Therapeutics of XIAP Degradation by Zinc Chelators

描述（由申请人提供）：雄激素非依赖型前列腺癌与目前治疗方式极差的治疗反应和有限的预后相关。因此，发展晚期前列腺癌的新治疗策略是一个具有巨大临床和科学价值的目标。我们实验室的研究结果表明，用锌螯合剂N，N，N‘，N’，-四（2-吡啶基甲基）乙二胺（TPEN）治疗前列腺癌细胞可诱导x -连锁凋亡蛋白抑制剂（XIAP）的选择性下调，并使癌细胞对死亡配体介导的凋亡敏感。我们还观察到，在用天然螯合分子原卟啉IX处理的细胞中，XIAP水平显著降低。此外，外源性给予其前体5-ALA后，原卟啉IX在细胞内的积累与PC-3前列腺癌细胞中XIAP表达的减少和对trail介导的凋亡的敏感性增加相一致。原卟啉IX及其衍生物在肿瘤病变中的优先积累已得到证实，并已广泛用于各种恶性肿瘤的光检测和光动力治疗。我们假设锌的置换通过下调XIAP使恶性细胞对细胞毒性药物敏感，因此，锌螯合可能代表前列腺癌治疗的新机制。重要的是，我们的数据和其他人的结果表明，XIAP本身的消耗足以逆转癌细胞对trail介导的凋亡的耐药性。为了验证我们的假设并评估锌螯合剂在前列腺癌中的治疗用途，我们提出以下具体目标：目的1：在体外鉴定具有提高前列腺癌细胞对细胞毒性药物敏化能力的5-ALA衍生物；目的2：研究5-ALA酯化衍生物的口服生物利用度和5-ALA诱导的PPIX在前列腺癌异种移植模型中的组织分布；目的3：研究5-ALA衍生物的体内抗肿瘤功效和毒性。在许多癌细胞系中，XIAP蛋白水平升高，抑制XIAP蛋白水平可使癌细胞对细胞毒性药物敏感。这使得XIAP成为设计新型抗肿瘤药物的一个有吸引力的靶点。公共卫生相关性：我们实验室的研究结果表明，用锌螯合剂N， N， N‘， N’， -四（2-吡啶基甲基）乙二胺（TPEN）和原卟啉IX治疗前列腺癌细胞可诱导凋亡蛋白x连锁抑制剂（XIAP）的下调。此外，外源性给予其前体5-氨基乙酰丙酸后，原卟啉IX在细胞内的积累与PC-3前列腺癌细胞中XIAP表达的减少和对trail介导的细胞凋亡的敏感性增加相一致。我们试图评估5-ALA治疗激素难治性前列腺癌的治疗用途。

DESCRIPTION (provided by applicant): Androgen-independent prostate cancer is associated with an extremely poor treatment response and a limited prognosis using current treatment modalities. Therefore, the development of new therapeutic strategies for advanced prostate cancer represents a goal with enormous clinical and scientific merit. Findings from our laboratory indicate that treatment of prostate cancer cells with the zinc chelating agent N,N,N',N',-tetrakis(2-pyridylmethyl) ethylenediamine (TPEN) induces selective down-regulation of the X-linked inhibitor of apoptosis protein (XIAP) and sensitizes cancer cells to death ligand-mediated apoptosis. We have also observed a significant reduction of XIAP levels in cells treated with protoporphyrin IX, a naturally occurring chelating molecule. Moreover, the intracellular accumulation of protoporphyrin IX, after exogenous administration of its precursor 5-ALA, coincides with reduced XIAP expression in PC-3 prostate cancer cells and an increased sensitivity to TRAIL-mediated apoptosis. The preferential accumulation of protoporphyrin IX and its derivatives in neoplastic lesions is well established and has been extensively employed for photodetection and photodynamic therapy in various malignancies. We hypothesize that displacement of zinc sensitizes malignant cells to cytotoxic agents via down-regulation of XIAP and, therefore, zinc chelation might represent a novel mechanism for prostate cancer therapy. Importantly, our data and the results of others demonstrate that the depletion of XIAP by itself is sufficient to reverse resistance to TRAIL-mediated apoptosis in cancer cells. To test our hypothesis and to evaluate the therapeutic uses of zinc chelating agents in prostate cancer, we propose the following Specific Aims: Aim 1: To identify 5-ALA derivatives with improved capability of sensitizing prostate cancer cells to cytotoxic agents in vitro; Aim 2: To examine the oral bioavailability of 5-ALA esterified derivatives and the tissue distribution of 5-ALA induced PPIX in a xenograft model of prostate cancer; Aim 3: To examine the in vivo anti-tumor efficacy and toxicity of 5-ALA derivatives. XIAP levels are elevated in many cancer cell lines, and suppression of XIAP protein levels can sensitize cancer cells to cytotoxic drugs. This makes XIAP an attractive target for the design of novel anti-tumor agents. PUBLIC HEALTH RELEVANCE: Findings from our laboratory indicate that treatment of prostate cancer cells with the zinc chelating agents N, N, N', N', -tetrakis (2-pyridylmethyl) ethlenediamine (TPEN) and protoporphyrin IX induces down-regulation of the X-linked inhibitor of apoptosis protein (XIAP). Moreover, the intracellular accumulation of protoporphyrin IX after exogenous administration of its precursor, 5-aminolevulinic acid, coincides with reduced XIAP expression in PC-3 prostate cancer cells and an increased sensitivity to TRAIL-mediated apoptosis. We seek to evaluate the therapeutic uses of 5-ALA for the treatment of hormone refractory prostate cancer.