Abstact

When tumor suppressor genes are lost through chromosomal deletion, deletion of adjacent genes can generate therapeutic vulnerabilities. MTAP is frequently co-deleted with the Chr9p21 tumor suppressor gene CDKN2A, creating synthetic lethal dependency on PRMT5. Telomeric to MTAP lies FOCAD, whose loss induces dependency on the HBS1L/PELO ribosome-rescue complex for translational maintenance. FOCAD is deleted in ~1/3 of MTAP-deleted cancers. We screened an IMiD-focused diversity library and identified a weak hit that bound cereblon, promoted HBS1L-CRBN-compound complex formation, and induced E3-ligase-dependent HBS1L ubiquitination and degradation. Guided by cryo-EM structures and proteome selectivity we developed TNG961, a potent, selective HBS1L degrader that disrupts the HBS1L/PELO complex, inducing translational arrest, unfolded protein response activation, and growth inhibition in FOCAD-negative models. Oral administration of TNG961 regresses FOCAD-negative xenografts, including PRMT5 inhibitor-refractory models, establishing HBS1L degradation as a strategy to exploit FOCAD loss and supporting clinical evaluation of TNG961 as a first-in-class precision oncology therapeutic.