ZIA BC 005598 (ZIA) | |||
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Title | Genetic Analysis of the Multidrug Resistance Phenotype in Tumor Cells | ||
Institution | NCI, Bethesda, MD | ||
Principal Investigator | Gottesman, Michael | NCI Program Director | N/A |
Cancer Activity | N/A | Division | CCR |
Funded Amount | $373,564 | Project Dates | 00/00/0000 - 00/00/0000 |
Fiscal Year | 2016 | Project Type | Intramural |
Research Topics w/ Percent Relevance | Cancer Types w/ Percent Relevance | ||
Bioengineering (10.0%) Cancer (100.0%) Chemotherapy (30.0%) Childhood Cancers (10.0%) Digestive Diseases (3.0%) Gene Therapy (20.0%) Organ Transplantation Research (10.0%) Taxol (30.0%) |
Brain (10.0%) Breast (13.0%) Central Nervous System - Not Including Brain (3.0%) Cervical Cancer (2.0%) Colon/Rectum (2.0%) Kaposi Sarcoma (10.0%) Kidney Disease (6.0%) Leukemia (12.0%) Liver Cancer (1.0%) Melanoma (20.0%) Multiple Myeloma (5.0%) Nervous System (18.0%) Non Hodgkins Lymphoma (3.0%) Ovarian Cancer (10.0%) Prostate (2.0%) Urinary System (6.0%) Kidney Cancer (4.0%) Sarcoma (2.0%) |
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Research Type | |||
Systemic Therapies - Discovery and Development Development and Characterization of Model Systems |
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Abstract | |||
Resistance to chemotherapy occurs in cancer cells because of intrinsic or acquired changes in expression of specific proteins. We have studied resistance to natural product chemotherapeutic agents such as doxorubicin, Vinca alkaloids, and taxol. In most cases, cells become simultaneously resistant to multiple drugs because of reductions in intracellular drug concentrations. For the natural product drugs, this cross-resistance is frequently due to expression of an energy-dependent drug efflux system (ABC transporter) known as P-glycoprotein (P-gp), the product of the MDR1 or ABCB1 gene, or to other members of the ABC transporter family, including ABCB2 and ABCB5. To explore the possibility that other members of the ABC family of transporters may be involved in drug resistance in cancer, we have developed real-time PCR for detection of most of the 48 known ABC transporters; these techniques have been used to correlate expression of novel ABC transporters in cancer cell lines of known drug resistance. Expression of approximately 30 ABC transporters has been shown to correlate in the NCI-60 cell lines with resistance to specific cytotoxic drugs. Furthermore, this analysis has revealed that some drugs are more toxic to P-gp-expressing cells than to non-expressors, suggesting a novel approach to treatment of MDR cancers. Several different chemical classes with this property, including thiosemicarbazides (e.g., NSC73306), have been identified. A quantitative structure activity analysis of NSC73306 analogs, a further correlation analysis in the NCI-60 cell lines, and a high-throughput screen for compounds in the U.S. Pharmacopeia that kill P-gp-expressing cells have yielded many additional compounds with improved ability to kill selectively P-gp-expressing cells, but also with improved solubility properties. In addition, the compound tiopronin, which is a sulfhydryl donor used clinically to treat cystinosis, and some of its derivatives have been shown to be powerful selective agents for killing MDR cells. In this case, expression of P-gp is not required for multidrug-resistant cells to be sensitive to tiopronin, which appears to kill by targeting glutathione peroxidase. In order to study the effect of these agents that target cancer cells expressing P-gp, we are developing an animal model of human adrenocortical carcimoma, a cancer that intrinsically expresses high level of P-gp. Studies on the normal function of P-gp suggest that it is involved in normal uptake and distribution of many drugs. C11-desmethyl-loperamide has been developed in collaboration with Robert Innis in NIMH to PET image distribution of this specific P-gp substrate in cancers and in the brain, with and without treatment with potent inhibitors of P-gp such as tariquidar. PET ligands that are weak bases are trapped in lysosomes, amplifying the uptake signal in the brain, in some normal tissues, and in cancers. We have shown that among three most prominent transporters at the blood-brain barrier (ABCB1, ABCC1, ABCG2), this compound is specific for ABCB1 (P-gp). We have developed a system for analysis of ABCG2 expression at the blood-brain and the blood-placental barriers based on the fact that luciferin is an ABCG2 substrate at these barriers and its passage into the brain or into developing fetuses can be detected in transgenic mice in which luciferase is expressed at the blood-brain barrier or blood-placental barrier. A synonymous polymorphism of P-gp (C3435T, no amino acid change) in the setting of a specific P-gp haplotype can affect efficiency of P-gp pumping by altering the rhythm of protein folding and changing substrate and inhibitor interactions with P-gp. The C3435T haplotype appears to change mRNA folding, and cause a major translational delay, which results in altered conformation of P-gp. Stable transfectants of porcine LLC-PK1 cells with the haplotype form of P-gp show altered drug resistance and inhibitor sensitivity compared to wild-type P-gp transfec |