Abstract A35: P-Glycoprotein is a resistance mechanism for conventional induction chemotherapy but not ALK inhibitors in high-risk neuroblastoma
Authors: Atkinson Caroline , Tactacan Carole , Kamili Alvin , Saletta Federica , Gana Christine , Eden Georgina , Mayoh Chelsea , Lock Richard , Norris Murray , Haber Michelle , Gifford Andrew , Trahair Toby , Fletcher Jamie 
Published: August 2020

Abstract
Background: Despite intensive treatment, patients with high-risk neuroblastoma (HR-NB) have a five-year survival rate of only 50%, largely due to intrinsic or acquired drug resistance. The multidrug transporter P-glycoprotein (P-gp; ABCB1) effluxes conventional agents used in HR-NB induction therapy, including vincristine, etoposide, and doxorubicin, and has been reported as a resistance mechanism to the ALK inhibitors crizotinib and ceritinib. We assessed the prevalence of P-gp expression and its role in resistance to standard-of-care chemotherapies and molecularly targeted therapies.
Methods and Results: Analysis of ABCB1 levels in large patient tumor datasets demonstrates that high expression is more common in neuroblastoma than in other cancers and may be attributable to the sympathoadrenal lineage of the disease. Moreover, high relative expression of ABCB1 in HR-NB tumors is associated with poorer outcome, consistent with its multidrug transporter function. Frequent high ABCB1/P-gp expression in HR-NB was confirmed using RNA-sequencing, immunohistochemistry, and Western blot on panels of neuroblastoma tumor samples, patient-derived xenograft models, and cell lines. We demonstrated that the P-gp inhibitor tariquidar and P-gp knockdown (shRNA) both strongly sensitize high P-gp expressing neuroblastoma cells to vincristine, doxorubicin, and etoposide but not to ALK inhibitors or to relapse therapy regimens. Further, P-gp knockdown sensitized human neuroblastoma xenografts to vincristine, substantially extending animal survival. We have generated ABCB1-null HR-NB cell lines by CRISPR/Cas9 gene editing to further assess the role of P-gp in HR-NB drug resistance, have established flow-based assays to measure P-gp activity in tumor samples, and are investigating the benefits of tariquidar as adjuncts to conventional chemotherapy in PDX models.
Conclusions: Elevated P-gp expression is common in HR-NB. In laboratory models, P-gp can confer resistance to standard-of-care chemotherapies but not to ALK inhibitors. Our findings suggest that tumor P-gp activity might be used to guide treatment options for individual patients in order to avoid ineffective treatments. The potential of P-gp inhibitors as adjuncts to conventional chemotherapy for HR-NB should be further investigated.
Citation Format: Caroline Atkinson, Carole Tactacan, Alvin Kamili, Federica Saletta, Christine Gana, Georgina Eden, Chelsea Mayoh, Richard Lock, Murray Norris, Michelle Haber, Andrew Gifford, Toby Trahair, Jamie Fletcher. P-Glycoprotein is a resistance mechanism for conventional induction chemotherapy but not ALK inhibitors in high-risk neuroblastoma [abstract]. In: Proceedings of the AACR Special Conference on the Advances in Pediatric Cancer Research; 2019 Sep 17-20; Montreal, QC, Canada. Philadelphia (PA): AACR; Cancer Res 2020;80(14 Suppl):Abstract nr A35.