Abstract 1028: Combination screening of KRASG12C specific inhibitors with other targeted therapies in patient-derived multicellular tumor spheroids
Authors: Dexheimer Thomas S. , Silvers Thomas , Delosh René , Laudeman Julie , Reinhart Russell , Ogle Chad , Coussens Nathan P. , Wright John , Teicher Beverly A. , Doroshow James H. 
Published: July 2021

Abstract
KRAS is one of the most frequently mutated oncogenes in cancer and efforts to directly target KRAS have been challenging. However, covalent inhibitors targeting a specific KRASG12C (Gly12 to Cys12) variant have recently been developed and have demonstrated encouraging clinical activity in patients with tumors driven by the mutant protein. Drug combinations are used to improve clinical efficacy, to minimize toxicity, and to reduce the development of resistance. Here, we investigate the growth inhibitory activity of two KRASG12C variant-specific inhibitors, AMG-510 and MRTX-1257, in combination with other targeted therapies. Twenty patient-derived cancer cell lines, which have been well-characterized for their KRAS status and related targets and are available from NCI, were grown as multicellular 3D complex spheroids (https://pdmr.cancer.gov/models/database.htm). The complex spheroids, a mixture of tumor cells, endothelial cells and mesenchymal stem cells, were established for 3 days before drug(s) were added. All agents were tested at concentrations up to their reported clinical Cmax values and cell viability for each individual drug treatment and drug combination was assayed using CellTiter-Glo 3D seven days after drug exposure. As single agents, AMG-510 and MRTX-1257 showed selectivity for the KRASG12C variant containing cancer cell lines. The pancreatic cancer cell line 323965-272-R-J2 carrying a KRASG12C variant exhibited an enhanced sensitivity to the combination of the mTOR inhibitor everolimus and a low concentration of either AMG-510 or MRTX-1257. Additive to greater than additive cytotoxicity for the combination of everolimus and the KRASG12C inhibitors was also observed in the KRASG12C variant melanoma cell line 299254-011-R-J1, while no effect was detected in cell lines with wildtype or other KRAS mutations. Similarly, combining the mTOR kinase inhibitor sapanisertib, which blocks both mTORC1 and mTORC2 activities, with MTRX-1257 also led to a notable reduction in cell viability in all three KRASG12C-containing cell lines. In the KRASG12C variant melanoma cell line 299254-011-R-J1, targeting of the upstream receptor tyrosine kinase FGFR with erdafitinib in combination with the KRASG12C inhibitors produced greater than additive cell killing over the concentration range from 0.1 to 10 µM. Lastly, both KRASG12C inhibitors and abemaciclib, demonstrated additive to greater than additive cytotoxicity in the pancreatic cancer cell line 323965-272-R-J2, but this outcome was not observed with the CDK4/6 inhibitor, palbociclib, or in the other KRASG12C variant cell lines. These preclinical findings provide guidance regarding selection of combination regimens with KRASG12C inhibitors that may result in increased clinical efficacy. This project was funded in part with federal funds from the NCI, NIH, under contract no. HHSN261200800001E.
Citation Format: Thomas S. Dexheimer, Thomas Silvers, René Delosh, Julie Laudeman, Russell Reinhart, Chad Ogle, Nathan P. Coussens, John Wright, Beverly A. Teicher, James H. Doroshow. Combination screening of KRASG12C specific inhibitors with other targeted therapies in patient-derived multicellular tumor spheroids [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 1028.