Small-Molecule Multidrug Resistance–Associated Protein 1 Inhibitor Reversan Increases the Therapeutic Index of Chemotherapy in Mouse Models of Neuroblastoma

Abstract

The multidrug resistance-associated protein 1 (MRP1) has been closely linked to poor treatment response in several cancers, most notably neuroblastoma. Homozygous deletion of the MRP1 gene in primary murine neuroblastoma tumors resulted in increased sensitivity to MRP1 substrate drugs (vincristine, etoposide, and doxorubicin) compared with tumors containing both copies of wild-type MRP1, indicating that MRP1 plays a significant role in the drug resistance in this tumor type and defining this multidrug transporter as a target for pharmacologic suppression. A cell-based readout system was created to functionally determine intracellular accumulation of MRP1 substrates using a p53-responsive reporter as an indicator of drug-induced DNA damage. Screening of small-molecule libraries in this readout system revealed pyrazolopyrimidines as a prominent structural class of potent MRP1 inhibitors. Reversan, the lead compound of this class, increased the efficacy of both vincristine and etoposide in murine models of neuroblastoma (syngeneic and human xenografts). As opposed to the majority of inhibitors of multidrug transporters, Reversan was not toxic by itself nor did it increase the toxicity of chemotherapeutic drug exposure in mice. Therefore, Reversan represents a new class of nontoxic MRP1 inhibitor, which may be clinically useful for the treatment of neuroblastoma and other MRP1-overexpressing drug-refractory tumors by increasing their sensitivity to conventional chemotherapy. [Cancer Res 2009;69(16):6573-80]

Increased Expression of P-Glycoprotein Is Associated with Doxorubicin Chemoresistance in the Metastatic 4T1 Breast Cancer Model

“…At 1 day after 4T1 cell injection, the mice were injected with 100 L of the chemotherapy drug by intraperitoneal injection, as described previously. 23 For each model, chemotherapy treatment of BALB/c mice was randomized into five groups of five mice each. The control group was injected with 0.9% saline.…”

Exposure of neuroblastoma cell lines to imatinib results in the upregulation of the CDK inhibitor p27KIP1 as a consequence of c-Abl inhibition

“…However, when evaluating this possibility the following points should be considered. First, imatinib is not a substrate for MRP1 [46] which in clinical settings [45] and in animal models [47] has been demonstrated to be a key factor for multidrug resistance in neuroblastoma. Second, although imatinib is a substrate of MDR1, the reported IC 50 of imatinib for MDR1 (3-8 mM) [48] is 1-2 log greater than the IC 50 of imatinib for its high affinity targets.…”

Small Molecule Drugs and Targeted Therapies for Neuroblastoma

“…This cross yielded murine neuroblastoma tumours that were either wild-type (MRP1 +/+ ) or homozygous null (MRP1 −/− ) for MRP1. Tumour cells of either MRP1 genotype were isolated and xenografted into nude mice and these mice were treated with clinically used drugs and monitored for tumour growth (Burkhart, Watt et al, 2009). Results showed that loss of MRP1 significantly increased the latency of tumour progression in response to vincristine and etoposide, both of which are known MRP1 substrates.…”