Thieno[2,3-b]pyridines--a new class of multidrug resistance (MDR) modulators.

To identify new potent multidrug resistance modulators, we have synthesized a series of novel thieno[2,3-b]pyridines and furo[2,3-b]pyridines, and examined their structure-activity relationships. All synthesized compounds were tested to determine BCRP1, P-gp, and MRP1 inhibitor activity, and most potent MDR modulators were also screened for their toxicity, cytotoxicity and Ca(2+) channel antagonist activity. Among these compounds, thieno[2,3-b]pyridine (6r) was found to exhibit a potent P-gp inhibitory action with EC50 = 0.3 ± 0.2 μM, MRP1 inhibitory action with EC50 = 1.1 ± 0.1 μM and BCRP1 inhibitory action with EC50 = 0.2 ± 0.05 μM and may represent suitable candidate for further pharmacological studies.