Molecular cancer radiosensitization by targeting Mcl-1

放射耐药显著损害放射治疗的疗效，并涉及防止辐射诱导的细胞死亡的细胞信号转导途径。Bcl-2家族中的蛋白是细胞凋亡和自噬的中心和双重调节因子，抑制细胞凋亡和/或自噬的成员，如Bcl-2和Mcl-1，在大多数癌症中过表达，并有助于肿瘤的发生、进展和对治疗的抵抗。通过基于计算结构的合理设计和结构优化，我们发现并合成了一系列Bcl-2/Mcl-1的小分子抑制剂（美国专利No.7,432,304，正在申请中），包括(-)-棉酚及其活性更高的衍生物如apogossypolone （ApoG2）。在纳米摩尔水平上，ApoG2对Mcl-1具有更高的亲和力，对小鼠前列腺癌细胞生长的抑制作用是(-)-棉酚的3倍，毒性是(-)-棉酚的8倍。这两种药物对具有高水平Bcl-2和/或Mcl-1的癌细胞显示出强大的治疗活性，以克服辐射抗性，但对正常细胞的影响很小。ApoG2能有效地降低Mcl-1并增加BH3-only蛋白Bim和NOXA，这表明靶向Mcl-1可能是一种有希望的方法来治疗高水平Mcl-1的人前列腺癌。基于我们有希望的初步结果，我们提出验证两个相互关联的基本假设：(1)Mcl-1蛋白在Mcl-1过表达的人前列腺癌细胞的辐射抗性中起关键作用；(2)新型Mcl-1抑制剂对Mcl-1的抑制可能通过上调Bim/Mcl-1和/或NOXA/Mcl-1比值来克服辐射耐药，恢复前列腺癌细胞对电离辐射的敏感性。我们建议在体外和体内研究Mcl-1抑制剂的放射增敏潜力，验证其在人前列腺癌细胞中的分子靶点，并描述Mcl-1抑制剂诱导放射增敏的分子作用机制。我们的目标是确定Mcl-1是Mcl-1过表达癌症放射增敏的一个有希望的新靶点，最终目标是建立Mcl-1的分子调节作为克服具有高水平Mcl-1的人类前列腺癌放射耐药的新方法。这个为期两年的项目的成功将为开发Mcl-1的分子调控作为克服人类前列腺癌高水平Mcl-1的辐射抗性的新方法提供重要的推动力。mcl -1靶向分子治疗与常规放疗相结合，可能成为当前提高肿瘤治疗疗效的一种有前景的策略。

Radioresistance markedly impairs the efficacy of radiotherapy and involves cell signal transduction pathways that prevent radiation-induced cell death. Proteins in the Bcl-2 family are central and dual regulators of apoptosis and autophagy, and members that inhibit apoptosis and/or autophagy, such as Bcl-2 and Mcl-1, are overexpressed in most of cancers and contribute to tumor initiation, progression and resistance to therapy. Through computational structure-based rational design and structure optimization, we have discovered and synthesized a series of small molecule inhibitors of Bcl-2/Mcl-1 (US Patent No.7,432,304 and pending), including (-)-gossypol and its more active derivatives such as apogossypolone (ApoG2). ApoG2 exhibits a much higher affinity for Mcl-1 at nanomolar level, and is 3-times more potent than (-)-gossypol in inhibiting prostate cancer cell growth, and 8-times less toxic than (-)-gossypol in mice. Both agents show potent therapeutic activity to overcome radiation-resistance in cancer cells with high levels of Bcl-2 and/or Mcl-1, but have minimal effect on normal cells. ApoG2 potently reduces Mcl-1 and increase BH3-only proteins Bim and NOXA, suggesting that targeting Mcl-1 may be a promising approach for radiosensitization of human prostate cancer with high levels of Mcl-1. Based upon our promising preliminary results, we propose to test two inter-related basic hypotheses: (1) Mcl-1 protein plays a critical role in radiation resistance of human prostate cancer cells with Mcl-1 overexpression; (2) Inhibition of Mcl-1 by the novel Mcl-1 inhibitors will overcome radioresistance and restore sensitivity of prostate cancer cells to ionizing radiation, potentially via upregulating Bim/Mcl-1 and/or NOXA/Mcl-1 ratio. We propose to investigate the radiosensitizing potential of Mcl-1 inhibitors and validate their molecular target(s) in human prostate cancer cells in vitro and in vivo, and to delineate the molecular mechanism(s) of action in the Mcl-1 inhibitors-induced radiosensitization. Our goal is to establish that Mcl-1 is a promising novel target for radiosensitization of cancer with Mcl-1-overexpression, with the ultimate goal to establish the molecular modulation of Mcl-1 as a novel approach for overcoming radiation resistance of human prostate cancer with high levels of Mcl-1. The success of this two-year project will provide important impetus to develop the molecular modulation of Mcl-1 as a novel approach for overcoming radiation resistance of human prostate cancer with high levels of Mcl-1. The combination of Mcl-1-targeted molecular therapy and conventional radiotherapy may become a promising strategy to enhance the efficacy of current cancer treatment.