Exploiting caveolae-dependent albumin endocytosis to optimize therapy in pancreatic cancer

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PROJECT ABSTRACT: Pancreatic adenocarcinoma (PC) is a disease typified by resistance to therapy and poor outcomes. There is a pressing need to discover new therapies and determine whether existing therapies will be ineffective in certain patients. Recently, the addition of nab-paclitaxel (Abraxane®) to gemcitabine has been shown to improve response rates and survival in PC, at the expense of added toxicity. Nab-paclitaxel is an albumin-bound chemotherapeutic which has been hypothesized to enter the cell through caveolae/gp60-mediated albumin endocytosis. Caveolae are 50-100 nM membrane invaginations responsible for endocytosis, cholesterol homeostasis, and signal transduction. Caveolin-1 (Cav-1) is the principal structural component of caveolae, and genetic knockdown of Cav-1 ablates caveolae. Our preliminary data indicate that Cav-1 is over-expressed and associated with poor prognosis in PC, and confers oncogenic properties including migration, invasion, and resistance to therapy. Our data also suggest that Cav-1 expression is important for intracellular transport of albumin and nab-paclitaxel into PC cells. Thus, we hypothesize that Cav-1 levels regulate entry and can predict response to nab-paclitaxel. In addition, we seek to improve upon nab-paclitaxel by identifying other strategies which increase nab-paclitaxel efficacy and by testing novel albumin-conjugated chemotherapeutics. Our specific aims include: (1) To determine whether Cav-1 expression mediates albumin uptake and response to nab-paclitaxel; (2) To determine whether Cav-1 expression mediates response to novel albumin-conjugated chemotherapeutics; and (3) To test strategies to improve response to nab-paclitaxel. We will test whether Cav- 1 levels affect response to nab-paclitaxel in a panel of PC cell lines through analysis of albumin and nab- paclitaxel uptake, cytotoxicity assays, and activation of apoptotic pathways. We will extend these studies in vivo to assess whether loss of Cav-1 alters response to nab-paclitaxel using patient-derived xenograft and autochthonous mouse models of PC. In addition, we will determine whether Cav-1 levels in tumor, stroma, and blood predict response to nab-paclitaxel in samples obtained from patients with PC receiving nab- paclitaxel. Furthermore, we will test novel albumin-chemotherapy conjugates that appear superior to nab- paclitaxel and determine whether Cav-1 levels also regulate their response. Lastly, we will test other strategies to increase Cav-1 expression in order to further sensitize cells to nab-paclitaxel. If successful, these studies will establish that Cav-1 is important for albumin entry in PC tumor cells and dictates response to albumin- bound chemotherapies. Furthermore, these studies could allow personalization of therapy by predicting which tumors are likely to benefit from nab-paclitaxel, by stratifying therapy based on Cav-1 expression. Finally, these studies are designed to be the first to refine an existing therapy in PC through targeting of the Cav-1/caveolae- dependent albumin endocytic pathway.