Abstract
The mechanism of reversal of resistance to Vinca alkaloids by cyclosporins is unclear. We investigated the molecular mechanism of reversal of Vinca alkaloid resistance by cyclosporin A (CsA) and its nonimmunosuppressive analog O-acetyl C9(1) CsA (SDZ 33-243) in multidrug resistant DC-3F/VCRd-5L Chinese hamster cells. CsA at 3 microM increased vincristine (VCR) sensitivity and almost totally reversed VCR resistance. SDZ 33-243 at 1 microM reduced the IC50 for VCR in resistant cells from 62.0 to 0.00062 microM. CsA and SDZ 33-243 at 10 microM increased [3H]vinblastine (VBL) accumulation in DC-3F/VCRd-5L cells by 27- and 22-fold, respectively. At 10 microM, these compounds also increased [3H]VCR accumulation by 3.5- and 4.0-fold, respectively. [3H]VCR uptake by membrane vesicles from DC-3F/VCRd-5L cells showed high and low affinity components with Michaelis-Menten kinetics, and apparent Km values were 0.140 +/- 0.0523 and 24.8 +/- 6.67 microM, respectively. Kinetic analysis of [3H]VCR uptake in membrane vesicles in the presence of 0.2 microM CsA revealed that CsA competitively inhibited the high affinity [3H]VCR uptake with an apparent inhibition constant (Ki) of 0.126 +/- 0.0173 microM. In addition, CsA and SDZ 33-243 inhibited VBL photoaffinity labeling of P-glycoprotein in a dose-dependent manner, with half-maximum inhibition at 0.5 and 0.4 microM, respectively, compared with that of VBL at 0.6 microM. These data confirm that cyclosporins modulate Vinca alkaloid resistance at least partially through interaction with P-glycoprotein.
Highlights
The mechanism of reversal of resistance to Vinca alkaloids by cyclosporins is unclear
We investigated the molecular mechanism of reversal of Vinca alkaloid resistance by cyclosporin A (CsA) and its nonimmunosuppressive analog 0-acetyl Cel CsA (SDZ 33-243) in multidrug resistant DC-3F/VCRd-5L
Since the molecular mechanisms of reversing multidrug resistance (MDR) by cyclosporins are not clear and since there is increasing evidence that many lipophilic agents may interact with P-gp to reverse MDR, we examined CsA and its nonimmunosuppressive analog 0-acetyl Cgl CsA (SDZ 33-243) [24] to determine whether interaction of these agents with P-gp is the mechanism of reversing Vinca alkaloid resistance
Summary
Ham’s nutrient mixture F-12 was purchased from GIBCO. Fetal bovine serum was obtained from Hyclone Laboratories, Inc. Vinblastine (VBL) and VCR were gifts from Eli Lily & Co. &A and 0-acetvl C,’ CsA (SDZ 33-243) were gifts from Sandoz N-Hydroxysuccinimidyl-4-azidosalicylate was obtained from Pierce Chemical Co. ATPrS was purchased from Boehringer. [3H]VBL (specific activity 23 Ci/mmol), [“HIVCR (specific activitv 6.2 Ci/mmol). All other chemicals were obtained commercially and were reagent grade
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