Up-regulation of integrin beta3 in radioresistant pancreatic cancer impairs adenovirus-mediated gene therapy

Tumor radiosensitization by monomethyl auristatin E: mechanism of action and targeted delivery

Intrinsic tumor resistance to radiotherapy limits the efficacy of ionizing radiation (IR). Sensitizing cancer cells specifically to IR would improve tumor control and decrease normal tissue toxicity. The development of tumor-targeting technologies allows for developing potent radiosensitizing drugs. We hypothesized that the anti-tubulin agent monomethyl auristatin E (MMAE), a component of a clinically approved antibody-directed conjugate, could function as a potent radiosensitizer and be selectively delivered to tumors using an activatable cell-penetrating peptide targeting matrix metalloproteinases and RGD-binding integrins (ACPP-cRGD-MMAE). We evaluated the ability of MMAE to radiosensitize both established cancer cells and a low-passage cultured human pancreatic tumor cell line using clonogenic and DNA damage assays. MMAE sensitized colorectal and pancreatic cancer cells to IR in a schedule- and dose-dependent manner, correlating with mitotic arrest. Radiosensitization was evidenced by decreased clonogenic survival and increased DNA double-strand breaks in irradiated cells treated with MMAE. MMAE in combination with IR resulted in increased DNA damage signaling and activation of CHK1. To test a therapeutic strategy of MMAE and IR, PANC-1 or HCT-116 murine tumor xenografts were treated with nontargeted free MMAE or tumor-targeted MMAE (ACPP-cRGD-MMAE). While free MMAE in combination with IR resulted in tumor growth delay, tumor-targeted ACPP-cRGD-MMAE with IR produced a more robust and significantly prolonged tumor regression in xenograft models. Our studies identify MMAE as a potent radiosensitizer. Importantly, MMAE radiosensitization can be localized to tumors by targeted activatable cell-penetrating peptides.

Tumor-stroma interactions reduce the efficacy of adenoviral therapy through the HGF-MET pathway

Many preclinical studies have shown the potential of adenovirus-based cancer gene therapy. However, successful translation of these promising results into the clinic has not yet been achieved. Pancreatic ductal adenocarcinoma (PDAC) is characterized by abundant desmoplastic stroma, and tumor-stromal cell interactions play a critical role in tumor progression. Therefore, we hypothesized that tumor-stroma interactions reduce the efficacy of adenoviral therapy. We investigated the effect of fibroblasts on adenovirus-based gene therapy using SUIT-2 and PANC-1 pancreatic cancer cells cultured with or without fibroblast-conditioned culture supernatant then infected with Ad-LacZ. After 48 h, the cells were stained for β-galactosidase. The results showed that the number of β-galactosidase-positive cells was significantly reduced after culture with fibroblast-conditioned supernatant (P < 0.05). Because the hepatocyte growth factor (HGF)/MET pathway plays an important role in tumor-stroma interactions we next investigated the involvement of this pathway in tumor-stroma interactions leading to the decreased efficacy of adenoviral therapy. SUIT-2 cells were cultured with or without SU11274 (a MET inhibitor) and/or fibroblast-conditioned culture supernatant, then infected with Ad-GFP. After 48 h, GFP-positive cells were counted. The number of GFP-positive cells in cultures containing fibroblast-conditioned supernatant plus SU11274 was significantly greater than in cultures without SU11274. In conclusion, our results suggest that stromal cells in PDAC reduce the efficacy of adenoviral therapy through a mechanism involving the HGF/MET pathway. Control of such tumor-stroma interactions may lead to improvements in adenoviral gene therapy for PDAC.