Increased expression of cyclin E is associated with an increased resistance to doxorubicin in rat fibroblasts

Cell cycle progression in eukaryotic cells is regulated by a family of cyclin-dependent kinases (CDKs). Cyclin E is a regulatory subunit of CDK2 and drives cells from G1 to S phase. Increased expression of cyclin E is a frequent event in human malignancies and has been associated with poor prognosis in various cancers. In this study, we evaluated the effects of cyclin E-overexpression on the sensitivity of rat fibroblasts to anticancer drugs. Cyclin E-overexpressing cells were less sensitive to doxorubicin-induced inhibition of cell growth but not to other antineoplastic drugs, such as paclitaxel, vincristine, etoposide and methotrexate. Cyclin E-overexpressing fibroblasts also displayed a reduction in ROS levels and a significantly lower increase following doxorubicin treatment compared with vector control cells. The expression of manganese superoxide dismutase (MnSOD) and its activity were increased (about 1.3-fold) in cyclin E-overexpressing derivatives compared with control cells. These results suggest that cyclin E overexpression might reduce tumour cells sensitivity to doxorubicin by affecting the expression of MnSOD and that determination of cyclin E expression levels might help to select patients to be treated with an anthracycline-based antineoplastic therapy.

Drug resistance associated with loss of p53 involves extensive alterations in microtubule composition and dynamics

In the present study, we compared the dynamics and composition of microtubules in cell lines derived from the human breast adenocarcinoma MCF-7 containing either the wild-type p53 (wt-p53; MN1) or a dominant-negative variant of p53 gene (mut-p53; MDD2). Mut-p53 cells were significantly resistant to the cytotoxicity of the microtubule-targeted drugs (vinca alkaloids and taxanes), as compared with wt-p53 cells. Studies by high-resolution time-lapse fluorescence microscopy in living cells indicated that the dynamics of microtubules of mut-p53 cells were altered in complex ways and were significantly increased as compared with microtubules in wt-p53 cells. The percentage of time microtubules spent in growing and shortening phases increased significantly, their catastrophe frequency increased, and their overall dynamicity increased by 33%. In contrast, their shortening rate and the mean length shortened decreased. Cells containing mut-p53 displayed increased polymerisation of tubulin, increased protein levels of the class IV beta-tubulin isotype, STOP and survivin, and reduced protein levels of class II beta-tubulin isotype, MAP4 and FHIT. We conclude that p53 protein may contribute to the regulation of microtubule composition and function, and that alterations in p53 function may generate complex microtubule-associated mechanisms of resistance to tubulin-binding agents.

Clinical implications of varying degrees of vancomycin susceptibility in methicillin-resistant Staphylococcus aureus bacteremia

We conducted a retrospective study of the clinical aspects of bacteremia caused by methicillin-resistant Staphylococcus aureus (MRSA) with heterogeneously reduced susceptibility to vancomycin. Bloodstream MRSA isolates were screened for reduced susceptibility by using brain-heart infusion agar, including 4 mg/L vancomycin with and without 4% NaCl. Patients whose isolates exhibited growth (case-patients) were compared with those whose isolates did not (controls) for demographics, coexisting chronic conditions, hospital events, antibiotic exposures, and outcomes. Sixty-one (41%) of 149 isolates exhibited growth. Subclones from 46 (75%) of these had a higher MIC of vancomycin than did their parent isolates. No isolates met criteria for vancomycin heteroresistance. No differences in potential predictors or in outcomes were found between case-patients and controls. These data show that patients with vancomycin-susceptible MRSA bacteremia have similar baseline clinical features and outcomes whether or not their bacterial isolates exhibit growth on screening media containing vancomycin.

HIV-1 protease and reverse transcriptase mutation patterns responsible for discordances between genotypic drug resistance interpretation algorithms

Several rules-based algorithms have been developed to interpret results of HIV-1 genotypic resistance tests. To assess the concordance of these algorithms and to identify sequences causing interalgorithm discordances, we applied four publicly available algorithms to the sequences of isolates from 2,045 individuals in northern California. Drug resistance interpretations were classified as S for susceptible, I for intermediate, and R for resistant. Of 30,675 interpretations (2,045 sequences x 15 drugs), 4.4% were completely discordant, with at least one algorithm assigning an S and another an R; 29.2% were partially discordant, with at least one algorithm assigning an S and another an I, or at least one algorithm assigning an I and another an R; and 66.4% displayed complete concordance, with all four algorithms assigning the same interpretation. Discordances between nucleoside reverse transcriptase inhibitor interpretations usually resulted from several simple, frequently occurring mutational patterns. Discordances between protease inhibitor interpretations resulted from a larger number of more complex mutation patterns. Discordances between nonnucleoside reverse transcriptase inhibitor interpretations were uncommon and resulted from a small number of individual drug resistance mutations. Determining the clinical significance of these mutation patterns responsible for interalgorithm discordances will improve interalgorithm concordance and the accuracy of genotypic resistance interpretation.

Multidrug resistance 1 gene (P-glycoprotein 170): an important determinant in gastrointestinal disease?

The interface between luminal contents and intestinal epithelium constitutes the largest area of interaction between the host and the environment. There is now strong evidence that the gene product of the multidrug resistant pump (MDR) plays a critical role in host-bacterial interactions in the gastrointestinal tract and maintenance of intestinal homeostasis. This review highlights the efflux mechanism in the intestinal epithelium which is mediated by the multidrug resistant pump, also known as P-glycoprotein 170. Current studies promise to provide further insights into the contribution of the MDR1 gene in the pathogenesis of inflammatory and malignant disorders of the gastrointestinal tract.

Is there a cloud in the silver lining for imatinib?

Imatinib mesylate (Gleevec) or Glivec), a small molecule tyrosine kinase inhibitor for the treatment of chronic myeloid leukaemia, has been said to herald the dawn of a new era of rationally designed, molecularly targeted oncotherapy. Lurking on the same new horizon, however, is the age-old spectre of drug resistance. This review sets the intoxicating clinical perspective against the more sobering laboratory evidence of such divergent mechanisms of imatinib resistance as gene amplification and stem cell quiescence. Polychemotherapy has already been considered to combat resistance, but a more innovative, as yet unformulated, approach may be advocated.

Class I integrons and SXT elements in El Tor strains isolated before and after 1992 Vibrio cholerae O139 outbreak, Calcutta, India

We examined the distribution of class I integrons and SXT elements in Vibrio cholerae O1 El Tor strains, isolated in Calcutta, India, before and after the V. cholerae O139 outbreak in 1992. Class I integrons, with aadA1 gene cassette, were detected primarily in the pre-O139 strains; the SXT element was found mainly in the post-O139 strains.

Reversal of Taxol resistance in hepatoma by cyclosporin A: involvement of the PI-3 kinase-AKT 1 pathway

Hepatoma cells are known to be highly resistant to chemotherapy. Previously, we have found differential Taxol resistance in human and murine hepatoma cells. The aim of this study was to examine the effect of a multidrug resistance inhibitor, cyclosporin A in combination with Taxol on hepatoma in vitro and in vivo, and to identify the possible mechanism involved in Taxol resistance. Simultaneous treatment of cyclosporin A (0-10 microM) and Taxol (0.1 microM) inhibited cell growth in vitro. Cyclosporin A interfered with Taxol (0.1 microM)-induced AKT activation and BAD phosphorylation. Cyclosporin A combined with Taxol treatment augments caspase-9, -3 activation and loss of mitochondrial membrane potential in HepG2 cells. PI3 kinase inhibitor, wortmannin, or a dominant-negative AKT1 expression vector treatment partially enhanced Taxol-induced apoptosis indicating that PI3 kinase-AKT pathway was involved in Taxol-resistance pathway. Moreover, combination treatment reduced tumour growth in SCID and C57BL/6 mice as compared to either Taxol or cyclosporin A treatment. Our results indicate that the combination of cyclosporin A and Taxol is effective in the reversal of Taxol resistance through the inhibition of PI3 kinase-AKT1 pathway.

Role of cystine transport in intracellular glutathione level and cisplatin resistance in human ovarian cancer cell lines

Transport system x(c)(-) is a member of plasma membrane heterodimeric amino-acid transporters and consists of two protein components, xCT and 4F2hc. This system mediates cystine entry coupled with the exodus of intracellular glutamate and regulates the intracellular glutathione (GSH) levels in most mammalian cultured cells. We studied the activity of system x(c)(-) and GSH content in human ovarian cancer cell line (A2780) and its cisplatin (CDDP)-resistant variant (A2780DDP). The rate of cystine uptake was approximately 4.5-fold higher in A2780DDP cells than in A2780 cells and the cystine uptake in A2780DDP cells was mediated by system x(c)(-). Intracellular GSH content was much higher in A2780DDP cells but it fell drastically in the presence of excess glutamate, which inhibited the cystine uptake competitively. xCT and 4F2hc mRNAs were definitely expressed in A2780DDP cells, but far less in A2780 cells. Expression of system x(c)(-) activity by transfection with cDNAs for xCT and 4F2hc made A2780 cells more resistant to CDDP. Similar results on the cystine uptake were obtained in human colonic cancer cell lines. These findings suggest that the system x(c)(-) plays an important role in maintaining the higher levels of GSH and consequently in CDDP resistance in cancer cell lines.

Cell proliferation is related to in vitro drug resistance in childhood acute leukaemia

Bone marrow and peripheral blood samples from 362 patients with acute lymphoblastic leukaemia (ALL) proliferating cell and 90 patients with acute myeloid leukaemia (AML) were analysed for S-phase fractions, Ki67 antigen, and proliferating cell nuclear antigen expression. The S-phase fractions were correlated with in vitro drug resistance to 15 different anticancer agents. Leukaemia cells isolated from bone marrow had higher S-phase fractions than leukaemia cells isolated from peripheral blood (in initial ALL, median values resp. 6.9 and 2.7%, in initial AML resp. 5.3 and 1.3%; both P<0.01). Relapse ALL samples derived from bone marrow showed increased S-phase fractions (median 9.9%) compared with initial ALL samples (median 6.9%; P<0.01). ALL samples obtained at initial diagnosis showed higher S-phase fractions (median 6.9%) and higher Ki67 expression (median 30%) than initial AML samples (median resp. 5.3 and 14%; both P<0.05). The S-phase fractions were not related to white blood cell count, age, or gender. Within initial ALL, the S-phase fraction correlated significantly but modestly strong (rho=0.3-0.5; P<0.05) with sensitivity to antimetabolites (cytarabine, mercaptopurine, thioguanine), L-asparaginase, teniposide, and vincristine. Similar results were found within subgroups of initial ALL (nonhyperdiploid and common/precursor-B-lineage ALL). In relapsed ALL and AML such correlations were not found. In conclusion, cell proliferation differs between leukaemia subgroups and increased proliferation is associated with increased in vitro sensitivity to several anticancer agents in initial ALL.

Using hospital antibiogram data to assess regional pneumococcal resistance to antibiotics

Antimicrobial resistance to penicillin and macrolides in Streptococcus pneumoniae has increased in the United States over the past decade. Considerable geographic variation in susceptibility necessitates regional resistance tracking. Traditional active surveillance is labor intensive and costly. We collected antibiogram reports from North Carolina hospitals and assessed pneumococcal susceptibility to multiple agents from 1996 through 2000. Susceptibility in North Carolina was consistently lower than the national average. Aggregating antibiogram data is a feasible and timely method of monitoring regional susceptibility patterns and may also prove beneficial in measuring the effects of interventions to decrease antimicrobial resistance.

Fluoroquinolone resistance in Campylobacter jejuni isolates in travelers returning to Finland: association of ciprofloxacin resistance to travel destination

Ciprofloxacin resistance was analyzed in 354 Campylobacter jejuni isolates collected during two study periods (1995-1997 and 1998-2000) from travelers returning to Finland. The increase in resistance between the two periods was significant among all isolates (40% vs. 60%; p<0.01), as well as among those from Asia alone (45% vs. 72%; p<0.01).

Mirtazapine for treatment-resistant depression: a preliminary report

OBJECTIVE

To describe the effectiveness and tolerability of mirtazapine, a noradrenergic and specific serotonergic antidepressant, in the open-label treatment of patients with depression who were resistant to other antidepressant agents.

METHODS

The charts of 24 patients who met the Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition, (DSM-IV) criteria for major depressive disorder and were treated with mirtazapine after partial or nonresponse to standard antidepressants were reviewed for clinical response. Outcome was determined by using the Clinical Global Impressions of Improvement (CGI-I) Scale.

RESULTS

Symptomatic improvement was observed in 9 (38%) of 24 patients during an average of 14.1 months of mirtazapine treatment at a mean dose of 36.7 mg/day. Five (21%) patients discontinued mirtazapine because of side effects such as fatigue, weight gain and nausea. Five (21%) patients were receiving combination therapy with another antidepressant when mirtazapine treatment was initiated.

CONCLUSIONS

This open-label study suggests that a subgroup of patients with treatment-resistant depression may benefit from mirtazapine treatment. Further controlled studies are required to demonstrate the efficacy of mirtazapine in treatment-resistant depression.

Antituberculosis drug resistance patterns in two regions of Turkey: a retrospective analysis

BACKGROUND

The emergence of Mycobacterium tuberculosis strains resistant to antituberculosis agents has recently received increased attention owing largely to the dramatic outbreaks of multi drug resistance tuberculosis (MDR-TB).

METHODS

Patients residing in Zonguldak and Kayseri provinces of Turkey with, pulmonary tuberculosis diagnosed between 1972 and 1999 were retrospectively identified. Drug susceptibility tests had been performed for isoniazid (INH), rifampin (RIF), streptomycin (SM), ethambutol (EMB) and thiacetasone (TH) after isolation by using the resistance proportion method.

RESULTS

Total 3718 patients were retrospectively studied. In 1972-1981, resistance rates for to SM and INH were found to be 14.8% and 9.8% respectively (n: 2172). In 1982-1991 period, resistance rates for INH, SM, RIF, EMB and TH were 14.2%, 14.4%, 10.5%, 2.7% and 2.9% (n: 683), while in 1992-1999 period 14.4%, 21.1%, 10.6%, 2.4% and 3.7% respectively (n: 863). Resistance rates were highest for SM and INH in three periods. MDR-TB patients constituted 7.3% and 6.6% of 1982-1991 and 1992-1999 periods (p > 0.05).

CONCLUSION

This study demonstrates the importance of resistance rates for TB. Continued surveillance and immediate therapeutic decisions should be undertaken in order to prevent the dissemination of such resistant strains.

Outpatient antibiotic use and prevalence of antibiotic-resistant pneumococci in France and Germany: a sociocultural perspective

The prevalence of penicillin-nonsusceptible pneumococci is sharply divided between France (43%) and Germany (7%). These differences may be explained on different levels: antibiotic-prescribing practices for respiratory tract infections; patient-demand factors and health-belief differences; social determinants, including differing child-care practices; and differences in regulatory practices. Understanding these determinants is crucial for the success of possible interventions. Finally, we emphasize the overarching importance of a sociocultural approach to preventing antibiotic resistance in the community.

Liposome formulations for effective administration of lipophilic malonatoplatinum(II) complexes

For effective administration of lipophilic trans(+/-)-1,2-diaminocyclohexaneplatinum(II) complexes of malonate derivatives [(dach)PtL, L=allylmalonate (AM), diallylmalonate (DAM), allylbenzylmalonate (ABM), or dibenzylmalonate (DBM)] in aqueous solution, we have applied three different liposome formulations and evaluated their physical and chemical properties, along with their in vitro cytotoxicity. The liposome formulations were composed of DMPC / DMPG [DMPC=1,2-dimyristoyl-sn-glycero-3-phosphocholine, DMPG=1,2-dimyristoyl-sn-glycero-3-(phospho-rac-1-glycerol) (sodium salt)] in different molar ratios (7/3 or 3/7) or an equimolar DOTAP/DOPE formulation (DOTAP=1,2-dioleoyl-3-trimethylammonium propane, DOPE=1,2-dioleoyl-sn-glycero-3-phosphoethanolamine). Preliposomal powders of the platinum complexes were prepared by lyophilization, and reconstituted in aqueous solution to obtain the final liposomal platinum complexes. Due to the lipophilicity of the malonatoplatinum complexes, the entrapment efficiency of drugs within the liposomes was over 90% except for the AM complex, and platinum drug stability was also satisfactory (>90%) in these liposomal systems. In vitro cytotoxicity was tested in human ovarian carcinoma cells sensitive (A2780) and resistant to cisplatin (A2780/PDD). In both cell lines, the liposomal DBM complex was much more cytotoxic than the corresponding DAM and ABM complexes, which means that the more hydrophobic benzyl substituent affords higher cytotoxicity than the allyl substituent in the malonato leaving group. Furthermore, the DBM complex in DMPC/DMPG formulations was effective against both sensitive and resistant A2780 cells (resistance indexes (RI)=1.10-1.49), showing lack of cross-resistance to cisplatin. Therefore, the liposomal DBM complex in the DMPC/DMPG formulations is a promising candidate for stable pharmaceutical liposomal platinum complexes.

Structure of HIV-2 reverse transcriptase at 2.35-A resolution and the mechanism of resistance to non-nucleoside inhibitors

The HIV-2 serotype of HIV is a cause of disease in parts of the West African population, and there is evidence for its spread to Europe and Asia. HIV-2 reverse transcriptase (RT) demonstrates an intrinsic resistance to non-nucleoside RT inhibitors (NNRTIs), one of two classes of anti-AIDS drugs that target the viral RT. We report the crystal structure of HIV-2 RT to 2.35 A resolution, which reveals molecular details of the resistance to NNRTIs. HIV-2 RT has a similar overall fold to HIV-1 RT but has structural differences within the "NNRTI pocket" at both conserved and nonconserved residues. The structure points to the role of sequence differences that can give rise to unfavorable inhibitor contacts or destabilization of part of the binding pocket at positions 101, 106, 138, 181, 188, and 190. We also present evidence that the conformation of Ile-181 compared with the HIV-1 Tyr-181 could be a significant contributory factor to this inherent drug resistance of HIV-2 to NNRTIs. The availability of a refined structure of HIV-2 RT will provide a stimulus for the structure-based design of novel non-nucleoside inhibitors that could be used against HIV-2 infection.

Drug resistance in HIV-1 protease: Flexibility-assisted mechanism of compensatory mutations

The emergence of drug-resistant variants is a serious side effect associated with acquired immune deficiency syndrome therapies based on inhibition of human immunodeficiency virus type 1 protease (HIV-1 PR). In these variants, compensatory mutations, usually located far from the active site, are able to affect the enzymatic activity via molecular mechanisms that have been related to differences in the conformational flexibility, although the detailed mechanistic aspects have not been clarified so far. Here, we perform multinanosecond molecular dynamics simulations on L63P HIV-1 PR, corresponding to the wild type, and one of its most frequently occurring compensatory mutations, M46I, complexed with the substrate and an enzymatic intermediate. The quality of the calculations is established by comparison with the available nuclear magnetic resonance data. Our calculations indicate that the dynamical fluctuations of the mutated enzyme differ from those in the wild type. These differences in the dynamic properties of the adducts with the substrate and with the gem-diol intermediate might be directly related to variations in the enzymatic activity and therefore offer an explanation of the observed changes in catalytic rate between wild type and mutated enzyme. We anticipate that this "flexibility-assisted" mechanism might be effective in the vast majority of compensatory mutations, which do not change the electrostatic properties of the enzyme.

Crosslinking of membrane-embedded cysteines reveals contact points in the EmrE oligomer

EmrE is a small multidrug transporter that extrudes various drugs in exchange with protons, thereby rendering Escherichia coli cells resistant to these compounds. In this study, relative helix packing in the EmrE oligomer solubilized in detergent was probed by intermonomer crosslinking analysis. Unique cysteine replacements in transmembrane domains were shown to react with organic mercurials but not with sulfhydryl reagents, such as maleimides and methanethiosulfonates. A new protocol was developed based on the use of HgCl(2), a compound known to react rapidly and selectively with sulfhydryl groups. The reaction can bridge vicinal pairs of cysteines and form an intermolecular mercury-linked dimer. To circumvent problems inherent to mercury chemistry, a second crosslinker, hexamethylene diisocyanate, was used. After the HgCl(2) treatment, excess reagent was removed and the oligomers were dissociated with a strong denaturant. Only those previously crosslinked reacted with hexamethylene diisocyanate. Thus, vicinal cysteine-substituted residues in the EmrE oligomer were identified. It was shown that transmembrane domain (TM)-1 and TM4 in one subunit are in contact with the corresponding TM1 and TM4, respectively, in the other subunit. In addition, TM1 is also in close proximity to TM4 of the neighboring subunit, suggesting possible arrangements in the binding and translocation domain of the EmrE oligomer. This method should be useful for other proteins with cysteine residues in a low-dielectric environment.

Molecular cytogenetic characterization of drug-resistant leukemia cell lines by comparative genomic hybridization and fluorescence in situ hybridization

Resistance to chemotherapeutic drugs is one of the major difficulties encountered during cancer chemotherapy. To detect genomic aberrations underlying the acquired drug resistance, we examined three cultured human myelomonocytic leukemia cell sublines each resistant to adriamycin (ADR), 1-beta-1-D-arabinofuranosylcytosine (ara-C), or vincristine (VCR), using comparative genomic hybridization (CGH), fluorescence in situ hybridization (FISH), RT-PCR, and western blot techniques. Chromosomes 7, 10 and 16 most conspicuously showed frequent aberrations among the resistant sublines as compared to the parental KY-821 cell line. In ADR-resistant cells, gains at 7q21, 16p12, 16p13.1-13.3, 16q11.1-q12.1, and losses at 7p22-pter, 7q36-qter, 10p12, 10p11.2-pter, 10q21-q25, 10q26-qter were notable. In ara-C-resistant cells, no remarkable gain or loss on chromosome 7, but losses at 10p14-pter, 10q26-qter and 16p11.2-p11.3 were observed. In VCR-resistant cells, gain at 7q21 and losses at 10p11-p13, 10p15 and 16p11.2-p13.3 were found. FISH identified amplified signals for the MDR-1 gene located at 7q21.1 in ADR- and VCR- but not ara-C-resistant cells, and for the MRP-1 gene located at 16p13.1 in ADR-resistant cells. These findings were validated at the mRNA and protein levels. Overlapping of the amplified MRP-1 gene with MDR-1 gene may play a critical part in the acquisition of resistance to ADR. Resistance to ara-C excluded MDR-1 gene involvement and highlighted other key genes such as MXR gene. Several other genes putatively involved in the development of drug resistance might lie in other aberrated chromosomal regions.

Crucial stages of protein folding through a solvable model: predicting target sites for enzyme-inhibiting drugs

An exactly solvable model based on the topology of a protein native state is applied to identify bottlenecks and key sites for the folding of human immunodeficiency virus type 1 (HIV-1) protease. The predicted sites are found to correlate well with clinical data on resistance to Food and Drug Administration-approved drugs. It has been observed that the effects of drug therapy are to induce multiple mutations on the protease. The sites where such mutations occur correlate well with those involved in folding bottlenecks identified through the deterministic procedure proposed in this study. The high statistical significance of the observed correlations suggests that the approach may be promisingly used in conjunction with traditional techniques to identify candidate locations for drug attacks.

Overcoming drug resistance in HIV-1 chemotherapy: the binding thermodynamics of Amprenavir and TMC-126 to wild-type and drug-resistant mutants of the HIV-1 protease

Amprenavir is one of six protease inhibitors presently approved for clinical use in the therapeutic treatment of AIDS. Biochemical and clinical studies have shown that, unlike other inhibitors, Amprenavir is severely affected by the protease mutation I50V, located in the flap region of the enzyme. TMC-126 is a second-generation inhibitor, chemically related to Amprenavir, with a reported extremely low susceptibility to existing resistant mutations including I50V. In this paper, we have studied the thermodynamic and molecular origin of the response of these two inhibitors to the I50V mutation and the double active-site mutation V82F/I84V that affects all existing clinical inhibitors. Amprenavir binds to the wild-type HIV-1 protease with high affinity (5.0 x 10(9) M(-1) or 200 pM) in a process equally favored by enthalpic and entropic contributions. The mutations I50V and V82F/I84V lower the binding affinity of Amprenavir by a factor of 147 and 104, respectively. TMC-126, on the other hand, binds to the wild-type protease with extremely high binding affinity (2.6 x 10(11) M(-1) or 3.9 pM) in a process in which enthalpic contributions overpower entropic contributions by almost a factor of 4. The mutations I50V and V82F/I84V lower the binding affinity of TMC-126 by only a factor of 16 and 11, respectively, indicating that the binding affinity of TMC-126 to the drug-resistant mutants is still higher than the affinity of Amprenavir to the wild-type protease. Analysis of the data for TMC-126 and KNI-764, another second-generation inhibitor, indicates that their low susceptibility to mutations is caused by their ability to compensate for the loss of interactions with the mutated target by a more favorable entropy of binding.

In vitro and in vivo activity and cross resistance profiles of novel ruthenium (II) organometallic arene complexes in human ovarian cancer

Ruthenium complexes offer the potential of reduced toxicity, a novel mechanism of action, non-cross resistance and a different spectrum of activity compared to platinum containing compounds. Thirteen novel ruthenium(II) organometallic arene complexes have been evaluated for activity (in vitro and in vivo) in models of human ovarian cancer, and cross-resistance profiles established in cisplatin and multi-drug-resistant variants. A broad range of IC50 values was obtained (0.5 to >100 microM) in A2780 parental cells with two compounds (RM175 and HC29) equipotent to carboplatin (6 microM), and the most active compound (HC11) equipotent to cisplatin (0.6 microM). Stable bi-dentate chelating ligands (ethylenediamine), a more hydrophobic arene ligand (tetrahydroanthracene) and a single ligand exchange centre (chloride) were associated with increased activity. None of the six active ruthenium(II) compounds were cross-resistant in the A2780cis cell line, demonstrated to be 10-fold resistant to cisplatin/carboplatin by a mechanism involving, at least in part, silencing of MLH1 protein expression via methylation. Varying degrees of cross-resistance were observed in the P-170 glycoprotein overexpressing multi-drug-resistant cell line 2780AD that could be reversed by co-treatment with verapamil. In vivo activity was established with RM175 in the A2780 xenograft together with non-cross-resistance in the A2780cis xenograft and a lack of activity in the 2780AD xenograft. High activity coupled to non cross-resistance in cisplatin resistant models merit further development of this novel group of anticancer compounds.

Inhibition of nucleotide excision repair by fludarabine in normal lymphocytes in vitro, measured by the alkaline single cell gel electrophoresis (Comet) assay

Alkylating agents or platinum analogues initiate several excision repair mechanisms, which involve incision of the DNA strand, excision of the damaged nucleotide, gap filling by DNA resynthesis, and rejoining by ligation. The previous study described that nucleotide excision repair permitted incorporation of fludarabine nucleoside (F-ara-A) into the repair patch, thereby inhibiting the DNA resynthesis. In the present study, to clarify the repair kinetics in view of the inhibition by F-ara-A, normal lymphocytes were stimulated to undergo nucleotide excision repair by ultraviolet C (UV) irradiation in the presence or absence of F-ara-A. The repair kinetics were determined as DNA single strand breaks resulting from the incision and the rejoining using the alkaline single cell gel electrophoresis (comet) assay. DNA resynthesis was evaluated in terms of the uptake of tritiated thymidine into DNA. The lymphocytes initiated the incision step maximally at 1 h, and completed the rejoining process within 4 h after UV exposure. UV also initiated thymidine uptake, which increased time-dependently and reached a plateau at 4 h. A 2-h pre-incubation with F-ara-A inhibited the repair in a concentration-dependent manner, with the maximal inhibition by 5 mM. This inhibitory effect was demonstrated by the reduction of the thymidine uptake and by the inhibition of the rejoining. A DNA polymerase inhibitor, aphidicolin, and a ribonucleotide reductase inhibitor, hydroxyurea, were not so inhibitory to the repair process as F-ara-A at equimolar concentrations. The present findings suggest that inhibition of nucleotide excision repair may represent a novel therapeutic strategy against cancer, especially in the context of resistant cells with an increased repair capacity.

Photodynamic therapy of DNA mismatch repair-deficient and -proficient tumour cells

Loss of DNA mismatch repair is a common finding in hereditary nonpolyposis colon cancer as well as in many types of sporadic human tumours. DNA mismatch repair-deficient cells have been reported to be resistant to many chemotherapeutic agents and to radiotherapy, and to have the potential of rapidly acquiring additional mutations leading to tumour progression. Photodynamic therapy is a new treatment modality using light to activate a photosensitiser that preferentially localises in tumour cells. An oxygen dependent photochemical reaction ensues, resulting in selective tumour necrosis. The effect of loss of DNA mismatch repair activity on the sensitivity to photodynamic therapy was tested using pairs of cell lines proficient or deficient in mismatch repair due to loss of either MLH1 or MSH2 protein function. Cells were incubated with the photosensitiser 5,10,15,20-meta-tetra(hydroxyphenyl)chlorin and exposed to laser light at 652 nm with various optical doses ranging from 0-1 J cm(-2). Cell survival was assessed using the clonogenic assay. Loss of MLH1 or MSH2 function was not associated with resistance to photodynamic therapy. MCF-7 cells repeatedly treated with photodynamic therapy expressed parental levels of MLH1, MSH2, MSH6, and PMS2. DNA mismatch repair-deficient and -proficient cells showed similar subcellular distributions of meta-tetra(hydroxyphenyl)chlorin as analysed by laser scanning and fluorescence microscopy. Therefore, repeated exposure of tumour cells to photodynamic therapy does not seem to result in loss of DNA mismatch repair, and loss of mismatch repair, in turn, does not seem to contribute to resistance to photodynamic therapy. Our results suggest recommending photodynamic therapy as a strategy for circumventing resistance due to loss of DNA mismatch repair.