Evaluation of quinacrine treatment for prion diseases

Based on in vitro observations in scrapie-infected neuroblastoma cells, quinacrine has recently been proposed as a treatment for Creutzfeldt-Jakob disease (CJD), including a new variant CJD which is linked to contamination of food by the bovine spongiform encephalopathy (BSE) agent. The present study investigated possible mechanisms of action of quinacrine on prions. The ability of quinacrine to interact with and to reduce the protease resistance of PrP peptide aggregates and PrPres of human and animal origin were analyzed, together with its ability to inhibit the in vitro conversion of the normal prion protein (PrPc) to the abnormal form (PrPres). Furthermore, the efficiencies of quinacrine and chlorpromazine, another tricyclic compound, were examined in different in vitro models and in an experimental murine model of BSE. Quinacrine efficiently hampered de novo generation of fibrillogenic prion protein and PrPres accumulation in ScN2a cells. However, it was unable to affect the protease resistance of preexisting PrP fibrils and PrPres from brain homogenates, and a "curing" effect was obtained in ScGT1 cells only after lengthy treatment. In vivo, no detectable effect was observed in the animal model used, consistent with other recent studies and preliminary observations in humans. Despite its ability to cross the blood-brain barrier, the use of quinacrine for the treatment of CJD is questionable, at least as a monotherapy. The multistep experimental approach employed here could be used to test new therapeutic regimes before their use in human trials.     

Uptake and Efflux of Quinacrine, a Candidate for the Treatment of Prion Diseases, at the Blood-Brain Barrier

1. A clinical trial of quinacrine in patients with Creutzfeldt-Jakob disease is now in progress. The permeability of drugs through the blood-brain barrier (BBB) is a determinant of their therapeutic efficacy for prion diseases. The mechanism of quinacrine transport across the BBB was investigated using mouse brain endothelial cells (MBEC4). 2. The permeability of quinacrine through MBEC4 cells was lower than that of sodium fluorescein, a BBB-impermeable marker. The basolateral-to-apical transport of quinacrine was greater than its apical-to-basolateral transport. In the presence of P-glycoprotein (P-gp) inhibitor, cyclosporine or verapamil, the apical-to-basolateral transport of quinacrine increased. The uptake of quinacrine by MBEC4 cells was enhanced in the presence of cyclosporine or verapamil. 3. Quinacrine uptake was highly concentrative, this event being carried out by a saturable and carrier-mediated system with an apparent Km of 52.1 microM. Quinacrine uptake was insensitive to Na+-depletion and changes in the membrane potential and sensitive to changes in pH. This uptake was decreased by tetraethylammonium and cimetidine, a substrate and an inhibitor of organic cation transporters, respectively. 4. These findings suggest that quinacrine transport at the BBB is mediated by the efflux system (P-gp) and the influx system (organic cation transporter-like machinery).     

High glucose decreases expression and activity of p-glycoprotein in cultured human retinal pigment epithelium possibly through iNOS induction

Inhibition of p-glycoprotein under hyperglycemic conditions has been reported in various barrier tissues including blood-brain barrier, intestine, and kidney, and has been linked to significant clinical complications. However, whether this is also true for the outer blood-retinal barrier constituted by retinal pigment epithelium, or has a role in pathogenesis of diabetic retinopathy is not yet clear. In this study, using cultured human retinal pigment epithelium cell line D407, we found that high glucose exposure induced a significant decrease in p-glycoprotein expression both at mRNA and at protein levels, accompanied by an attenuated p-glycoprotein activity determined by intracellular rhodamine 123 retention. In marked contrast, the expressions of both mRNA and protein levels of inducible nitrate oxide synthase (iNOS) increased, and were accompanied by increased extracellular nitrate/nitrite production by Griess reaction. In addition, mRNA levels of nuclear receptors revealed a decreased expression of pregnane X receptor after the exposure of high glucose. However, the subsequent alterations in production of nitrate/nitrite, functional expression of p-glycoprotein, and mRNA levels of pregnane X receptor were partially blocked when pretreated with S,S′-1,3-phenylene-bis(1,2-ethanediyl)-bis-isothiourea•2HBr (PBITU), a selective iNOS inhibitor. Moreover, the effects of PBITU were antagonized with the addition of L-arginine, a substrate for NO synthesis. Our in vitro results suggest for the first time that iNOS induction plays a novel role in decreased p-glycoprotein expression and transport function at the human outer blood-retinal barrier under hyperglycemic conditions and further support the concept of inhibiting iNOS pathway as a therapeutic strategy for diabetic retinopathy.     

Effect of chronic haloperidol and quinacrine coadministration on striatal HVA levels and stereotypic behaviors in response to apomorphine in the rat

The effects of chronic administration of quinacrine, a phospholipase A2 inhibitor, on striatal homovanillic acid (HVA) levels and behavioral sensitivity to challenge with a dopamine agonist were examined in rats. Moreover, the ability of chronic phospholipase A2 inhibition to modulate the behavioral supersensitivity and striatal HVA reduction induced by chronic haloperidol administration was also examined. Daily intraperitoneal injection of quinacrine resulted in a significant reduction of striatal HVA levels. Coadministration of haloperidol with quinacrine in this paradigm caused a more profound reduction of striatal HVA levels than either drug administered alone. That this effect of combined administration is not simply due to postsynaptic effects of quinacrine on dopamine receptor sensitivity is suggested by the fact that behavioral supersensitivity was not induced by quinacrine alone nor was the behavioral supersensitivity induced by the quinacrinehaloperidol combination greater than that induced by chronic haloperidol administration alone. There were no effects of any treatment condition on striatal levels of serotonin (5-HT) or 5-hydroxyindoleacetic acid (5-HIAA). These data implicate phospholipase A2 activity in the regulation of dopaminergic transmission.     

Combined Efficacy of Cediranib and Quinacrine in Glioma Is Enhanced by Hypoxia and Causally Linked to Autophagic Vacuole Accumulation

We have previously reported that the in vivo anti-glioma efficacy of the anti-angiogenic receptor tyrosine kinase inhibitor cediranib is substantially enhanced via combination with the late-stage autophagy inhibitor quinacrine. The current study investigates the role of hypoxia and autophagy in combined cediranib/quinacrine efficacy. EF5 immunostaining revealed a prevalence of hypoxia in mouse intracranial 4C8 glioma, consistent with high-grade glioma. MTS cell viability assays using 4C8 glioma cells revealed that hypoxia potentiated the efficacy of combined cediranib/quinacrine: cell viability reductions induced by 1 µM cediranib +2.5 µM quinacrine were 78±7% (hypoxia) vs. 31±3% (normoxia), p<0.05. Apoptosis was markedly increased for cediranib/quinacrine/hypoxia versus all other groups. Autophagic vacuole biomarker LC3-II increased robustly in response to cediranib, quinacrine, or hypoxia. Combined cediranib/quinacrine increased LC3-II further, with the largest increases occurring with combined cediranib/quinacrine/hypoxia. Early stage autophagy inhibitor 3-MA prevented LC3-II accumulation with combined cediranib/quinacrine/hypoxia and substantially attenuated the associated reduction in cell viability. Combined efficacy of cediranib with bafilomycin A1, another late-stage autophagy inhibitor, was additive but lacked substantial potentiation by hypoxia. Substantially lower LC3-II accumulation was observed with bafilomycin A1 in comparison to quinacrine. Cediranib and quinacrine each strongly inhibited Akt phosphoryation, while bafilomycin A1 had no effect. Our results provide compelling evidence that autophagic vacuole accumulation plays a causal role in the anti-glioma cytotoxic efficacy of combined cediranib/quinacrine. Such accumulation is likely related to stimulation of autophagosome induction by hypoxia, which is prevalent in the glioma tumor microenvironment, as well as Akt signaling inhibition from both cediranib and quinacrine. Quinacrine''s unique ability to inhibit both Akt and autophagic vacuole degradation may enhance its ability to drive cytotoxic autophagic vacuole accumulation. These findings provide a rationale for a clinical evaluation of combined cediranib/quinacrine therapy for malignant glioma.     

Role of P-glycoprotein in tissue uptake of indinavir in rat

The effect of p-glycoprotein inhibition on tissue distribution of indinavir, an anti-HIV (human immunodeficiency virus) protease inhibitor drug, has been evaluated. Indinavir was co-administered intravenously in rats along with a p-glycoprotein inhibitor, PSC833, and the drug concentrations in plasma and various tissues were determined using a HPLC method. Additionally, initial uptake clearance of indinavir was evaluated in the brain and testes. The highest increasing effect of p-glycoprotein inhibition on the tissue uptake ratios of indinavir was found in central nervous system (CNS). The estimated tissue extraction the drug was indicative of (i) limited drug entry to brain parenchyma, which was increased significantly by p-glycoprotein inhibition, (ii) non-restricted drug entry to testes, heart and spleen, which was increased significantly in the case of heart and decreased in the case of testes and spleen as a result of p-glycoprotein inhibition, and (iii) drug accumulation in liver and small intestine and, to a lesser extent, kidney, which was not affected by p-glycoprotein inhibition. The uptake clearances of indinavir by brain parenchyma in PSC833-treated and control rats were 68.80+/-8.65 and 21.63+/-4.28 micro/min/g and the corresponding values for the testes were 39.84+/-4.90 and 36.65+/-2.54 microl/min/g. The difference was significant only in the case of brain parenchyma (P<0.001). These data showed that p-glycoprotein inhibition increases the CNS uptake of indinavir markedly and has some transient minor effects on drug uptake by some other tissues.     

Modulation of Multidrug Resistance in Cancer Cells by Liposome Encapsulated Doxorubicin

Abstract

A major problem in the chemotherapy of solid tumors and hematologic malignancies is the intrinsic as well as acquired cross resistance to multiple chemotherapeutic agents. Recently, this type of multidrug resistance has been related to a gene, MDR1, and its gene product, p-glycoprotein, which functions as the efflux pump, prevents accumulation of drugs and alters their cytotoxicity. Many drug-resistant human tumors express the MDR1 gene and MDR1 RNA levels are elevated in many cancers that have not responded to chemotherapy. The same persistent observation has been made in recurrent tumors who have responded initially to chemotherapy.

Doxorubicin is one of the most important anticancer agent having significant single agent activity in a variety of cancer types and is now the cornerstone of some widely used combination regimens. Despite the clinical effectiveness of the drug, doxorubicin resistance that arises in malignant cells following repeated courses of treatment is the major problem in the clinical management of neoplastic diseases. Recently, extensive studies have demonstrated that liposome encapsulated doxorubicin effectively modulates the multidrug resistance phenotype in cancer cells by altering the function of p-glycoprotein. This modulation of MDR phenotype by liposomes has been demonstrated in vitro in human breast cancer cells, ovarian cancer cells, human promyelocytic leukemia cells and in human colon cancer cells and in vivo in transgenic mice transfected with a functional MDR1 gene. It appears liposomes can play an effective role as a new modality of treatment for human cancers which have become refractory to chemotherapy. An exciting area of research which soon will emerge will exploit the different binding sites on p-glycoprotein by using combination of liposomes with other pharmacological modulators of MDR to impart maximal overcoming of multidrug resistance in cancer patients.     

Evidence for p-glycoprotein modification of insecticide toxicity in mosquitoes of the Culex pipiens complex

Pesticide resistance has parallels with multi-drug resistance syndrome of tumours in clinical medicine, which has been linked to an ATP-dependent pump, p-glycoprotein (P-gp). P-gps pump drugs out of the cell, thereby reducing cellular concentrations of the chemical. P-gps have been found in several invertebrate species and have been shown to provide a defence against environmental xenobiotics, including pesticides. This study used a model cell culture system to investigate the interaction of pesticides with P-gp. Ivermectin and endosulfan were shown to be strong inhibitors of dye transport out of cells, which is a standard measure of P-gp modulation. We then investigated the action of a P-gp inhibitor, verapamil (calcium channel blocker), on insecticide toxicity to fourth-instar mosquito larvae of the Culex pipiens L. complex (Diptera: Culicidae). Verapamil increased toxicity to examples of three insecticide classes (cypermethrin, endosulfan, ivermectin), but not to chlorpyrifos (organophosphate). The discovery of a novel protective mechanism in mosquitoes, with a wide substrate range, has implications for the control of important pest and vector species.     

Quinacrine is not a vital fluorescent probe for vesicular ATP storage

Quinacrine, a fluorescent amphipathic amine, has been used as a vital fluorescent probe to visualize vesicular storage of ATP in the field of purinergic signaling. However, the mechanism(s) by which quinacrine represents vesicular ATP storage remains to be clarified. The present study investigated the validity of the use of quinacrine as a vial fluorescent probe for ATP-storing organelles. Vesicular nucleotide transporter (VNUT), an essential component for vesicular storage and ATP release, is present in very low density lipoprotein (VLDL)-containing secretory vesicles in hepatocytes. VNUT gene knockout (Vnut^−/−) or clodronate treatment, a VNUT inhibitor, disappeared vesicular ATP release (Tatsushima et al., Biochim Biophys Acta Molecular Basis of Disease 2021, e166013). Upon incubation of mice’s primary hepatocytes, quinacrine accumulates in a granular pattern into the cytoplasm, sensitive to 0.1-μM bafilomycin A₁, a vacuolar ATPase (V-ATPase) inhibitor. Neither Vnut^−/− nor treatment of clodronate affected quinacrine granular accumulation. In vitro, quinacrine is accumulated into liposomes upon imposing inside acidic transmembranous pH gradient (∆pH) irrespective of the presence or absence of ATP. Neither ATP binding on VNUT nor VNUT-mediated uptake of ATP was affected by quinacrine. Consistently, VNUT-mediated uptake of quinacrine was negligible or under the detection limit. From these results, it is concluded that vesicular quinacrine accumulation is not due to a consequence of its interaction with ATP but due to ∆pH-driven concentration across the membranes as an amphipathic amine. Thus, quinacrine is not a vital fluorescent probe for vesicular ATP storage.     

Tricyclic antidepressants, quinacrine and a novel, synthetic chimera thereof clear prions by destabilizing detergent-resistant membrane compartments

Prion diseases are invariably fatal, neurodegenerative diseases transmitted by an infectious agent, PrPSc, a pathogenic, conformational isoform of the normal prion protein (PrPC). Heterocyclic compounds such as acridine derivatives like quinacrine abolish prion infectivity in a cell culture model of prion disease. Here, we report that these compounds execute their antiprion activity by redistributing cholesterol from the plasma membrane to intracellular compartments, thereby destabilizing membrane domains. Our findings are supported by the fact that structurally unrelated compounds with known cholesterol-redistributing effects - U18666A, amiodarone, and progesterone - also possessed high antiprion potency. We show that tricyclic antidepressants (e.g. desipramine), another class of heterocyclic compounds, displayed structure-dependent antiprion effects and enhanced the antiprion effects of quinacrine, allowing lower doses of both drugs to be used in combination. Treatment of ScN2a cells with quinacrine or desipramine induced different ultrastructural and morphological changes in endosomal compartments. We synthesized a novel drug from quinacrine and desipramine, termed quinpramine, that led to a fivefold increase in antiprion activity compared to quinacrine with an EC50 of 85 nm. Furthermore, simvastatin, an inhibitor of cholesterol biosynthesis, acted synergistically with both heterocyclic compounds to clear PrPSc. Our data suggest that a cocktail of drugs targeting the lipid metabolism that controls PrP conversion may be the most efficient in treating Creutzfeldt-Jakob disease.     

Genetic Studies of Acridine-Induced Mutants in STREPTOCOCCUS PNEUMONIAE

The mutagenic properties of acridines on pneumococcus are described. All seven acridines tested were mutagenic at the amiA locus conferring a resistance to 10^-5 m aminopterin. The effects of quinacrine were more specifically investigated. It was observed that: mutants can be obtained only by treatment of exponentially growing cells; a sharp maximum mutagenic effect occurs at a concentration slightly lower than the bacteriostatic value; and the amount of quinacrine required to yield the maximum mutagenic effect decreases with the pH of the medium. Moreover, the number of mutants detected after quinacrine treatment varies from locus to locus. The majority of quinacrine-induced mutants are readily reverted by quinacrine, but not by nitrosoguanidine treatment. This suggests that in pneumococcus quinacrine induces mainly frameshift mutations. A further study of the revertants obtained by quinacrine treatment of quinacrine-induced mutants strengthens this interpretation: most of the revertants result from a mutation at the same site; some partial revertants exhibiting an intermediate resistance to aminopterin were found to contain two very closely linked mutated sites, each mutation conferring the maximum level of resistance to aminopterin. Thus, the majority of quinacrine-induced mutants at the amiA locus of pneumococcus consists of frameshift mutations. Nearly all of the isolated mutants induced by quinacrine as well as other acridines belong to the low efficiency class of transformation. It was concluded that the mismatch resulting from the pairing between the wild type and the frameshift-containing sequence is recognized by the excision-repair system involved in the discrimination function in a way similar to that in which it recognizes mismatched base pairs between a transition mutation and the wild-type sequence.     

Verapamil versus hydrochlorothiazide in the treatment of hypertension: results of long term double blind comparative trial. Verapamil versus Diuretic (VERDI) Trial Research Group.

OBJECTIVE--To compare the efficacy and tolerability of hydrochlorothiazide, sustained release verapamil, and their combination in patients with mild to moderate hypertension. DESIGN--Randomised multicentre trial of 48 weeks'' duration with a double blind comparison of hydrochlorothiazide and verapamil followed by an open trial of combined treatment for patients not achieving the target diastolic blood pressure (less than 90 mm Hg) during treatment with a single drug. SETTING--Outpatient departments in 10 clinics and 10 private practices of general practitioners or internists. PATIENTS--369 Hypertensive patients with a diastolic blood pressure of 95-120 mm Hg during a placebo run in period of two weeks. INTERVENTIONS--Initial treatment consisted of 12.5 mg hydrochlorothiazide (n = 187) or 120 mg sustained release verapamil (n = 182) once daily (regimen I). If the target diastolic blood pressure of less than 90 mm Hg was not achieved within four weeks doses were increased to 25 mg hydrochlorothiazide or 240 mg verapamil once (regimen II) and twice daily (regimen III). Patients not achieving target blood pressure were given the combination of hydrochlorothiazide and verapamil--that is, 25 and 240 mg once (regimen IV) and twice daily (regimen V). MAIN OUTCOME MEASURE--Blood pressure determined with a device permitting automatic repeated measurements with printouts. RESULTS--After eight weeks of treatment with a single drug 76 out of 178 (43%) and 101 out of 175 (58%) patients achieved the target blood pressure with hydrochlorothiazide and verapamil, respectively. During follow up until 48 weeks patients treated with verapamil reached the target blood pressure more often and at lower doses and were less likely to switch to combination treatment than patients randomised to hydrochlorothiazide treatment. Adding verapamil to hydrochlorothiazide was more effective than the addition of hydrochlorothiazide to verapamil. At the end of the study 42 out of 169 (25%) and 73 out of 163 (45%) patients initially randomised to hydrochlorothiazide and verapamil, respectively, were at target blood pressure without combination treatment. After adding verapamil to hydrochlorothiazide or hydrochlorothiazide to verapamil an additional 58 (34%) and 29 (18%) patients reached the target blood pressure, respectively. Altogether 92 out of 332 (28%) patients failed to achieve target blood pressure with regimen V. There were four, 10, seven, and seven withdrawals due to possible adverse effects to treatment with hydrochlorothiazide, verapamil, combining verapamil with hydrochlorothiazide, and combining hydrochlorothiazide with verapamil, respectively. CONCLUSIONS--In doses currently used in antihypertensive treatment verapamil was more effective than hydrochlorothiazide as a single agent and in combination in mild to moderate hypertension, whereas withdrawal rates caused by side effects possibly related to treatment were similar.     

The biology of the P-glycoproteins

Conclusions The initial discovery of p-glycoprotein in the plasma membrane of MDR cancer cell lines was followed quickly by the cloning of its gene. Sequence analysis of cloned cDNAs revealed that p-glycoprotein was a member of the ABC family of membrane transporters. Subsequent biochemical characterization demonstrated the binding of chemotherapeutic drugs and ATP to p-glycoprotein. P-glycoprotein-mediated drag transport and drug-stimulated ATPase activity were documented in plasma membrane vesicles and in proteoliposomes containing the partially purified protein. P-glycoprotein was shown to be phosphorylated and the effect of this modification on the protein's biological function was explored. P-glycoproteins were found in many normal tissues and their overexpression was documented in numerous cancers. An important role for p-glycoprotein in intrinsic and acquired drug resistance in clinical oncology was established. Despite all that has been learned about p-glycoprotein over the last few years, additional studies will be necessary to address the many questions that have been left unanswered. Determination of p-glycoprotein structure and membrane topology should help elucidate the nature of chemotherapeutic drug binding sites and the mechanism whereby drug movement is coupled to ATP hydrolysis. Complete purification and functional reconstitution of p-glycoprotein into defined lipid vesicles will permit further characterization of drug transport and ATPase activity and give us the means by which p-glycoprotein's apparent dual function as a transporter and a channel can be clarified. Structural and functional studies on p-glycoprotein will also provide information needed to develop specified inhibitors that can be used clinically to overcome MDR in cancer patients. Further study of the mechanisms whereby p-glycoprotein expression is induced and regulated during malignant transformation is indicated. The development of biliary phospholipid deficiency in mdr2 knockout mice and xenobiotic hypersensitivity in mdr3 knockout mice have given us the first clues into the normal physiologic roles for the p-glycoproteins. The search for endogenous substrates for the p-glycoproteins will continue to be an area of active investigation.Continued investigation of p-glycoprotein's functions should result in better understanding of an important class of prokaryotic and eukaryotic membrane transporters. The potential of exploiting the knowledge garnered from these studies in the treatment of neoplastic, parasitic and inherited and acquired liver disease may be greater than we can now imagine.     

Effects of quinacrine on endothelial cell morphology and transcription factor-DNA interactions

Quinacrine has been used for decades and the beneficial effects of this drug are as numerous as its toxic effects. Since endothelial cells (EC) are in many cases the first cells coming in contact with drugs, the effect of quinacrine on certain aspects of EC biology were studied. The presented data demonstrate that quinacrine can have a marked impact on the integrity on EC monolayer without grossly interfering with cell viability. The described impact of quinacrine on EC might explain, at least in part, the toxic effects of this drug observed in the past. Furthermore, quinacrine profoundly effects gene regulation in EC. Quinacrine binds to DNA in a sequence-specific manner. While NF-kappa B-DNA interactions are not effected, AP-1-DNA binding is blocked by quinacrine. Such differential effects are presumably due to intercalation of quinacrine into the AP-1 consensus element. Preincubation of oligonucleotides resembling this sequence blocked the subsequent binding of nuclear extract containing AP-1 protein(s). Taken together, these data suggest that quinacrine interferes with EC physiology and alters the repertoire of EC to respond to stimuli. Furthermore, the differential effects of quinacrine might be exploited to study and gain additional insight in the involvement of AP-1 and NF-kappa B in gene regulation.     

Clinical Efficacy of Chemotherapy Combined with Verapamil in Metastatic Colorectal Patients

In order to determine the clinical efficacy and adverse reactions of chemotherapy and verapamil infusion through a target artery to treat colorectal cancer patients with metastasis after failure with previous conventional treatments. Patients with metastatic colon cancer (n = 36) received an infusion of verapamil, interleukin-2, oxaliplatin (or hydroxy camptothecin or irinotecan hydrochloride), fluorouracil and calcium folinate through target artery using the Seldinger puncture technique. From the second day of infusion, the patients were treated with fluorouracil and calcium folinate via systematic intravenous injection for 2–3 days. Efficacy was evaluated after at least two treatment courses. The objective response including complete or partial response was 58.3% in the 36 patients; clinical benefit rate, evaluated by Karnofsky Performance Status score was 91.7%; by weight was 83.3%; by the amount of painkiller consumed was 80.6%. No patient experienced side effects associated with heart function. Post-treatment, the P–R period, Q–T period, QRS, and heart rate were not significantly different than before treatment. Liver function was significantly improved. Side effects of chemotherapy were minor in comparison to those observed with intravenous chemotherapy. Infusion of verapamil and chemotherapy directly into pelvic tumor tissue can increase treatment efficacy and has been shown to be a relatively safe technique.     

Optical studies of complexes of quinacrine with DNA and chromatin: implications for the fluorescence of cytological chromosome preparations

The fluorescence and circular dichroism of quinacrine complexed with nucleic acids and chromatin were measured to estimate the relative magnitudes of factors influencing the fluorescence banding patterns of chromosomes stained with quinacrine or quinacrine mustard. DNA base composition can influence quinacrine fluorescence in at least two ways. The major effect, evident at low ratios of quinacrine to DNA, is a quenching of dye fluorescence, correlating with G-C composition. This may occur largely prior to relaxation of excited dye molecules. At higher dye/DNA saturations, which might exist in cytological chromosome preparations stained with high concentrations of quinacrine, energy transfer between dye molecules converts dyes bound near G-C base pairs into energy sinks. In contrast to its influence on quinacrine fluorescence, DNA base composition has very little effect on either quinacrine binding affinity or the circular dichroism of bound quinacrine molecules. The synthetic polynucleotides poly(dA-dT) and poly(dA)-poly(dT) have a similar effect on quinacrine fluorescence, but differ markedly in their affinity for quinacrine and in the circular dichroism changes associated with quinacrine binding. Quinacrine fluorescence intensity and lifetime are slightly less when bound to calf thymus chromatin than when bound to calf thymus DNA, and minor differences in circular dichroism between these complexes are observed. Chromosomal proteins probably affect the fluorescence of chromosomes stained with quinacrine, although this effect appears to be much less than that due to variations in DNA base composition. The fluorescence of cytological chromosome preparations may also be influenced by fixation effects and macroscopic variations in chromosome coiling.     

Synergy between verapamil and other multidrug-resistance modulators in model membranes

Various cationic lipophilic compounds can reverse the multidrug resistance of cancer cells. Possible interaction between these compounds, which are known as modulators, has been assessed by measuring leakage of Sulphan blue from anionic liposomes, induced both by verapamil alone and by verapamil in combination with diltiazem, quinine, thior idazine or clomipramine. An equation was derived to quantify the permeation doses and Hill coefficients of the drugs and mixtures between them by simultaneous fitting of the experimental data. The interaction was tested by two methods, the competition plot and the isobole method; both showed synergy between verapamil and each of diltiazem, qui nine and thioridazine. The dose factor of potentiation for verapamil determined within membranes was 4.0 ± 0.4 with diltiazem, 3.2 ± 0.4 with quinine and 2.4 ± 0.3 with thior idazine. The results suggest that the effectiveness of reversing multidrug resistance may be increased with modulators such as verapamil and diltiazem that have a much greater effect in combination than what would be expected from their effects when considered separately.     

Ventilator associated pneumonia and infection control

Rifampicin, an important drug in the treatment of tuberculosis, is used extensively despite its broad effects on drug-drug interactions, creating serious problems. The clinical importance of such interactions includes autoinduction leading to suboptimal or failed treatment. The concomitantly administered effects of rifampicin on other drugs can result in their altered metabolism or transportation that are metabolised by cytochromes P450 or transported by p-glycoprotein in the gastrointestinal tract and liver. This review paper summarises recent findings with emphases on the molecular mechanisms used to explain these broad drug-drug interactions. In general, rifampicin can act on a pattern: rifampicin activates the nuclear pregnane X receptor that in turn affects cytochromes P450, glucuronosyltransferases and p-glycoprotein activities. This pattern of action may explain many of the rifampicin inducing drug-drug interactions. However, effects through other mechanisms have also been reported and these make any explanation of such drug-drug interactions more complex.