Biological activities of bombolitins from Bombus ardens, B. consobrinus, B. terrestris and B. ussurensis (bombolitinsA, C, T and U, respectively) were examined using hemolytic, anti-microbial, anti-fungal and anti-tumor activity assays.Among the four bombolitins tested, bombolitin T showed the highest hemolytic and anti-tumor activities. All bombolitinsexhibited strong anti-microbial and anti-fungal activities, and bombolitin A specifically possessed the highest anti-microbialactivity against the Gram-negative bacteria Escherichia coli. Circular dichroism spectrometry analysis revealed that allfour bombolitins had over 61.7% and 45.5% of α-helicity in 30 mM sodium dodecyl sulfate and 50% trifluoroethanolbuffers, respectively, which form lipid-membrane-mimicking environments. Bombolitin T showed the lowest IC50 valuesof 8.5 μM and 8.8 μM against SK-OV-3 and NIH-OVCAR-3 cell lines, respectively, after 72 h of treatment, but itsrelative hemolytic activity at a concentration of 200 μM was 2.3-fold higher than that of 0.1% Triton X-100. Thisstudy provides new information on the biological and molecular properties of venom peptides of bumblebees. However,further studies on reducing cytotoxicity of bombolitins are needed for designing selective anti-tumor peptides.

Abaecin is a proline-rich anti-bacterial peptide which is known to have high activity against Gram-negative bacteria and it is originally isolated from honeybee Apis mellifera. Since the anti-bacterial peptides including abaecin were identified in the hemolymph of A. mellifera infected with Gram-negative bacteria Escherichia coli, this result implies that honeybees express abaecin for defense against natural infection. Anti-microbial peptides including abaecin were also identified in the adult hemolymph of bumblebees. To investigate pharmacological and toxicological properties of abaecin from Bombus ussurensis, biological activities were evaluated by conducting anti-tumor, anti-microbial and cytotoxic activity assays. Abaecin exhibited significantly high anti-tumor activity against ovarian tumor cells SK-OV-3 and NIH; OVCAR-3 at 100 μM after 72 h treatment. Interestingly, abaecin showed none of anti-microbial activity against Gram-negative and Gram-positive bacteria. Since abaecin exhibited extremely low level of hemolytic activity against human erythrocytes, it may serve as a good model peptide for studying its potential as a selective anti-tumor drug.

Bombolitin is a venom peptide originally isolated from bumblebees and possesses various biological activities, including hemolytic activity. Bombolitins exhibit amphipathic α-helical structure in lipid-membrane-mimicking environments. To investigate their pharmacological and toxicological properties, anti-tumor, anti-microbial and cytotoxic activities of bombolitins from Bombus ardens and Bombus ussurensis were evaluated. Bombolitins of the two species exhibited extremely high anti-tumor activity against ovarian tumor cells SK-OV-3 and NIH; OVCAR-3 at 25-50 μM, which is 2-fold more potent than other wasp venom peptides studied to date (Yoon et al., 2015; Yoon et al., 2016). The two bombolitins showed significantly high antimicrobial activity. However, bombolotin of B. ussurensis showed no antimicrobial activity against Escherichia coli. In addition to their high levels of anti-tumor activity, bombolitins showed considerable levels of hemolytic activity. Thus, to utilize bombolitins as a potential candidate for anti-tumor peptide drugs, further studies for reducing cytotoxic properties of bombolitns is essential.