Mechanistic studies of oxaliplatin-induced cold hypersensitivity

N. Saleque, C. Gentry, S. Bevan, D. Andersson. King's College London, London, United Kingdom.

Introduction: Oxaliplatin is a platinum based chemotherapeutic drug used to treat colorectal cancer (1). Although oxaliplatin is an efficacious treatment of solid tumours, it is associated with dose limiting side effects; including acute cold induced dysaesthesias, which is a property unique to oxaliplatin (2). The ionic mechanisms responsible for cold hypersensitivity are unclear. Here, we examined the cold sensitivities of sensory neurons from oxaliplatin-treated mice.

Method: Animals. 8– 10-week-old C57Bl/6J mice received a single intraperitoneal (i.p) injection (6mg/kg) or daily injections with 3mg/kg oxaliplatin over 4 days. Paw withdrawal latencies were assessed using a 10°C cold plate. [Ca²⁺]_i-imaging. Dorsal root ganglion (DRG) neurons were dissociated enzymatically 3-4 days post final injection. Microfluorometric [Ca²⁺]_i -measurements were made using Fura-2 loaded DRG neurons 12-18 hours after dissociation. Cells were superfused with temperature controlled solutions and stimulated with a 35-10°C cold ramp. Analysis. One-way ANOVA with Tukey’s post-hoc was used for statistical analysis of in vivo data, χ², Fisher’s exact t-test, two-tailed for the proportion of cold-sensitive neurons and a non-parametric test (Mann-Whitney U) was used for analysis of cold activation temperatures.

Results: A single and repeated i.p. injections of oxaliplatin decreased the paw withdrawal latencies to the cold stimulus (10°C) 4-96 hours post-injection (p<0.001). There was a significant increase (p=0.042) in the proportion of cold sensitive DRG neurons isolated from mice treated with a single dose of oxaliplatin (6.7%) compared to vehicle treated mice (4.9%). In addition, there was an increased (p=0.023) percentage of cold-sensitive DRG neurons (6.4%) after repeated oxaliplatin injections compared to vehicle treatment (4.7%). Surprisingly, the average temperature threshold for activation was significantly shifted (p=0.003) towards colder temperatures in neurons from oxaliplatin-treated (23.88±0.5°C) compared to vehicle-treated mice (26.02±0.5°C) after a single oxaliplatin injection. This was also seen after repeated oxaliplatin injections where temperature thresholds from oxaliplatin-treated DRG neurons were significantly shifted (p=0.0001) towards colder thresholds (22.21±0.4°C) when compared to vehicle-treated mice (25.18±0.6°C).

Conclusions: It is likely that the limited recruitment of cold sensitive neurons in vitro failed to account fully for the behavioural sensitisation in vivo. Other in vitro or ex vivo approaches will therefore be explored to identify the ionic mechanisms responsible for oxaliplatin-evoked cold pain.

References:

1. Saif MW, Reardon J. (2005). Ther Clin Risk Manag. 1:249–58.

2. Deuis JR, Zimmermann K, Romanovsky AA, Possani LD, Cabot PJ, Lewis RJ, et al. (2013). Pain. 154:1749–57.