Development of Targeted Damaging Agents for the Treatment of Drug-Resistant Gliomas

项目总结 O6-甲基鸟嘌呤甲基转移酶(MGMT)的表达缺失在癌症中很常见，并增加了敏感性 DNA烷化剂，如替莫唑胺(TMZ)。通过启动子超甲基化抑制MGMT的表观遗传沉默 在约50%的胶质母细胞瘤(GBM)和大多数具有异柠檬酸脱氢酶-1/2的低级别胶质瘤中发现 (IDH1/2)突变。MGMT在其他癌症中也是沉默的，包括高达40%的结肠癌，35%的小结肠癌 细胞性肺癌和25%的非小细胞肺癌。在缺乏MGMT表达的细胞中(称为MGMT- 细胞)，TMZ衍生的O6-甲基鸟嘌呤(O6MeG)损伤在DNA复制过程中与胸腺嘧啶错配，原因是 改变氢碱基配对，导致错配修复途径(MMR)的激活。MMR尝试 通过切除新合成的链来修复这些损伤，但胸腺嘧啶再次插入到与 O6MeG。这种重新插入会再次触发MMR，导致DNA修复的循环迭代，最终 细胞凋亡。临床上，MGMT启动子去甲基化很少见，而MMR突变经常发生在 在许多肿瘤类型中对TMZ耐药的主要机制。因为MGMT沉默在许多 癌症，克服MMR耐药性的DNA损伤(同时仍可通过MGMT解决，以便 维持治疗指数(TI)将产生广泛的影响。此外，由于这个生物标记物即使在 治疗难治性环境(即，在MMR缺陷的背景下)，我们认为MGMT表达的丢失 没有被充分利用来获得治疗收益。基于上面提出的发现，我们试图开发一种新的 在Ranjit Bindra博士和Seth Herzon博士的实验室中发现的一类产生O6MeG病变的药物 在健康细胞中对MGMT去除敏感(“MGMT依赖”)，但可以克服MMR 电阻(“MMR独立”)。为此，Bindra博士和Herzon博士共同创立了KL50治疗公司， 他们的研究导致了KL50的鉴定，KL50是一种新型的烷基化试剂，对MMR-细胞更有活性 MMR+细胞系，同时保持MGMT的分辨能力。这种分子表现出极高的灵敏度。 在MGMT缺乏的细胞中，与MMR状态无关，在MGMT熟练的细胞中活性可忽略不计，并具有 TI大约是TMZ的30倍。在这些成就的基础上，在这个快速通道SBIR项目中，我们 建议进行引线优化以提高中枢神经系统(CNS)的渗透率，确定集合 在小鼠高级别胶质瘤(HGG)模型中发现具有体内疗效的小分子，并进一步发展这些 用于1期临床试验的化合物。这些依赖于MGMT和不依赖于MMR的烷基化试剂是 预计将拥有TMZ的积极属性，同时规避不可避免的MMR损失 耐药机制，并因此对我们治疗基底膜和其他缺乏的肿瘤的方式有重大影响 MGMT。这些分子可能代表着肿瘤学的范式转变，因为它们极大地改善了它们的 治疗指数。如果成功，我们的方法将显著提高dna烷化剂的安全性和有效性。 并将扩大其在更广泛的复发性胶质瘤和许多其他癌症中的应用。

PROJECT SUMMARY Loss of O6-methylguanine methyltransferase (MGMT) expression is common in cancers and confers sensitivity to DNA alkylators, such as temozolomide (TMZ). Epigenetic silencing of MGMT via promoter hypermethylation is found in ~50% of glioblastomas (GBMs), and in most lower grade gliomas with isocitrate dehydrogenase-1/2 (IDH1/2) mutations. MGMT is also silenced in other cancers, including up to 40% of colon cancers, 35% of small cell lung cancers, and 25% of non-small cell lung cancers. In cells that lack MGMT expression (termed MGMT- cells), TMZ-derived O6-methylguanine (O6MeG) lesions mispair with thymine, during DNA replication, due to altered hydrogen base pairing, leading to activation of the mismatch repair pathway (MMR). MMR attempts to repair these lesions by resecting the newly synthesized strand, but thymine once again is inserted opposite of O6MeG. This reinsertion again triggers MMR, leading to iterative “futile cycles” of DNA repair and ultimately apoptosis. Clinically, MGMT promoter demethylation is rare, whereas MMR mutations occur frequently as a dominant mechanism of resistance to TMZ in many tumor types. Because MGMT silencing is found in many cancers, DNA lesions that overcome the MMR resistance (while still being resolvable by MGMT, so as to maintain a therapeutic index (TI)) will have a broad impact. Furthermore, as this biomarker persists even in the treatment-refractory setting (i.e., in the context of MMR defects), we argue that loss of MGMT expression has not been fully exploited for therapeutic gain. Based on the findings presented above, we seek to develop a new class of agents discovered in the laboratory of Drs. Ranjit Bindra and Seth Herzon that generate O6MeG lesions that are susceptible to MGMT removal (“MGMT dependent”) in healthy cells, but which can overcome MMR resistance (“MMR independent”). To this end, Drs. Bindra and Herzon have co-founded KL50 Therapeutics, LLC, and their studies lead to the identification of KL50, a novel alkylation agent that is more active against MMR- cell lines than MMR+ cell lines, while retaining MGMT resolvability. This molecule demonstrates exquisite sensitivity in MGMT-deficient cells independent of MMR status, with negligible activity in MGMT-proficient cells, and has a TI approximately 30 times greater than TMZ. Building on these achievements, in this fast-track SBIR project, we propose to conduct lead optimization to improve central nervous system (CNS) penetration, identify a collection of small molecules with in vivo efficacy in mouse models of high-grade gliomas (HGG), and further develop these compounds for use in a Phase 1 clinical trial. These MGMT dependent–MMR independent alkylating agents are anticipated to possess the positive attributes of TMZ, while circumventing the unavoidable MMR loss mediated resistance mechanism and, thereby, have a major impact on the way we treat GBMs and other tumors lacking MGMT. These molecules could represent a paradigm shift in oncology by dramatically improving their therapeutic index. If successful, our approach will significantly increase the safety and efficacy of DNA alkylators and will expand their use for a broader range of recurrent gliomas and many other cancers.