Poster Presentation Advances in Neuroblastoma Research Congress 2016

New, highly selective MRP1 inhibitors show promising preclinical activity in neuroblastoma (#249)

Christine Gana , Denise Yu 1 , Jayne Murray 1 , Leanna Cheung 1 , Claudia Flemming 1 , Jamie Fletcher 1 , Murray Norris 1 , Michelle Haber 1
  1. Children's Cancer Institute, Lowy Cancer Research Centre, University of New South Wales, Sydney, NSW, Australia

We have previously shown that multidrug resistance protein 1 (MRP1) is highly prognostic of clinical outcome in neuroblastoma (1,2) and contributes to chemoresistance in a neuroblastoma mouse model (3). Although MRP1 inhibitors would have substantial clinical potential, allowing improved cancer control and reduction in the dose of chemotherapeutics used, there are no available agents that are both selective for MRP1 and suitable for in vivo use. Based on our previously identified MRP1 inhibitor Reversan (3), we have developed a series of highly promising new MRP1 inhibitors with a view to identifying a candidate molecule suitable for clinical use.

Methods: To determine in vitro activity and selectivity, cells overexpressing clinically relevant drug transporters (MRP1, P-glycoprotein or ABCG2) were treated with established drug substrates in combination with MRP1 inhibitors and viability assessed. Levels of the endogenous MRP1 substrate glutathione (GSH) were assessed by GSH recycling assay. In vivo activity was assessed in the Th-MYCN mouse neuroblastoma model in combination with the MRP1 substrate drug etoposide.

Results: Our inhibitors demonstrated unprecedented selectivity for MRP1 over P-glycoprotein and ABCG2, and sensitized neuroblastoma cell lines three-fold to the frontline cancer drugs etoposide and vincristine in vitro (P<0.001). The inhibitors showed very promising preclinical activity in the Th-MYCN mouse model, doubling median survival over etoposide alone (11 days to 21–23 days; P<0.001) without impacting on etoposide pharmacokinetics. Surprisingly, these inhibitors also strongly depleted intracellular GSH in an MRP1-dependent manner. This effect was synergistic with the GSH synthesis inhibitor buthionine sulfoximine.

Conclusion: The selectivity of our inhibitors for MRP1 over other clinically relevant drug transporters and their demonstrated preclinical activity is a major advance over previously developed compounds. MRP1-dependent depletion of GSH may provide an additional therapeutic window in MRP1 overexpressing tumours.

  1. Haber, M, et al (2006) Association of high-level MRP1 expression with poor clinical outcome in a large prospective study of primary neuroblastoma. J Clin Oncol 24, 1546-1553
  2. Norris, MD, et al (1996) Expression of the gene for multidrug-resistance-associated protein and outcome in patients with neuroblastoma. N Engl J Med 334, 231-238
  3. Burkhart, CA, et al (2009) Small-molecule multidrug resistance-associated protein 1 inhibitor reversan increases the therapeutic index of chemotherapy in mouse models of neuroblastoma. Cancer Res 69, 6573-6580