TY - JOUR T1 - Combined MEK and STAT3 inhibition reprograms stromal inflammation to overcome immunotherapy resistance in pancreatic cancer JF - bioRxiv DO - 10.1101/2021.03.07.434236 SP - 2021.03.07.434236 AU - Jashodeep Datta AU - Xizi Dai AU - Anna Bianchi AU - Iago De Castro Silva AU - Siddharth Mehra AU - Vanessa Garrido AU - Purushottam Lamichhane AU - Samara Singh AU - Zhiqun Zhou AU - Austin R. Dosch AU - Fanuel Messaggio AU - Yuguang Ban AU - Oliver Umland AU - Peter J. Hosein AU - Nagaraj S. Nagathihalli AU - Nipun B. Merchant Y1 - 2022/01/01 UR - http://biorxiv.org/content/early/2022/02/23/2021.03.07.434236.abstract N2 - Pancreatic ductal adenocarcinoma (PDAC) is characterized by immune exclusion, pro-inflammatory polarization of cancer-associated fibroblasts (CAF), and resistance to immune checkpoint inhibition (ICI). We have previously demonstrated that reciprocally activated RAS/MEK/ERK and JAK/STAT3 pathways mediate therapeutic resistance, while combined MEK and STAT3 inhibition (MEKi+STAT3i) overcomes such resistance in preclinical models. We now show that combined MEKi+STAT3i not only alters stromal architecture but also uncovers stromal plasticity by revealing a substantial attenuation of Il6/Cxcl1-expressing secretory and Lrrc15-expressing myofibroblastic CAF phenotypes with a concomitant enrichment of Ly6a/Cd34-expressing CAF phenotypes exhibiting mesenchymal progenitor-like properties via single-cell RNA sequencing in Ptf1acre/+;LSL-KrasG12D/+;Tgfbr2flox/flox(PKT) mice. This remodeling of CAF heterogeneity is associated with reprogramming of immunosuppressive myeloid populations and enhanced trafficking of CD8+ T-cells which exhibit a distinct effector transcriptional program. These MEKi+STAT3i-mediated repercussions are in part CAF-dependent, since CRISPR/Cas9 genetic silencing of CAF-restricted Mek1/Stat3 mitigates inflammatory CAF polarization and myeloid infiltration in vivo. Addition of MEKi+STAT3i to PD-1 blockade overcomes ICI resistance by significantly augmenting anti-tumor responses and dramatically improving survival in PKT mice compared with anti-PD-1 monotherapy. The addition of MEKi+STAT3i to PD-1 blockade not only augments the recruitment of activated and memory T-cell populations, but also improves their degranulating capacity and functional cytotoxicity compared to PD-1 blockade alone. Importantly, treatment of a patient with chemotherapy-refractory metastatic PDAC with MEKi (Trametinib), STAT3i (Ruxolitinib), and PD-1 inhibitor (Nivolumab) was well-tolerated and yielded clinical benefit. These data uncover a novel paradigm in which combined MEKi+STAT3i reprograms stromal inflammation and immune tolerance to overcome immunotherapy resistance in PDAC.Competing Interest StatementThe authors have declared no competing interest. ER -