Predictive and Prognostic Relevance of ABC Transporters for Resistance to Anthracycline Derivatives

Anthracyclines have been clinically well established in cancer chemotherapy for decades. The main limitations of this drug class are the development of resistance and severe side effects. In the present investigation, we analyzed 30 anthracyclines in a panel of 59 cell lines of the National Cancer Institute, USA. The log₁₀IC₅₀ values varied from -10.49 M (3'-deamino-3'-(4″-(3″-cyano)morpholinyl)-doxorubicin, <b>1</b>) to -4.93 M (<i>N</i>,<i>N</i>-dibenzyldaunorubicin hydrochloride, <b>30</b>). Multidrug-resistant NCI-ADR-Res ovarian cancer cells revealed a high degree of resistance to established anthracyclines (between 18-fold to idarubicin (<b>4</b>) and 166-fold to doxorubicin (<b>13</b>) compared to parental, drug-sensitive OVCAR8 cells). The resistant cells displayed only low degrees of resistance (1- to 5-fold) to four other anthracyclines (<b>7</b>, <b>18</b>, <b>28</b>, <b>30</b>) and were even hypersensitive (collaterally sensitive) to two compounds (<b>1</b>, <b>26</b>). Live cell time-lapse microscopy proved the cross-resistance of the three chosen anthracyclines (<b>4</b>, <b>7</b>, <b>9</b>) on sensitive CCRF/CEM and multidrug-resistant CEM/ADR5000 cells. Structure-activity relationships showed that the presence of tertiary amino functions is helpful in avoiding resistance, while primary amines rather increased resistance development. An α-aminonitrile function as in compound <b>1</b> was favorable. Investigating the mRNA expression of 49 ATP-binding cassette (ABC) transporter genes showed that <i>ABCB1/MDR1</i> encoding P-glycoprotein was the most important one for acquired and inherent resistance to anthracyclines. Molecular docking demonstrated that all anthracyclines bound to the same binding domain at the inner efflux channel side of P-glycoprotein with high binding affinities. Kaplan-Meier statistics of RNA sequencing data of more than 8000 tumor biopsies of TCGA database revealed that out of 23 tumor entities high <i>ABCB1</i> expression was significantly correlated with worse survival times for acute myeloid leukemia, multiple myeloma, and hepatocellular carcinoma patients. This indicates that <i>ABCB1</i> may serve as a prognostic marker in anthracycline-based chemotherapy regimens in these tumor types and a target for the development of novel anthracycline derivatives.