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

描述(申请人提供)：这项提案概述了一系列研究，以评估放射性标记的α-黑素细胞刺激素(a-MSH)多肽类似物的细胞毒性和治疗效果，该多肽类似物针对向黑色素瘤细胞核发射放射性同位素的a-粒子。在靶向放射治疗中，选择性靶向α粒子放射治疗正在成为一种令人兴奋和潜在有效的新治疗策略。阿尔法辐射是如此密集的电离，以至于它直接形成破坏性的自由基，与组织的氧含量无关，其细胞毒性与剂量率无关，从而产生潜在的强大的治疗指数。α粒子的路径较短，在55-80m(~4-6个细胞直径)数量级，因此，α-粒子的细胞毒性特性高度集中，从而最大限度地减少了对健康组织的附带辐射损伤。根据对α粒子细胞毒性的微剂量学研究，似乎α粒子必须穿过细胞核才能有效地导致细胞死亡。设计一种生物靶向载体，将a发射体沉积在细胞的细胞核中将是非常有利的。为此，开发了一种核靶向α-MSH多肽的原型(DOTA-NT-MSH)，并通过荧光成像显示其定位于黑色素瘤细胞的细胞核中。这项拟议研究的目的是在黑色素瘤动物模型中，在体外细胞水平和体内水平上确定靶向a发射的放射性核素到细胞核的有效性。本研究的具体目的是：1)优化核靶向多肽的放射性标记效率和纯化，2)检测212Pb标记的DOTA-NT-MSH和对照的DOTA-NT-MSH的体外亚细胞分布和细胞毒性；3)测定DOTA-NT-MSH和DOTA-NDPMSH多肽在荷瘤小鼠体内的生物分布。恶性黑色素瘤是一种严重的健康问题，其原因是发病率的增加以及对常规化疗和外照射的抵抗。尽管最近癌症治疗取得了进展，但播散性转移性疾病患者的平均预期寿命仍为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。针对恶性黑色素瘤的靶向a-治疗的发展是有吸引力的，因为a-发射体的短颗粒路径特别适合表现转移性疾病特征的小的播散性肿瘤细胞簇。我们实验室的初步结果表明，在临床前治疗研究中，多肽靶向α-发射体对黑色素瘤的治疗非常有效。通过放射性核素的核定位来改进多肽靶向a治疗方法，应该会因为更高的细胞杀伤效率而在潜在的较低剂量下导致治疗效果的改善。多肽靶向治疗转移性黑色素瘤具有提供肿瘤特异性和有效治疗晚期疾病的潜力，而晚期疾病对当前的治疗方法具有抵抗力。

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.