Abstract 1016: Inhibition of chemokine-induced myeloid cells potentiates the anti-PD-1 response in KRAS/LKB1 mutant non-small cell lung cancer
Authors: Li Rui , Salehi-Rad Ramin , Momcilovic Milica , Ong Stephanie , Lim Raymond , Huang Zi Ling , Tran Linh , Jing Zhe , Paul Manash , Teitell Michael , Minna John , Shackelford David , Kostyantyn Krysan , Liu Bin , Dubinett Steven 
Published: September 2020

Abstract
Dysregulated inflammation dictated by oncogene/tumor suppressor mutations can often lead to an immune suppressive tumor microenvironment (TME). Lung tumors with LKB1 mutations account for 30% of KRAS-mutant non-small cell lung cancer (NSCLC). These tumors are particularly aggressive and resistant to immunotherapy despite a high mutational burden (TMB). The mechanisms of this impaired immunogenicity remain obscure. Here, we report that LKB1 loss leads to a heightened secretion of the ELR(+) CXC chemokines, including CXCL1, CXCL2, CXCL3, CXCL5, and CXCL8, in premalignant and cancerous cells in vitro. Among multiple NSCLC cell lines, cancer cells with both KRAS and LKB1 mutations tend to express higher levels of these ELR(+) CXC chemokines. Consistently, ectopic expression of LKB1 in LKB1-null cancer cells decreases the chemokine production. In a genetically-engineered mouse model, an elevation of these chemokines is also observed in KrasG12D;Lkb1-/- (KL) tumors compared to their KrasG12D (K) or KrasG12D;Tp53-/- (KP) counterparts. Mechanistic studies reveal that the LKB1-MARK axis regulates these chemokines in the premalignant cells. Immune phenotyping of KL or KrasG12D;Tp53+/-;Lkb1-/- (KPL) tumors in vivo demonstrates significantly increased granulocytic myeloid-derived suppressor cells (G-MDSCs), which harbor high levels of reactive oxygen species (ROS). Utilizing a syngeneic murine lung cancer model with a high TMB, we demonstrate that KPL tumors have a minimal response to anti-PD-1 therapy compared to KP tumors. Therefore, we hypothesize that G-MDSCs may cause resistance to anti-PD-1 monotherapy in KPL tumors. We find that inhibition of the G-MDSCs either by depletion or by reduction of ROS can potentiate the anti-PD-1 response and subsequently eliminate the KPL tumors. Investigation of the TME reveals that G-MDSC depletion primes tumor-infiltrating lymphocytes (TILs) for activation: there is an increased percentage of TILs with high Ki67 and PD-1 expression and an increased percentage of antigen presenting cells (macrophages and dendritic cells) with high PD-L1 expression. Combination with anti-PD-1 therapy enhances the function of these TILs, evidenced by IFN-γ and TNF-α secretion. Re-challenge of these mice three months after the initial combination therapy leads to a rapid tumor rejection, suggesting a durable systemic anti-tumor immune response. In conclusion, we find that LKB1 deficiency leads to an increased ELR(+) CXC chemokine production and tumor infiltration of G-MDSCs. Inhibition of G-MDSC enhances the efficacy of anti-PD-1 blockade in LKB1-deficient tumors bearing a high TMB.
Citation Format: Rui Li, Ramin Salehi-Rad, Milica Momcilovic, Stephanie Ong, Raymond Lim, Zi Ling Huang, Linh Tran, Zhe Jing, Manash Paul, Michael Teitell, John Minna, David Shackelford, Krysan Kostyantyn, Bin Liu, Steven Dubinett. Inhibition of chemokine-induced myeloid cells potentiates the anti-PD-1 response in KRAS/LKB1 mutant non-small cell lung cancer [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 1016.