Di-2-pyridylketone 4,4-Dimethyl-3-thiosemicarbazone (Dp44mT) Overcomes Multidrug-Resistance by a Novel Mechanism Involving the Hijacking of Lysosomal P-Glycoprotein (Pgp). [Cell Biology]

February 26th, 2015 by Jansson, P. J., Yamagishi, T., Arvind, A., Seebacher, N., Gutierrez, E., Stacy, A., Maleki, S., Sharp, D., Sahni, S., Richardson, D. R.

Multidrug-resistance (MDR) is a major obstacle in cancer treatment. More than half of human cancers express multidrug-resistant (MDR) P-glycoprotein (Pgp), which correlates with a poor prognosis. Intriguingly, through an unknown mechanism, some drugs have greater activity in drug-resistant tumor cells than their drug-sensitive counterparts. Herein, we investigate how the novel anti-tumor agent, di-2-pyridylketone 4,4-dimethyl-3-thiosemicarbazone (Dp44mT), overcomes MDR. Four different cell-types were utilized to evaluate the effect of Pgp-potentiated lysosomal targeting of drugs to overcome MDR. To assess the mechanism of how Dp44mT overcomes drug resistance, cellular studies utilized: Pgp inhibitors, Pgp-silencing, lysosomotropic agents, proliferation assays, immunoblotting, a Pgp-ATPase activity assay, radio-labeled drug uptake/efflux, a Rh123-retention assay, lysosomal-membrane permeability assessment and DCF redox studies. Anti-tumor activity and selectivity of Dp44mT in Pgp-expressing, MDR cells versus drug-sensitive cells were studied using a BALB/c nu/nu xenograft mouse model. We demonstrate that Dp44mT is transported by the lysosomal Pgp drug pump, causing lysosomal-targeting of Dp44mT and resulting in enhanced cytotoxicity in MDR cells. Lysosomal Pgp and pH were shown to be crucial for increasing Dp44mT-mediated lysosomal damage and subsequent cytotoxicity in drug-resistant cells, with Dp44mT being demonstrated to be a Pgp substrate. Indeed, Pgp-dependent lysosomal damage and cytotoxicity of Dp44mT were abrogated by Pgp inhibitors, Pgp-silencing, or by increasing lysosomal pH using lysosomotropic bases. In vivo, Dp44mT potently targeted chemotherapeutic resistant human Pgp-expressing xenografted tumors relative to non-Pgp-expressing tumors in mice. This study highlights a novel Pgp-hijacking strategy of the unique DpT series of thiosemicarbazones that overcome MDR via utilization of lysosomal-Pgp transport activity.
  • Posted in Journal of Biological Chemistry, Publications
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