Role of purine metabolism in chemoresistance

项目摘要 胶质母细胞瘤（GBM）是一种IV级肿瘤，是最具侵袭性和浸润性的脑癌之一。 目前诊断为胶质母细胞瘤（GBM）的患者预后非常差。中位生存期 即使在手术切除然后烷基化的标准护理方案之后， 化疗（通常为替莫唑胺或TMZ）和放疗。这是因为在几乎所有的患者中， 治疗后复发，因为GBM细胞可能对治疗产生抗性。我们的目标是开发一种治疗方法， GBM将降低复发率，从而改善患者的预后。其中一个区别 癌症的特征是其不受控制的细胞分裂。由于癌细胞比正常细胞分裂得更快， 它们需要更多的嘌呤，DNA和RNA的基本组成部分。(The嘌呤生物合成途径以前 与化疗耐药性有关）。嘌呤是由氨基酸和其他小分子合成的。 分子通过从头生物合成途径或从微环境中再循环， 补救途径癌细胞通常使用从头生物合成途径，而中枢神经 系统通常更多地依赖于救助途径。通过初步分析，我们确定ARL 13 B是一个新的 化疗期间嘌呤生物合成途径的调节剂。ARL 13 B是ADP核糖基化的一员， 负责纤毛维持的因子样家族蛋白，直接与肌苷一磷酸相互作用 脱氢酶2（IMPDH 2），嘌呤生物合成的限速酶。在我们最初的研究中， ARL 13 B抑制TMZ处理后GBM细胞对从头途径的利用，并增加TMZ处理后GBM细胞对 补救生物合成途径。TMZ治疗的有效性在体外和体内也有所提高 在ARL 13 B敲除之后。因此，我们假设ARL 13 B-IMPDH 2调节的从细胞外基质的转换， 从补救途径到从头嘌呤生物合成途径是GBM细胞适应烷基化所必需的。 基础化疗。本研究的目的是通过以下目的进一步研究这一假设： 1)研究ARL 13 B在调节嘌呤代谢中的作用; 2）阐明嘌呤代谢在 促进对TMZ的抗性; 3）调节嘌呤生物合成途径以克服对TMZ的抗性。 烷基化化疗总之，我们希望获得新的见解嘌呤代谢的作用， GBM在治疗耐药性的背景下，最终目标是开发一种转化疗法， GBM复发！

PROJECT SUMMARY Glioblastoma (GBM), a grade IV tumor, is one of the most aggressive and infiltrative forms of brain cancer. Patients that are currently diagnosed with Glioblastoma (GBM) have a very poor prognosis. Median survival is around 8-10 months even after the standard care protocol of surgical resection followed by alkylating chemotherapy (typically temozolomide or TMZ) and radiotherapy. This is because in nearly all patients the tumor recurs after treatment since GBM cell can become resistant to therapy. Our goal is to develop a treatment for GBM that will reduce recurrence rate and thereby improve the prognosis for patients. One of the distinguishing characteristics of cancer is its uncontrolled cell division. Since cancer cells divide more rapidly than normal cells, they require more purines, the building blocks of DNA and RNA. (The purine biosynthesis pathway has previously been implicated in resistance to chemotherapy). Purines are either synthesized from amino acids and other small molecules through the de novo biosynthesis pathway or are recycled from the microenvironment through the salvage pathway. Cancer cells typically use the de novo biosynthesis pathway, whereas the central nerves system usually rely more on the salvage pathway. Through initial analysis, we have identified ARL13B as a novel regulator of the purine biosynthesis pathway during chemotherapy. ARL13B, a member of the ADP-ribosylation factor-like family protein accountable for cilia maintenance, directly interacts with inosine monophosphate dehydrogenase 2 (IMPDH2), the rate-limiting enzyme purine biosynthesis. In our initial studies knocking-down ARL13B inhibited GBM cells’ utilization of the de novo pathway after TMZ treatment and increased utilization of the salvage biosynthesis pathway. The effectiveness of TMZ treatment was also elevated in vitro and in vivo following ARL13B knockdown. We therefore hypothesize that the ARL13B-IMPDH2 regulated switch from the salvage pathway to the de novo purine biosynthesis pathway is necessary for GBM cells’ adaptation to alkylating- based chemotherapy. The goal of this study is to further investigate this hypothesis through the following aims: 1) examine the role of ARL13B in regulating purine metabolism; 2) elucidate the role of purine metabolism in promoting resistance to TMZ; 3) modulate the purine biosynthesis pathway to overcome the resistance against the alkylating-based chemotherapy. Overall, we hope to gain novel insight into the role of purine metabolism in GBM in the context of therapeutic resistance with the end goal of developing a translational therapy to prevent GBM recurrence.!