Discovery of BBO-8520, a first-in-class direct and covalent dual inhibitor of GTP-bound (ON) and GDP-bound (OFF) KRASG12C

Approved inhibitors of KRASG12C prevent oncogenic activation by sequestering the inactive, GDP-bound (OFF) form rather than directly binding and inhibiting the active, GTP-bound (ON) form of the protein. This suboptimal mechanism provides no direct target coverage against KRASG12C(ON). Expectedly, adaptive resistance to KRASG12C (OFF)-only inhibitors is observed in association with increased expression and activity of KRASG12C(ON). To provide optimal KRASG12C target coverage, we have developed BBO-8520, a first-in-class, direct dual inhibitor of KRASG12C(ON) and (OFF) forms. BBO-8520 binds in the Switch-II/Helix3 pocket, covalently modifies the target cysteine and disables effector binding to KRASG12C(ON). BBO-8520 exhibits potent signaling inhibition in growth factor activated states where current (OFF)-only inhibitors demonstrate little measurable activity. In vivo, BBO-8520 demonstrates rapid target engagement and inhibition of downstream signaling, resulting in durable tumor regression in multiple models, including those resistant to KRASG12C (OFF)-only inhibitors. Overall design: To investigate the transcriptional regulation of BBO-8520, a dual KRAS G12C (OFF) and (ON) inhibitor, compared to KRAS G12C (OFF) inhibitors in the the KRAS G12C homozygous pancreatic cell line MIA PaCa-2 MIA PaCa-2 cells were treated with DMSO, BBO-8520 (30nM), adagrasib (300nM) or sotorasib (1uM ) for 24 hours with 5 replicates/condition and collected for RNA-seq analysis We then performed gene expression profiling anlysis using data obtained from RNA-seq of the MIA PaCa-2 cell line treated with the 4 different compounds