Potential safety concerns of TLR4 antagonism with irinotecan: a preclinical observational report

Purpose: Irinotecan-induced gut toxicity is mediated in part by Toll-Like receptor 4 (TLR4) signalling. The primary purpose of this preclinical study was to determine whether blocking TLR4 signalling by administering (−)-naloxone, a TLR4 antagonist, would improve irinotecan-induced gut toxicity. Our secondary aim was to determine the impact of (−)-naloxone on tumour growth. Methods: Female Dark Agouti (DA) tumour-bearing rats were randomly assigned to four treatments (n = 6 in each); control, (−)-naloxone (100 mg/kg oral gavage at −2, 24, 48, and 72 h), irinotecan (175 mg/kg intraperitoneal at 0 h), and (−)-naloxone and irinotecan. Body weight and tumour growth were measured daily, and diarrhoea incidence and severity were recorded 4× per day up to 72 h post-treatment. Results: At 72 h, all rats that received irinotecan lost weight compared to controls (p = 0.03). In addition, rats that received (−)-naloxone and irinotecan lost significantly more weight compared to controls (p < 0.005) than irinotecan only compared to controls (p = 0.001). (−)-Naloxone did not attenuate irinotecan-induced severe diarrhoea at 48 and 72 h. Finally, (−)-naloxone caused increased tumour growth compared to control at 72 h (p < 0.05) and significantly reduced the efficacy of irinotecan (p = 0.001). Conclusions: (−)-Naloxone in our preclinical model was unable to block irinotecan-induced gut toxicity and decreased the efficacy of irinotecan. As (−)-naloxone-oxycodone combination is used for cancer pain, this may present a potential safety concern for patients receiving (−)-naloxone-oxycodone and irinotecan concurrently and requires further investigation.