in lung cancers with amplification of or mutations in ERBB2. This activity is enhanced by cotreatment with irreversible pan-HER inhibitors, or ADC switching to T-DXd. These results may help address unmet needs of patients with HER2-activated tumors and no approved targeted therapy.See related commentary by Rolfo and Russo, p. 643.This article is highlighted in the In This Issue feature, p. 627.

Resistance to TRK inhibition mediated by convergent MAPK pathway activation.

TRK fusions are found in a variety of cancer types, lead to oncogenic addiction, and strongly predict tumor-agnostic efficacy of TRK inhibition1-8. With the recent approval of the first selective TRK inhibitor, larotrectinib, for patients with any TRK-fusion-positive adult or pediatric solid tumor, to identify mechanisms of treatment failure after initial response has become of immediate therapeutic relevance. So far, the only known resistance mechanism is the acquisition of on-target TRK kinase domain mutations, which interfere with drug binding and can potentially be addressable through second-generation TRK inhibitors9-11. Here, we report off-target resistance in patients treated with TRK inhibitors and in patient-derived models, mediated by genomic alterations that converge to activate the mitogen-activated protein kinase (MAPK) pathway. MAPK pathway-directed targeted therapy, administered alone or in combination with TRK inhibition, re-established disease control. Experimental modeling further suggests that upfront dual inhibition of TRK and MEK may delay time to progression in cancer types prone to the genomic acquisition of MAPK pathway-activating alterations. Collectively, these data suggest that a subset of patients will develop off-target mechanisms of resistance to TRK inhibition with potential implications for clinical management and future clinical trial design.

Stromal Microenvironment Shapes the Intratumoral Architecture of Pancreatic Cancer.

Single-cell technologies have described heterogeneity across tissues, but the spatial distribution and forces that drive single-cell phenotypes have not been well defined. Combining single-cell RNA and protein analytics in studying the role of stromal cancer-associated fibroblasts (CAFs) in modulating heterogeneity in pancreatic cancer (pancreatic ductal adenocarcinoma [PDAC]) model systems, we have identified significant single-cell population shifts toward invasive epithelial-to-mesenchymal transition (EMT) and proliferative (PRO) phenotypes linked with mitogen-activated protein kinase (MAPK) and signal transducer and activator of transcription 3 (STAT3) signaling. Using high-content digital imaging of RNA in situ hybridization in 195 PDAC tumors, we quantified these EMT and PRO subpopulations in 319,626 individual cancer cells that can be classified within the context of distinct tumor gland "units." Tumor gland typing provided an additional layer of intratumoral heterogeneity that was associated with differences in stromal abundance and clinical outcomes. This demonstrates the impact of the stroma in shaping tumor architecture by altering inherent patterns of tumor glands in human PDAC.

Targeting the CBM complex causes Treg cells to prime tumours for immune checkpoint therapy.

Solid tumours are infiltrated by effector T cells with the potential to control or reject them, as well as by regulatory T (Treg) cells that restrict the function of effector T cells and thereby promote tumour growth1. The anti-tumour activity of effector T cells can be therapeutically unleashed, and is now being exploited for the treatment of some forms of human cancer. However, weak tumour-associated inflammatory responses and the immune-suppressive function of Treg cells remain major hurdles to broader effectiveness of tumour immunotherapy2. Here we show that, after disruption of the CARMA1-BCL10-MALT1 (CBM) signalosome complex, most tumour-infiltrating Treg cells produce IFNγ, resulting in stunted tumour growth. Notably, genetic deletion of both or even just one allele of CARMA1 (also known as Card11) in only a fraction of Treg cells-which avoided systemic autoimmunity-was sufficient to produce this anti-tumour effect, showing that it is not the mere loss of suppressive function but the gain of effector activity by Treg cells that initiates tumour control. The production of IFNγ by Treg cells was accompanied by activation of macrophages and upregulation of class I molecules of the major histocompatibility complex on tumour cells. However, tumour cells also upregulated the expression of PD-L1, which indicates activation of adaptive immune resistance3. Consequently, blockade of PD-1 together with CARMA1 deletion caused rejection of tumours that otherwise do not respond to anti-PD-1 monotherapy. This effect was reproduced by pharmacological inhibition of the CBM protein MALT1. Our results demonstrate that partial disruption of the CBM complex and induction of IFNγ secretion in the preferentially self-reactive Treg cell pool does not cause systemic autoimmunity but is sufficient to prime the tumour environment for successful immune checkpoint therapy.

KRAS G12C NSCLC Models Are Sensitive to Direct Targeting of KRAS in Combination with PI3K Inhibition.

PURPOSE: KRAS-mutant lung cancers have been recalcitrant to treatments including those targeting the MAPK pathway. Covalent inhibitors of KRAS p.G12C allele allow for direct and specific inhibition of mutant KRAS in cancer cells. However, as for other targeted therapies, the therapeutic potential of these inhibitors can be impaired by intrinsic resistance mechanisms. Therefore, combination strategies are likely needed to improve efficacy.Experimental Design: To identify strategies to maximally leverage direct KRAS inhibition we defined the response of a panel of NSCLC models bearing the KRAS G12C-activating mutation in vitro and in vivo. We used a second-generation KRAS G12C inhibitor, ARS1620 with improved bioavailability over the first generation. We analyzed KRAS downstream effectors signaling to identify mechanisms underlying differential response. To identify candidate combination strategies, we performed a high-throughput drug screening across 112 drugs in combination with ARS1620. We validated the top hits in vitro and in vivo including patient-derived xenograft models. RESULTS: Response to direct KRAS G12C inhibition was heterogeneous across models. Adaptive resistance mechanisms involving reactivation of MAPK pathway and failure to induce PI3K-AKT pathway inactivation were identified as likely resistance events. We identified several model-specific effective combinations as well as a broad-sensitizing effect of PI3K-AKT-mTOR pathway inhibitors. The G12Ci+PI3Ki combination was effective in vitro and in vivo on models resistant to single-agent ARS1620 including patient-derived xenografts models. CONCLUSIONS: Our findings suggest that signaling adaptation can in some instances limit the efficacy of ARS1620 but combination with PI3K inhibitors can overcome this resistance.

Restoring PUMA induction overcomes KRAS-mediated resistance to anti-EGFR antibodies in colorectal cancer.

Intrinsic and acquired resistance to anti-EGFR antibody therapy, frequently mediated by a mutant or amplified KRAS oncogene, is a significant challenge in the treatment of colorectal cancer (CRC). However, the mechanism of KRAS-mediated therapeutic resistance is not well understood. In this study, we demonstrate that clinically used anti-EGFR antibodies, including cetuximab and panitumumab, induce killing of sensitive CRC cells through p73-dependent transcriptional activation of the pro-apoptotic Bcl-2 family protein PUMA. PUMA induction and p73 activation are abrogated in CRC cells with acquired resistance to anti-EGFR antibodies due to KRAS alterations. Inhibition of aurora kinases preferentially kills mutant KRAS CRC cells and overcomes KRAS-mediated resistance to anti-EGFR antibodies in vitro and in vivo by restoring PUMA induction. Our results suggest that PUMA plays a critical role in meditating the sensitivity of CRC cells to anti-EGFR antibodies, and that restoration of PUMA-mediated apoptosis is a promising approach to improve the efficacy of EGFR-targeted therapy.

MM-151 overcomes acquired resistance to cetuximab and panitumumab in colorectal cancers harboring EGFR extracellular domain mutations.

The anti-epidermal growth factor receptor (EGFR) antibodies cetuximab and panitumumab are used to treat RAS wild-type colorectal cancers (CRCs), but their efficacy is limited by the emergence of acquired drug resistance. After EGFR blockade, about 20% of CRCs develop mutations in the EGFR extracellular domain (ECD) that impair antibody binding and are associated with clinical relapse. We hypothesized that EGFR ECD-resistant variants could be targeted by the recently developed oligoclonal antibody MM-151 that binds multiple regions of the EGFR ECD. MM-151 inhibits EGFR signaling and cell growth in preclinical models, including patient-derived cells carrying mutant EGFR. Upon MM-151 treatment, EGFR ECD mutations decline in circulating cell-free tumor DNA (ctDNA) of CRC patients who previously developed resistance to EGFR blockade. These data provide molecular rationale for the clinical use of MM-151 in patients who become resistant to cetuximab or panitumumab as a result of EGFR ECD mutations.

Sensitivity to Entrectinib Associated With a Novel LMNA-NTRK1 Gene Fusion in Metastatic Colorectal Cancer.

In metastatic colorectal cancer (CRC), actionable genetic lesions represent potential clinical opportunities. NTRK1, 2, and 3 gene rearrangements encode oncogenic fusions of the tropomyosin-receptor kinase (TRK) family of receptor tyrosine kinases in different tumor types. The TPM3-NTRK1 rearrangement is a recurring event in CRC that renders tumors sensitive to TRKA kinase inhibitors in preclinical models. We identified abnormal expression of the TRKA protein in tumor and liver metastases of a CRC patient refractory to standard therapy. Molecular characterization unveiled a novel LMNA-NTRK1 rearrangement within chromosome 1 with oncogenic potential, and the patient was treated with the pan-TRK inhibitor entrectinib, achieving partial response with decrease in hepatic target lesions from 6.8 and 8.2cm in longest diameter to 4.7 and 4.3cm, respectively. To our knowledge, this is the first clinical evidence of efficacy for therapeutic inhibition of TRKA in a solid tumor, illuminating a genomic-driven strategy to identify CRCs reliant on this oncogene to be clinically targeted with entrectinib.

Acquired Resistance to the TRK Inhibitor Entrectinib in Colorectal Cancer.

UNLABELLED: Entrectinib is a first-in-class pan-TRK kinase inhibitor currently undergoing clinical testing in colorectal cancer and other tumor types. A patient with metastatic colorectal cancer harboring an LMNA-NTRK1 rearrangement displayed a remarkable response to treatment with entrectinib, which was followed by the emergence of resistance. To characterize the molecular bases of the patient's relapse, circulating tumor DNA (ctDNA) was collected longitudinally during treatment, and a tissue biopsy, obtained before entrectinib treatment, was transplanted in mice (xenopatient), which then received the same entrectinib regimen until resistance developed. Genetic profiling of ctDNA and xenopatient samples showed acquisition of two point mutations in the catalytic domain of NTRK1, p.G595R and p.G667C. Biochemical and pharmacologic analysis in multiple preclinical models confirmed that either mutation renders the TRKA kinase insensitive to entrectinib. These findings can be immediately exploited to design next-generation TRKA inhibitors. SIGNIFICANCE: We provide proof of principle that analyses of xenopatients (avatar) and liquid biopsies allow the identification of drug resistance mechanisms in parallel with clinical treatment of an individual patient. We describe for the first time that p.G595R and p.G667C TRKA mutations drive acquired resistance to entrectinib in colorectal cancers carrying NTRK1 rearrangements.