Tumour-selective activity of RAS-GTP inhibition in pancreatic cancer.

Broad-spectrum RAS inhibition has the potential to benefit roughly a quarter of human patients with cancer whose tumours are driven by RAS mutations1,2. RMC-7977 is a highly selective inhibitor of the active GTP-bound forms of KRAS, HRAS and NRAS, with affinity for both mutant and wild-type variants3. More than 90% of cases of human pancreatic ductal adenocarcinoma (PDAC) are driven by activating mutations in KRAS4. Here we assessed the therapeutic potential of RMC-7977 in a comprehensive range of PDAC models. We observed broad and pronounced anti-tumour activity across models following direct RAS inhibition at exposures that were well-tolerated in vivo. Pharmacological analyses revealed divergent responses to RMC-7977 in tumour versus normal tissues. Treated tumours exhibited waves of apoptosis along with sustained proliferative arrest, whereas normal tissues underwent only transient decreases in proliferation, with no evidence of apoptosis. In the autochthonous KPC mouse model, RMC-7977 treatment resulted in a profound extension of survival followed by on-treatment relapse. Analysis of relapsed tumours identified Myc copy number gain as a prevalent candidate resistance mechanism, which could be overcome by combinatorial TEAD inhibition in vitro. Together, these data establish a strong preclinical rationale for the use of broad-spectrum RAS-GTP inhibition in the setting of PDAC and identify a promising candidate combination therapeutic regimen to overcome monotherapy resistance.

Tumor-selective effects of active RAS inhibition in pancreatic ductal adenocarcinoma.

Broad-spectrum RAS inhibition holds the potential to benefit roughly a quarter of human cancer patients whose tumors are driven by RAS mutations. However, the impact of inhibiting RAS functions in normal tissues is not known. RMC-7977 is a highly selective inhibitor of the active (GTP-bound) forms of KRAS, HRAS, and NRAS, with affinity for both mutant and wild type (WT) variants. As >90% of human pancreatic ductal adenocarcinoma (PDAC) cases are driven by activating mutations in KRAS, we assessed the therapeutic potential of RMC-7977 in a comprehensive range of PDAC models, including human and murine cell lines, human patient-derived organoids, human PDAC explants, subcutaneous and orthotopic cell-line or patient derived xenografts, syngeneic allografts, and genetically engineered mouse models. We observed broad and pronounced anti-tumor activity across these models following direct RAS inhibition at doses and concentrations that were well-tolerated in vivo. Pharmacological analyses revealed divergent responses to RMC-7977 in tumor versus normal tissues. Treated tumors exhibited waves of apoptosis along with sustained proliferative arrest whereas normal tissues underwent only transient decreases in proliferation, with no evidence of apoptosis. Together, these data establish a strong preclinical rationale for the use of broad-spectrum RAS inhibition in the setting of PDAC.

Efficacy of a Small-Molecule Inhibitor of KrasG12D in Immunocompetent Models of Pancreatic Cancer.

Mutations in the KRAS oncogene are found in more than 90% of patients with pancreatic ductal adenocarcinoma (PDAC), with Gly-to-Asp mutations (KRASG12D) being the most common. Here, we tested the efficacy of a small-molecule KRASG12D inhibitor, MRTX1133, in implantable and autochthonous PDAC models with an intact immune system. In vitro studies validated the specificity and potency of MRTX1133. In vivo, MRTX1133 prompted deep tumor regressions in all models tested, including complete or near-complete remissions after 14 days. Concomitant with tumor cell apoptosis and proliferative arrest, drug treatment led to marked shifts in the tumor microenvironment (TME), including changes in fibroblasts, matrix, and macrophages. T cells were necessary for MRTX1133's full antitumor effect, and T-cell depletion accelerated tumor regrowth after therapy. These results validate the specificity, potency, and efficacy of MRTX1133 in immunocompetent KRASG12D-mutant PDAC models, providing a rationale for clinical testing and a platform for further investigation of combination therapies. SIGNIFICANCE: Pharmacologic inhibition of KRASG12D in pancreatic cancer models with an intact immune system stimulates specific, potent, and durable tumor regressions. In the absence of overt toxicity, these results suggest that this and similar inhibitors should be tested as potential, high-impact novel therapies for patients with PDAC. See related commentary by Redding and Grabocka, p. 260. This article is highlighted in the In This Issue feature, p. 247.

Ultrasound-Guided Orthotopic Implantation of Murine Pancreatic Ductal Adenocarcinoma.

The recent success of immune checkpoint blockade in melanoma and lung adenocarcinoma has galvanized the field of immuno-oncology as well as revealed the limitations of current treatments, as the majority of patients do not respond to immunotherapy. Development of accurate preclinical models to quickly identify novel and effective therapeutic combinations are critical to address this unmet clinical need. Pancreatic ductal adenocarcinoma (PDA) is a canonical example of an immune checkpoint blockade resistant tumor with only 2% of patients responding to immunotherapy. The genetically engineered KrasG12D+/-;Trp53R172H+/-;Pdx-1 Cre (KPC) mouse model of PDA recapitulates human disease and is a valuable tool for assessing therapies for immunotherapy resistant in the preclinical setting, but time to tumor onset is highly variable. Surgical orthotopic tumor implantation models of PDA maintain the immunobiological hallmarks of the KPC tissue-specific tumor microenvironment (TME) but require a time-intensive procedure and introduce aberrant inflammation. Here, we use an ultrasound-guided orthotopic tumor implantation model (UG-OTIM) to non-invasively inject KPC-derived PDA cell lines directly into the mouse pancreas. UG-OTIM tumors grow in the endogenous tissue site, faithfully recapitulate histological features of the PDA TME, and reach enrollment-sized tumors for preclinical studies by four weeks after injection with minimal seeding on the peritoneal wall. The UG-OTIM system described here is a rapid and reproducible tumor model that may allow for high throughput analysis of novel therapeutic combinations in the murine PDA TME.