Lipid excipients Peceol and Gelucire 44/14 decrease P-glycoprotein mediated efflux of rhodamine 123 partially due to modifying P-glycoprotein protein expression within Caco-2 cells

PURPOSE

The objective of this study was to determine the influence of two lipid excipients, Peceol(c) and Gelucire(c) 44/14 on P-glycoprotein (Pgp) activity and protein expression in human colon adenocarcinoma cells (Caco-2). Lipid excipients are increasingly used as drug delivery systems for hydrophobic drugs to increase their bioavailability by overcoming the barrier of low absorption. This study will probe a novel mechanism by which lipid excipients reduce Pgp-mediated efflux and thereby increase bioavailability of orally administered therapeutics.

METHODS

Non-cytotoxic concentrations of Peceol(c) and Gelucire(c) 44/14 were determined for 24-hour treatments of Caco-2 cells using integrity of the cell membranes and mitochondrial respiration as markers. Pgp activity after treatment with non-cytotoxic concentrations of Peceol(c) and Gelucire(c) 44/14 was measured with a fluorescent Pgp substrate, rhodamine 123 (Rh123). The activity of Pgp was ascertained by measuring accumulation and the directional flux of Rh123 using the Transwell(c) semi-permeable cell culture support system. To assess the effect of Peceol(c) and Gelucire(c) 44/14 on Pgp protein expression, Western blotting with a specific Pgp antibody was performed. RESULTS. The two assays for cytotoxicity were in agreement and showed that concentrations of less than 0.5% (v/v) Peceol(c) and less than 0.02% (w/v) Gelucire(c) 44/14 were not toxic to Caco-2 cells. Rh123 accumulation was increased up to 3-fold in cells treated with sub-toxic concentrations of the excipients. The flux of Rh123 across the cell monolayer was unaffected by treatment in the absorptive (apical to basolateral) direction but the efflux transport was reduced after treatment with Peceol(c), Gelucire(c) 44/14 or the positive control , 100microM verapamil. Some of the reduction in Pgp efflux activity can be explained by the reduction in protein expression after treatment with the lipid excipients; treatment with 0.25% (v/v) and 0.5% (v/v) Peceol(c) reduced Pgp protein levels to 62.4% and 68.4% of the control respectively while Gelucire(c) 44/14 treatments of 0.01% (w/v) and 0.02% (w/v) reduced Pgp to 64.5% and 51.8% respectively.

CONCLUSION

In this study we utilized established methodologies to assess the inhibitory effect of the excipients on the Pgp-mediated efflux of the probe, Rh123 and tested the hypothesis that long-term treatment of Caco-2 cells with the lipid excipients, Peceol(c) and Gelucire(c) 44/14, decreased Pgp protein expression. The results suggest a new mechanism which may contribute to the improved bioavailability seen for drugs formulated with lipid-based excipients.

Ultrasound-Induced hyperthermia increases cellular uptake and cytotoxicity of P-glycoprotein substrates in multi-drug resistant cells

PURPOSE

Localized hyperthermia has been shown previously to augment the cytotoxicity of some lipophilic anticancer drugs. Because many of the substrates for the multi-drug resistance (MDR) transporter P-glycoprotein (P-gp) are lipophilic in nature, studies were conducted to test the hypothesis that hyperthermia induced by ultrasound could also increase cellular uptake and cytotoxicity of P-gp substrates by P-gp-expressing cells.

METHODS

To test this hypothesis, we studied the effects of hyperthermia and ultrasound on cellular accumulation of putative P-gp substrates, rhodamine 123 (R123) and doxorubicin (DOX), and cytotoxicity of DOX in the parent and MDR variants of two human cancer cell lines.

RESULTS

Treatment of cells with hyperthermia or ultrasound (20 min at 41 degrees C) both caused a significant increase over controls (no ultrasound treatment) in R123 and DOX accumulation in the parent and MDR lines of MV522 and KB cells. Ultrasound also substantially increased the antiproliferative effects of DOX in both the parent and MDR variants of MV522 and KB cell lines when compared with controls. Our results also indicated that ultrasound exerted a much greater effect on cellular accumulation of R123 and DOX and cytotoxicity enhancement of DOX in the MDR variants than putative P-gp antagonist such as verapamil.

CONCLUSION

The present results point to the potential use of ultrasound-induced hyperthermia as a much safer alternative to P-gp antagonist for reversal of MDR.

Comparative in vitro evaluation of dequalinium B, a new boron carrier for neutron capture therapy (NCT)

A boronated derivative of dequalinium, a delocalized lipophilic cation (DLC), was synthesized as a potential boron carrier for the selective targeting of mitochondria in malignant versus benign cells for boron neutron capture therapy (BNCT), a binary modality for the treatment of cancer. This agent, designated DEQ-B, was taken up and retained in vitro in the KB, F98, and C6 tumor cell lines but not in the normal epithelial cell line CV1. DEQ-B was also less toxic in the latter cell line at lower exposure concentrations The uptake, retention, and toxicity profiles of DEQ-B are comparable to those of the non-boronated DLCs, dequalinium, MKT 077, RH 123, and tetraphenylphosphonium chloride. Our results suggest that the synthesis and further evaluation of boronated DLCs as potential delivery agents for BNCT is warranted.