5-fluorouracil (5-FU) and doxorubicin (DOX) are potent anti-tumour agents commonly
used for colon and breast cancer therapy, respectively. However, their clinical application is limited
by their side effects and the development of drug resistance. Honeybee venom is a complex mixture
of substances that has been reported to be effective against different cancer cells. Its active compound
is melittin, a positively charged amphipathic peptide that interacts with the phospholipids of the
cell membrane, forming pores that enable the internalization of small molecules with cytotoxic
activities,. and consequently, causing cell death. Some central nervous system (CNS) drugs have
recently demonstrated great anti-cancer potential, both in vitro, in vivo and in clinical trials, being
promising candidates for drug repurposing in oncology. The present work evaluated the anti-cancer
efficacy of honeybee venom in combination with chemotherapeutic or CNS drugs in HT-29 colon and
MCF-7 breast cancer cell lines. The chemical characterization of a Portuguese sample of honeybee
venom was done by LC-DAD-ESI/MSn analysis. For single treatments, cells were incubated with
increasing concentrations of bee venom. For combination treatments, increasing concentrations of bee
venom were first combined with the half-maximal inhibitory concentration (IC50) of 5-FU and DOX,
in HT-29 and MCF-7 cells, respectively. Cells were also treated with increasing concentrations of bee
venom in combination with the IC50 value of four CNS drugs (fluphenazine, fluoxetine, sertraline
and thioridazine). Cytotoxicity was evaluated by MTT and SRB assays. The combination index (CI)
value was calculated using CompuSyn software, based on the Chou–Talalay method. Synergy scores
of different reference models (HSA, Loewe, ZIP and Bliss) were also calculated using SynergyFinder.
The results demonstrate that honeybee venom is active against HT-29 colon and MCF-7 breast cancer
cells, having better anti-tumour activity in MCF-7 cells. It was found that bee venom combined with
5-FU and fluphenazine in HT-29 cells resulted in less cytotoxic effects compared to the co-treatment
of fluoxetine, sertraline and thioridazine plus bee venom, which resulted in less than 15% of viable
cells for the whole range of concentrations. The combination of MCF-7 cells with repurposed drugs
plus honeybee venom resulted in better anti-cancer efficacies than with DOX, notably for lower
concentrations. A combination of fluoxetine and thioridazine plus honeybee venom resulted in less
than 40% of viable cells for all ranges of concentrations. These results support that the combination
of honeybee venom with repurposed drugs and chemotherapeutic agents can help improve their
anti-cancer activity, especially for lower concentrations, in both cell lines. Overall, the present
study corroborates the enormous bioactive potential of honeybee venom for colon and breast cancer
treatments, both alone and in combination with chemotherapy or repurposed drugs.
