Abstract 4152: Preclinical evaluation of PRKC fusions and GNA11/GNAQ mutations as genetic drivers of PKC activation in non-MUM indications to support a phase 1/2 basket trial of IDE196

Abstract

Abstract Background: IDE196 is a potent and selective PKC inhibitor targeting the novel (δ, ϵ, η, θ) and classical (α, β) PKC isoforms that has demonstrated preliminary clinical activity in patients with metastatic uveal melanoma (MUM). IDE196 is being further evaluated for safety and efficacy as a monotherapy in a Phase1/2 basket trial in non-MUM patients whose tumors harbor GNAQ/GNA11 hotspot mutations (Clinicialtrials.gov: NCT03947385). Patients with solid tumors harboring PRKC fusions or GNAQ/11 non-hotspot mutations may be eligible after preclinical validation of the activity of these fusions and mutations in non-MUM indications. PRKC gene fusions exist at very low frequencies with various gene partners across multiple indications. Hotspot mutations in GNAQ/GNA11 (codons Q209 and R183) constitutively activate the PKC pathway in 90% of MUM patients and may also occur in non-MUM indications such as colorectal cancer (CRC) and cutaneous melanoma. Furthermore, there are additional non-hotspot mutations found in these GTPases across various non-MUM indications. To help identify patients that may benefit from IDE196 in this basket trial, we assessed the sensitivity of non-MUM cell lines that have PRKC gene fusions or GNAQ/11 hotspot/non-hotspot mutations to IDE196. Methods The most prevalent fusions in patient samples listed in TCGA are the HIF1A-PRKCH (n=20) and RP11-47I22.3-PRKCH (n=3) fusions, therefore cell lines containing PRKCH fusions listed in CCLE were prioritized for cell viability screening using short (3-day) and long-term (10-day) assays after IDE196 treatment. For PD analyses, cells were treated for 3hrs with IDE196. Expression of the fusions and pharmacodynamic modulation of phospho-MARCKS was assessed using western blotting (WB). RNASeq data was used to determine fusion structure, size and whether the fusion was in-frame. Results 8/10 PRKCH fusion lines were highly resistant to IDE196 (IC50>10μM, including HIF1A-PRKCH and RP11-47I22.3-PRKCH fusion lines), whereas 2/10 showed sensitivity at high doses in the long-term viability assay (IC50≥1μM, lines with PRKCH-SPTB or VWA2-PRKCH fusions). PD assessment showed that the PKC substrate, pMARCKS, was decreased in all cell lines by IDE196 at doses similar to those seen in the MUM cell line, 92.1 (≥0.3μM). Fusion protein expression was not detectable by WB consistent with literature suggesting that PKC fusions are unstable (1). In summary, cell lines with clinically prevalent PRKCH fusions were insensitive to IDE196 despite robust PD modulation. Assessment of cell lines harboring GNAQ/GNA11 hotspot/non-hotspot mutations for IDE196 sensitivity is ongoing. (1) An-Angela N. Van, Timothy R. Baffi, Maya T. Kunkel, Corina E. Antal and Alexandra C. Newton, FASEB J. (2018); vol 32, suppl.no. 1, abstract 687.6. Citation Format: Marie Wagle, Nandini Ravindran, Carol O'Brien, Christian Frey, Julie Hambleton, Mark R. Lackner, Zineb Mounir. Preclinical evaluation of PRKC fusions and GNA11/GNAQ mutations as genetic drivers of PKC activation in non-MUM indications to support a phase 1/2 basket trial of IDE196 [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 4152.