Abstract 3449: Development of MRT-2359, an orally bioavailable GSPT1 molecular glue degrader, for the treatment of lung cancers with MYC-induced translational addiction

Abstract MYC transcription factors are well-established drivers of human cancers but despite being amongst the most frequently altered oncogenes, no approved therapy targeting MYC-driven tumors has been developed to date. MYC-driven cancers are known to be addicted to protein translation. This addiction creates a dependency on critical components of the translational machinery providing in turn a unique opportunity for therapeutic intervention. We hypothesized that targeting the translation termination factor GSPT1, a key regulator of protein synthesis, would constitute a vulnerability for MYC-driven tumors. Herein we further describe MRT-2359 a potent, selective and orally bioavailable degrader of GSPT1. MRT-2359 was rationally designed using our QuEENTM discovery engine and optimized to achieve a profound and preferential antiproliferative activity in MYC-driven cell lines, such as high N- and L-MYC mRNA expressing non-small cell lung cancer (NSCLC) and small cell lung cancer (SCLC) lines. In line with expectations, MRT-2359 activity is dependent on both CRBN and the GSPT1 G-loop degron. We further demonstrate using an inducible system that the sole expression of either N- or L-MYC is sufficient to sensitize initially resistant NSCLC cells to MRT-2359. These studies therefore establish a causal link between N- and L-MYC expression and sensitivity to MRT-2359. Unlike MRT-2359, agents targeting the protein translation initiation machinery or repressing MYC transcription (CDK9 inhibitor) failed to show such differential activity. Mechanistically, RiboSeq and polysome profiling revealed that treatment with MRT-2359 in the N- or L-MYC high cell lines induces ribosome stalling at the stop codon, increased monosomes and decreased polysomes. These changes are indicative of translational repression and were confirmed using puromycilation assays. Proteomics and RNAseq studies finally demonstrated a significant reduction in the total levels of N- or L-MYC leading in turn to the downmodulation of MYC target genes. Despite robust degradation of GSPT1, no marked effect was observed in these assays in low N- or L-MYC lines, confirming the selective activity of MRT-2359 in MYC-driven lung cancers. Last, the anti-tumor activity of MRT-2359 was assessed in 80 lung patient-derived xenografts (PDXs). MRT-2359 demonstrated preferential activity in N- and L-MYC high NSCLC and SCLC PDXs, including numerous instances of tumor regressions, when dosed orally daily or intermittently. Similar levels of anti-tumor activity were also observed in neuroendocrine lung cancer and lymphoma PDXs. Together these results warrant further investigations in the clinic. Oral MRT-2359 is currently in a Phase 1/2 clinical trial in selected cancer patients with MYC-driven NSCLC, SCLC, high grade neuroendocrine cancers and diffuse large B-cell lymphoma (NCT05546268). Citation Format: Gerald Gavory, Mahmoud Ghandi, Anne-Cecile d’Alessandro, Debora Bonenfant, Maciej Cabanski, Lisa Cantagallo, Agustin Chicas, Qian Chen, Anna Diesslin, Christopher King, Vittoria Massafra, Rajiv Narayan, Arnaud Osmont, Dave Peck, Carolina Perdomo Ortiz, Martin Schillo, Ambika Singh, Ralph Tiedt, Simone Tortoioli, Silvia Buonamici, Filip Janku, Owen Wallace, Bernhard Fasching. Development of MRT-2359, an orally bioavailable GSPT1 molecular glue degrader, for the treatment of lung cancers with MYC-induced translational addiction abstract. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts) ; 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83 (7Suppl): Abstract nr 3449.