PGP and colorectal carcinoma: Therefore, to prove the synergistic effect on the MDR reversal activity due to dual P-gp/CA XII inhibition, the selected compounds were evaluated by the Rhd 123 uptake test, on human colorectal carcinoma LoVo/DOX cells, which overexpress both P-gp and CA XII, as confirmed by the RT-PCR analysis performed on both resistant and parental cell lines (LoVo/DOX, LoVo).