Therapeutic Associations Comprising Anti-PD-1/PD-L1 in Breast Cancer: Clinical Challenges and Perspectives

Despite a few cases of long-responder patients, immunotherapy with anti-PD-(L)1 has so far proved rather disappointing in monotherapy in metastatic breast cancer, prompting the use of synergistic therapeutic combinations incorporating immunotherapy by immune-checkpoint inhibitors. In addition, a better understanding of both the mechanisms of sensitivity and resistance to immunotherapy, as well as the immunological effects of the usual treatments for breast cancer, make it possible to rationally consider this type of therapeutic combination. For several years, certain treatments, commonly used to treat patients with breast cancer, have shown that in addition to their direct cytotoxic effects, they may have an impact on the tumor immune microenvironment, by increasing the antigenicity and/or immunogenicity of a “cold” tumor, targeting the immunosuppressive microenvironment or counteracting the immune-exclusion profile. This review focuses on preclinical immunologic synergic mechanisms of various standard therapeutic approaches with anti-PD-(L)1, and discusses the potential clinical use of anti-PD-1/L1 combinations in metastatic or early breast cancer.

Exogenous and Endogenous Triggers Differentially Stimulate Pigr Expression and Antibacterial Secretory Immunity in the Murine Respiratory Tract

Purpose Transport of secretory immunoglobulin A (SIgA) through the airway epithelial cell barrier into the mucosal lumen by the polymeric immunoglobulin receptor (pIgR) is an important mechanism of respiratory mucosal host defense. Identification of immunomodulating substances that regulate secretory immunity might have therapeutic implications with regard to an improved immune exclusion. Thus, we sought to analyze secretory immunity under homeostatic and immunomodulating conditions in different compartments of the murine upper and lower respiratory tract (URT&LRT). Methods Pigr gene expression in lung, trachea, and nasal-associated lymphoid tissue (NALT) of germ-free mice, specific pathogen-free mice, mice with an undefined microbiome, as well as LPS- and IFN-γ-treated mice was determined by quantitative real-time PCR. IgA levels in bronchoalveolar lavage (BAL), nasal lavage (NAL), and serum were determined by ELISA. LPS- and IFN-γ-treated mice were colonized with Streptococcus pneumoniae and bacterial CFUs were determined in URT and LRT. Results Respiratory Pigr expression and IgA levels were dependent on the degree of exposure to environmental microbial stimuli. While immunostimulation with LPS and IFN-γ differentially impacts respiratory Pigr expression and IgA in URT vs. LRT, only prophylactic IFN-γ treatment reduces nasal colonization with S. pneumoniae. Conclusion Airway-associated secretory immunity can be partly modulated by exposure to microbial ligands and proinflammatory stimuli. Prophylactic IFN-γ-treatment modestly improves antibacterial immunity in the URT, but this does not appear to be mediated by SIgA or pIgR.

909 Differentiation subgroups within LKB1-deficient lung cancer influence both the immune exclusion phenotype and cellular composition of the immune microenvironment

BackgroundLKB1 (STK11) is a commonly disrupted tumor suppressor in NSCLC. Its loss promotes an immune exclusion phenotype with evidence of low expression of interferon stimulated genes (ISG) and decreased microenvironment immune infiltration.1 2 Clinically, LKB1 loss induces primary immunotherapy resistance.3 LKB1 is a master regulator of a complex downstream kinase network and has pleiotropic effects on cell biology. Understanding the heterogeneous phenotypes associated with LKB1 loss and their influence on tumor-immune biology will help define and overcome mechanisms of immunotherapy resistance within this subset of lung cancer.MethodsWe applied multi-omic analyses across multiple lung adenocarcinoma datasets2 4–6 (>1000 tumors) to define transcriptional and genetic features enriched in LKB1-deficient lung cancer. Top scoring phenotypes exhibited heterogeneity across LKB1-loss tumors, and were further interrogated to determine association with increased or decreased markers of immune activity. Further, immune cell-types were estimated by Cibersort to identify effects of LKB1 loss on the immune microenvironment. Key conclusions were confirmed by blinded pathology review.ResultsWe show that LKB1 loss significantly affects differentiation patterns, with enrichment of ASCL1-expressing tumors with putative neuroendocrine differentiation. LKB1-deficient neuroendocrine tumors had lower expression of Interferon Stimulated Genes (ISG), MHC1 and MHC2 components, and immune infiltration compared to LKB1-WT and non-neuroendocrine LKB1-deficient tumors (figure 1).The abundances of 22 immune cell types assessed by Cibersort were compared between LKB1-deficient and LKB1-WT tumors. We observe skewing of immune microenvironmental composition by LKB1 loss, with lower abundance of dendritic cells, monocytes, and macrophages, and increased levels of neutrophils and plasma cells (table 1). These trends were most pronounced among tumors with neuroendocrine differentiation, and were concordant across three independent datasets. In a confirmatory subset of 20 tumors, plasma cell abundance was assessed by a blinded pathologist. Pathologist assessment was 100% concordant with Cibersort prediction, and association with LKB1 loss was confirmed (P=0.001).Abstract 909 Figure 1Immune-associated Gene Expression Profiles Affected by Neuroendocrine Differentiation within LKB1-Deficient Lung Adenocarcinomas. Gene expression profiles corresponding to five immune-associated phenotypes are shown with bars indicating average GEP scores for tumors grouped according to LKB1 and neuroendocrine status as indicated. P-values represent results from Student’s T-test between groups as indicated.Abstract 909 Table 1LKB1 Loss Affects Composition of Immune Microenvironment. Values indicate log10 P-values comparing LKB1-loss to LKB1-WT tumors. Positive (red) indicates increased abundance in LKB1 loss. Negative (blue) indicates decreased abundance.ConclusionsWe conclude that tumor differentiation patterns strongly influence the immune microenvironment and immune exclusion characteristics of LKB1-deficient tumors. Neuroendocrine differentiation is associated with the strongest immune exclusion characteristics and should be evaluated clinically for evidence of immunotherapy resistance. A novel observation of increased plasma cell abundance is observed across multiple datasets and confirmed by pathology. Causal mechanisms linking differentiation status to immune activity is not well understood, and the functional role of plasma cells in the immune biology of LKB1-deficient tumors is undefined. These questions warrant further study to inform precision immuno-oncology treatments for these patients.AcknowledgementsThis work was funded by SITC AZ Immunotherapy in Lung Cancer grant (SPS256666) and DOD Lung Cancer Research Program Concept Award (LC180633).ReferencesSkoulidis F, Byers LA, Diao L, et al. Co-occurring genomic alterations define major subsets of KRAS-mutant lung adenocarcinoma with distinct biology, immune profiles, and therapeutic vulnerabilities. Cancer Discov 2015;5:860–77.Schabath MB, Welsh EA, Fulp WJ, et al. Differential association of STK11 and TP53 with KRAS mutation-associated gene expression, proliferation and immune surveillance in lung adenocarcinoma. Oncogene 2016;35:3209–16.Skoulidis F, Goldberg ME, Greenawalt DM, et al. STK11/LKB1 mutations and PD-1 inhibitor resistance in KRAS-mutant lung adenocarcinoma. Cancer Discovery 2018;8:822-835.Cancer Genome Atlas Research Network. Comprehensive molecular profiling of lung adenocarcinoma. Nature 2014;511:543–50.Chitale D, Gong Y, Taylor BS, et al. An integrated genomic analysis of lung cancer reveals loss of DUSP4 in EGFR-mutant tumors. Oncogene 2009;28:2773–83.Shedden K, Taylor JM, Enkemann SA, et al. Gene expression-based survival prediction in lung adenocarcinoma: a multi-site, blinded validation study. Nat Med 2008;14:822–7.

737 Inhibition of P21-activated kinase 4 (PAK4) reverts immune exclusion and restores anti-tumor immunity in the tumor microenvironment

BackgroundP21-activated kinase 4 (PAK4) is a serine/threonine protein kinase that is mostly expressed in tumor and stroma cells. PAK4 activates tumor WNT/β-catenin pathway and regulates cellular morphology, motility, EMT, cell proliferation and survival. Recent studies also showed that PAK4 can actively exclude T cells from tumors, suggesting that therapeutic inhibition of PAK4 can increase T cell infiltration in tumor microenvironment and overcome resistance to checkpoint inhibitor immunotherapy.1MethodsWe generated PAK4 knockout (KO) clones in human and mouse tumor cells to validate its biology in vitro and in vivo. We also performed pharmacological evaluation of PAK4 inhibition using Pfizer compounds (referred to as 'PAK4i compounds' below) for their potential tumor-intrinsic and immune-regulatory roles.ResultsNanostring, qPCR and RNASeq analysis showed that PAK4 depletion led to increase of cytokine expression in tumor, including conventional dendritic cell (cDC)- recruiting chemokine CCL4, and type I IFN / ISG pathway genes that are associated with MHC upregulation such as CXCL10. In addition, PAK4 KO sensitizes B16F10 tumors to anti-PD-1 treatment and increases infiltration of cDC and T cells in the tumor microenvironment.We also showed that small molecule PAK4i compounds induced more potent cancer cell growth inhibition over treated normal PBMCs. PAK4i compounds also increased immune-activating and decreased immune exclusion genes in B16F10 cells and tumor explants in vitro. Although PAK4 target engagement is demonstrated by CETSA assay, the compound potency on modulating PAK4 downstream Wnt/ β-catenin pathway is low, suggesting that the aforementioned phenotypic changes induced by PAK4i compounds may be partially attributed to other off-target effects.ConclusionsCollectively, our data suggests that genetic depletion or pharmacological inhibition of PAK4 may induce immune-activating cytokine production in tumor cells, revert immune cell exclusion in tumor microenvironment, and synergize with checkpoint blockade therapies. However, further optimization on these PAK4i compounds is needed to improve its specificity on modulating PAK4 enzyme activities.ReferenceAbril-Rodriguez G, Torrejon DY, Liu W, Zaretsky JM, Nowicki TS, Tsoi J, Puig-Saus C, Baselga-Carretero I, Medina E, Quist MJ, Garcia AJ, Senapedis W, Baloglu E, Kalbasi A, Cheung-Lau G, Berent-Maoz B, Comin-Anduix B, Hu-Lieskovan S, CWang CY, Grasso CS & Ribas A. PAK4 inhibition improves PD-1 blockade immunotherapy. Nat Cancer 2020;1:46–58.Ethics ApprovalAll animal studies were conducted in accordance with protocols approved by the Institutional Animal Care and Use Committee of Pfizer. Approved protocol # LAJ-2019-01347

Chromosomal instability mediates immune exclusion and response to cytotoxic chemotherapy in colorectal liver metastases

The genomic drivers of immune exclusion in colorectal cancer liver metastases (CRCLM) remain poorly understood. Chromosomal instability (CIN), resulting in aneuploidy and genomic rearrangements, is the central pathway of mismatch repair-proficient colorectal cancer pathogenesis; however, it is unknown whether CIN impacts the outcomes of patients with limited spread of CRCLM treated with curative intent cytotoxic chemotherapy and surgery. Herein, we examined the relationship between CIN and the molecular subtypes of CRCLM, immune signaling, treatment sensitivity, and patient outcomes in three independent CRCLM patient cohorts. We established that a previously developed 70-gene CIN signature (CIN70) is a reliable measure of CIN, encompassing features of both aneuploidy and cellular proliferation. We demonstrated that tumors with the canonical subtype of CRCLM exhibit elevated levels of CIN and aneuploidy. Genomically unstable tumors were associated with an immune-depleted tumor microenvironment, and patients with genomically unstable tumors were at increased risk for disease progression in adverse metastatic sites, resulting in poor progression-free and overall survival. However, high-CIN tumors were particularly susceptible to DNA-damaging chemotherapies, including topoisomerase inhibitors, as well as radiation therapy. Treatment with genotoxic agents depleted CIN-rich cell populations, which resulted in a concomitant increase in intratumoral CD8+ T-cells in patients with primary rectal, breast, and bladder cancer. Taken together, we propose a mechanistic explanation for why cytotoxic chemotherapy can augment anti-tumor immunity and improve outcomes in patients with genomically unstable cancers.