Development Of Novel Therapeutic Agents Targeting Multidrug Resistance In Cancer

Multidrug resistance (MDR) frequently develops in cancer patients exposed to chemotherapeutic agents and is usually accomplished by over-expression of P-glycoprotein (P-gp), a MDR1gene encoded protein. P-gp acts as a drug efflux pump to reduce the intracellular concentration of the drug(s). Inhibiting the transport function of P-gp is an effective way of reversing MDR, against this target, three generations of P-gp inhibitors has been developed but none of them has been successful on the market due to severe side effect. Therefore, it is necessary to develop some agents which can effectively reverse MDR with low or no pharmacology defects.1-(2,6-dimethylphenoxy)-2-(3,4-dimethoxyphenylethylamino) propane hydrochloride (phenoprolamine hydrochloride,1416) is a new verapamil analogue with a higher IC50for blocking calcium channel currents than verapamil. We examined the inhibition effect of1416on P-gp both in vitro and in vivo.1416significantly enhanced cytotoxicity of vinblastine in P-gp overexpressed human multidrug-resistant K562/ADM and KBV cells, but had no such effect on the parent K562and KB cells. The MDR-modulating function of1416was further confirmed by increasing intracellular Rhodanmine123content in MDR cells. Human K562/ADM xenograft-nude mice model verified that1416potentiate the antitumor activity of vinblastine in vivo. RT-PCR and FACS analysis demonstrated that the expression of MDR1/P-gp was not affected by1416treatment. All these observations suggested that1416would be a promising agent for overcoming MDR in cancer chemotherapy.Epigenetics is the study of epigenetic inheritance, a set of reversible heritable changes in gene function or other cell phenotype that occur without a change in DNA sequence (genotype). Many studies have shown that the MDR phenotype is associated with epigenetic regulation. We established a MDR cell line (K562/ADM) from human leukemia cell K562by stepwise increase adriamycine concentration in culture medium and then MDR phenotype (MDR1gene upregulation, P-gp overexpression and increased substrate efflux) was confirmed in K562/ADM as compared to parental K562cells. Thereafter, we investigated the epigenetic variation in K562/ADM cells: DNA methylation level was decreased in whole genome as well as in the promoter region of MDR1; Chromatin structure became more decompacting; Small RNA expression profiles were dysregulated. These findings may help us to discover epigenetic biomarkers for the molecular diagnosis of MDR and may constitute potentially novel targets for therapy.Small non-coding RNAs have now become the hot spot in medical research and were reported to paly critical roles in gene regulation. Here we present evidence that microRNAs can regulate the expression of the MDR1gene. Using high-throughput sequencing and bioinformatics prediction, we identified and validated two candidate microRNAs, miR-381and miR-495, that were strongly down-regulated in MDR cell lines. Functional analysis indicated that restoring expression of candidate miRNAs in K562/ADM cells led to reduced expression of MDR1/P-gp and increased drug uptake by the cells. We also discovered a microRNA cluster on a potentially unstable chromosomal region which may have a close relationship to the development of multidrug resistance.