Targeting the Inhibitor of Apoptosis Proteins as a Novel Therapeutic Strategy in Medulloblastoma

Abstract

Medulloblastoma is the most common malignant brain tumor of childhood. Novel therapeutic strategies are urgently needed to overcome cytotoxic resistance. We hypothesized that antiapoptotic signals contribute to resistance and that treatment with proapoptotic agents could increase the efficacy of conventional therapies. A PCR array was used to assess the status of the apoptotic signaling pathway in medulloblastoma cells after treatment with cytotoxic chemotherapy. Treatment with cisplatin led to the upregulation of antiapoptotic signals, including inhibitor of apoptosis proteins (IAP), in medulloblastoma cells. We subsequently investigated the synergistic effect of a small-molecule IAP inhibitor, LBW242, in combination with cisplatin and/or radiotherapy in three human medulloblastoma cell lines and 5 short term primary patient medulloblastoma cultures. The addition of LBW242 to chemotherapy resulted in significantly increased antitumor activity with a similar effect observed in combination with radiotherapy. Measurement of caspase-8 and -9 activity indicated that the synergy resulted from induction of both the intrinsic and extrinsic apoptotic pathways. Apoptosis was confirmed by Annexin V staining and activation of caspases 3/7. Xenograft models were used to evaluate the mechanism of action and efficacy in vivo. The combination therapy significantly reduced the tumor burden in a medulloblastoma xenograft model and TUNEL analysis in a medulloblastoma orthograft confirmed in vivo induction of apoptosis. These findings support the strategy of targeting IAPs in combination with cytotoxic therapy as a novel treatment strategy for patients with medulloblastoma.

Systems biology of cisplatin resistance: past, present and future

“…81, 173, 174 This said, only a few of these factors have been formally correlated with CDDP resistance in clinical studies, including various BCL-2-like proteins such as BCL-2 itself, BCL-X L and MCL-1, 175, 176, 177, 178 survivin, a caspase inhibitor that is often upregulated in response to CDDP, 179, 180, 181, 182 as well as other members of the baculoviral IAP repeat-containing (BIRC) protein family. 183 In line with this notion, small molecules that antagonize the anti-apoptotic effects of BCL-2-like proteins (e.g., ABT-263) as well as IAP inhibitors (e.g., YM155, LY2181308, LBW242) have been intensively investigated in clinical trials, either as standalone anticancer interventions or in combination with various chemotherapeutics including CDDP. 184, 185, 186, 187, 188 In spite of an acceptable safety profile and promising antineoplastic activity, the clinical development of all these agents appears to stand at an impasse, at least as judged by the low rate of ongoing versus completed, terminated or withdrawn trials (source www.clinicaltrials.gov).…”

IAP proteins as targets for drug development in oncology

“…Considerable efforts were invested to improve the affinity of the compounds to the IAP BIR domains, to improve their ability to antagonize IAPs,104–107 to improve cellular delivery and activity (ie, their capacity to induce apoptosis or to sensitize to apoptotic agents), and to improve their in vivo stability and bioavailability. The preclinical assays demonstrated their capacity to inhibit tumor growth in multiple solid tumors,102,107,108 acute lymphoblastic leukemia (ALL),108 and multiple myeloma109 xenograft models and to sensitize cells to TRAIL, proteasome inhibitors, B-cell lymphoma protein 2 (Bcl-2) family-targeting compounds, and more conventional therapeutic agents, such as radiation, melphalan, or cisplatin 103,109–114. Importantly, these compounds were well tolerated by animals and did not display toxicity against normal lymphocytes and bone marrow stromal cells109 or normal mammary epithelial cells 115.…”

Antitumor activity of IL-32β through the activation of lymphocytes, and the inactivation of NF-κB and STAT3 signals

“…29, 30 Apoptosis is mediated by the two major pathways: the extrinsic (extracellular receptor and ligand) and the intrinsic (mitochondria-associated) pathways. 31, 32 The extrinsic pathway is triggered by death receptor, which initiates a signaling cascade mediated by caspase-8 activation. Caspase-8 activates caspase-3 and stimulates the release of cytochrome c by the mitochondria.…”