COBRA-1: A Novel Tubulin Depolymerizing Anticancer Agent

描述（由申请人提供）：微管由α/β-微管蛋白异源二聚体自缔合形成，为细胞提供结构支持，并在细胞运动、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点，表明它们在维持细胞活力方面的重要性。目前可用的微管蛋白结合抗癌药物，包括新的紫杉醇衍生物和埃博霉素，与α/β-微管蛋白异二聚体的β-微管蛋白亚基相互作用，对微管负端没有影响。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。我们使用的三维计算机模型的微管蛋白构建的基础上，其最近解决的电子晶体结构的合理设计的一种新的单四氢呋喃（THF）的合成抗癌药物的目标是一个独特的狭窄的结合腔表面上的α-微管蛋白。我们发现了一个先前未鉴定的区域，具有显著丰富的亮氨酸残基，其位于GDP/GTP结合位点和紫杉醇结合位点之间。这个独特的区域包含一个细长尺寸的狭窄空腔，可以容纳长度高达12个碳原子的完全拉伸的脂肪链。使用该模型，在帕克休斯研究所药物发现计划中的有机化合物文件的全面结构搜索导致最近报道的手性THF-环氧化物作为合理合成新型抗癌药物的潜在分子模板的鉴定，所述新型抗癌药物含有能够与微管蛋白的这种富含亮氨酸的结合腔进行疏水结合相互作用的结构元件。我们的先导化合物命名为COBRA-1，在无细胞浊度测定中抑制GTP诱导的微管蛋白聚合。用COBRA-1处理人乳腺癌和脑肿瘤（胶质母细胞瘤）细胞引起微管组织的破坏和凋亡。与其他微管干扰剂一样，COBRA-1激活了促凋亡c-Jun N-末端激酶（JNK）信号转导途径，这一点可以通过快速诱导c-Jun表达来证明。COBRA-1作为抗癌剂的进一步开发将取决于在相关动物模型中的体内功效和毒性研究。我们现在建议使用严重联合免疫缺陷（SCID）小鼠模型，详细的体内抗肿瘤活性的SCID小鼠与人乳腺癌或胶质母细胞瘤细胞的挑战。我们的具体目标是：（i）研究COBRA-1在BALB/c小鼠中的体内毒性特征和（ii）研究COBRA-1在转移性人乳腺癌和胶质母细胞瘤的SCID小鼠模型中的体内抗癌活性。从具体目标1-2中描述的这些研究中获得的知识预计将有助于设计采用COBRA-1治疗转移性实体瘤的创新治疗方案。

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.