Unraveling New Cytokine-Mediated Mechanisms to Enhance Response to CDK4/6 inhibition in ER+/HER2-Metastatic Breast Cancer

Impact:We propose a bedside/bench/bedside translational project that will test the validity of our clinical findings in the lab to impact the care of patients with metastatic breast cancer. We have identified that X-C motif chemokine ligand 1 (XCL1) and Interleukin 24 (IL-24) expression is associated with enhanced response to palbociclib supporting a role for these cytokines as novel biomarkers. This finding could aid in patient stratification and increased opportunities to match therapies to patient populations, paving the way towards personalized medicine. Equally important is shedding light on underlying biology, which may provide opportunities for new strategies to increase response rates. Thus, our proposed work could lead to a breakthrough in this field, improving the treatment options for thousands of HR+/HER2- breast cancer patients. Background/Rationale: We conducted a large–panel gene expression analysis by using tissues from patients enrolled in the PALOMA 3 clinical trial to identify biomarkers associated with the effectiveness of combined palbociclib and fulvestrant. Cyclin E1 mRNA expression was found to be associated with relative resistance to palbociclib, whereas cytokines XCL1 and IL-24 were among nine genes identified whose expression was associated with enhanced benefit from palbociclib (9). Natural Killer (NK) cells serve as the major producer of XCL1, and through its expression it drives conventional type 1 Dendritic Cell (cDC1) recruitment, and resultantly cytotoxic T cells, to the tumor microenvironment (10). IL-24 is a member of the IL-10 family of cytokines whose expression has been shown to lead to irreversible growth inhibition and cancer-specific cell killing in a unique non-immune mediated fashion (11-13). Given the distinct pathways/processes regulated by these cytokines, the significance of these findings will be evaluated using available clinical samples/specimens and mechanistic insights will be gained through pre-clinical models. Successful completion of this work will 1) provide solid evidence regarding the use of these cytokines as predictive molecular biomarkers for response to CDK4/6 inhibition, and 2) offer an unprecedented opportunity to unravel mechanisms to enhance treatment response. We will facilitate these efforts with the integration of a collaborative team of both basic scientists and clinicians with complementary expertise and strong research backgrounds in areas closely related to the major challenges/questions to be addressed in this proposal. Approach: We propose two specific aims: 1) Determine the role of a Natural Killer (NK) cell/XCL1/ conventional type 1 Dendritic Cell (cDC1) functional axis in driving immune-mediated responses to CDK4/6 inhibition. A retrospective analysis in patient samples will be performed to assess the associations between XCL1 mRNA expression and patient progression, antiproliferative response and efficacy among intrinsic molecular subtypes. Presence of NK, cDC1 and CD8+ T cells within the tumor microenvironment will be assessed using multiplex immunohistochemical tissue staining, flow cytometry, and molecular profiling all of which will be correlated to response to CDK4/6 inhibition. Finally, Circulating Tumor Cells (CTC) counts will be combined with peripheral blood NK and DC immunophenotypes to predict treatment response and outcomes. 2) Determine the role of IL-24 in enhancing responses to CDK4/6 inhibition through non-immune-modulating mechanisms.We will assess the effect of combining IL-24 with CDK4/6 inhibition in HR+/HER2- breast cance