P-glycoprotein as a chemotherapy resistance mechanism and biomarker of poor response in high-risk neuroblastoma

<h2>Abstract</h2><h3>Background</h3> Half of all children with high-risk neuroblastoma progress or relapse. We identified <i>ABCB1,</i> encoding for the ATP binding cassette transporter P-glycoprotein (P-gp), as a candidate drug resistance mechanism based on differential expression in survivors and non-survivors and investigated whether P-gp expression limits the effectiveness of chemotherapy. <h3>Methods</h3> P-gp/<i>ABCB1</i> expression and regulation were assessed in tumours, PDX models in NSG mice, and cell lines by RNA-sequencing, immunohistochemistry, western blotting and through publicly available ChIP-Seq and RNA-Seq data. Response to standard-of-care induction therapies and targeted agents was assessed <i>in vitro</i> and <i>in vivo</i> using cell line and PDX models with genetic and pharmacological P-gp inhibition. <h3>Results</h3> P-gp expression is common in high-risk neuroblastoma and elevated compared to other cancers. High relative expression at diagnosis is associated with poorer outcome, consistent with drug efflux. Pharmacological or genetic targeting of P-gp partially restores sensitivity of neuroblastoma cells to vincristine, doxorubicin, etoposide, and some targeted agents, but not to the ALK inhibitors crizotinib, ceritinib, alectinib and lorlatinib and sensitizes neuroblastoma xenografts to vincristine, extending survival. <h3>Conclusions</h3> P-gp is a clinically relevant drug resistance mechanism for high-risk neuroblastoma. Tumour P-gp levels could inform treatment options for individual patients to avoid ineffective treatments and unnecessary toxicities.