P-glycoprotein (Pgp) and breast cancer resistance protein (BCRP) are ATP binding cassette (ABC) transporters that are overexpressed in different drug-resistant cancer cell lines. In this study, we investigated whether doxorubicin promotes Pgp and/or BCRP expression to induce drug resistance in colon cancer cells under hypoxic conditions. We analyzed HIF-1α activity via ELISA, Pgp, and BCRP expression by qRT-PCR and the relationship between doxorubicin uptake and ABC transporter expression via confocal microscopy in HT-29WT and HT-29 doxorubicin-resistant colon cancer cells (HT-29DxR). These cells were treated with doxorubicin and/or CoCl (chemical hypoxia), and reactive oxygen species inductors. We found that the combination of chemically induced hypoxia and doxorubicin promoted Pgp mRNA expression within 24 h in HT-29WT and HT-29DxR cells. Both doxorubicin and CoCl alone or in combination induced Pgp and BCRP expression, as demonstrated via confocal microscopy in each of the above two cell lines. Thus, we surmised that Pgp and BCRP expression may result from synergistic effects exerted by the combination of doxorubicin-induced ROS production and HIF-1α activity under hypoxic conditions. However, HIF-1α activity disruption via the administration of E3330, an APE-1 inhibitor, downregulated Pgp expression and increased doxorubicin delivery to HT-29 cells, where it served as a substrate for Pgp, indicating the existence of an indirect relationship between Pgp expression and doxorubicin accumulation. Thus, we concluded that Pgp and BCRP expression can be regulated via cross-talk between doxorubicin and hypoxia, promoting drug resistance in HT-29 WT, and HT-29DxR cells and that this process may be ROS dependent. J. Cell. Biochem. 118: 1868-1878, 2017. © 2017 Wiley Periodicals, Inc.

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La utilización de actividades académicas extra clase se presenta como una estrategia útil para que el estudiante reconozca críticamente sus debilidades y busque autónomamente soluciones, y para que el tutor trascienda los procesos de aprendizaje de saberes hacia la formación del individuo. La aplicación extracurricular de cuatro tipos de actividades que incluyeron el afianzamiento de conceptos y su aplicación a la solución de problemas en la asignatura de Bioquímica dictada a estudiantes de medicina, permitió que ellos demostraran su capacidad para desarrollar responsabilidad y autonomía frente a su proceso de aprendizaje e impactaran positiva y significativamente en su rendimiento académico. El tipo de actividad realizada y la frecuencia de asistencia favorecieron el proceso y los resultados incidieron sobre la superación de la mortalidad histórica de esta asignatura

Introduction: Drug resistance mechanisms may be associated with decreased cell death and its induction may depend on the response to oxidative stress caused by hypoxia. The correlation between hypoxia-inducible factor HIF-1α, the number of reactive oxygen species and their effect on cell survival has not yet been evaluated.Objective: The purpose of this study was to evaluate the effect of HIF-1α activity and reactive oxygen species (ROS) accumulation in apoptosis of colon cancer cells.Materials and methods: HT29 colon cancer cells were treated with CoCl2 or doxorubicin and the activity of HIF-1α was determined by ELISA assay. ROS were determined using fluorescence probe carboxy-H2DFFDA. Apoptosis was assessed by caspase-3 activation analysis, and PUMA and BAX mRNA levels by qRT-PCR. The reduction of the antiapoptotic effect due to hypoxia was attenuated by use of the endonuclease APE-1 (E3330) inhibitor. The endonuclease E3330 APE-1 inhibitor allowed evaluating the effect of ROS generated by doxorubicin and CoCl2 on apoptosis.Results: Chemical hypoxia in combination with doxorubicin is an oxidative stressor in HT29 cells and induces a reduction in the apoptotic process in a time-dependent manner.Conclusion: Resistance to hypoxia and doxorubicin-mediated cell death could be controlled by a mechanism related to the activity of HIF-1α and the amount of reactive oxygen species generated.