Dexverapamil as resistance modifier in acute myeloid leukaemia

Novel Quinoline Compound Derivatives of NSC23925 as Potent Reversal Agents Against P-Glycoprotein-Mediated Multidrug Resistance

Multidrug resistance is a serious problem and a common cause of cancer treatment failure, leading to patient death. Although numerous reversal resistance inhibitors have been evaluated in preclinical or clinical trials, efficient and low-toxicity reversal agents have not been identified. In this study, a series of novel quinoline compound derivatives from NSC23925 were designed to inhibit P-glycoprotein (P-gp). Among them, YS-7a showed a stronger inhibitory effect against P-gp than verapamil, as a positive control, when co-incubated with chemotherapy drugs at minimally cytotoxic concentrations. YS-7a suppressed the P-gp transport function without affecting the expression of P-gp but stimulated the ATPase activity of P-gp in a dose-dependent manner. Next, molecular docking was used to predict the six most probable binding sites, namely, SER270, VAL273, VAL274, ILE354, VAL357, and PHE390. Moreover, YS-7a had no effect on cytochrome P450 3A4 activity and showed little toxicity to normal cells. In addition, combined treatment of YS-7a with vincristine showed a better inhibitory effect than the positive control verapamil in vivo without a negative effect on mouse weight. Overall, our results showed that YS-7a could reverse cancer multidrug resistance through the inhibition of P-gp transport function in vitro and in vivo, suggesting that YS-7a may be a novel therapeutic agent.

Hydrocinchonine, cinchonine, and quinidine potentiate paclitaxel-induced cytotoxicity and apoptosis via multidrug resistance reversal in MES-SA/DX5 uterine sarcoma cells

Multidrug resistance (MDR) is one of important issues to cause the chemotherapy failure against cancers including gynecological malignancies. Despite some MDR reversal evidences of natural compounds including quinidine and cinchonine, there are no reports on MDR reversal activity of hydrocinchonine with its analogues quinidine and cinchonine especially in uterine sarcoma cells. Thus, in the current study, we comparatively investigated the potent efficacy of hydrocinchonine and its analogues quinidine and cinchonine as MDR-reversal agents for combined therapy with antitumor agent paclitaxel (TAX). Hydrocinchonine, cinchonine, and quinidine significantly increased the cytotoxicity of TAX in P-glycoprotein (gp)-positive MES-SA/DX5, but not in the P-gp-negative MES-SA cells at nontoxic concentrations by 3-(4,5-dimethylthiazol-2-yl)-2,5--diphenyltetrazolium bromide (MTT) assay. Rhodamine assay also revealed that hydrocinchonine, cinchonine, and quinidine effectively enhanced the accumulation of a P-gp substrate, rhodamine in TAX-treated MES-SA/DX5 cells compared with TAX-treated control. In addition, hydrocinchonine, cinchonine, and quinidine effectively cleaved poly (ADP-ribose) polymerase (PARP), activated caspase-3, and downregulated P-gp expression as well as increased sub-G1 apoptotic portion in TAX-treated MES-SA/DX5 cells. Taken together, hydrocinchonine exerted MDR reversal activity and synergistic apoptotic effect with TAX in MES-SA/DX5 cells almost comparable with quinidine and cinchonine as a potent MDR-reversal and combined therapy agent with TAX.

Effect of PSC 833, verapamil and amiodarone on adriamycin toxicity in cultured rat cardiomyocytes

Primary cultures of heart myocytes from neonatal rats were used as an in vitro cardiac cell system to study the effects of the p-170kDa glycoprotein (Pgp) blockers PSC 833 [(3'-keto-Bmt1)-(Val2)-cyclosporine], verapamil and amiodarone on adriamycin cardiotoxicity. Immunostaining revealed the presence of Pgp in the cardiomyocytes. Adriamycin induced a concentration-dependent increase in creatine kinase (CK) leakage, a parameter indicating cell death. None of the Pgp blockers was toxic up to 10 microM, but amiodarone markedly increased CK leakage at 25 microM. 1 microM of the Pgp blockers did not increase adriamycin induced CK leakage, whereas 10 microM of the Pgp blockers significantly augmented adriamycin-induced CK leakage. In parallel, cytoplasmic vacuolization and plasma membrane disruptions were observed. Frequency of contraction of cardiomyocytes, as determined by digital image analysis, was concentration-dependently decreased by adriamycin. 1 microM PSC 833 had no additional effect on contractility, only 10 microM PSC 833 enhanced the impairment of contractility induced by adriamycin. Amiodarone and verapamil alone and in combination with adriamycin already at concentrations of 1 microM completely blocked contractility of cardiomyocytes. The results suggest that the increased toxicity of adriamycin in the presence of amiodarone, verapamil and PSC 833 is mediated by an effective blockage of the Pgp efflux pump. The results further indicate that the combination of adriamycin and PSC 833 might be better tolerated with regard to cardiac side-effects, than the combination of adriamycin and verapamil or amiodarone.

Triggering Noncycling Hematopoietic Progenitors and Leukemic Blasts to Proliferate Increases Anthracycline Retention and Toxicity by Downregulating Multidrug Resistance

Expression of the multidrug resistance (MDR) mechanisms P-glycoprotein (Pgp) and MDR-related protein (MRP) decrease cellular retention and consequently cytotoxicity of anthracyclines. MDR is expressed on normal human hematopoietic progenitors and leukemic blasts. Normal CD34+ progenitors showed rhodamine efflux in 20% to 30% of the cells, which could be blocked by verapamil. These cells appeared noncycling, in contrast to the proliferating rhodamine bright (RhoB) cells. We postulated that MDR expression can be downregulated by proliferation induction. Triggering rhodamine dull (RhoD) CD34+ cells to proliferate indeed resulted in a higher rhodamine retention and significantly decreased efflux modulation by verapamil (P = .04). Also in acute myeloid leukemia (AML), the proliferation rate (percentage S/G2+M and Iododeoxyuridine labelings index) was significantly less in the RhoD blasts (P ≤ .008) and proliferation induction of RhoD blasts resulted in increased rhodamine retention. Anthracycline cytotoxicity was less for RhoD than RhoB cells in both normal progenitors and leukemic blasts. Proliferation induction of the RhoD cells resulted in increased anthracycline sensitivity. We conclude that noncycling progenitors, both normal and leukemic, have a relatively high MDR expression. Triggering these cells into proliferation downregulates MDR expression. These findings can be exploited to overcome MDR in the treatment of AML patients.