Abstract 1453: Specific detection of mutant Ras oncoproteins in cell and tissue lysates by multiplex immunoassay

Abstract Ras proteins (HRAS, KRAS, and NRAS) are small GTPases that function as molecular switches by alternating between inactive GDP-bound and active GTP-bound states. Ras-GTP activates downstream pathways, including MAPK, by binding to Raf kinase and phosphatidylinositol 3-kinase (PI3K) to promote cellular proliferation, survival, growth and differentiation. Oncogenic mutations in Ras are found in approximately 25% of human cancers. Furthermore, 90% of pancreatic cancers harbor KRAS mutations with 80% of KRAS mutations occurring at codon 12 with G12V and G12D being the most prevalent. The Ras-Raf-MEK pathway can also be activated downstream of Ras. BRAF is a well-established oncogene, with the BRAF V600E mutation being prevalent in melanoma. While targeting this BRAF oncoprotein has had therapeutic efficacy, treating cancers driven by Ras oncoproteins remains an urgent unmet clinical need. We developed a novel multiplex immunoassay capable of simultaneously detecting total Ras, RasG12V, RasG12D, phospho-MEK1 (S217/S221), phospho-BRAF (S446) and phospho-CRAF (S338) in a single well. This multiplex assay detects the H-Ras, N-Ras, and K-Ras isoforms for total Ras, RasG12D, and RasG12V. To confirm specific recognition of mutant Ras oncoproteins, this kit was able to detect the known KRAS G12V mutation found in the COR-L23 cell line and the NRAS G12D mutation found in THP-1 cell line, respectively. In addition, the response to BRAF inhibitors vemurafenib and dabrafenib was compared between MDA-MB-435S cells, which harbor the BRAF V600E mutation, and insensitive cell lines, using multiplex immunoassays. While COR-L23 and THP-1 cells were not responsive to vemurafenib and dabrafenib, MDA-MB-435S cells showed a dramatic reduction in pMEK1 and pERK, consistent with inhibition of mutant BRAF protein. We then analyzed commercially-sourced tissue lysates, using tumor and adjacent tissue from a patient with colon cancer harboring a KRAS G12D mutation. While multiplex protein analysis revealed a similar phosphorylation pattern for Raf and MEK proteins, the RasG12D oncoprotein was specifically observed in lysate from the tumor but not the adjacent tissue. Finally, exosomes were enriched from pancreatic cancer serum and tested using the Ras-Raf Oncoprotein panel. These exosomal preparations yielded detectable signal for Total Ras and phospho-BRAF. Our data demonstrate the utility of studying the effects of Ras oncoproteins by multiplex immunoassay in multiple sample types, including cell, tissue, and exosomal lysates. Citation Format: Joseph B. Hwang, Anthony Saporita, Qiang Xiao. Specific detection of mutant Ras oncoproteins in cell and tissue lysates by multiplex immunoassay [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 1453.