Interaction of new sulfaphenazole derivatives with human liver cytochrome p450 2Cs: structural determinants required for selective recognition by CYP 2C9 and for inhibition of human CYP 2Cs.

A series of new derivatives of sulfaphenazole (SPA), in which the NH(2) and phenyl substituents of SPA are replaced by various groups or in which the sulfonamide function of SPA is N-alkylated, were synthesized in order to further explore CYP 2C9 active site and to determine the structural factors explaining the selectivity of SPA for CYP 2C9 within the human P450 2C subfamily. Compounds in which the NH(2) group of SPA was replaced with R(1) = CH(3), Br, CH = CH(2), CH(2)CH = CH(2), and CH(2)CH(2)OH exhibited a high affinity for CYP 2C9, as shown by the dissociation constant of their CYP 2C9 complexes, K(s), which was determined by difference visible spectroscopy (K(s) between 0.1 and 0.4 microM) and their constant of CYP 2C9 inhibition (K(i) between 0.3 and 0.6 microM). This indicates that the CYP 2C9-iron(III)-NH(2)R bond previously described to exist in the CYP 2C9-SPA complex does not play a key role in the high affinity of SPA for CYP 2C9. Compounds in which the phenyl group of SPA was replaced with various aryl or alkyl R(2) substituents only exhibited a high affinity for CYP 2C9 if R(2) is a freely rotating and sufficiently electron-rich aryl substituent. Finally, compounds resulting from a N-alkylation of the SPA sulfonamide function (R(3) = CH(3), C(2)H(5), or C(3)H(7)) did not retain the selective inhibitory properties of SPA toward CYP 2C9. However, they are reasonably good inhibitors of CYP 2C8 and CYP 2C18 (IC(50) approximately 20 microM). These data allow one to better understand the structural factors that are important for selective binding in the CYP 2C9 active site. They also provide us with clues towards new selective inhibitors of CYP 2C8 and CYP 2C18.

Synthesis of sulfaphenazole derivatives and their use as inhibitors and tools for comparing the active sites of human liver cytochromes P450 of the 2C subfamily.

Twenty-three new derivatives of sulfaphenazole (SPA) were synthesized to further explore the topology of the active sites of human liver cytochromes P450 of the 2C subfamily and to find new selective inhibitors of these cytochromes. These compounds are derived from SPA by replacement of the NH(2) and H (of the SO(2)NH function) substituents of SPA with various R(1) and R(2) groups, respectively. Their inhibitory effects were studied on recombinant CYP 2C8, 2C9, 2C18, and 2C19 expressed in yeast. High affinities for CYP 2C9 (IC(50) < 1 microM) were only observed for SPA derivatives having the SO(2)NH function and a relatively small R(1) substituent (R(1) = NH(2), CH(3)). Any increase in the size of R(1) led to a moderate decrease of the affinity, and the N-alkylation of the SO(2)NH function of SPA to a greater decrease of this affinity. The same structural changes led to opposite effects on molecular recognition by CYP 2C8 and 2C18, which generally exhibited similar behaviors. Thus, contrary to CYP 2C9, CYP 2C8 and 2C18 generally prefer neutral compounds with relatively large R(1) and R(2) substituents. CYP 2C19 showed an even lower affinity for anionic compounds than CYP 2C8 and 2C18. However, as CYP 2C8 and 2C18, CYP 2C19 showed a much better affinity for neutral compounds derived from N-alkylation of SPA and for anionic compounds bearing a larger R(1) substituent. One of the new compounds (R(1) = methyl, R(2) = propyl) inhibited all human CYP 2Cs with IC(50) values between 10 and 20 microM, while another one (R(1) = allyl, R(2) = methyl) inhibited all CYP 2Cs except CYP 2C9, and a third one (R(1) = R(2) = methyl) inhibited all CYP 2Cs except CYP 2C8. Only 2 compounds of the 25 tested derivatives were highly selective toward one human CYP 2C; these are SPA and compound 1 (R(1) = CH(3), R(2) = H), which acted as selective CYP 2C9 inhibitors. However, some SPA derivatives selectively inhibited CYP 2C8 and 2C18. Since CYP 2C18 is hardly detectable in human liver, these derivatives could be interesting molecules to selectively inhibit CYP 2C8 in human liver microsomes. Thus, compound 11 (R(1) = NH(2), R(2) = (CH(2))(2)CH(CH(3))(2)) appears to be particularly interesting for that purpose as its IC(50) value for CYP 2C8 is low (3 microM) and 20-fold smaller than those found for CYP 2C9 and 2C19.