Abstract B8: Caveolae-mediated endocytosis is critical for tumor cell response to nab-paclitaxel

INTRODUCTION: Pancreatic cancer is the fourth leading cause of cancer-related deaths in the United States and is typified by poor outcomes. Gemcitabine with nab-paclitaxel is a standard chemotherapy combination which recently demonstrated superiority compared to gemcitabine alone in a randomized trial. However, a predictive biomarker to select patients who may benefit from nab-paclitaxel is currently lacking. Nab-paclitaxel is a nanoparticle composed of paclitaxel bound to human albumin. Caveolin-1 (Cav-1) is a 22kD structural component of caveolae, 50-100 nM invaginations of the cell membrane. Cav-1 has been demonstrated to be an important component of albumin uptake in endothelial cells, and Cav-1 is overexpressed in pancreatic cancer. We hypothesize that Cav-1 expression may predict response to nab-paclitaxel therapy. METHODS: We compared Cav-1 expression to nab-paclitaxel sensitivity in a panel of pancreatic and non-small cell lung cancer cell lines. We stably knocked down Cav-1 expression in H23 and MIA-PaCa2 cells and performed cytotoxicity assays. In addition, we measured albumin and nab-paclitaxel uptake into tumor cells with immunoblotting, immunofluorescence and mass spectrometry. Sensitivity to the therapy was confirmed by quantifying apoptosis via flow cytometry and immunoblotting for activation of apoptotic pathway intermediates. Nab-paclitaxel resistant cell lines were created by selecting resistant cells over a period of time. Results were confirmed in vivo in a nude mouse model. RESULTS: Cav-1 expression in a panel of pancreatic cancer and non-small cell lung cancer (NSCLC) cell lines negatively correlated with their corresponding IC50 values for nab-paclitaxel, indicating a positive correlation with sensitivity to nab-paclitaxel. Cav-1 depletion resulted in reduced albumin uptake in tumor cells, reduced intracellular paclitaxel, and protection from nab-paclitaxel both in vitro and in vivo, while overexpression of Cav-1 enhanced sensitivity to nab-paclitaxel. Creation of nab-paclitaxel resistant cell lines demonstrated loss of Cav-1 expression in resistant cells. In support of our preclinical data, higher Cav-1 expression in the tumor microenvironment in patients with metastatic cancer treated with nab-paclitaxel also correlates with improved response and longer survival. CONCLUSIONS: Our data indicate that Cav-1 expression mediates entry of albumin and nab-paclitaxel, subsequent response to nab-paclitaxel, and that downregulation or re-expression of Cav-1 impairs or facilitates nab-paclitaxel uptake and response, respectively. This data supports further testing of Cav-1 as a potential predictive biomarker of response to nab-paclitaxel. Citation Format: Moumita Chatterjee, Marall Vedaie, Ryan Robb, Star Seum, Adriana Estrada-Bernal, Thirumoorthy Krishnan, Palanichamy Kamalakanan, Chen Lin, Arnab Chakravarti, Terence M. Williams. Caveolae-mediated endocytosis is critical for tumor cell response to nab-paclitaxel. [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2015 Nov 5-9; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2015;14(12 Suppl 2):Abstract nr B8.