Amplification of specific DNA sequences correlates with multi-drug resistance in Chinese hamster cells

Mammalian cells selected for resistance to certain cytotoxic drugs frequently develop cross-resistance to a broad spectrum of other drugs unrelated in structure to the original selective agent. This phenomenon constitutes a major problem in cancer chemotherapy. Multi-drug resistance arises from decreased intracellular drug accumulation, apparently due to an alteration of the plasma membrane. The observation of double minute chromosomes or homogeneously staining regions in some of the multi-drug-resistant cell lines suggests that gene amplification underlies this phenomenon. We have used the technique of DNA renaturation in agarose gels to detect, compare and clone amplified DNA sequences in Adriamycin- and colchicine-resistant sublines of Chinese hamster cells. We show that both Adriamycin- and colchicine-resistant cells contain amplified DNA fragments, some of which are amplified in both of these independently derived cell lines. Furthermore, loss of the multi-drug resistance phenotype on growth in the absence of drugs correlates with the loss of amplified DNA. These results strongly suggest that the DNA sequences which are amplified in common in multi-drug-resistant cell lines include the gene(s) responsible for a common mechanism of multi-drug resistance in these cells. We have cloned one of the commonly amplified DNA fragments and show that the degree of amplification of this fragment in the cells correlates with the degree of their drug resistance

Positron emission tomography studies on binding of central nervous system drugs and P-glycoprotein function in the rodent brain

The permeability of the blood-brain barrier (BBB) is one of the factors determining the bioavailability of drugs in the brain. The BBB only allows passage of lipophilic drugs by passive diffusion. However, some lipophilic drugs hardly enter the brain. The transmembrane protein P-glycoprotein (P-gp) is one of the carrier systems that is responsible for transportation of drugs out of the brain. P-Glycoprotein affects the pharmacokinetics of many drugs and can be inhibited by administration of modulators or competitive substrates. Identification and classification of central nervous system (CNS) drugs as P-gp substrates or inhibitors are of crucial importance in drug development. Positron emission tomography (PET) studies can play an important role in the screening process as a follow-up of high-throughput in vitro assays. Several rodent studies have shown the potential value of PET to measure the effect of P-gp on the pharmacokinetics and brain uptake of radiolabeled compounds. P-Glycoprotein-mediated effects were observed for two 5-HT1a receptor ligands, [F-18]MPPF vs. [carbonyl-C-11] WAY100635. Under control conditions, the specific brain uptake of [F-18]MPPF is five- to eightfold lower than that of [C-11]WAY100635. After cyclosporin A (CsA) modulation, [F-18]MPPF uptake in the rat brain increased five- to tenfold. Cerebral uptake of [carbonyl-C-11]WAY100635 was also increased by modulation, but in general the increase was lower than that observed for [F-18]MPPF (two- to threefold). Brain uptake of the P-adrenergic receptor ligands [C-11]carazolol and [F-18]fluorocarazolol was increased in P-gp knockout mice and CsA-treated rats. Both the specific and nonspecific binding of [F-18]fluorocarazolol were doubled by CsA. Cerebral uptake of [C-11]carazolol in rats was much lower than that of [18F]fluorocarazolol and no specific binding was measured. After CsA modulation, the uptake of [C-11]carazolol increased five- to sixfold, but this uptake was not receptor-mediated. Quantitative PET studies in rodents on P-gp functionality demonstrated a dose-dependent increase of radioligands after administration of CsA. Studies with [C-11]verapamil and [C-11]carvedilol showed that complete modulation was achieved at 50 mg/kg CsA. The distribution volume of [C-11]carvedilol increased from 0.25 in the control study to 1.0 after full modulation with CsA. By quantitative PET measurement of P-gp function, the dose of modulators required to increase the concentration of CNS drugs may be determined, which may result in improved drug therapy

State of progress in treating cystic fibrosis respiratory disease

<p>Abstract</p> <p>Since the discovery of the gene associated with cystic fibrosis (CF), there has been tremendous progress in the care of patients with this disease. New therapies have entered the market and are part of the standard treatment of patients with CF, and have been associated with marked improvement in survival. Now there are even more promising therapies directed at different components of the pathophysiology of this disease. In this review, our current knowledge of the pathophysiology of lung disease in patients with CF is described, along with the current treatment of CF lung disease, and the therapies in development that offer great promise to our patients.</p