Cell Culture. The murine melanoma cell line B16F10 was obtained from the UCSF Cell Culture Facility. The cells were cultured in pre-warmed medium (MEM Eagle's with EBSS medium containing 10% fetal bovine serum, 1% MEM nonessential amino acids, 110 mg/L sodium pyruvate, and 1% penicillin−streptomycin) at 37 °C in a humidified atmosphere composed of 5% CO2. MDA-MB-231 and MDA-MB-435 breast cancer cell lines were cultured in a medium consisting of Dulbecco's Modified Earl's medium (DME) H-16, containing 10% FBS and 1% MEM nonessential amino acids. The medium for culturing the monkey kidney fibroblast CV-1 cells consisted of DME H-21 (high glucose 4.5 g/L) containing 10% fetal bovine serum, 1% MEM nonessential amino acids, 1% HEPES buffer, and 1% penicillin−streptomycin. For all of our experiments, cells were harvested from subconfluent cultures using trypsin-versene (0.05 and 0.02% respectively) and were suspended in medium. Cell viability was determined using the trypan blue exclusion method.