Targeting the apoptotic machinery in pancreatic cancers using small-molecule antagonists of the X-linked inhibitor of apoptosis protein

Abstract

Resistance to apoptosis is a hallmark of many solid tumors, including pancreatic cancers, and may be the underlying basis for the suboptimal response to chemoradiation therapies. Overexpression of a family of inhibitor of apoptosis proteins (IAP) is commonly observed in pancreatic malignancies. We determined the therapeutic efficacy of recently described small-molecule antagonists of the X-linked IAP (XIAP) in preclinical models of pancreatic cancer. Primary pancreatic cancers were assessed for XIAP expression by immunohistochemistry, using a pancreatic cancer tissue microarray. XIAP small-molecule antagonists (''XAntag''; compounds 1396-11 and 1396-12) and the related compound 1396-28 were tested in vitro in a panel of human pancreatic cancer cell lines (Panc1, Capan1, and BxPC3) and in vivo in s.c. xenograft models for their ability to induce apoptosis and impede neoplastic growth. In addition, pancreatic cancer cell lines were treated with XAntags in conjunction with either tumor necrosis factor -related apoptosis-inducing ligand (TRAIL) or with radiation to determine potential synergy for such dual targeting of the apoptotic machinery. XIAP was overexpressed in 14 of 18 (77%) of primary pancreatic cancers. The XAntags1396-11 and 1396-12, but not the inactive isomer 1396-28, induced profound apoptosis in multiple pancreatic cancer cell lines tested in vitro, with a IC 50 in the range of 2 to 5 Mmol/L. Mechanistic specificity of the XAntags for the baculoviral IAP repeat-2 domain of XIAP was shown by preferential activation of downstream ''effector'' caspases (caspase-3 and caspase-7) versus the upstream ''initiator'' caspase-9. S.c. BxPC3 xenograft growth in athymic mice was significantly inhibited by monotherapy with XAntags; treated xenografts showed marked apoptosis and increased cleavage of caspase-3. Notably, striking synergy was demonstrable when XAntags were combined with either TRAIL or radiation therapy, as measured by growth inhibition in vitro and reduced colony formation in soft agar of pancreatic cancer cell lines, at dosages where these therapeutic modalities had minimal to modest effects when used alone. Finally, XAntags in combination with the standard-of-care agent for advanced pancreatic cancer, gemcitabine, resulted in significantly greater inhibition of in vitro growth than gemcitabine alone. Our results confirm that pharmacologic inhibition of XIAP is a potent therapeutic modality in pancreatic cancers. These antagonists are independently capable of inducing pancreatic cancer cell death and also show synergy when combined with proapoptotic ligands (TRAIL), with radiation, and with a conventional antimetabolite, gemcitabine. These preclinical results suggest that targeting of the apoptotic machinery in pancreatic cancers with XAntags is a promising therapeutic option that warrants further evaluation. [Mol Cancer Ther 2007;6(3):957 -66]

CTGF antagonism with mAb FG-3019 enhances chemotherapy response without increasing drug delivery in murine ductal pancreas cancer

“…3 A and B). This effect was most pronounced in FG-3019/ gemcitabine combination-treated mice, consistent with the ability of Xiap silencing (33) or Xiap chemical inhibition (34) to sensitize PDA cell lines to additional therapies. Xiap mRNA levels were also significantly reduced by FG-3019 in the presence and absence of gemcitabine (Fig.…”

A Novel Paradigm to Trigger Apoptosis in Chronic Lymphocytic Leukemia

“…Beyond CLL, XIAP inhibitors have recently been reported by our group and other investigators to act in concert with TRAIL to trigger apoptosis in childhood acute leukemia, pancreatic, colon, or breast carcinoma cells (29,43,44). In addition, low-molecular weight Smac mimetics displayed antitumor activities as single agents in multiple myeloma and several solid cancers (45)(46)(47)(48)(49).…”

TRAIL-Induced Apoptosis Is Preferentially Mediated via TRAIL Receptor 1 in Pancreatic Carcinoma Cells and Profoundly Enhanced by XIAP Inhibitors

“…Previously, we demonstrated that neutralizing XIAP either by RNA interferencemediated knockdown or by small molecule inhibitors acted in concert with soluble recombinant TRAIL to induce apoptosis in pancreatic cancer in vitro and in vivo (16)(17)(18). In addition, XIAP small molecule antagonists that target the BIR2 domain of XIAP were reported to synergize with TRAIL in pancreatic cancer (17,43). Compared with these earlier reports that focus on soluble recombinant TRAIL, the current study shows for the first time that the antitumor activity of TRAIL receptor-specific antibodies is profoundly enhanced by neutralizing XIAP in pancreatic cancer cells.…”