Abstract A159: Mechanisms of uveal melanoma sensitivity to velcrin treatment and SLFN12-mediated cancer cell death

Abstract

Velcrins are a novel class of compounds that kill cancer cells expressing elevated levels of PDE3A and SLFN12. These compounds induce PDE3A-SLFN12 heterotetramer complex formation, resulting in upregulation of the RNase activity of SLFN12. SLFN12 cleaves tRNA-Leu-TAA, which leads to the inhibition of global translation and, consequently, apoptosis of cells expressing sufficient levels of both proteins. Uveal melanoma, a type of melanoma that occurs in the eye, is genomically distinct from cutaneous melanoma. Whereas mutations of BRAF, NRAS, KRAS, and HRAS are common in cutaneous melanoma, uveal melanomas instead harbor mutually exclusive mutations of the G protein alpha subunits, GNAQ and GNA11. Around 50% of patients will develop metastatic disease with a very poor prognosis. Immunotherapy is not effective for these patients, nor are any targeted therapies available beyond tebentafusp, with an ORR of 9%.  We found that a subset of uveal melanoma cell lines expresses elevated levels of PDE3A and SLFN12 and is sensitive to velcrin treatment.  We are currently assessing whether velcrin treatment of these cell lines results in cleavage of tRNA-Leu-TAA, inhibition of protein synthesis, and tumor cell death, with the goal of developing a new treatment for uveal melanoma patients.   To further understand the mechanism of velcrin-induced cancer cell death, we hypothesized that the primary function of PDE3A in the PDE3A-SLFN12 heterotetramer is the dimerization of SLFN12. Based on our cryo-EM structure of the PDE3A-SLFN12 complex, we identified SLFN12 I131 as a critical residue in the SLFN12 homodimer interface. We showed that a SLFN12 I131Q mutation disrupts SLFN12 dimerization and prevents tRNA-Leu-TAA cleavage in vitro. We have also shown that wild-type SLFN12 can dimerize independently of PDE3A or PDE3A-velcrin interactions. In PDE3A-depleted cells, the overexpression of wild-type SLFN12 results in cell death. We are currently testing SLFN12 I131Q for its ability to initiate SLFN12-dependent cytotoxicity in cells. Additionally, we are preparing different SLFN12 constructs that would allow us to induce chemical dimerization of SLFN12 and we plan to test if the forced dimerization of SLFN12 rescues its RNase activity and results in cell death.

Citation Format: Kristyna Kotynkova, Sawyer Andersen, Colin Garvie, Xiaoyun Wu, Sooncheol Lee, Joseph McGaunn, Bethany Kaplan, Moony Tseng, Andrew D Cherniack, Matthew Meyerson, Heidi Greulich. Mechanisms of uveal melanoma sensitivity to velcrin treatment and SLFN12-mediated cancer cell death [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 A159.