Effect of DUAL pharmacological blockade of AURKA and PD-L1 pathways on plasticity and metastasis for triple negative breast cancer.

e13100 Background: Aurora-A mitotic kinase (AURKA) plays a pivotal role in Triple Negative Breast Cancer (TNBC) progression through activation of epithelial to mesenchymal transition (EMT)-mediated cancer cell plasticity. Cancer cells that undergo EMT acquire a CD44high/CD24low and/or ALDHhigh cancer stem-like phenotype (Cancer Stem Cells) characterized by high self-renewal capacity and intrinsic drug resistance. Cancer Stem Cells (CSCs) also shows high PD-L1 expression that plays a critical role in inducing tumor immune escape through CD8+ T-cells exhaustion. For these reasons, molecular characterization of oncogenic pathways that promote stemness and intra-tumoral PD-L1 expression is essential to evaluate whether novel combinatorial therapeutic strategies aimed to inhibit cancer cell plasticity, immune evasion capacity and organ metastasis may impact cancer progression. Methods: (1) TNBC Models: MDA-MB 231 and variant MDA-MB 231/LM cells, and unique TNBC-M40 cells established from metastatic PDXs; (2) In Vitro Studies: TNBC cells were treated with the AURKA inhibitor alisertib (50nM). PD-L1 expression was evaluated by immunoblotting assay. Apoptosis was measured by immunofluorescence using Cleaved-PARP antibodies. To assess stemness capacity, TNBC cells were cultured under non-adherent conditions to form mammospheres. ALDH activity (functional stemness marker) was measured using the Aldefluor Kit. (3) In Vivo Studies: 1x106 MDA-MB 231/LM cells were injected into the mammary fat pad of humanized NSG-CD34+ female mice. Animals were randomized into four groups (5 mice per group) and treated with anti-PD-L1 ICI atezolizumab (20 mg/Kg) and alisertib (25 mg/Kg) as monotherapy or in combination. Control groups were treated with saline solution placebo. PD-L1, CD44, Vimentin expression and tumor infiltration of CD8+ T-cells were assessed by immunofluorescence. Results: Treatment of MDA-MB 231/LM xenografts with alisertib decreased the levels of CD44 and PD-L1 expression and increased CD8+ T-cells tumor infiltration. Because PD-L1 genetic targeting enhanced in vitro alisertib-induced apoptosis, MDA-MB 231/LM xenografts were treated with alisertib and the anti-PD-L1 ICI atezolizumab. Combination of atezolizumab and alisertib resulted in the reduced expression of the EMT marker vimentin that was linked to lack of organ metastasis. Remarkably, combination of atezolizumab and alisertib also induced a significant reduction of ALDHHigh CSC in ex-vivo 3D-Organoids established from TNBC-M40 cells. Conclusions: This study provides innovative pre-clinical rationale for combining AURKA inhibitors with ICIs to impair cancer cell plasticity, immune evasion capacity and halt the progression of metastatic TNBCs that currently has limited effective therapeutic options.