The Effect of Breast Cancer Resistance Protein, Multidrug Resistant Protein 1, and Organic Anion-Transporting Polypeptide 1B3 on the Antitumor Efficacy of the Lipophilic Camptothecin 7-t-Butyldimethylsilyl-10-Hydroxycamptothecin (AR-67) In Vitro

Abstract

AR-67 (7-t-butyldimethylsilyl-10-hydroxycamptothecin) is a lipophilic camptothecin analog, currently under early stage clinical trials. Transporters are known to have an impact on the disposition of camptothecins and on the response to chemotherapeutics in general due to their expression in tumor tissues. Therefore, we investigated the interplay between the breast cancer resistance protein (BCRP), multidrug resistant protein 1 (MDR1), and organic anion-transporting polypeptide (OATP) 1B1/1B3 transporters and AR-67 and their impact on the toxicity profile of AR-67. Using cell lines expressing the aforementioned transporters, we showed that the lipophilic AR-67 lactone form is a substrate for efflux transporters BCRP and MDR1. Additionally, OATP1B1 and OATP1B3 facilitated the uptake of AR-67 carboxylate in SLCO1B1-and SLCO1B3-transfected cell systems compared with the mocktransfected ones. Notably, both BCRP and MDR1 conferred resistance to AR-67 lactone. Prompted by recent studies showing increased OATP1B3 expression in certain cancer types, we investigated the effect of OATP1B3 expression on cell viability after exposure to AR-67 carboxylate. OATP1B3-expressing cells had increased carboxylate uptake as compared with mock-transfected cells but were not sensitized because the intracellular amount of lactone was 50-fold higher than that of carboxylate and comparable between OATP1B3-expressing and OATP1B3-nonexpressing cells.In conclusion, BCRP-and MDR1-mediated efflux of AR-67 lactone confers resistance to AR-67, but OATP1B3-mediated uptake of the AR-67 carboxylate does not sensitize OATP1B3-expressing tumor cells.

Selectivity and Potency of Microcystin Congeners against OATP1B1 and OATP1B3 Expressing Cancer Cells

“…Thus HeLa and RKO cell lines were obtained from ATCC and transfected with expression vectors for OATP1B1 and OATP1B3. Individual clones were isolated by a limiting dilution, and isolated clones showing high levels of expression by PCR were further characterized as previously described [72] , [93] . Individual HeLa and RKO clones were selected for further study by demonstration of increased uptake [ 3 H]-BQ123, a substrate for both transporters.…”

“…After 24 hours, medium containing MC structural variants was added to the cells. After another 3 days, cell survival was determined with a sulforhodamine-based assay as we have previously described [93] – [95] . As the dose response curves for the apoptosis causing microcystins are steep and go down to 0 within 72 hours, the sulforhodamine assay is indicative of cell death [72] , [93] .…”

Synthesis, Biological Activity and Preliminary in Silico ADMET Screening of Polyamine Conjugates with Bicyclic Systems

“…The viability of the treated cells was normalized to the viability of the untreated (control) cells, and cell viability fractions were plotted versus drug concentrations in the logarithmic scale. IC 50 values were reported as mean values [ 47 , 48 ]. All experiments were performed in triplicates.…”

Silicon‐containing analogs of camptothecin as anticancer agents

“…The lactone form of compound 7j was a substrate for transporters BCRP and MDR1. The transporters OATP1B1 and OATP1B3 were mediators of the uptake of carboxylate form compound 7j in SLCO1B1‐ and SLCO1B3‐transfected cell systems …”