To confirm that MDR1 was the primary effector of compound 3 or 8, mutant strains deficient in efflux pumps,including DSY488 (cdrlΔ/Δ), DSY653 (cdr2Δ/Δ), DSY465 (mdrlΔ/Δ), and DSY659 (cdrlΔ/Δ, cdr2Δ/Δ), were examined for susceptibility to the combination treatment of FLC and compound 3 or 8.