MSC-4381 (MCT4-IN-1) is an orally active and selective monocarboxylate transporter 4 (MCT4/SLC16A3) inhibitor with an IC 50 of 77 nM and a K i of 11 nM. MSC-4381 targets to the cytosolic domain of MCT4 . MSC-4381 results in lactate efflux inhibition and reduction of cellular viability in MCT4 high expressing cells. MSC-4381 has the potential for MCT4 transporter inhibition research In Vitro MSC-4381 (compound 18n) inhibits lactate efflux in the MDA-MB-231 cell line with an IC 50 of 1 nM. The on-target activity is confirmed with a K i of 11 nM by fluorescence cross-correlation spectroscopy (FCCS). ?\nMSC-4381 does not inhibit lactate efflux to a similar extent in SNU-398 and MiaPaca2, and only 600-fold less in RT-4 cell lines. MCE has not independently confirmed the accuracy of these methods. They are for reference only. In Vivo MSC-4381 (compound 18n; 30 mg/kg; PO; single dose) only combined with MCT1/2 inhibitor exhibits a significant tumoral intracellular lactate accumulation . ?\nMSC-4381 (30 mg/kg/day; for 15 days) shows no significant antitumor activity . ?\nMSC-4381 (0.2 mg/kg; iv) has a T 1/2 of 1 hours, a CL of 0.33 L/h?kg, a C max of 489 ng/mL and a V ss of 0.4 L/kg for mice . MCE has not independently confirmed the accuracy of these methods. They are for reference only. Animal Model: MC38 tumor-bearing C57/BL6 mice Dosage: 30 mg/kg Administration: PO; single dose Result: Only combined with MCT1/2 inhibitor exhibited a significant tumoral intracellular lactate accumulation. Animal Model: Mice Dosage: 0.2 mg/kg (Pharmacokinetic Analysis) Administration: IV Result: Had a T 1/2 of 1 hours, a CL of 0.33 L/h•kg, a C max of 489 ng/mL and a V ss of 0.4 L/kg for mice. Form:Solid IC50& Target:MCT4 77 nM (IC 50 ) MCT4 11 nM (Ki)