Abstract B025: The next generation farnesyltransferase inhibitor, KO-2806, blocks oncogenic signaling at multiple nodes to enhance the antitumor efficacy of KRASG12C inhibitor adagrasib in KRASG12C non-small cell lung carcinoma
Authors: Patel Hetika V , Smith Alison , Chan Stacia , Kessler Linda , Burrows Francis , Malik Shivani 
Published: December 2023

Abstract
Emerging clinical and preclinical data have shown that responses to KRASG12C inhibition are limited by the activation of compensatory signaling proteins, including receptor tyrosine kinases (RTKs) and mTOR. Combination therapeutic strategies co-targeting these nodes are needed to fully realize the potential of breakthrough KRASG12C-selective inhibitors. We propose that, given its multipronged mechanism of action, KO-2806, a next-generation farnesyltransferase inhibitor (FTI) with increased potency and improved pharmacokinetic properties relative to earlier FTI candidates that is poised to enter a first-in-human clinical trial, is a uniquely suited combination partner for KRASG12C inhibitors. Here, we evaluate the therapeutic potential of combined KO-2806 and adagrasib in preclinical models of KRASG12C non-small cell lung cancer (NSCLC). Our previous work indicated that FTIs amplify the antitumor effects of PI3Kα inhibition by blocking compensatory mTOR signaling. As activation of compensatory signaling is a well-described bypass mechanism to escape KRAS inhibition, we asked whether KO-2806 could improve the in vivo efficacy of adagrasib. Combination of KO-2806 with adagrasib led to markedly enhanced antitumor effects in KRASG12C-mutant NSCLC cell line- and patient-derived xenograft models compared to adagrasib alone. Tumor regression in the combination group corresponded to increased apoptosis, as evidenced by higher cleaved caspase 3 staining in combination-treated tumors compared to single agent groups. Intriguingly, adagrasib induced expression of the RTK HER3, a potential driver of bypass signaling, while HER3 expression in combination-treated tumors was lower than in vehicle-treated tumors. To further interrogate the mechanistic basis of the observed in vivo synergy, we cultured KRASG12C-mutant cell lines as 3D tumor spheroids and exposed them to KO-2806 and/or adagrasib. Consistent with the xenograft tumor data, spheroids exposed to the combination expressed lower levels of the upstream receptor HER3 (total and phosphorylated forms) and higher levels of apoptotic markers cleaved PARP and cleaved caspase 3. Concurrently, activity of the downstream effectors ERK and mTOR was reduced. Co-exposure to KO-2806 and adagrasib potently inhibited phosphorylation of ERK and its substrate p90 RSK as well as phosphorylation of mTOR substrates p70 S6K, 4EBP1, and S6. The mTOR signaling reduction paralleled defarnesylation of the farnesylation-dependent mTOR activator RHEB, so we depleted RHEB expression in spheroids and assayed their growth. Genetic depletion of RHEB phenocopied the antiproliferative effects of KO-2806 in combination with adagrasib, implicating RHEB as an important farnesylated target in KRASG12C NSCLC. These preclinical results suggest that KO-2806 is an effective combination partner for KRASG12C inhibitors by simultaneously targeting an upstream activator (HER3) and a downstream effector (RHEB/mTOR) of KRAS, leading to improved antitumor activity in KRASG12C-mutant NSCLC models.
Citation Format: Hetika V Patel, Alison Smith, Stacia Chan, Linda Kessler, Francis Burrows, Shivani Malik. The next generation farnesyltransferase inhibitor, KO-2806, blocks oncogenic signaling at multiple nodes to enhance the antitumor efficacy of KRASG12C inhibitor adagrasib in KRASG12C non-small cell lung carcinoma [abstract]. In: Proceedings of the AACR-NCI-EORTC Virtual International Conference on Molecular Targets and Cancer Therapeutics; 2023 Oct 11-15; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2023;22(12 Suppl):Abstract nr B025.