The effects of Fungizone (Amphotericin B and deoxycholic acid) on cultured B16-F10 murine melanoma cells

Effect of penicillin-streptomycin and other antibiotics on melanogenic parameters in cultured B16/F10 melanoma cells

Penicillin and streptomycin, the most widely used antibiotics in mammalian cell cultures, caused a moderate stimulation in dopa oxidase and tyrosine hydroxylase activities, but a slight inactivation in the dopachrome tautomerase activity of B16/F10 melanoma cells at the routine concentration (100 units/ml penicillin and 100 micrograms/ml streptomycin) used for preventing bacterial growth in cultured animal cells. At these concentrations, tyrosinase activities and melanin content augmented with time during the first 24-48 hr. The opposite effect acted on cell viability. After withdrawal of the antibiotics from the culture medium, the recovery of melanogenic parameters to normal values was fully reached after few hours (around 10), and it was already noticeable as soon as 4 hr after removal. Other antibiotics used in cell culture, like kanamycin, gentamicin, and the antimicotic nystatin, exerted similar low effects at the recommended concentrations, always lower than two-fold and thus lower than those reported for amphotericin B. Taking into account these relatively low effects, and the high risk of contamination of mammalian cells culture without antibiotics, penicillin and streptomycin may still be routinely used in experiments leading to explore the melanogenic activity of malignant melanocytes in culture, unless very precise studies and strict conditions were needed.

Tumor suppression in Xiphophorus by an accidentally acquired promoter

Melanoma formation in the teleost Xiphophorus is caused by a dominant genetic locus, Tu. This locus includes the Xmrk oncogene, which encodes a receptor tyrosine kinase. Tumor induction is suppressed in wild-type fish by a tumor suppressor locus, R. Molecular genetic analyses revealed that the Tu locus emerged by nonhomologous recombination of the Xmrk proto-oncogene with a previously uncharacterized sequence, D. This event generated an additional copy of Xmrk with a new promoter. Suppression of the new Xmrk promoter by R in parental fish and its deregulation in hybrids explain the genetics of melanoma formation in Xiphophorus.

Effect of amphotericin B on dopachrome tautomerase activity and other melanogenic parameters in cultured B16/F10 melanoma cells

The antifungal reagent Fungizone (amphotericin B and deoxycholate) caused an activation in dopachrome tautomerase and dopa oxidase activities of B16/F10 melanoma cells at the routine concentration (2.5 micrograms/ml) used for preventing molds and yeast growth in cultures of animal cells. However, higher amphotericin B concentrations caused a significant cell death and the inhibition of enzymatic activities. At the optimal concentration of Fungizone, the enzymatic activities and melanin content were augmented as incubation time increased. The detergent sodium deoxycholate alone exerted no effect on these melanogenic parameters, eliminating the possibility that this detergent was partially responsible for melanogenic modifications produced by Fungizone. After withdrawal of Fungizone from the reaction medium, the recovery of melanogenic parameters to normal values was slower for DCT than for tyrosinase. The behavior of dopa oxidase was very similar to that reported by Johnson and Bagnara (Pigment Cell Res. 3, 173-175) for tyrosine hydroxylase.