On top of the many cardiometabolic benefits claimed for diet pill Acomplia (rimonabant) comes another intriguing finding by Italian researchers: the possibility that Acomplia may slow the spread of one of the more dangerous forms of breast cancer.

In a paper that has been accepted for publication in a future issue of Molecular Pharmacology, lead researcher Maurizio Bifulco of the Università degli Studi di Salerno reports that the CB1 cannabinoid receptor Acomplia "inhibited human breast cancer cell proliferation" in both rodent and test tube studies.

Perhaps most intriguing was the discovery that rimonabant was most effective in inhibiting the growth of a highly aggressive metastatic breast cancer cell line called MBA-MB-231.

The metastatic spread of breast tumors accounts for the majority of cancer-related deaths, and these tumor colonies typically fail to respond to conventional therapies.

In their test tube studies, the researchers said they checked the effect of different doses of rimonabant on tumor cell proliferation against highly invasive metastatic, estrogen receptor negative MDA-MB-231 breast cancer cells as well as against less invasive estrogen receptor positive T47D and MCF-7 cells.

"The growth of highly invasive metastatic MDA-MB-231 cells was inhibited
more efficaciously than that of less invasive T47D and MCF-7 cells," the researchers reported.

In their tests using mice, the researchers injected the mice with MDA-MB-231 cancer cells and when tumors were clearly detectable 15 days later, gave the mice either rimonabant or a placebo.

"Tumor growth was monitored and the data revealed that exposure to
rimonabant led to a significant decrease in tumor mass compared to control-treated mice," the researchers said. The mice treated with rimonabant "exhibited no outward signs of toxic or hypolocomotor effects," the researchers added.

The findings of the Italian researchers are one more building block in the growing understanding of the endocannabinoid system, which they describe as "an almost ubiquitous signalling system involved in the control of cell fate."

One key observation is that the CB1 receptor -- which rimonabant blocks -- is found to a greater extent in some lines of breast cancer than in others, and that the effectiveness of rimonamant against breast cancer tumors is to some extent dependent on the expression levels of CB1 receptor.

"The present findings provide unequivocal evidence for the role of the CB1 receptor and its antagonist/inverse-agonist rimonabant in breast tumor cell proliferation," the researchers concluded.

For those with a scientific background who would like to read the report by the Italian researchers in its entirety, it can be found at http://molpharm.aspetjournals.org/cgi/reprint/mol.106.025601v1

The Italian study was partially funded by the developer of Acomplia, Sanofi-Aventis.