Aberrant activation of RAS signaling is a major driver of lung cancer resulting from gain-in-function mutations in RAS genes often caused by tobacco-derived carcinogens. Constitutive activation of RAS, a GTPase, stimulates a cascade of downstream kinases to activate genes encoding for proteins essential for multiple aspects of tumorigenesis, including tumor cell proliferation, survival, and metastasis. Because KRAS is mutated during early stages of lung cancer and a major driver of tumor promotion and progression, a direct-acting, reversible, small molecule inhibitor of activated RAS holds great potential for lung cancer chemoprevention or the treatment of individuals with early stage disease. Unfortunately, previous attempts to develop RAS inhibitors were unsuccessful, in part, because of the scarcity of sites on the protein amenable to small-molecule binding. However, ongoing clinical trials of two covalent inhibitors of the relatively rare KRAS G12C mutation have validated this approach that can be expanded to inhibitors effective for a much broader spectrum of RAS mutations prevalent in lung cancer patients and other RAS-driven malignancies. A long-running medicinal chemistry program undertaking the synthesis of a focused library of indenes and screening in a cell-based assay for RAS selectivity resulted in the discovery of a novel class of RAS inhibitors. MCI-062 emerged as a lead compound following extensive chemical optimization and iterative target-directed screening. In vitro treatment of lung cancer cells harboring mutant RAS with MCI-062 inhibited growth with IC50 values as low as 2 nM, while human normal airway epithelial cells or tumor cells with low levels of activated RAS were essentially insensitive. MCI-062 was effective regardless of the RAS isozyme or mutational codon and appreciably more potent than covalent mutant-specific inhibitors of KRAS in clinical trials. Multiple lines of evidence indicate that MCI-062 inhibits tumor cell growth by directly interacting with RAS to inhibit GTP binding, blocking RAS-effector interaction, suppressing RAF/MAPK and PI3K/AKT signaling, resulting in selective apoptosis of RAS mutant tumor cells. As proof-of-concept, MCI-062 and a prototype prodrug, MCI-316, inhibited tumor growth in vivo, although further chemical optimization is needed to develop an oral formulation suitable for preclinical development. A new prodrug, MCI-1004 recently emerged from ongoing synthetic efforts with attractive drug-like properties that merit in vivo testing. We propose aims to: 1) gain further insight into how MCI- 062 selectively inhibits the growth of lung cancer cells with activated RAS; 2) synthesize new analogs and prodrugs to improve antitumor activity by oral delivery and benchmark them against MCI-1004, and 3) evaluate antineoplastic activity of MCI-1004 and a second prodrug lead in mouse models of lung cancer chemoprevention and treatment that are relevant to the clinic.
The aims are structured to be conducted in parallel and designed to be translational with the goals of optimizing and selecting a drug development candidate for IND-enabling safety assessment and to gain a mechanistic rationale for biomarkers that will aid in selecting patient cohorts for future clinical trials.
Tobacco-derived carcinogens can cause gain-in-function mutations in RAS genes encoding for RAS proteins that constitutively activate cellular processes responsible for multiple aspects of tumorigenesis. Because RAS is mutated during early stages of lung cancer and a well-validated, high-value, yet elusive, cancer target, we seek to further study and develop a novel class of RAS inhibitors for lung cancer chemoprevention or early treatment that has ultra-high potency and selectivity for killing lung cancer cells with mutant RAS. The proposed research will precisely define the mechanism of action, optimize oral delivery by further synthetic chemistry of analogs and prodrugs, and evaluate antitumor efficacy in mouse models of lung cancer in a comprehensive manner; all with the goals of identifying a drug development candidate for IND-enabling safety assessment and to gain insight into potential biomarkers needed to conduct clinical chemoprevention trials of individuals at risk of developing lung cancer or malignant progression.
