Distinct groups of multidrug resistance modulating agents are distinguished by competition of P-glycoprotein-specific antibodies

PK11195, a peripheral benzodiazepine receptor (pBR) ligand, broadly blocks drug efflux to chemosensitize leukemia and myeloma cells by a pBR-independent, direct transporter-modulating mechanism

“…46 Consistent with these reports, VPL and CSA increased UIC2 immunoreactivity in Pgp-expressing cells (data not shown). PK11195 also increased UIC2 binding in KG1a and DOX40 cells (both P Ͻ .05) and tended to increase UIC2 immunostaining in VCR and DOX6 cells (P ϭ .07, P ϭ .09, respectively) but did not change UIC2 immunostaining in Pgp-negative HL60 or 8226 cells ( Figure 7D).…”

“…Therefore, we prepared PMs from DOX40 cells to further characterize PK11195 binding in Pgp-expressing cells and documented that PM fractions contained Pgp but were depleted of mitochondrial inner and outer mitochondrial membrane markers ( Figure 6A). DOX40 PM fractions showed specific 3 H-CSA binding, consistent with documented Pgp binding by CSA, 31,32,[43][44][45][46][47][48][49][50][51] and specific 3 H-PK11195 binding was also reproducibly measured in DOX40 PMs. Specific PK11195 binding that was measured in 8226 PM assays (data not shown) suggests that pBR can be PM-localized, consistent with other reports.…”

“…CSA and many other efflux modulators bind transporters directly. 31,32,[43][44][45][46][47][48][49][50][51] First, we asked whether PK11195 binds Pgp, first by comparing PK11195 binding in 9 primary AML samples for which additional aliquots were available. CSA and PK11195 had increased dye retention in 5 of these samples (Pgp-positive AMLs), whereas 4 samples showed no efflux capacity (Pgp-negative AMLs).…”

Raft and cytoskeleton associations of an ABC transporter: P‐glycoprotein

“…Drug transport activity of Pgp was measured applying calcein accumulation assay as described in (31,32 …”

“…To elucidate whether cholesterol depletion and the consequent disruption of cholesterol-rich membrane microdomains affect Pgp function, we measured calcein accumulation (31,32) in mdr1-transfected and non-transfected NIH 3T3 cells. As shown in Figure 1, pretreatment of cells with 5 mM MBCD, which was expected to de- Ϫ parental cells, similarly to cyclosporine A applied at a concentration that completely inhibited the pump (FL1 ϭ 994 Ϯ 37).…”