Encequidar mesylate (HM30181; HM-30181A; Oraxol), the mesylate salt of encequidar, is a novel, highly specific, and orally bioavailable inhibitor of P-glycoprotein (P-gp), which is an adenosine triphosphate (ATP)-binding cassette (ABC) transporter. It was designed to improve the oral bioavailability of drugs that are P-gp substrates that can be pumped out of cells by P-gp, resulting in drug resistance. The combination of oral paclitaxel and encequidar is being developed for cancer treatment. Paclitaxel cannot be administered orally, because it is a substrate of the P-glycoprotein (P-gp), and the bioavailability of paclitaxel is improved when oral paclitaxel is administered with the highly specific, potent P-gp inhibitor encequidar. Oral paclitaxel and encequidar is the first world taxane to demonstrate superiority in radiologically confirmed tumor response rate, with reduced neuropathy and alopecia compared to IV paclitaxel in women with metastatic breast cancer. Encequidar was supported by FDA in March 2021 for the new drug application for combination with oral paclitaxel in the treatment of patients with metastatic breast cancer. Encequidar showed the highest potency (IC(50)=0.63nM) among several MDR1 inhibitors, including cycloporin A, XR9576, and GF120918, and effectively blocked transepithelial transport of paclitaxel in MDCK monolayers (IC(50)=35.4nM). Encequidar is currently under clinical trials.

*Note: Please select an appropriate solvent for the preparation of stock solution based on your experiment needs. For most products, DMSO can be used for preparing stock solutions (e.g. 5 mM, 10 mM, or 20 mM concentration); some products with high aqueous solubility may be dissolved in water directly. Solubility information is available at the above Solubility Data section. Once the stock solution is prepared, aliquot it to routine usage volumes and store at -20°C or -80°C. Avoid repeated freeze and thaw cycles.