Morphine Relieves Pain and Inhibits Tumor Growth

To that end, they treated a population of nude mice that had been loaded with mouse Lewis lung carcinoma cells (LLCs) with continuous slow-release morphine pellets. The pellets provided constant morphine plasma levels within the range of 250 ng/mL - 400 ng/mL.

Results published in the July 8, 2010, online edition of the American Journal of Pathology revealed that chronic morphine treatment significantly reduced tumor cell-induced angiogenesis and tumor growth when compared with placebo treatment. Morphometric analysis for blood vessel formation further confirmed that morphine significantly reduced blood vessel density, vessel branching, and vessel length when compared with placebo treatment. Morphine's effect was abolished in mice that were treated with the classical opioid receptor antagonist, naltrexone, and in mice that had been genetically engineered to lack the mu-opioid receptor.

The investigators found that at the molecular level morphine's inhibitory effect was mediated through the suppression of the hypoxia-induced mitochondrial p38 mitogen-activated protein kinase (MAPK) pathway.

The authors concluded that, "Morphine is a potential inhibitor of tumor growth, through the suppression of tumor cell-induced angiogenesis and hypoxia-induced p38 MAPK activation of HIF-1. In addition to its analgesic potential, morphine can be exploited for its antiangiogenic potential in cancer pain management; these findings support the use of morphine for cancer pain management.”

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