Evaluation of the Near Infrared Compound Indocyanine Green as a Probe Substrate of P‑Glycoprotein

The efflux transporter P-glycoprotein (P-gp) affects the pharmacokinetics of many drugs. Currently used methods for characterization of P-gp’s functional activity <i>in vivo</i> involve the use of radiolabeled substrates, are costly, and are technically demanding. Our objective was to evaluate whether the FDA-approved near-infrared compound indocyanine green (ICG) can be used as a probe substrate of P-gp. We also characterized the interaction of ICG with another efflux transporter, the breast cancer resistance protein (BCRP). We evaluated ICG accumulation and transport in MDCK cells overexpressing P-gp or BCRP (MDCK-MDR1 and MDCK-BCRP, respectively) compared to control MDCK cells, in the presence or the absence of transporter inhibitors. <i>In vivo</i> imaging of ICG biodistribution in mice was conducted over 3.5 h using valspodar as the P-gp inhibitor. The EC₅₀ values for ICG accumulation in control MDCK and MDCK-MDR1 cells were 9.0 × 10^–6 ± 5.7 × 10^–7 M and 1.5 × 10^–5 ± 1.1 × 10^–6 M, respectively. The efflux ratio for ICG in MDCK-MDR1 cells was 6.8-fold greater than in control cells. P-gp inhibition attenuated ICG efflux from MDR1-MDCK cells, and their effects in those cells were greater than in control MDCK cells. In contrast, BCRP level of expression or pharmacological inhibition did not significantly affect ICG cellular accumulation. <i>In vivo</i> imaging indicated enhanced cerebral ICG distribution with valspodar (brain – foot area under the concentration–time curves of 3.0 × 10¹⁰, 5.6 × 10¹⁰ and 3.7 × 10¹⁰ h·[p/s/sr]/μW in valspodar-treated mice vs 9.0 × 10⁹ and 5.3 × 10⁹ h·[p/s/sr]/μW in controls). The findings from this pilot study suggest that near-infrared imaging using ICG as the probe substrate should be further characterized as a methodology for <i>in vivo</i> evaluation of P-gp activity

DataSheet1_Metabolomic profiling of triple negative breast cancer cells suggests that valproic acid can enhance the anticancer effect of cisplatin.docx

Cisplatin is an effective chemotherapeutic agent for treating triple negative breast cancer (TNBC). Nevertheless, cisplatin-resistance might develop during the course of treatment, allegedly by metabolic reprograming, which might influence epigenetic regulation. We hypothesized that the histone deacetylase inhibitor (HDACi) valproic acid (VPA) can counter the cisplatin-induced metabolic changes leading to its resistance. We performed targeted metabolomic and real time PCR analyses on MDA-MB-231 TNBC cells treated with cisplatin, VPA or their combination. 22 (88%) out of the 25 metabolites most significantly modified by the treatments, were acylcarnitines (AC) and three (12%) were phosphatidylcholines (PCs). The most discernible effects were up-modulation of AC by cisplatin and, contrarily, their down-modulation by VPA, which was partial in the VPA-cisplatin combination. Furthermore, the VPA-cisplatin combination increased PCs, sphingomyelins (SM) and hexose levels, as compared to the other treatments. These changes predicted modulation of different metabolic pathways, notably fatty acid degradation, by VPA. Lastly, we also show that the VPA-cisplatin combination increased mRNA levels of the fatty acid oxidation (FAO) promoting enzymes acyl-CoA synthetase long chain family member 1 (ACSL1) and decreased mRNA levels of fatty acid synthase (FASN), which is the rate limiting enzyme of long-chain fatty acid synthesis. In conclusion, VPA supplementation altered lipid metabolism, especially fatty acid oxidation and lipid synthesis, in cisplatin-treated MDA-MB-231 TNBC cells. This metabolic reprogramming might reduce cisplatin resistance. This finding may lead to the discovery of new therapeutic targets, which might reduce side effects and counter drug tolerance in TNBC patients.</p