Dual inhibition of GTP-bound (ON) and GDP-bound (OFF) KRAS ^G12C suppresses PI3Kα and leads to potent tumor inhibition

Current approved KRAS ^G12C inhibitors covalently bind the inactive GDP-bound (OFF) form of KRAS ^G12C . Recently, KRAS ^G12C inhibitors that selectively bind to the GTP-bound (ON) form of both KRAS ^G12C (ON) and (OFF) forms have been reported and entered clinical testing. In principle, KRAS ^G12C (ON) inhibitors may be less susceptible to adaptive mechanisms that promote resistance to (OFF) inhibitors, however the specific mechanisms that differentiate the activity of (ON) versus (OFF) inhibition are not well understood. We profiled the activity of BBO-8520, a covalent dual inhibitor of GTP-bound (ON) and GDP-bound (OFF) KRAS ^G12C , in KRAS ^G12C -mutant non-small cell lung cancer models. BBO-8520 exerted more potent and sustained inhibition of KRAS ^G12C and anti-tumor activity in vitro and in vivo compared with sotorasib, a KRAS ^G12C (OFF)-only inhibitor. While cells treated with BBO-8520 or sotorasib both exhibited feedback reactivation of MAPK signaling driven by wild-type HRAS/NRAS isoforms, more durable suppression of KRAS ^G12C by BBO-8520 was associated with decreased PI3Kα-AKT activation in vitro . Disruption of the interaction between RAS and PI3Kα using a novel protein:protein interaction inhibitor suppressed PI3Kα-AKT activation and increased the tumor response to sotorasib to a similar level as BBO-8520. Moreover, in some contexts, disruption of RAS-PI3Kα further increased the anti-tumor activity of BBO-8520 monotherapy. These results reveal mechanistic differences between KRAS (ON) and (OFF) inhibitors, highlight the importance of PI3Kα-AKT signaling in driving resistance to KRAS inhibition in lung cancer, and suggest combination strategies that suppress PI3Kα-AKT to improve the response to KRAS inhibitors.