Tumor Microenvironment Remodeling Enables Bypass of Oncogenic KRAS Dependency in Pancreatic Cancer

Abstract

Oncogenic KRAS (KRAS*) is a key tumor maintenance gene in pancreatic ductal adenocarcinoma (PDAC), motivating pharmacologic targeting of KRAS* and its effectors. Here, we explored mechanisms involving the tumor microenvironment (TME) as a potential basis for resistance to targeting KRAS*. Using the inducible <i>Kras</i> ^G12D;<i>Trp53</i> ^-/- PDAC mouse model, gain-of-function screens of epigenetic regulators identified <i>HDAC5</i> as the top hit enabling KRAS* independent tumor growth. <i>HDAC5</i>-driven escaper tumors showed a prominent neutrophil-to-macrophage switch relative to KRAS*-driven tumors. Mechanistically, HDAC5 represses <i>Socs3</i>, a negative regulator of chemokine CCL2, resulting in increased CCL2, which recruits CCR2⁺ macrophages. Correspondingly, enforced <i>Ccl2</i> promotes macrophage recruitment into the TME and enables tumor recurrence following KRAS* extinction. These tumor-associated macrophages in turn provide cancer cells with trophic support including TGFβ to enable KRAS* bypass in a SMAD4-dependent manner. Our work uncovers a KRAS* resistance mechanism involving immune cell remodeling of the PDAC TME. SIGNIFICANCE: Although KRAS* is required for PDAC tumor maintenance, tumors can recur following KRAS* extinction. The capacity of PDAC cancer cells to alter the TME myeloid cell composition to support KRAS*-independent tumor growth illuminates novel therapeutic targets that may enhance the effectiveness of therapies targeting KRAS* and its pathway components.<i>See related commentary by Carr and Fernandez-Zapico, p. 910</i>.<i>This article is highlighted in the In This Issue feature, p. 890</i>.