Preclinical investigations with inhibitors of DNA double-strand break repair for improved chemotherapy of malignant brain tumours

多形性胶质母细胞瘤（GBM，根据世卫组织星形细胞瘤III级和IV级）是一种非常具有侵袭性的脑肿瘤，预后差，对标准治疗反应弱，因此需要新的化疗方法。本研究的主要模型将是GBM细胞系和免疫缺陷裸鼠的异种移植。我们将在实验中使用烷基化药物替莫唑胺（TMZ）和氯硝基源（CNUs） CCNU和ACNU。由于其DNA烷基化的作用方式和对癌细胞的杀伤活性，TMZ和CNUs被用作原发性脑肿瘤和各种来源的转移性肿瘤辅助化疗的首选药物。在癌细胞中，它们诱导致命的次级DNA双链断裂（DSB），可以通过DSB修复途径进行修复：同源重组（HR）和parp依赖性非同源末端连接。为了调制DSB修复和对TMZ和CNUs的敏感性，我们将使用特定的HRi （RAD51i RI-1和B02）和PARPi。我们已经证明，在皮下异种移植模型中，RI-1增加了对CCNU的敏感性。PARPi olaparib最近在美国和欧洲被批准用于卵巢癌的治疗。研究PARPi是否能有效杀死胶质母细胞瘤细胞，这取决于它们的药效学。然而，奥拉帕尼是细胞外排泵机制的底物，因此我们将PARPi veliparib纳入我们的研究中，PARPi veliparib不是底物，与RAD51i结合可能显示出更好的杀伤效果和“合成致死”效应。这些组合在体外确实显示出更高的疗效，将在动物实验（皮下异种移植）中进行测试，并进一步在颅内模型中进行测试。

Glioblastoma multiforme (GBM, according to WHO astrocytoma grade III and IV) is a very aggressive type of brain tumour with bad prognosis and weak response to standard therapies, therefore new chemotherapeutic approaches are needed. The main models of the present study will be GBM cell lines and xenografts in immunodeficient nude mice. We will use in our experiments the alkylating drugs temozolomide (TMZ) and the chloronitrosoureas (CNUs) CCNU and ACNU. Due to the DNA alkylating mode of action and cancer cell killing activity, TMZ and the CNUs are used as first choice drugs for adjuvant chemotherapy of primary brain tumors and metastases of various origins. In cancer cells they induce lethal secondary DNA double-strand breaks (DSB) that can be repaired by DSB repair pathways: homologus recombination (HR) and PARP-dependent non-homologous end-joining. For modulation of DSB repair and the sensitivity against TMZ and CNUs, we will use specific HRi (the RAD51i RI-1 and B02) and PARPi. We have already demonstrated that RI-1 increases the sensitivity to CCNU in the subcutaneous xenograft model. The PARPi olaparib has been recently approved for the treatment of ovarian carcinomas in the USA and Europe. It is of interest to investigate if PARPi, depending on their pharmacodynamics, are efficient in killing glioblastoma cells. Olaparib, however, is a substrate of the cellular efflux pump mechanisms, therefore we include in our studies the PARPi veliparib which is not a substrate and may display a better killing efficacy and ‘synthetic lethality’-like effects in combination with RAD51i. The combinations, which do show increased efficacy in vitro, will be tested in animal experiments (subcutaneous xenografts) and, further, in the intracranial model.