PGP and cancer: Overall, ribociclib decreases the resistance to colchicine and doxorubicin in KB-C2 cancer cells by 1) interacting with the P-gp protein and inhibiting the efflux function, thereby increasing the intracellular accumulation of these anticancer drugs and 2) decreasing the expression of the P-gp transporter, which decreases the number of transporters and thus, drug efflux.