8-aminoguanine for prevention and treatment of chemotherapy-induced peripheral neuropathy

Current treatment protocols for most types of cancers require chemotherapeutic agents which are associated with significant side effects, including chemotherapy-induced peripheral neuropathy (CIPN). CIPN manifests as numbness and tingling in the glabrous skin of the hands and feet which often progresses to pain and hypersensitivity to mechanical and cold stimuli. We tested the hypothesis that CIPN is due, at least in part to an increase in purine nucleoside phosphorylase (PNPase) activity, resulting in a shift from anti- to pro-inflammatory purine metabolites. A key prediction of this hypothesis is that inhibition of PNPase can prevent or reverse CIPN. We confirmed a robust mechanical hypersensitivity and loss of intra-epidermal nerve fiber (IENF) density in the glabrous skin following administration of paclitaxel (PAC). The endogenous inhibitor of PNPase, 8-aminoguanine (8-AG), given prior to PAC or 72 hours following the last dose of PAC blocked mechanical hypersensitivity and loss of IENF. Importantly, 8-AG given 72 hours after PAC: 1) reduced levels of pro-inflammatory purines and a biomarker for oxidative stress, 2) increased expression of Growth Associated Protein-43 (GAP-43), 3) increased expression of Mst3b (facilitates axonal regeneration), 4) decreased expression of the membrane protein neurite outgrowth inhibitor-A (Nogo-A), and 5) increased expression of NMNAT2 (an NAD+ producing enzyme). We replicated the effect of 8-AG on PAC-induced mechanical hypersensitivity with shRNA-induced knockdown of PNPase. These findings are consistent with the hypothesis that CIPN is due in part to increased PNPase activity such that PNPase inhibition reduces oxidative injury and cellular damage associated with PAC treatment.目前多数癌症的治疗方案均需使用化疗药物，而这类药物常伴随严重不良反应，其中包括化疗诱导周围神经病（chemotherapy-induced peripheral neuropathy, CIPN）。CIPN以手足无毛皮肤的麻木、刺痛为主要临床表现，病情常进展为疼痛以及对机械、冷刺激的超敏反应。本研究验证了如下假说：CIPN的发生至少部分源于嘌呤核苷磷酸化酶（purine nucleoside phosphorylase, PNPase）活性升高，使得炎症相关嘌呤代谢物从抗炎型转向促炎型。该假说的核心预测为，抑制PNPase可预防或逆转CIPN。本研究证实，给予紫杉醇（paclitaxel, PAC）后，受试对象的手足无毛皮肤可出现显著的机械性超敏反应，且表皮内神经纤维（intra-epidermal nerve fiber, IENF）密度降低。在PAC给药前或末次PAC给药72小时后给予PNPase的内源性抑制剂8-氨基鸟嘌呤（8-aminoguanine, 8-AG），可阻断机械性超敏反应与IENF密度丢失。尤为关键的是，在PAC给药72小时后给予8-AG可实现以下效果：1）降低促炎型嘌呤代谢物水平与氧化应激生物标志物水平；2）上调生长相关蛋白43（Growth Associated Protein-43, GAP-43）的表达；3）上调Mst3b的表达（该蛋白可促进轴突再生）；4）下调膜蛋白神经突生长抑制剂-A（neurite outgrowth inhibitor-A, Nogo-A）的表达；5）上调NMNAT2的表达（该蛋白为一类烟酰胺腺嘌呤二核苷酸（nicotinamide adenine dinucleotide, NAD+）合成酶）。本研究通过短发夹RNA（short hairpin RNA, shRNA）介导的PNPase敲低实验，重复验证了8-AG对PAC诱导的机械性超敏反应的改善效果。上述研究结果与"CIPN部分源于PNPase活性升高"的假说相符，即抑制PNPase可减轻PAC治疗相关的氧化损伤与细胞损伤。