Using Drosophila melanogaster to identify chemotherapy toxicity genes

The severity of the toxic side effects of chemotherapy shows a great deal of interindividual variability, and much of this variation is likely genetically based. Simple DNA tests predictive of toxic side effects could revolutionize the way chemotherapy is carried out. Due to the challenges in identifying polymorphisms that affect toxicity in humans, we use Drosophila fecundity following oral exposure to carboplatin, gemcitabine and mitomycin C as a model system to identify naturally occurring DNA variants predictive of toxicity. We use the Drosophila Synthetic Population Resource (DSPR), a panel of recombinant inbred lines derived from a multiparent advanced intercross, to map quantitative trait loci affecting chemotoxicity. We identify two QTL each for carboplatin and gemcitabine toxicity and none for mitomycin. One QTL is associated with fly orthologs of a priori human carboplatin candidate genes ABCC2 and MSH2, and a second QTL is associated with fly orthologs of human gemcitabine candidate genes RRM2 and RRM2B. The third, a carboplatin QTL, is associated with a posteriori human orthologs from solute carrier family 7A, INPP4A&B, and NALCN. The fourth, a gemcitabine QTL that also affects methotrexate toxicity, is associated with human ortholog GPx4. Mapped QTL each explain a significant fraction of variation in toxicity, yet individual SNPs and transposable elements in the candidate gene regions fail to singly explain QTL peaks. Furthermore, estimates of founder haplotype effects are consistent with genes harboring several segregating functional alleles. We find little evidence for nonsynonymous SNPs explaining mapped QTL; thus it seems likely that standing variation in toxicity is due to regulatory alleles.化疗毒性副作用的严重程度存在显著的个体间差异，其中绝大多数变异可能由遗传因素介导。可预测毒性副作用的简易DNA检测技术，或将彻底革新化疗的临床实施范式。由于鉴定影响人类毒性的多态性存在诸多挑战，我们以果蝇经口暴露于卡铂、吉西他滨及丝裂霉素C后的繁殖力作为模型系统，用于筛选可预测毒性的天然DNA变异。我们采用果蝇合成种群资源（Drosophila Synthetic Population Resource, DSPR）——一种由多亲本高级互交（multiparent advanced intercross）群体衍生而来的重组近交系（recombinant inbred lines）面板——来定位影响化学毒性的数量性状位点（Quantitative Trait Locus, QTL）。我们分别鉴定出与卡铂、吉西他滨毒性相关的2个QTL，未发现与丝裂霉素C毒性相关的QTL。其中一个QTL与预先筛选的人类卡铂候选基因ABCC2和MSH2的果蝇同源基因相关；另一个QTL则与人类吉西他滨候选基因RRM2和RRM2B的果蝇同源基因相关。第三个卡铂相关QTL与溶质载体家族7A、INPP4A&B及NALCN的人类同源基因相关；第四个吉西他滨相关QTL（同时影响甲氨蝶呤毒性）与人类同源基因GPx4相关。已定位的QTL均可解释显著比例的毒性变异，但候选基因区域内的单个单核苷酸多态性（Single Nucleotide Polymorphism, SNPs）及转座元件（transposable elements）无法单独解释QTL峰值。此外，亲本单倍型效应的估算结果与携带多个分离功能等位基因的基因特征相符。我们未发现可解释已定位QTL的非同义SNPs的显著证据，由此推测，毒性相关的存留遗传变异大概率由调控等位基因介导。