Drug resistance takes many forms with P-gp-mediated efflux of chemotherapeutic drugs being one of the most common. Anthracyclines contain a sugar moiety important in the drug’s efficacy. These sugar moieties alter pharmacokinetic profiles, target specificity, and drug resistance. Through modification of the sugar moiety we propose to overcome P-gp-related drug resistance and determine if alternative drug resistance forms exist. We created daunorubicin derivatives with sugar structure alterations. Changing the amino group to an azido group or conversion of a monosaccharide to a disaccharide made P-gp binding less favorable. Modification changes the compound's specificity during DNA interchelation which changes microRNA expression. We identified two new analogs (ADNR, ADNR3) which avert P-gp binding and overcome resistance. These studies provide an understanding of the critical sugar moiety elements of anthracyclines, and provide a starting point for more effective drug design.
To study other mechanisms of resistance in leukemia, doxorubicin, daunorubicin, ADNR, and ADNR3 were used to induce microRNA associated drug resistance. We found that 5-15 microRNAs were up-regulated by at least 1.5-fold, and 2-122 microRNAs were down-regulated by 2 to 4852-fold in the resistant cells by doxorubicin, daunorubicin, ADNR, and ADNR3. miR-221 and miR-222 were down-regulated by 2 to 15-fold in all four resistant cells. miR-221 and miR-222 in these drug-resistant cells up-regulate 4 to 8-fold expression of Kit, a receptor tyrosine kinase for cell survival. Transfection of miR-221 and miR-222 into drug-resistant cells regained drug sensitivity indicating that down-regulation of miR-221 and miR-222 and subsequent up-regulation of Kit provides a novel mechanism for drug resistance in leukemia.
miR-26a was down-regulated by 1.49 to 3.60-fold in doxorubicin and daunorubicin resistant K562 cells. miR-26a in the two cell lines up-regulate the expression of cdk6 by 3.65 and 4.42-fold. The miR-26a/cdk6 regulation mechanism was confirmed through transfection of miR-26a into resistant cells where cdk6 expression was knocked out, and drug sensitivity restored. DOX and DNR IC50 values decreased by 11.01-fold and 12.97-fold, respectively, indicating that down-regulation of miR-26a and subsequent up-regulation of cdk6 provides a novel mechanism for drug resistance. miR-26a regulation of cdk6 allows for research into cell cycle regulation by microRNA.
Anthracycline treatment up-regulates microRNA, including miR-21 which was up-regulated by 2.51 to 6.51-fold in the resistant cells. miR-21 is important due to its regulation PTEN, a tumor suppressor. Up-regulation led to no PTEN expression in the resistant cells. AntimiR-21 transfection reduced miR-21 levels which unblocked PTEN translation. The IC50 values of doxorubicin, daunorubicin, ADNR, and ADNR3 were reduced by 2.81 to 13.12-fold in the resistant cell lines after antimir-21 transfection. This use of antimir therapy will increase PTEN levels and reverse drug resistance in vitro.
K562 cell treatment with anthracyclines leads to specific microRNA expression profiles. The down-regulation of microRNA, including miR-221, miR-222, and miR-26a, leads to an increase in drug resistance. MicroRNA up-regulation also increases drug resistance through the miR-21/PTEN regulation pathway. Understanding the structural effects of chemical biological modification of anthracyclines on microRNA expression can lead to better drug development and patient treatment through reduced drug resistance in leukemia.