Project Summary/Abstract: 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.