A RAS(ON) Multi-Selective Inhibitor Combination Therapy Triggers Long-term Tumor Control through Senescence-Associated Tumor-Immune Equilibrium in Pancreatic Ductal Adenocarcinoma

Pharmacological inhibition of oncogenic RAS represents an attractive strategy to target pancreatic ductal adenocarcinoma (PDAC), an almost ubiquitously RAS-driven disease. However, initial responses to targeted monotherapy inhibition of active RAS can be followed by relapses, potentially driven by the persistence of drug-tolerant tumor cells. To target these "persister" cells, we investigated strategies to increase their immune visibility in mouse models of PDAC. We show that combining a RAS(ON) multi-selective inhibitor with the CDK4/6 inhibitor palbociclib drives persister cells into a senescent-like state, which coincides with improved tumor control and substantial remodeling of the tumor microenvironment. Combining RAS(ON) and CDK4/6 inhibition with a CD40 agonist results in durable regressions and CD4 T cell-dependent tumor-immune equilibrium. Our studies reveal a combinatorial approach that circumvents resistance to RAS(ON) inhibitor monotherapy in preclinical models and demonstrates a mechanism by which therapy-induced senescence can be reinforced by the immune system, resulting in durable tumor control. SIGNIFICANCE: Our preclinical studies highlight an opportunity to exploit the senescence program and CD4 T cell-mediated mechanisms to achieve long-term tumor-immune equilibrium and control with RAS-targeted therapies. This work advances our understanding of therapy-induced senescence and suggests new avenues for combination therapies with the potential to benefit patients with PDAC. See related commentary by Lasse Opsahl and Pasca di Magliano, p. 1537.