Search

Mutant BRAF V600E is one of the most common oncogenic drivers in metastatic melanoma. While first generation BRAF V600E inhibitors are capable of controlling tumors systemically, they are unable to adequately treat tumors that have metastasized to the brain due to insufficient penetration across the blood-brain barrier (BBB). Through a combination of structure-based drug design (SBDD) and the optimization of physiochemical properties to enhance BBB penetration, we herein report the discovery of the brain-penetrant BRAF V600E inhibitor PF-07284890 ( ARRY-461 ) . In mice studies, ARRY-461 proved to be highly brain-penetrant and was able to drive regressions of A375 BRAF V600E tumors implanted both subcutaneously and intracranially. Based on compelling preclinical safety and efficacy studies, ARRY-461 was progressed into a Phase 1 A/B clinical trial (NCT04543188).

KRAS G12D , the most common oncogenic KRAS mutation, is a promising target for the treatment of solid tumors. However, when compared to KRAS G12C , selective inhibition of KRAS G12D presents a significant challenge due to the requirement of inhibitors to bind KRAS G12D with high enough affinity to obviate the need for covalent interactions with the mutant KRAS protein. Here, we report the discovery and characterization of the first noncovalent, potent, and selective KRAS G12D inhibitor, MRTX1133, which was discovered through an extensive structure-based activity improvement and shown to be efficacious in a KRAS G12D mutant xenograft mouse tumor model.

Capping off an era marred by drug development failures and punctuated by waning interest and presumed intractability toward direct targeting of KRAS, new technologies and strategies are aiding in the target's resurgence. As previously reported, the tetrahydropyridopyrimidines were identified as irreversible covalent inhibitors of KRAS G12C that bind in the switch-II pocket of KRAS and make a covalent bond to cysteine 12. Using structure-based drug design in conjunction with a focused in vitro absorption, distribution, metabolism and excretion screening approach, analogues were synthesized to increase the potency and reduce metabolic liabilities of this series. The discovery of the clinical development candidate MRTX849 as a potent, selective covalent inhibitor of KRAS G12C is described.

Despite decades of research, efforts to directly target KRAS have been challenging. MRTX849 was identified as a potent, selective, and covalent KRAS G12C inhibitor that exhibits favorable drug-like properties, selectively modifies mutant cysteine 12 in GDP-bound KRAS G12C , and inhibits KRAS-dependent signaling. MRTX849 demonstrated pronounced tumor regression in 17 of 26 (65%) KRAS G12C -positive cell line- and patient-derived xenograft models from multiple tumor types, and objective responses have been observed in patients with KRAS G12C -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 KRAS G12C 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 ., (©2019 American Association for Cancer Research.)