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KRAS is one of the most commonly mutated proteins in cancer, and efforts to directly inhibit its function have been continuing for decades. The most successful of these has been the development of covalent allele-specific inhibitors that trap KRAS G12C in its inactive conformation and suppress tumour growth in patients1–7. Whether inactive-state selective inhibition can be used to therapeutically target non-G12C KRAS mutants remains under investigation. Here we report the discovery and characterization of a non-covalent inhibitor that binds preferentially and with high affinity to the inactive state of KRAS while sparing NRAS and HRAS. Although limited to only a few amino acids, the evolutionary divergence in the GTPase domain of RAS isoforms was sufficient to impart orthosteric and allosteric constraints for KRAS selectivity. The inhibitor blocked nucleotide exchange to prevent the activation of wild-type KRAS and a broad range of KRAS mutants, including G12A/C/D/F/V/S, G13C/D, V14I, L19F, Q22K, D33E, Q61H, K117N and A146V/T. Inhibition of downstream signalling and proliferation was restricted to cancer cells harbouring mutant KRAS, and drug treatment suppressed KRAS mutant tumour growth in mice, without having a detrimental effect on animal weight. Our study suggests that most KRAS oncoproteins cycle between an active state and an inactive state in cancer cells and are dependent on nucleotide exchange for activation. Pan-KRAS inhibitors, such as the one described here, have broad therapeutic implications and merit clinical investigation in patients with KRAS-driven cancers.

Since the discovery of mutationally activated RAS in human cancers, small molecule inhibitors have been long sought but disappointingly elusive. RAS is in an inactive, “off” state when bound to guanosine diphosphate (GDP) and in an active, “on” state when bound to guanosine triphosphate (GTP). According to dogma, mutationally activated RAS is insensitive to GTPase activating proteins (GAPs) that accelerate conversion of active GTP-bound RAS to inactive, GDP-bound RAS. Yet, a small molecule blocks the growth of cancer cells expressing a KRAS Gly(12)→Cys (KRAS(G12C)) mutant, despite binding only GDP-bound KRAS(G12C) (1). The US Food and Drug Administration recently approved sotorasib, a KRAS(G12C) off inhibitor, and more are in the pipeline. How can there be sufficient GDP-bound KRAS(G12C) to enable inhibitor efficacy? On page 197 of this issue, Li et al. (2) find that a GAP for heterotrimeric Gα subunits can also promote GTP hydrolysis to stimulate formation of GDP-bound KRAS(G12C).

KRAS GTPases are activated in one-third of cancers, and KRAS(G12C) is one of the most common activating alterations in lung adenocarcinoma1,2. KRAS(G12C) inhibitors3,4 are in phase-I clinical trials and early data show partial responses in nearly half of patients with lung cancer. How cancer cells bypass inhibition to prevent maximal response to therapy is not understood. Because KRAS(G12C) cycles between an active and inactive conformation4–6, and the inhibitors bind only to the latter, we tested whether isogenic cell populations respond in a non-uniform manner by studying the effect of treatment at a single-cell resolution. Here we report that, shortly after treatment, some cancer cells are sequestered in a quiescent state with low KRAS activity, whereas others bypass this effect to resume proliferation. This rapid divergent response occurs because some quiescent cells produce new KRAS(G12C) in response to suppressed mitogen-activated protein kinase output. New KRAS(G12C) is maintained in its active, drug-insensitive state by epidermal growth factor receptor and aurora kinase signalling. Cells without these adaptive changes—or cells in which these changes are pharmacologically inhibited—remain sensitive to drug treatment, because new KRAS(G12C) is either not available or exists in its inactive, drug-sensitive state. The direct targeting of KRAS oncoproteins has been a longstanding objective in precision oncology. Our study uncovers a flexible non-uniform fitness mechanism that enables groups of cells within a population to rapidly bypass the effect of treatment. This adaptive process must be overcome if we are to achieve complete and durable responses in the clinic. Populations of KRAS(G12C)-mutant cancer cells can rapidly bypass the effects of treatment with KRAS(G12C) inhibitors because a subset of cells escapes drug-induced quiescence by producing new KRAS(G12C) that is maintained in its active, drug-insensitive state.

The principles that govern the evolution of tumors exposed to targeted therapy are poorly understood. Here we modeled the selection and propagation of an amplification in the BRAF oncogene (BRAFamp) in patient-derived tumor xenografts (PDXs) that were treated with a direct inhibitor of the kinase ERK, either alone or in combination with other ERK signaling inhibitors. Single-cell sequencing and multiplex fluorescence in situ hybridization analyses mapped the emergence of extra-chromosomal amplification in parallel evolutionary trajectories that arose in the same tumor shortly after treatment. The evolutionary selection of BRAFamp was determined by the fitness threshold, the barrier that subclonal populations need to overcome to regain fitness in the presence of therapy. This differed for inhibitors of ERK signaling, suggesting that sequential monotherapy is ineffective and selects for a progressively higher BRAF copy number. Concurrent targeting of the RAF, MEK and ERK kinases, however, imposed a sufficiently high fitness threshold to prevent the propagation of subclones with high-level BRAFamp. When administered on an intermittent schedule, this treatment inhibited tumor growth in 11/11 PDXs of lung cancer or melanoma without apparent toxicity in mice. Thus, gene amplification can be acquired and expanded through parallel evolution, enabling tumors to adapt while maintaining their intratumoral heterogeneity. Treatments that impose the highest fitness threshold will likely prevent the evolution of resistance-causing alterations and, thus, merit testing in patients.

KRAS GTPases are activated in one-third of cancers, and KRAS(G12C) is one of the most common activating alterations in lung adenocarcinoma

KRAS GTPases are activated in one-third of cancers and KRAS G12C is the most common activating alteration in lung adenocarcinoma. KRAS G12C-specific inhibitors (G12Ci) are in Phase-I clinical trials and early data show only partial responses in lung cancer patients. How cancer cells bypass inhibition, to prevent maximal responses to therapy, is not understood. Because KRAS G12C cycles between an active and inactive conformation, and the covalent G12Ci only bind to the latter, we tested whether isogenic cell populations respond non-uniformly by studying the effect of treatment at a single-cell resolution. Using single-cell RNA sequencing and a fluorescent quiescence biosensor, we show that shortly after treatment, most cancer cells are sequestered in a quiescent state with low KRAS activity, while a small population reactivates KRAS to resume proliferation. This rapid divergent response is due to synthesis of new, drug-free KRAS protein, resulting from increased KRAS transcription in response to suppressed MAPK signaling. Combining cell fate-specific gene expressions and results from a CRISPR-Cas9 screen, we identified that adaptive signals such as epidermal growth-factor receptor and aurora kinase A signaling modulate the heterogeneous response to treatment with G12Ci. These upstream signals help to maintain new KRAS G12C protein in its active, drug-insensitive state, which restores KRAS signaling and transcriptional output in a subset of cells to allow escape from G12Ci-induced quiescence. Cells without these adaptive changes (or cells where they are pharmacologically inhibited) remain sensitive to G12Ci treatment, because new KRAS G12C is either not available, or it exists in its inactive, drug-sensitive state. Combined inhibition of these adaptive signals along with KRAS G12C produced more potent antitumor effects in xenograft models. The direct targeting of KRAS oncoproteins has been a longstanding objective in precision oncology. Our study uncovers a flexible non-uniform fitness mechanism that enables groups of cells within a population to rapidly bypass the effect of treatment. This adaptive process must be overcome to maximize the therapeutic potential of conformation-specific KRAS G12C inhibitors in the clinic. Citation Format: Jenny Y. Xue, Yulei Zhao, Jordan Aronowitz, Trang T. Mai, Alberto Vides, Besnik Qeriqi, Dongsung Kim, Chuanchuan Li, Elisa de Stanchina, Linas Mazutis, Davide Risso, Piro Lito. Rapid non-uniform adaptation to conformation-specific KRAS G12Cinhibition [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 622.

Resumen La intoxicación por acetaminofén es una de las causas más frecuentes de falla hepática aguda fulminante y una de las principales causas de atención en los servicios de urgencias, por intoxicación debida a medicamentos. Recientemente, se han registrado avances en la comprensión fisiopatológica, diagnóstico y tratamiento de esta entidad clínica. Los mecanismos de estrés oxidativo y daño del ADN mitocondrial explican los daños producidos en esta intoxicación. En esta revisión se presentan aspectos referentes a la epidemiología, mecanismos fisiopatológicos, diagnóstico y tratamiento de la intoxicación por acetaminofén. Abstract Acetaminophen poisoning is one of the most frequent causes of acute fulminant hepatic failure and one of the main causes of care in emergency services due to drug intoxication. Recent progress has been made in the pathophysiological understanding, diagnosis and treatment of this clinical entity. The mechanisms of oxidative stress and mitochondrial DNA damage explain the damage caused by this intoxication. This review presents aspects related to the epidemiology, pathophysiological mechanisms, diagnosis and treatment of acetaminophen intoxication.

The principles that govern the evolution of tumors exposed to targeted therapy are poorly understood. Here we modeled the selection and propagation of an amplification in the BRAF oncogene (BRAF

KRAS GTPases are activated in one-third of cancers and KRAS G12C is the most common activating alteration in lung adenocarcinoma. KRAS G12C inhibitors are in Phase-I clinical trials and early data show only partial responses in lung cancer patients. How cancer cells bypass inhibition, to prevent maximal responses to therapy, is not understood. Because KRAS G12C cycles between an active and inactive conformation, and the inhibitors only bind to the latter, we hypothesized that isogenic cell populations respond non-uniformly. Here we studied the effect of treatment at the single cell level and showed that shortly after treatment, some cancer cells were sequestered in a quiescent state with low KRAS activity, while others reactivated KRAS to resume proliferation. By combining cell fate-specific gene expressions and results from a CRISPR-Cas9 screen, we identified that this rapid divergent response is due to new KRAS G12C produced in response to suppressed MAPK output. Upstream-acting adaptive signals, such as epidermal growth-factor receptor and aurora kinase signaling, maintain new KRAS G12C protein in its active/drug-insensitive state to restore KRAS output. Cells without these adaptive changes (or cells where they are pharmacologically inhibited) remain sensitive to drug treatment, because new KRAS G12C is either not available, or it exists in its inactive/drug-sensitive state. Combined inhibition of these adaptive signals along with KRAS G12C produced more potent antitumor effects in vivo. Our study uncovers a flexible non-uniform fitness mechanism that enables groups of cells within a population to rapidly bypass the effect of treatment. This adaptive process must be overcome to maximize the therapeutic potential of conformation-specific KRAS G12C inhibitors in the clinic. Citation Format: Jenny Xue, Yulei Zhao, Jordan Aronowitz, Trang T Mai, Alberto Vides, Besnik Qeriqi, Dongsung Kim, Chuanchuan Li, Elisa de Stanchina, Linas Mazutis, Davide Risso, Piro Lito. Rapid non-uniform adaptation to conformation-specific KRAS G12C inhibition [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference on Molecular Targets and Cancer Therapeutics; 2019 Oct 26-30; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2019;18(12 Suppl):Abstract nr LB-A04. doi:10.1158/1535-7163.TARG-19-LB-A04

Tumors evolve as they adapt to environmental cues. The principles governing evolution of tumors under the selective pressure of targeted therapy are not well understood. We aimed to evaluate the evolution of resistance and to identify therapeutic modalities that prevent this process in BRAFV600E-mutant tumors. We modeled the selection and propagation of BRAFV600E amplification (BRAFamp) in patient-derived tumor xenografts (PDX) treated with a direct ERK inhibitor. Single-cell sequencing and multiplex-fluorescence in situ hybridization mapped the emergence of extra-chromosomal amplification in multiple subclones of the same tumor shortly after treatment. The evolutionary selection of BRAFamp is determined by the fitness threshold, the barrier subclonal populations need to overcome to regain fitness in the presence of therapy. This differed for ERK signaling inhibitors, and single-cell sequencing of a melanoma PDX model showed that drugs of the same pathway do not necessarily select for the same subclones. These data suggest that sequential monotherapy is not optimal, but concurrent targeting of RAF, MEK, and ERK, however, imposes a sufficiently high fitness threshold to prevent the propagation of subclones with high-level amplification. Administered on an intermittent schedule, this treatment inhibited tumor growth without apparent toxicity in 11/11-lung cancer and melanoma PDX models with various additional alterations. Thus, gene amplification can be acquired and expanded through parallel evolution, enabling tumors to adapt while maintaining their intratumoral heterogeneity. Treatments that impose a high fitness threshold, such as our intermittent triple therapy, will likely prevent the evolution of resistance-causing alterations and merit testing in patients. Citation Format: Yaohua Xue, Luciano Martelotto, Timour Baslan, Alberto Vides, Martha Solomon, Kalyani Chadalavada, Elisa DeStanchina, Gouri Nanjangud, Michael Berger, Scott Lowe, Jorge S. Reis-Filho, Neal Rosen, Piro Lito. An approach to suppress the evolution of resistance in BRAFV600E-mutant cancer [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2017 Oct 26-30; Philadelphia, PA. Philadelphia (PA): AACR; Mol Cancer Ther 2018;17(1 Suppl):Abstract nr B015.