Using a novel method to investigate platinum accumulation in rat dorsal root ganglia following oxaliplatin or Pt(dach)Cl2 treatments & investigating oxaliplatin- induced peripheral neuropathies

Abstract

Oxaliplatin is routinely prescribed for the treatment and management of metastatic colorectal cancers; however, long-term clinical use is impeded by the development of acute and chronic peripheral neuropathies. Although the mechanisms responsible for symptom development are unclear, platinum accumulation in nervous tissues is a potential pain-state contributor. It is not known where in the dorsal root ganglion (DRG) platinum from oxaliplatin accumulates, nor is it well understood what role Pt(dach)Cl2, as a metabolite of oxaliplatin, has in the development of oxaliplatin-induced neuropathic pain. This limits our understanding of the mechanisms responsible for chemotherapy-induced peripheral neuropathy which impinge on the development of long-lasting therapeutic options for patients. This study sought to develop a novel methodology for detecting platinum accumulation sites within rodent DRGs in an effort to refine our understanding of platinum/neuropathy interactions. Methods: behavioural observations were made in 21 Long-Evans rats separated into three clusters consisting of a control and two drugtreatments groups given either oxaliplatin (2.5mg/kg) or Pt(dach)Cl2 (2.39 mg/kg) intraperitoneally every three days for four injections. Immunohistochemistry was performed on harvested spinal cord sections for glia activation assessment while scanning electron microscopy, secondary ion mass spectrometry (SIMS) and mass spectrometry were utilised in a new methodology for identifying platinum accumulation in dorsal root ganglia (DRG). The former technique utilised full spectrum X-ray mapping coupled with energy dispersive spectroscopy to discern sites of platinum accumulation within DRG tissue sections. Morphometric studies of harvested DRG were also performed looking at eccentric nuclei and axonal G-ratios to assess the contributions of structural changes to neuropathy development. Results: platinum was discovered in the periphery of DRG cell bodies through full-spectrum X-ray analysis; however, this was at the detection limit of the SEM. Conversely, a larger aggregate of platinum was observed within the resin surrounding the DRG. Neither mass spectrometry, nor SIMS analysis detected platinum within DRG tissue. Astrocytitic, but not microglial, activity was significantly increased in the spinal cord dorsal horn following oxaliplatin-, but not Pt(dach)Cl2-treatments. Morphometry assessment of dorsal root ganglia tissue revealed slight atrophy of oxaliplatin-treated DRG cell bodies with a larger proportion of damaged axon fibres. However, there was no change in G-ratio between the treatment groups and controls, nor was any difference in C-fibre axonal area observed. Conclusions: The development of oxaliplatin-induced peripheral neuropathies is likely multifactorial. In the current investigation four intraperitoneal injections of oxaliplatin and Pt(dach)Cl2 did not produce significant changes in behaviour or dorsal root ganglia cell morphology. However, astrocyte activation following oxaliplatin administrations were observed which may contribute to the development of pain states reported by other researchers. The development of novel techniques for the identification of platinum within DRG tissue and resin was successful using full spectrum X-ray mapping, which can be further refined and improved for future studies.

Date of Award	2018
Original language	English