Validation of thiosemicarbazone compounds as P-glycoprotein inhibitors in human primary brain-blood barrier and glioblastoma stem cells

P-glycoprotein (Pgp) is highly expressed on blood-brain barrier (BBB) cells and glioblastoma (GB) cells, in particular on cancer stem cells (SC). Pgp recognizes a broad spectrum of substrates, limiting the therapeutic efficacy of several chemotherapeutic drugs in eradicating GB SC. Finding effective and safe inhibitors of Pgp that improve drug delivery across BBB and target GB SC is open to investigations. We previously identified a series of thiosemicarbazone compounds that inhibit Pgp with an EC50 in the nanomolar range and herein we investigate the efficacy of three of them in bypassing the Pgp-mediated drug efflux in primary human BBB and GB cells. At 10 nM concentration the compounds were not cytotoxic for brain microvascular endothelial hCMEC/D3 cell line, but they markedly enhanced the permeability of the Pgp-substrate doxorubicin through BBB. Thiosemicarbazone derivatives increased doxorubicin uptake in GB, with greater effects in the Pgp-rich SC clones than in the differentiated clones derived fr...