Inhibitors of XIAP sensitize CD40-activated chronic lymphocytic leukemia cells to CD95-mediated apoptosis

Abstract

IntroductionPatients with chronic lymphocytic leukemia (CLL) who received intravenous infusions of autologous leukemia cells transfected with an adenovirus vector encoding the CD40 ligand (Ad-CD154) experienced acute reductions in leukemia cell counts and lymph node size. 1 This rapid cytoreduction was unexpected and suggested the possible contribution of innate immune-effector mechanisms to the early clearance of CLL cells following CD154 gene therapy.Following intravenous infusion of Ad-CD154-transduced CLL cells, we observed that bystander, nontransduced CLL cells were induced to express Fas (CD95) and DR5, 1,2 a receptor for the tumor necrosis factor (TNF)-receptor apoptosis-inducing ligand (TRAIL). Furthermore, activated CD4 T cells of patients treated with CD154 gene therapy were noted to express the ligands for such death receptors, namely Fas ligand (CD178) and TRAIL. 2 In vitro studies demonstrated that cells that expressed both CD178 and TRAIL could kill CLL cells within 1 day after CD40 ligation in a CD95-dependent fashion through coligation of both CD95 and DR5. 2 Moreover, CLL cells became increasingly sensitive to apoptosis induced by cells bearing CD178 and/or TRAIL over 3 to 5 days following CD40 activation. 2,3 CLL cells also can be induced to express high levels of CD95 and DR5 following coculture with CD154-bearing cells in vitro.Although initially resistant to CD95-or DR5-mediated apoptosis 1 day after such coculture, CD40-activated CLL cells become increasingly sensitive to apoptosis triggered by ligation of such extrinsic death receptors over the ensuing 3 to 5 days, an phenomenon termed "latent sensitivity to Fas-mediated apoptosis". 2,3 The initial resistance of CLL cells to CD95-mediated apoptosis following CD40 ligation may be secondary to CLL cell expression of inhibitors of apoptosis proteins (IAPs), such as the X-linked IAP (XIAP). IAPs negatively regulate apoptosis by inhibiting caspase activity directly. 4 Moreover, IAPs can block the execution phase of apoptosis through direct inhibition of the effector caspase-3 and/or caspase-7. 5 In addition, IAPs can prevent initiation of the intrinsic caspase activation cascade by directly inhibiting the apical caspase-9. Finally, high-level expression of XIAP, such as that found in CLL, 6-8 can inhibit CD95-mediated apoptosis of cells that express CD95. 9 Conversely, the latent sensitivity of CLL cells to CD95-mediated apoptosis following CD40 ligation may be due to release of intrinsic inhibitors to the IAPs that are sequestered within the 2 In different cell lines, it has been shown that Bid is degraded following ligation of extrinsic death receptors, such as CD95 or DR5, thereby generating a small truncated Bid (tBid) that rapidly trafficks to the mitochondria where it can trigger the release of the second mitochondria-derived activator of caspases (Smac), a potent natural IAP inhibitor that also is referred to as the direct IAP-binding protein with low isoelectric point (pI) (DIABLO). [11][12][13][14] Conceivably, inhibition of IAPs by ...

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

“…In contrast, the small-molecule antagonists described in this study are readily suited for systemic administration. In our limited studies, as well as previous reports (23,25,26), XAntags do not seem to cause incidental adverse effects in xenograft-bearing mice. We were able to achieve impressive down-regulation of pancreatic cancer xenograft growth in vivo with XAntag monotherapy, further validating XIAP as a target in pancreatic cancer.…”

Exploiting inhibitor of apoptosis proteins as therapeutic targets in hematological malignancies

“…57 Besides TRAIL, a XIAP antagonist was reported to significantly enhance CD95-induced apoptosis in CLL cells. 104 Together, these studies indicate that the combination of IAP inhibitors and TRAIL may present a new therapeutic approach especially in CLL patients with poor prognosis.…”

Double inhibition of XIAP and Bcl-2 axis is beneficial for retrieving sensitivity of renal cell cancer to apoptosis

“…P-values between each pair of the cells calculated with the post-test are presented in Figure 5A. As XIAP inhibition sensitised chronic lymphocytic leukaemia cells (Kater et al, 2005) and RCC cells (Mizutani et al, 2007) to Fas-induced apoptosis, we treated the parental cells, mock transfectants, and clone nos. 14 and 19 with CH11 IgM Fasstimulating monoclonal antibody ( Figure 5B).…”