Wortmannin inhibits PKB/Akt phosphorylation and promotes gemeitabine antitumor activity in orthotopic human pancreatic cancer xenografts in immunodeficient mice

Pancreatic cancer Is resistant to almost all classes of cytotoxic agents. G emcitabine seems to be the current drug of choice. We have recently reporte d that inhibition of the phosphatidylinositide 3-kinase-protein kinase B (P KB/Akt) cell survival pathway by wortmannin enhances gemcitabine-induced ap optosis In cultured human pancreatic cancer cells (1). The present study in vestigated the effects of wortmannin on orthotopic human pancreatic cancer xenografts implanted in severe combined immunodeficient mice. Animals were given single i.v. bolus injections of 0.175, 0.35, or 0.7 mg/kg of wortmann in and killed at 0.5, 1, 2, or 4 h after treatment. Phosphorylated PKB/Akt levels in tumor tissues were measured by fluorescence image analysis. Wortm annin was found to inhibit PKB/Akt phosphorylation in a time- and dose-depe ndent manner, reaching a plateau at 4 h and at 0.7 mg/kg. The levels of pho sphorylated PKB/Akt were maximally decreased by similar to 50% relative to the vehicle control. Subsequently, the extent of apoptosis in tumors treate d with gemcitabine or wortmannin alone or in combination was determined usi ng terminal deoxynucleotidyl transferase-mediated nick end labeling assay a nd computerized image analysis. Orthotopic tumors exposed to 80 mg/kg gemci tabine for 48 h and then 0.7 mg/kg wortmannin for 4 h showed a 5-fold incre ase (P = 0.002) in apoptosis compared with those treated with each agent al one and with the vehicle control. The combination treatment also significan tly (P < 0.001) inhibited tumor growth. Taken together, our findings suppor t the potential of phosphatidylinositide 3-kinase inhibitors as adjuncts to conventional chemotherapy in the treatment of pancreatic cancer.