COBRA-1: A Novel Tubulin Depolymerizing Anticancer Agent

描述(申请人提供)：微管是由α/β-微管蛋白异源二聚体自结合形成的，为细胞提供结构支持，在细胞运动、有丝分裂和减数分裂中发挥关键作用。它们也是几种抗癌药物的靶标，表明它们在维持细胞活力方面的重要性。目前已有的微管蛋白结合性抗癌药物，包括新的紫杉醇衍生物和伊波硫酮，与α/β-微管蛋白异源二聚体的β-微管蛋白亚基相互作用，对微管末端没有影响。此外，β-微管蛋白表达谱改变的癌细胞可能对这些药物具有耐药性。我们使用基于微管蛋白最近解析的电子晶体结构构建的三维计算机模型来合理设计一种新型的单四氢呋喃(THF)合成抗癌药物，靶向是在α-微管蛋白表面形成一个独特的狭窄结合腔。我们发现了一个先前未知的区域，其亮氨酸残基非常丰富，位于GDP/GTP结合部位和紫杉醇结合部位之间。这个独特的区域包含一个狭长尺寸的空腔，它可以容纳一个长达12个碳原子的完全伸展的脂肪链。利用这个模型，对Parker Hughes Institute药物发现计划中的有机化合物文件进行全面的结构搜索，确定了最近报道的手性四氢呋喃-环氧化物是合理合成新型抗癌药物的潜在分子模板，这些结构元素能够与微管蛋白的这个富含亮氨酸的结合空腔发生疏水结合作用。我们的先导化合物COBRA-1在无细胞浊度分析中抑制了GTP诱导的微管蛋白聚合。COBRA-1治疗人乳腺癌和脑肿瘤(胶质母细胞瘤)细胞引起微管组织破坏和细胞凋亡。与其他微管干扰剂一样，COBRA-1激活促凋亡的c-jun氨基末端激酶(JNK)信号转导通路，快速诱导c-jun的表达。COBRA-1作为抗癌药物的进一步发展将取决于体内疗效和相关动物模型的毒性研究。我们现在提议使用严重联合免疫缺陷(SCID)小鼠模型来详细研究用人乳腺癌或胶质母细胞瘤细胞攻击的SCID小鼠的体内抗癌活性。我们的具体目标是：(1)研究COBRA-1在BALB/c小鼠体内的毒性分布；(2)研究COBRA-1在人转移性乳腺癌和胶质母细胞瘤SCID小鼠模型中的体内抗癌活性。从具体目标1-2项下描述的这些研究中获得的知识有望促进使用COBRA-1治疗转移性实体肿瘤的创新治疗方案的设计。

DESCRIPTION (provided by applicant): Microtubules, which are formed by the self-association of the alpha/beta-tubulin heterodimers, provide structural support for a cell and play key roles in cell motility, mitosis, and meiosis. They are also the targets of several anticancer agents, indicating their importance in maintaining cell viability. Currently available tubulin binding anticancer drugs, including new taxol derivatives and epothilones, interact with beta-tubulin subunit of the alpha/beta-tubulin heterodimers and have no effect on microtubule minus ends. Furthermore, cancer cells with an altered beta-tubulin expression profile may be resistant to these agents. We used a three-dimensional computer model of tubulin constructed based upon its recently resolved electron crystallographic structure for rational design of a novel mono-tetrahydrofuran (THF)-containing synthetic anticancer drug targeting a unique narrow binding cavity on the surface of alpha-tubulin. We discovered a previously unidentified region with a remarkable abundance of leucine residues, which is located between the GDP/GTP binding site and the taxol binding site. This unique region contains a narrow cavity with elongated dimensions, which could accommodate a fully stretched aliphatic chain with a length of up to twelve carbon atoms. Using this model, a comprehensive structure search of the organic compound files in the Parker Hughes Institute Drug Discovery Program led to the identification of the recently reported chiral THF-epoxides as potential molecular templates for the rational synthesis of novel anti-cancer drugs containing structural elements capable of hydrophobic binding interactions with this leucine-rich binding cavity of tubulin. Our lead compound designated as COBRA-1, inhibited GTP-induced tubulin polymerization in cell free turbidity assays. Treatment of human breast cancer and brain tumor (glioblastoma) cells with COBRA-1 caused destruction of microtubule organization and apoptosis. Like other microtubule-interfering agents, COBRA-1 activated the pro-apoptotic c-Jun N-terminal kinase (JNK) signal transduction pathway, as evidenced by rapid induction of c-jun expression. The further development of COBRA-1 as an anticancer agent will depend on in vivo efficacy, and toxicity studies in relevant animal models. We are now proposing to use the severe combined immunodeficiency (SCID) mouse model for detailed in vivo anticancer activity in SCID mice challenged with human breast cancer or glioblastoma cells. Our specific aims are: (i) To study the in vivo toxicity profile of COBRA-1 in BALB/c mice and (ii) To study the in vivo anti-cancer activity of COBRA-1 in a SCID mouse model of metastatic human breast cancer and glioblastoma. The knowledge gained from these studies described under Specific Aims 1-2 is expected to facilitate the design of innovative treatment regimens employing COBRA-1 for the treatment of metastatic solid tumors.