Abstract
Pancreatic ductal adenocarcinoma (PDAC) is highly malignant disease that is the fourth leading cause of cancer-related death in the US. Gene therapy using AAV vectors to selectively deliver genes to PDAC cells is an attractive treatment option for pancreatic cancer. However, most AAV serotypes display a broad spectrum of tissue tropism and none of the existing serotypes specifically target PDAC cells. This study tests the hypothesis that AAV2 can be genetically re-engineered to specifically target PDAC cells by modifying the capsid surface to display a peptide that has previously been shown to bind plectin-1. Toward this end, a Plectin-1 Targeting Peptide (PTP) was inserted into the loop IV region of the AAV2 capsid, and the resulting capsid (AAV-PTP) was used in a series of in vitro and in vivo experiments. In vitro, AAV-PTP was found to target all five human PDAC cell lines tested (PANC-1, MIA PaCa-2, HPAC, MPanc-96, and BxPC-3) preferentially over two non-neoplastic human pancreatic cell lines (human pancreatic ductal epithelial and human pancreatic stellate cells). In vivo, mice bearing subcutaneous tumor xenografts were generated using the PANC-1 cell line. Once tumors reached a size of ∼1–2 mm in diameter, the mice were injected intravenously with luciferase reporter vectors packaged in the either AAV-PTP or wild type AAV2 capsids. Luciferase expression was then monitored by bioluminescence imaging on days 3, 7, and 14 after vector injection. The results indicate that the AAV-PTP capsid displays a 37-fold preference for PANC-1 tumor xenographs over liver and other tissues; whereas the wild type AAV2 capsid displays a complementary preference for liver over tumors and other tissues. Together, these results establish proof-of-principle for the ability of PTP-modified AAV capsids to selectively target gene delivery to PDAC cells in vivo, which opens promising new avenues for the early detection, diagnosis, and treatment of pancreatic cancer.
Highlights
Pancreatic ductal adenocarcinoma (PDAC) is the fourth leading cause of cancer-related death in the United States
Compared to the control capsid (AAV2∆LoopIV), the pancreatic cancer-targeted capsid (AAV-Plectin-1 Targeting Peptide (PTP)) was 4, 13, 6, 4, and 30 times more efficient at the transduction of PDAC cell lines PANC-1, MiaPaCa2, HPAC, MPanc-96, and BxPC-3, respectively; than it was at transducing the non-neoplastic cell lines (HPDE and human pancreatic stellate cells (hPSC), Figure 1)
These results show that the AAV2 vector bearing the PTP peptide preferentially transduces and expresses recombinant genes in human PDAC cell lines over non-neoplastic human pancreatic cell lines, albeit with some loss in overall efficiency relative to AAV2
Summary
Pancreatic ductal adenocarcinoma (PDAC) is the fourth leading cause of cancer-related death in the United States. PDAC shows a rapid clinical course, with a median survival of 6 months and a 5year survival rate of only 3% (Geer and Brennan, 1993; Hezel et al, 2006). The high mortality rate in PDAC patients is linked to the nature of underlying tumor biology. PDAC is highly malignant, metastasizes extensively, and has late onset of clinical symptoms. As pancreatic cancer is highly resistant to chemotherapy and radiotherapy, the only potential cure currently available is complete surgical resection of the tumor. Complete resection of the primary as well as secondary tumors is rarely achieved (Hezel et al, 2006). Novel and more effective treatments are needed to improve the survival of pancreatic cancer patients. Targeted gene therapy using an AAV vector designed to selectively deliver therapeutic genes is an attractive and efficient option to treat pancreatic cancer
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