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.