| Multidrug resistance (MDR) is defined as resistance of tumor cells to the cytostatic or cytotoxic actions of multiple, structurally and functionally divergent drugs. MDR is termed 'intrinsic' when the disease is refractory to chemotherapy from the outset, or 'acquired' when the disease becomes insensitive to treatment upon relapse. MDR is responsible for the overall poor efficacy of cancer chemotherapy.The nature of clinicl drug resistance is multifactorial . Resistance may be due to pharmacological, cancer multicellular and cancer unicellular mechanisms. Pharmacological mechanisms include mechanisms that affect the ability of the drug to reach the target cell (e.g. cell metabolism and Pharmacokinetics). Multicellular mechanisms are related to the three-dimensional structure of a tumor and include changes in local permeability to drug and the extracellular microenvironment (e.g. changes in pH, hypoxia), and cellular mechanisms that are regulated by intercellular communication and contact. Cellular mechanisms include mechanisms that affect the ability of anticancer drugs to reach the intracellular target( regulating drug influx, efflux, intracellular redistribution), mechanisms that regulate drug chemical activation/inactivation , qualitative and/or quantitative modifications to drug targets, and alterations in the molecular pathways regulating the cellular response to drug-induced damage(e.g. apoptosis ).Among the cellular mechanisms that regulate the ability of an anticancer drug to reach its intracellular target, the efflux mechanism based on the function of ATP binding cassette protein is called classical Multidrug resistance.P-gp is the first and the most studied protein that its overexpression can confer a multidrug-resistant phenotype in vitro and in vivo. In past decades , P-gp was researched as the most important MDR modulators'drug target and several reversals have been developed. So far, there had been three generation MDR modulators be studied. First-generation agents( e.g. cyclosporine, verapamil ) were limited by unacceptable toxicity, whereas second-generation agents ( e.g. valspodar, biricodar ) had better tolerability but were confounded by unpredictable pharmacokinetic interactions and interactions with other transporter proteins. Third-generation inhibitors (e.g. tariquidar XR9576, zosuquidar LY335979 ) have high potency and specificity for P-gp. Recently, more and more people pay attention to the transcription of the P-gp coding gene mdr1 and hope to search deal MDR modulators that inhibit P-gp overexpression in transcriptional level.The aim of this research is to establish of high throughput screening model not only for P-gp functional inhibitors but also for MDR1 gene promoter inhibitors and to applicate the model to traditional Chinese medicine library to find novel MDR modulators.To establish P-gp functional inhibitors' high throughput screening model, we used Rhol23 as indicator to measure the activity of the sample. To establish mdr1 promoter inhibitors' high throughput screening model, we constructed mdr1-luc+ reporter vector, following by transfect in HepG2 cells to measure the activity of the sample. After screening to traditional Chinese medicine, we used dose-activity assay, reversal assay and RT-PCR to identify the activity of the positive samples.The result is that the Z'factor of the P-gp functional and mdr1 promotor inhibitor model are 0.72 and 0.65 respectively and two positive samples were identified with high activity respectively.The research we described here provides a screening platform to MDR modulators' development. But there are still a lot of works to do including screening to more and more compound library that cover with various chemical structures and purifying the traditional Chinese medicine samples and clarifying its action mechanism as clear as possible. So our research just the first step of the MDR modulators' development, the conquer of MDR needs remorseless effort.
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