Targeting alpha particle-emitting radionuclides to the nuclei of cancer cells

描述（由申请人提供）：本提案概述了一个研究体，以评估放射性标记的α -黑色素细胞刺激激素（a- msh）肽类似物的细胞毒性和治疗效果，该类似物靶向向黑色素瘤细胞核发射放射性同位素的a粒子。选择性靶向α粒子放射同位素用于癌症治疗是一种令人兴奋和潜在的强大的靶向放疗新治疗策略。α辐射是如此密集的电离，它直接形成破坏性自由基，不依赖于组织的氧含量，它的细胞毒性不依赖于剂量率，导致潜在的强大的治疗指数。a-粒子的路径很短，约为55-80¿m（约4-6个细胞直径），因此，a-粒子的细胞毒性特性高度集中，最大限度地减少了对健康组织的附带辐射损伤。根据对a粒子细胞毒性的微剂量学研究，似乎a粒子必须穿过细胞核才能有效地引起细胞死亡。设计一种将a-发射器放置在细胞核中的生物靶向载体将是非常有利的。为此，开发了一种靶向a- msh肽的原型核（DOTA-NT-MSH），并通过荧光成像显示其定位于黑色素瘤细胞核中。本研究的目的是在体外细胞水平和体内黑色素瘤动物模型中确定靶向向细胞核发射放射性核素的功效。本研究的具体目的是：1)利用α -发射体212 Bi的亲本212 Pb优化核靶向肽的放射性标记效率和纯化；2)检测212 Pb标记的DOTA-NT-MSH和对照dota -非特异性肽的体外亚细胞分布和细胞毒性；3)确定DOTA-NT-MSH和DOTA-NDPMSH肽在黑色素瘤小鼠体内的生物分布。恶性黑色素瘤是一个严重的健康问题，由于发病率的增加和对常规化疗和外部束辐射的耐药性。尽管最近癌症治疗取得了进展，但弥散性转移性疾病患者的中位预期寿命仍为12-15个月。显然需要开发新的有效的治疗药物来攻击恶性黑色素瘤。靶向a治疗恶性黑色素瘤的发展是有吸引力的，因为a发射器的短粒子路径长度特别适合转移性疾病特征的弥散性肿瘤细胞的小簇。我们实验室的初步结果表明，在临床前治疗研究中，肽靶向a-发射器在治疗黑色素瘤方面非常有效。通过放射性核素的核定位改进肽靶向治疗方法，由于细胞杀伤效率更高，可能在更低剂量下提高治疗效果。针对转移性黑色素瘤的肽靶向α治疗有可能提供肿瘤特异性和有效的晚期疾病治疗，这对目前的治疗方法有耐药性。

DESCRIPTION (provided by applicant): This proposal outlines a body of research to evaluate the cytotoxicity and therapeutic efficacy of radiolabeled alpha-melanocyte stimulating hormone (a-MSH) peptide analogs that target a-particle emitting radioisotopes to the nuclei of melanoma cells. The selective targeting of alpha-particle emitting radioisotopes for cancer therapy is emerging as an exciting and potentially powerful new treatment strategy in targeted radiotherapy. Alpha-radiation is so densely ionizing that it forms destructive radicals directly, independent of oxygen content of the tissue and its cytotoxicity is independent of the dose rate, resulting in potentially powerful therapeutic index. The pathlengths of a-particles are short, on the order of 55-80 ¿m (~4-6 cell diameters), therefore, the cytotoxic properties of a-particles are highly focused, which minimizes collateral radiation damage of healthy tissues. Based on microdosimetry studies on a-particle cytotoxicity, it appears that a-particles must traverse the cell nucleus to be effective in causing cell death. Designing a biological targeting vehicle that would deposit an a-emitter in the nucleus of a cell would be highly advantageous. To that end a prototype nuclear targeting a-MSH peptide (DOTA-NT-MSH) was developed and shown to localize in the nuclei of melanoma cell by fluorescence imaging. The goal of the proposed research is to determine the efficacy targeting a- emitting radionuclides to the nucleus in vitro at the cellular level and in vivo in melanoma animal models. The specific objectives of this research are: 1) optimize the radiolabeling efficiency and purification of the nuclear targeting peptide with 212 Pb the parent of the alpha emitter 212 Bi, 2) examine the in vitro subcellular distribution and cytotoxicity of 212 Pb-labeled DOTA-NT-MSH and a control DOTA-nonspecific peptide, 3) determine the biodistribution of DOTA-NT-MSH and DOTA-NDPMSH peptides in melanoma bearing mice. Malignant melanoma is a serous health problem due to an increase in incidence and resistance to conventional chemotherapeutics and external beam radiation. In spite of recent advances in cancer therapy, the median life expectancy for patients with disseminated metastatic disease remains at 12-15 months. There is a clear need for the development of new and efficacious therapy agents to attack malignant melanoma. The development of targeted a-therapy for malignant melanoma is attractive since the short particle pathlength of a-emitters is particularly well match small clusters of disseminated tumor cells that characterize metastatic disease. Preliminary results from our laboratory have demonstrated that peptide targeted a-emitters are very effective in treating melanoma in pre-clinical therapy studies. Refinement of the peptide-targeted a-therapy approach through nuclear localization of radionuclides should result in improved therapeutic efficacy at potentially lower doses due to higher cell killing efficiencies. Peptide targeted alpha-therapy for metastatic melanoma has the potential to provide tumor-specific and efficacious treatment of advanced stage disease, which is resistant to current therapeutic approaches.