– ABCB1-IN-3 (Compound K27) is an orally active ABCB1 inhibitor that induces apoptosis. It binds directly to ABCB1, inhibiting its efflux function and maintaining stable intracellular paclitaxel (PTX) concentrations without affecting the normal expression of ABCB1. In vitro, ABCB1-IN-3 significantly increases ABCB1-mediated multidrug resistance (MDR) sensitivity to PTX, leading to cell cycle arrest and inhibition of cell proliferation. When combined with PTX, ABCB1-IN-3 demonstrates strong antitumor effects in vivo without causing toxicity.