Tumor cell permeability to peplomycin

The uptake of [3H]peplomycin-Cu(II) ([3H]PEP-Cu(II)) into various tumor cell lines was studied. The time course of [3H]PEP-Cu(II) uptake into AH66, AH66F, Ehrlich and P388 cells was biphasic. The first phase of uptake was completed within 5 minutes. The second, slower phase, of uptake into AH66, AH66F and Ehrlich cells increased linearly with incubation time, but that into P388 cells reached a plateau level. In L1210 cells, only the first rapid uptake was observed. The lower uptake into P388 and L1210 cells during the second phase may be related to their insensitivity to PEP. However, the uptake into AH66F cells was higher than that into AH66 cells, although AH66F cells were less sensitive to PEP than AH66 cells. Deamide PEP was detected in intact cells which had taken up [3H]PEP-Cu(II) during 4 hours. This confirmed that PEP-Cu(II) was transported into the cell, the copper removed and PEP metabolized to deamide PEP. [3H]PEP-Cu(II) uptake into AH66 and AH66F cells increased in proportion to the extracellular concentration of drug up to at least 200 micrograms/ml, suggesting that uptake was not mediated by a carrier system. Metabolic inhibitors such as NaN3 and 2,4-dinitrophenol enhanced [3H]PEP-Cu(II) uptake, but did not influence efflux. Uptake was also enhanced by membrane modifiers such as dibucaine and chlorpromazine which increase the fluidity of lipid membranes. The results suggest that PEP-Cu(II) was taken up into tumor cells by passive diffusion, controlled by an energy-dependent cell membrane barrier.