Abstract:
Platinum-based anticancer drugs are used clinically for the routine treatment of a variety of cancer types, but are also known for causing dose-limiting peripheral neurotoxicity. Cell body atrophy of sensory neurons within dorsal root ganglia (DRG) is a morphological hallmark of this toxicity. However, the mechanism by which platinum drugs induce neuronal atrophy and peripheral neurotoxicity has not been fully elucidated. Primary cultures of rat DRG cells were used to investigate the role of platinum-DNA damage and transcriptional inhibition in platinum drug-induced neuronal cell body atrophy and peripheral neurotoxicity. Platinum-DNA damage was determined by measuring the amount of platinum binding to DNA. Transcriptional activity was indicated by the levels of RNAincorporated 5-ethynyl uridine (EU) or [3H]uridine, or total RNA content. Neuronal cell body size was represented by the cross-sectional areas of neuronal cell bodies. Click chemistry quantitative fluorescence imaging of RNA-incorporated EU showed high, but wide ranging, basal levels of global transcription in individual neurons that correlated with their cell body size. Oxaliplatin-induced platinum-DNA damage appeared to have occurred before the induction of transcriptional inhibition, while neuronal cell body atrophy appeared delayed until after the occurrence of platinum-DNA damage and inhibition of transcription. Both sodium thiosulfate and cimetidine reduced platinum-DNA damage, and protected cells from both the transcriptional inhibition and neuronal cell body atrophy induced by oxaliplatin. Treatment with four different platinum-based anticancer drugs, cisplatin, carboplatin, oxaliplatin and ormaplatin, and two pairs of enantiomers of diaminocyclohexane (DACH) platinum compounds, ormaplatin and Pt(DACH)Cl2, resulted in different levels of platinum-DNA damage, which corresponded to the effects of the different treatments on transcription and neuronal cell body size. A model transcriptional inhibitor, actinomycin D, also reduced neuronal cell body size following its inhibition of transcription. In conclusion, these findings point to a stepwise mechanism of platinum drug-induced peripheral neurotoxicity, whereby platinum-DNA damage induces transcriptional inhibition leading in turn to DRG neuronal cell body atrophy. DRG neurons may be particularly vulnerable to platinum drugs due to their high basal transcriptional activity. Limiting platinum-DNA damage in DRG neurons may be a potential therapeutic strategy for protecting against platinum drug-induced peripheral neurotoxicity.