Hypomethylation agent decitabine restores drug sensitivity by depressing P-glycoprotein activity through MAPK signaling pathway.

The multidrug resistance (MDR) continues to be an obstacle in the treatment of both hematological and solid tumors. Hypomethylation agent, decitabine (5-Aza-dC), is an experimental agent in MDR therapy, while the mechanism is not very clear. In the present study, we demonstrated 5-Aza-dC may reverse MDR induced by P-glycoprotein (P-gp) coded by mdr1 gene in both hematologic K562/ADR cells and solid tumor MCF-7/ADR cells with time and dose-dependent manner. 5-Aza-dC significantly increased drug sensitivity in patients' leukemic cells which had higher expression of mdr1 gene. Both total protein and membrane P-gp expression were up-regulated with 5-Aza-dC treatment in K562/ADR and MCF-7/ADR cells. However, accumulation of adriamycin and rhodamine 123 were increased which suggested the depression of P-gp activity. Gene expression profiling was performed and activation of MAPK signaling pathway was identified as the most significant change affected by 5-Aza-dC. Inhibition of MAPK pathway could increase P-gp activity. Our data suggested that hypomethylation agent decitabine restores drug sensitivity in the P-gp-induced MDR phenotype by depressing of P-gp activity as drug pump partly through MAPK signaling pathway.

Nuclear Transcription Factor Kappa B Downregulation Reduces Chemoresistance in Bone Marrow-derived Cells Through P-glycoprotein Modulation.

BACKGROUND AND AIMS: Nuclear transcription factor kappa B (NF-κB) is associated with many types of refractory cancer. However, despite multiple strategies to treat cancer and novel target drugs, multidrug resistance still causes relapses. The best-characterized mechanism responsible for multidrug resistance involves the expression of the MDR-1 gene product, P-glycoprotein (P-gp). Because the direct inhibition of this protein is very toxic, other methods of multidrug resistance (MDR) regulation have been proposed. The MDR-1 promoter sequence contains a κB site, which is recognized by NF-κB. The aim of this work was to characterize whether NF-κB modulation changes the response of bone marrow-derived cells (BMDCs) to chemotherapy. RESULTS: We exposed BMDCs to etoposide and doxorubicin, two of the most used antineoplastic drugs. BMDCs presented high tolerance to these drugs, which correlated with high intrinsic P-gp activity and strong protein expression of NF-κB. To determine the mechanism behind the poor sensitivity of BMDCs to chemotherapy, we blocked the activity of the heterodimer protein NF-κB using the pharmacological inhibitor Bay 11-7085 and through the transfection of an adenovirus negative mutant of I kappa B alpha. The multidrug resistance phenotype of BMDCs was reversed by inhibiting the NF-κB pathway, and this change was accompanied by a decrease in P-gp activity. CONCLUSIONS: NF-κB is a possible target for improving the antineoplastic response.

GP responses to price regulation: evidence from a French nationwide reform.

This paper uses a French reform to evaluate the impacts of overbilling restrictions on general practitioner (GP) care provision, fees and incomes. Since 1990, this reform has introduced conditions self-employed GPs must fulfil to be permitted to bill freely. We exploit 2005 and 2008 public health insurance administrative data on GP activity and fees. We use fuzzy regression discontinuity techniques to estimate local causal impacts for GPs who established practices in 1990 and who were constrained by the new regulation to charge regulated prices (compliers). We find that those GPs practices to income effects. In the regulated fee regime, GPs face prices lower by 42% and provide 50% more care than they would do in the unregulated fee regime. Male care provision increasing reaction is larger than the female one, which results in a higher male labour income in the regulated fee regime than with unregulated fees, whereas it is the opposite for women. With regulated fees, GPs limit side-salaried activities, use more lump-sum payment schemes and occupy more often gatekeeper positions.

From mixed sigma-2 receptor/P-glycoprotein targeting agents to selective P-glycoprotein modulators: small structural changes address the mechanism of interaction at the efflux pump.

Generations of modulators of the efflux pump P-glycoprotein (P-gp) have been produced as tools to counteract the Multidrug Resistance (MDR) phenomenon in tumor therapy, but clinical trials were not successful so far. With the aim of contributing to the development of novel P-gp modulators, we started from recently studied high-affinity sigma-2 (σ2) receptor ligands that showed also potent interaction with P-gp. For σ2 receptors high-affinity binding, a basic N-atom is a strict requirement. Therefore, we reduced the basic character of the N-atom present in these ligands, and we obtained potent P-gp modulators with poor or null σ2 receptor affinity. We also evaluated whether modulation of P-gp by these novel compounds involved consumption of ATP (as P-gp substrates do), as a source of energy to support the efflux. Surprisingly, even small structural changes resulted in opposite behavior, with amide 13 depleting ATP, in contrast to its isomer 18. Two compounds, 15 and 25, emerged for their potent activity at P-gp, and deserve further investigations as tools for P-gp modulation.