Boronated nucleosides for neutron capture therapy of brain tumors

描述（由申请人提供）：传统癌症治疗的进步并未对多形性胶质母细胞瘤（GBM）的治疗产生任何显著的改善。因此，进一步发展新的GBM治疗方式，如硼中子俘获疗法（BNCT），仍然是美国卫生科学界的紧迫任务。本次拨款申请的主题是继续开发3-碳硼基胸苷类似物（3cta），这是一种用于治疗GBM的新型BNCT药物。3cta的作用机制主要基于它们作为人胸苷激酶1 （TK1）底物的能力，TK1仅在增殖细胞中有活性。通过脑内或瘤内注射N5-2OH（目前3CTA文库的先导化合物）对荷瘤啮齿动物进行BNCT治疗，可减少肿瘤生长，延长生存时间。另一方面，同样的研究也揭示了N5-2OH和其他3cta的两个主要局限性。这些问题是：(1)在TK1的底物结合位点与内源性胸腺嘧啶（Thd）竞争不佳；(2)缺乏水溶性，这就需要使用有机溶剂来溶解3cta进行生物学研究。此外，3cta的关键生化和生物学特性仍然未知。这些是(3)3cta在单磷酸化步骤之外的合成代谢，包括它们可能并入DNA，以及(4)3cta及其代谢物进入和退出细胞的机制。为了解决这些缺点，制定了以下具体目标：(1)合成在TK1活性位点与Thd竞争能力增强的3cta，用TK1评价其底物和抑制能力，并确定其理化性质；(2)合成N5-2OH水溶性氨基酸前药，并评价其在体外给药中的适用性。(3)研究特异性目的1和2中产生的具有改善的药物样和酶性质的N5-2OH和3cta的体外代谢以及核苷酸激酶和DNA聚合酶的酶测定；(4)研究特异性目的1和2中产生的具有改善的药物样和酶性质的N5-2OH和3cta的细胞内流和外排机制及其体外代谢产物；(5)优化从Specific Aims 1- 4中获得的具有最佳药物样和酶性质的3CTA给药RG2胶质瘤大鼠的体外给药参数，并确定可能的神经毒性。公共卫生相关性：新型硼化核苷将被开发用于硼中子俘获疗法（BNCT）治疗脑肿瘤。BNCT是一种双重治疗方式，既依赖于化学成分，也依赖于辐射成分。多形性胶质母细胞瘤是所有癌症中最致命的。传统癌症治疗的进步并没有对这些脑肿瘤的治疗产生任何显著的改善。这些含硼核苷的脑肿瘤的BNCT可能有提高生存率的潜力。

DESCRIPTION (provided by applicant): Advances in conventional cancer therapy have not produced any significant improvement in the treatment of glioblastoma multiforme (GBM). Therefore, the further development of novel treatment modalities for GBM, such as boron neutron capture therapy (BNCT), remains a pressing task for the health science community in the USA. Subject of the present grant application is the continued development of 3-carboranyl thymidine analogues (3CTAs), a novel class of BNCT agents for the treatment of GBM. The mechanism of action of 3CTAs is primarily based on their ability to function as substrates of human thymidine kinase 1 (TK1), which is only active in proliferating cells. BNCT of tumor-bearing rodents that had received N5-2OH, the current lead compound of our 3CTA library, via intracerebral (i.c.) or intratumoral (i.t.) injection resulted in reduced tumor growth and prolonged survival times. On the other hand, the same studies have revealed two major limitations of N5-2OH and other 3CTAs. These are (1) the suboptimal competition with endogenous thymidine (Thd) at the substrate-binding site of TK1 and (2) the lack of water-solubility, which necessitated the use of organic solvents to solubilize 3CTAs for biological studies. In addition crucial biochemical and biological features of 3CTAs are still unknown. These are (3) the anabolism of 3CTAs beyond the monophosphorylation step, including their possible incorporation into DNA, and (4) the mechanisms that 3CTAs and their metabolites recruit to enter and exit cells. To address these shortcomings, the following SPECIFIC AIMS were developed: (1) To synthesize 3CTAs with improved ability to compete with Thd at the active site of TK1, to evaluate their substrate and inhibitory capacities in enzyme assays with TK1, and to determine their physicochemical properties, (2) to synthesize water-soluble amino acid prodrugs of N5-2OH and to evaluate their applicability for i.c. administration, (3) To study the metabolism of N5-2OH and 3CTAs with improved drug-like and enzymatic properties that emerged from Specific Aims 1 and 2 in vitro and in enzyme assays with nucleotide kinases and DNA polymerase, (4) to study the mechanisms of cellular influx and efflux of N5-2OH, 3CTAs with improved drug-like and enzymatic properties that emerged from Specific Aims 1 and 2, and their metabolites in vitro, and (5) to optimize parameters for i.c. administration of the 3CTA with the most improved drug-like and enzymatic properties that emerged from Specific Aims 1- 4 to RG2 glioma bearing rats and to determine possible neurotoxicity. PUBLIC HEALTH RELEVANCE: Novel boronated nucleosides will be developed for the treatment of brain tumors by boron neutron capture therapy (BNCT). BNCT is a binary treatment modality for cancer that relies both on a chemical and a radiation component. Brain tumors called glioblastoma multiforme are among the deadliest of all cancers. Advances in conventional cancer therapy have not produced any significant improvement in the treatment of these brain tumors. BNCT of these brain tumors with boronated nucleosides may have the potential to improve survival rates.