Acquired Resistance to KRASG12C Inhibition in Cancer.

BACKGROUND: Clinical trials of the KRAS inhibitors adagrasib and sotorasib have shown promising activity in cancers harboring KRAS glycine-to-cysteine amino acid substitutions at codon 12 (KRASG12C). The mechanisms of acquired resistance to these therapies are currently unknown. METHODS: Among patients with KRASG12C -mutant cancers treated with adagrasib monotherapy, we performed genomic and histologic analyses that compared pretreatment samples with those obtained after the development of resistance. Cell-based experiments were conducted to study mutations that confer resistance to KRASG12C inhibitors. RESULTS: A total of 38 patients were included in this study: 27 with non-small-cell lung cancer, 10 with colorectal cancer, and 1 with appendiceal cancer. Putative mechanisms of resistance to adagrasib were detected in 17 patients (45% of the cohort), of whom 7 (18% of the cohort) had multiple coincident mechanisms. Acquired KRAS alterations included G12D/R/V/W, G13D, Q61H, R68S, H95D/Q/R, Y96C, and high-level amplification of the KRASG12C allele. Acquired bypass mechanisms of resistance included MET amplification; activating mutations in NRAS, BRAF, MAP2K1, and RET; oncogenic fusions involving ALK, RET, BRAF, RAF1, and FGFR3; and loss-of-function mutations in NF1 and PTEN. In two of nine patients with lung adenocarcinoma for whom paired tissue-biopsy samples were available, histologic transformation to squamous-cell carcinoma was observed without identification of any other resistance mechanisms. Using an in vitro deep mutational scanning screen, we systematically defined the landscape of KRAS mutations that confer resistance to KRASG12C inhibitors. CONCLUSIONS: Diverse genomic and histologic mechanisms impart resistance to covalent KRASG12C inhibitors, and new therapeutic strategies are required to delay and overcome this drug resistance in patients with cancer. (Funded by Mirati Therapeutics and others; ClinicalTrials.gov number, NCT03785249.).

Regulation of atrial natriuretic peptide secretion by a novel Ras-like protein.

Atrial cardiomyocytes, neurons, and endocrine tissues secrete neurotransmitters and peptide hormones via large dense-core vesicles (LDCVs). We describe a new member of the Ras family of G-proteins, named RRP17, which is expressed specifically in cardiomyocytes, neurons, and the pancreas. RRP17 interacts with Ca(2+)-activated protein for secretion-1 (CAPS1), one of only a few proteins known to be associated exclusively with LDCV exocytosis. Ectopic expression of RRP17 in cardiomyocytes enhances secretion of atrial natriuretic peptide (ANP), a regulator of blood pressure and natriuresis. Conversely, genetic deletion of RRP17 in mice results in dysmorphic LDCVs, impaired ANP secretion, and hypertension. These findings identify RRP17 as a component of the cellular machinery involved in regulated secretion within the heart and potential mediator of the endocrine influence of the heart on other tissues.

A Phase 1b Study of Telisotuzumab Vedotin in Combination With Nivolumab in Patients With NSCLC.

INTRODUCTION: Telisotuzumab vedotin (Teliso-V) is an anti-c-Met-directed antibody-drug conjugate that has exhibited antitumor activity as monotherapy in NSCLC. Its potential activity combined with programmed cell death protein-1 inhibitors has not been previously evaluated. METHODS: In a phase 1b study (NCT02099058), adult patients (≥18 y) with advanced NSCLC received combination therapy with Teliso-V (1.6, 1.9, or 2.2 mg/kg, every 2 wk) plus nivolumab (3 mg/kg, 240 mg, or per locally approved label). The primary objective was to assess safety and tolerability; secondary objectives included the evaluation of antitumor activity. RESULTS: As of January 2020, a total of 37 patients received treatment with Teliso-V (safety population) in combination with nivolumab; 27 patients (efficacy population) were c-Met immunohistochemistry-positive. Programmed death-ligand 1 (PD-L1) status was evaluated in the efficacy population (PD-L1-positive [PD-L1+]: n = 15; PD-L1-negative [PD-L1-]: n = 9; PD-L1-unknown: n = 3). The median age was 67 years and 74% (20 of 27) of patients were naive to immune checkpoint inhibitors. The most common any-grade treatment-related adverse events were fatigue (27%) and peripheral sensory neuropathy (19%). The pharmacokinetic profile of Teliso-V plus nivolumab was similar to Teliso-V monotherapy. The objective response rate was 7.4%, with two patients (PD-L1+, c-Met immunohistochemistry H-score 190, n = 1; PD-L1-, c-Met H-score 290, n = 1) having a confirmed partial response. Overall median progression-free survival was 7.2 months (PD-L1+: 7.2 mo; PD-L1-: 4.5 mo; PD-L1-unknown: not reached). CONCLUSIONS: Combination therapy with Teliso-V plus nivolumab was well tolerated in patients with c-Met+ NSCLC with limited antitumor activity.

First-in-Human Phase I/IB Dose-Finding Study of Adagrasib (MRTX849) in Patients With Advanced KRASG12C Solid Tumors (KRYSTAL-1).

PURPOSE: Adagrasib (MRTX849) is an oral, highly selective, small-molecule, covalent inhibitor of KRASG12C. We report results from a phase I/IB study of adagrasib in non-small-cell lung cancer, colorectal cancer, and other solid tumors harboring the KRASG12C mutation. MATERIALS AND METHODS: Patients with advanced KRASG12C-mutant solid tumors were treated with adagrasib 150 mg orally once daily, 300 mg once daily, 600 mg once daily, 1,200 mg once daily, or 600 mg orally twice a day using an accelerated titration design, which transitioned to a modified toxicity probability interval design when a predefined degree of toxicity was observed or target adagrasib exposure was achieved. Safety, pharmacokinetics, and clinical activity were evaluated. RESULTS: Twenty-five patients were enrolled and received at least one dose of adagrasib. The recommended phase II dose (RP2D) was 600 mg twice a day on the basis of safety, tolerability, and observed pharmacokinetics properties. No maximum tolerated dose was formally defined. After a median follow-up of 19.6 months, eight of 15 patients (53.3%; 95% CI, 26.6 to 78.7) with RECIST-evaluable KRASG12C-mutant non-small-cell lung cancer treated at 600 mg twice a day achieved a confirmed partial response. The median duration of response was 16.4 months (95% CI, 3.1 to not estimable). The median progression-free survival was 11.1 months (95% CI, 2.6 to not estimable). One of two patients with KRASG12C-mutant colorectal cancer treated at 600 mg twice a day achieved a partial response (duration of response, 4.2 months). At the RP2D, the most common treatment-related adverse events (any grade) were nausea (80.0%), diarrhea (70.0%), vomiting (50.0%), and fatigue (45.0%). The most common grade 3-4 treatment-related adverse event was fatigue (15.0%). CONCLUSION: Adagrasib 600 mg twice a day was well tolerated and exhibited antitumor activity in patients with advanced solid tumors harboring the KRASG12C mutation.

American Radium Society Appropriate Use Criteria for Radiation Therapy in Oligometastatic or Oligoprogressive Non-Small Cell Lung Cancer.

PURPOSE: Recent randomized studies have suggested improvements in progression-free and overall survival with the addition of stereotactic body radiation therapy (SBRT, also known as SABR) in patients with oligometastatic non-small cell lung cancer. Given the novelty and complexity of incorporating SBRT in the oligometastatic setting, the multidisciplinary American Radium Society Lung Cancer Panel was assigned to create appropriate use criteria on SBRT as part of consolidative local therapy for patients with oligometastatic and oligoprogressive non-small cell lung cancer. METHODS AND MATERIALS: A review of the current literature was conducted from January 1, 2008, to December 25, 2020, using the Preferred Reporting Items for Systematic Reviews and Meta-analyses (PRISMA) guidelines to systematically search the PubMed database to retrieve a comprehensive set of relevant articles. RESULTS: Based on representation in existing randomized trials, the panel defined the term "oligometastasis" as ≤3 metastatic deposits (not including the primary tumor) in the previously untreated setting or after first-line systemic therapy after the initial diagnosis. "Oligoprogression" also referred to ≤3 discrete areas of progression in the setting of prior or ongoing receipt of systemic therapy. In all appropriate patients, the panel strongly recommends enrollment in a clinical trial whenever available. For oligometastatic disease, administering first-line systemic therapy followed by consolidative radiation therapy (to all sites plus the primary/nodal disease) is preferred over up-front radiation therapy. Owing to a dearth of data, the panel recommended that consolidative radiation therapy be considered on a case-by-case basis for 4 to 5 sites of oligometastatic disease, driver mutation-positive oligometastatic disease without progression on up-front targeted therapy, and oligoprogressive cases. CONCLUSIONS: Although SBRT/SABR appears to be both safe and effective in treating patients with limited metastatic sites of disease, many clinical circumstances require individualized management and strong multidisciplinary discussion on account of the limited existing data.

Pembrolizumab-Induced Vitiligo in Esophageal Squamous Cell Carcinoma Patient With Durable Complete Response.

Immune checkpoint inhibitors have emerged as a valuable therapeutic strategy in cancer treatment. Pembrolizumab is an inhibitor of programmed cell death protein 1 (PD-1) and its ligands 1 (PD-L1) and 2 (PD-L2). Disrupting the interaction between PD-L1 expressed on the cancer cell and PD-1 transmembrane protein on immune cells results in reactivation of T cell-mediated cellular immunity. This immune modulation has increased the risk of autoimmune adverse events, which can affect any organ system. Here, we present a case of delayed immune checkpoint inhibitor-induced vitiligo in a 74-year-old female with recurrent metastatic esophageal carcinoma who remains in remission more than five years after initiation of pembrolizumab.

Impact of Oral Chemotherapy Management Program on Capecitabine Toxicity Management.

PURPOSE: Increasing use of oral chemotherapy has created unique challenges related to patient safety and compliance. To address this issue, the Henry Ford Cancer Institute at Henry Ford Health System developed and implemented a system-wide, multidisciplinary program named the Oral Chemotherapy Management Program (OCMP). The purpose of this study was to evaluate the impact of OCMP on patient outcomes in those receiving capecitabine. METHODS: This was a retrospective, quasi-experimental study that compared outcomes in patients receiving capecitabine before and after OCMP implementation. The co-primary outcomes were incidence(s) of grade 1-4 and grade 3-4 adverse effects (AEs) associated with capecitabine. Secondary outcomes were emergency department (ED) visits, hospitalizations because of toxicity, and adherence rate. RESULTS: OCMP patients had significantly lower overall incidence of AE of any grade (58.9% v 70.3%; 95% CI, 0.39 to 0.94; P = .03). OCMP implementation significantly lowered incidence of any grade and grade 3-4 nausea, vomiting, and/or diarrhea, and grade 3-4 hand-foot syndrome. It resulted in the decreased number of ED visits (8.9% v 18.9%; P = .005) and hospitalizations (6.3% v 17.1%; P = .002), as well as improved medication adherence rates (0.94 v 0.97; P = .03). CONCLUSION: Most patients who developed capecitabine-related AE required intervention by OCMP. Implementation of OCMP reduced the incidence of high-grade AE, decreased the number of ED visits and hospitalizations because of AE, and improved the medication adherence rate.

American Radium Society Appropriate Use Criteria: Radiation Therapy for Limited-Stage SCLC 2020.

INTRODUCTION: Combined modality therapy with concurrent chemotherapy and radiation has long been the standard of care for limited-stage SCLC (LS-SCLC). However, there is controversy over best combined modality practices for LS-SCLC. To address these controversies, the American Radium Society (ARS) Thoracic Appropriate Use Criteria (AUC) Committee have developed updated consensus guidelines for the treatment of LS-SCLC. METHODS: The ARS AUC are evidence-based guidelines for specific clinical conditions that are reviewed by a multidisciplinary expert panel. The guidelines include a review and analysis of current evidence with application of consensus methodology (modified Delphi) to rate the appropriateness of treatments recommended by the panel for LS-SCLC. Agreement or consensus was defined as less than or equal to 3 rating points from the panel median. The consensus ratings and recommendations were then vetted by the ARS Executive Committee and subject to public comment before finalization. RESULTS: The ARS Thoracic AUC committee developed multiple consensus recommendations for LS-SCLC. There was strong consensus that patients with unresectable LS-SCLC should receive concurrent chemotherapy with radiation delivered either once or twice daily. For medically inoperable T1-T2N0 LS-SCLC, either concurrent chemoradiation or stereotactic body radiation followed by adjuvant chemotherapy is a reasonable treatment option. The panel continues to recommend whole-brain prophylactic cranial irradiation after response to chemoradiation for LS-SCLC. There was panel agreement that prophylactic cranial irradiation with hippocampal avoidance and programmed cell death protein-1/programmed death-ligand 1-directed immune therapy should not be routinely administered outside the context of clinical trials at this time. CONCLUSIONS: The ARS Thoracic AUC Committee provide consensus recommendations for LS-SCLC that aim to provide a groundwork for multidisciplinary care and clinical trials.

American Radium Society Appropriate Use Criteria on Radiation Therapy for Extensive-Stage SCLC.

INTRODUCTION: The standard-of-care therapy for extensive-stage SCLC has recently changed with the results of two large randomized trials revealing improved survival with the addition of immunotherapy to first-line platinum or etoposide chemotherapy. This has led to a lack of clarity around the role of consolidative thoracic radiation and prophylactic cranial irradiation in the setting of chemoimmunotherapy. METHODS: The American Radium Society Appropriate Use Criteria are evidence-based guidelines for specific clinical conditions that are reviewed by a multidisciplinary expert panel. The guidelines include a review and analysis of current evidence with the application of consensus methodology (modified Delphi) to rate the appropriateness of treatments recommended by the panel for extensive-stage SCLC. RESULTS: Current evidence supports either prophylactic cranial irradiation or surveillance with magnetic resonance imaging every 3 months for patients without evidence of brain metastases. Patients with brain metastases should receive whole-brain radiation with a recommended dose of 30 Gy in 10 fractions. Consolidative thoracic radiation can be considered in selected cases with the recommended dose ranging from 30 to 54 Gy; this recommendation was driven by expert opinion owing to the limited strength of evidence, as clinical trials addressing this question remain ongoing. CONCLUSIONS: Radiation therapy remains an integral component in the treatment paradigm for ES-SCLC.

Transcriptional coactivator PGC-1 alpha controls the energy state and contractile function of cardiac muscle.

Skeletal and cardiac muscle depend on high turnover of ATP made by mitochondria in order to contract efficiently. The transcriptional coactivator PGC-1alpha has been shown to function as a major regulator of mitochondrial biogenesis and respiration in both skeletal and cardiac muscle, but this has been based only on gain-of-function studies. Using genetic knockout mice, we show here that, while PGC-1alpha KO mice appear to retain normal mitochondrial volume in both muscle beds, expression of genes of oxidative phosphorylation is markedly blunted. Hearts from these mice have reduced mitochondrial enzymatic activities and decreased levels of ATP. Importantly, isolated hearts lacking PGC-1alpha have a diminished ability to increase work output in response to chemical or electrical stimulation. As mice lacking PGC-1alpha age, cardiac dysfunction becomes evident in vivo. These data indicate that PGC-1alpha is vital for the heart to meet increased demands for ATP and work in response to physiological stimuli.

The KRASG12C Inhibitor MRTX849 Provides Insight toward Therapeutic Susceptibility of KRAS-Mutant Cancers in Mouse Models and Patients.

Despite decades of research, efforts to directly target KRAS have been challenging. MRTX849 was identified as a potent, selective, and covalent KRASG12C inhibitor that exhibits favorable drug-like properties, selectively modifies mutant cysteine 12 in GDP-bound KRASG12C, and inhibits KRAS-dependent signaling. MRTX849 demonstrated pronounced tumor regression in 17 of 26 (65%) KRASG12C-positive cell line- and patient-derived xenograft models from multiple tumor types, and objective responses have been observed in patients with KRASG12C-positive lung and colon adenocarcinomas. Comprehensive pharmacodynamic and pharmacogenomic profiling in sensitive and partially resistant nonclinical models identified mechanisms implicated in limiting antitumor activity including KRAS nucleotide cycling and pathways that induce feedback reactivation and/or bypass KRAS dependence. These factors included activation of receptor tyrosine kinases (RTK), bypass of KRAS dependence, and genetic dysregulation of cell cycle. Combinations of MRTX849 with agents that target RTKs, mTOR, or cell cycle demonstrated enhanced response and marked tumor regression in several tumor models, including MRTX849-refractory models. SIGNIFICANCE: The discovery of MRTX849 provides a long-awaited opportunity to selectively target KRASG12C in patients. The in-depth characterization of MRTX849 activity, elucidation of response and resistance mechanisms, and identification of effective combinations provide new insight toward KRAS dependence and the rational development of this class of agents.See related commentary by Klempner and Hata, p. 20.This article is highlighted in the In This Issue feature, p. 1.

Calcineurin is necessary for the maintenance but not embryonic development of slow muscle fibers.

Skeletal muscles are a mosaic of slow and fast twitch myofibers. During embryogenesis, patterns of fiber type composition are initiated that change postnatally to meet physiological demand. To examine the role of the protein phosphatase calcineurin in the initiation and maintenance of muscle fiber types, we used a "Flox-ON" approach to obtain muscle-specific overexpression of the modulatory calcineurin-interacting protein 1 (MCIP1/DSCR1), an inhibitor of calcineurin. Myo-Cre transgenic mice with early skeletal muscle-specific expression of Cre recombinase were used to activate the Flox-MCIP1 transgene. Contractile components unique to type 1 slow fibers were absent from skeletal muscle of adult Myo-Cre/Flox-MCIP1 mice, whereas oxidative capacity, myoglobin content, and mitochondrial abundance were unaltered. The soleus muscles of Myo-Cre/Flox-MCIP1 mice fatigued more rapidly than the wild type as a consequence of the replacement of the slow myosin heavy chain MyHC-1 with a fast isoform, MyHC-2A. MyHC-1 expression in Myo-Cre/Flox-MCIP1 embryos and early neonates was normal. These results demonstrate that developmental patterning of slow fibers is independent of calcineurin, while the maintenance of the slow-fiber phenotype in the adult requires calcineurin activity.

Conditional expression of SV40 T-antigen in mouse cardiomyocytes facilitates an inducible switch from proliferation to differentiation.

Studies of cardiac muscle gene expression and signaling have been hampered by the lack of immortalized cardiomyocyte cell lines capable of proliferation and irreversible withdrawal from the cell cycle. With the goal of creating such cell lines, we generated transgenic mice using cardiac-specific cis-regulatory elements from the mouse Nkx2.5 gene to drive the expression of a simian virus 40 large T-antigen (TAg) gene flanked by sites for recombination by Cre recombinase. These transgenic mice developed tumors within the ventricular myocardium. Cells isolated from these tumors expressed cardiac markers and proliferated rapidly during serial passage in culture, without apparent senescence. However, they were unable to exit the cell cycle and failed to exhibit morphological features of terminal differentiation. Introduction of Cre recombinase to these cardiac cell lines by adenoviral delivery resulted in the elimination of TAg expression, accompanied by rapid cessation of cell division, and increase in cell size without an apparent induction of cellular differentiation. Incubation of cells lacking TAg in serum-deficient media with various pharmacological agents (norepinephrine, phenylephrine, or bone morphogenetic protein-2/4) or constitutively active calcium/calmodulin-dependent protein kinase I and/or calcineurin led to the formation of sarcomeres and up-regulation of cardiac genes involved in excitation-contraction coupling. The combination of TAg expression under the control of an early cardiac promoter and Cre-mediated recombination allowed us to derive an immortal cell line from the ventricular myocardium that could be controllably withdrawn from the cell cycle. The conditional expression of TAg in this manner permits propagation and regulated growth termination of cell types that are otherwise unable to be maintained in cell culture and may have applications for cardiac repair technologies.