Abstract
We have studied the ability of cyclosporin A (CsA) and a non-immunosuppressive analogue, O-acetyl cyclosporin A (OACsA, B3-243) to inhibit the growth of human lung cancer cells in vitro. Using continuous drug exposure and the MTT colorimetric assay to determine cell growth we found that CsA produced partial growth inhibition at doses ranging from 0.5 to 3.0 micrograms ml-1 (0.4-2.4 microM). At progressively higher doses, complete growth inhibition and in situ cell lysis were seen. The P-glycoprotein expressing multidrug resistant (MDR) variant H69/LX4 of the small cell line H69/P was less sensitive to cyclosporins than the parent line, but this was not true of the non-P-glycoprotein expressing MDR variants of large cell line COR-L23 or adenocarcinoma line MOR. Sensitivity to OACsA was approximately 2-fold higher than that to CsA in most of the lines although not in the most sensitive line, COR-L88. Even in COR-L88, exposed to CsA or OACsA for 24 h, clonogenic cell survival was reduced only to 50%. There was no reduction in polyamine content of COR-L23 or COR-L88 cells following 48 h of exposure to CsA or OACsA. The effects on cell growth could not be inhibited by the addition of exogenous putrescine, nor could they be enhanced by the addition of alpha-difluoromethylorthinine. It does not appear therefore that inhibition of polyamine synthesis is the basis of the observed growth inhibition.
Highlights
SummanWte have studied the ability of cyclosporin A (CsA) and a non-immunosuppressive analogue
The P-glycoprotein expressing multidrug resistant (MDR) variant H69 LX4 of the small cell line H69 P was less sensitive to cyclosporins than the parent line. but this was not true of the non-P-glycoprotein expressing MDR variants of large cell line COR-L23 or adenocarcinoma line MOR
In two recent studies of the effect of CsA in hamster pancreatic and mouse colon cancer cell lines, it was found that the effects could be blocked by the addition of the polyamine. putrescine. and enhanced by the addition of the polyamine biosynthesis inhibitor a-difluoromethylorthinine (Saydjari et al.. 1986. 1987)
Summary
SummanWte have studied the ability of cyclosporin A (CsA) and a non-immunosuppressive analogue. B3-243) to inhibit the growth of human lung cancer cells in vitro. The effects on cell growth could not be inhibited bs the addition of exogenous putrescine. A specific inhibition of T-cell proliferation occurs at an early stage following activation This results in a failure of T-cells both to express receptors for IL-2 or to secrete IL-2 In two recent studies of the effect of CsA in hamster pancreatic and mouse colon cancer cell lines, it was found that the effects could be blocked by the addition of the polyamine. An additional potential role for CsA in cancer therapy has recentlv been developed in that the compound has been found to act as an effective modifier of multidrug resistance (MDR) both in vitro and in vivo In our studies of CsA and various analogues as resistance modifiers in human lung cancer cells. This paper describes a series of experiments designed to study these effects in more detail and to determine whether or not inhibition of polvamine synthesis is involved
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