Structure–Activity Relationships of Chromone Derivatives toward the Mechanism of Interaction with and Inhibition of Breast Cancer Resistance Protein ABCG2

Abstract

We recently identified a chromone derivative, 5-(4-bromobenzyloxy)-2-(2-(5-methoxyindolyl)ethyl-1-carbonyl)-4H-chromen-4-one, named here as chromone 1, as a potent, selective, nontoxic, and nontransported inhibitor of ABCG2-mediated drug efflux (Valdameri et al. J. Med. Chem. 2012, 55, 966). We have now synthesized a series of 14 derivatives to study the structure-activity relationships controlling both drug efflux and ATPase activity of ABCG2 and to elucidate their molecular mechanism of interaction and inhibition. It was found that the 4-bromobenzyloxy substituent at position 5 and the methoxyindole are important for both inhibition of mitoxantrone efflux and inhibition of basal ATPase activity. Quite interestingly, methylation of the central amide nitrogen strongly altered the high affinity for ABCG2 and the complete inhibition of mitoxantrone efflux and coupled ATPase activity. These results allowed the identification of a critical central inhibitory moiety of chromones that has never been investigated previously in any series of inhibitors.

New, highly potent and non-toxic, chromone inhibitors of the human breast cancer resistance protein ABCG2

“…Indeed, the dealkylation or the suppression of the alkyloxy group led to a sharp decrease of activity in 5a (4.35 mM) and 5e (1.05 mM) as compared to MBL-II-141. This is consistent with previous observation that a methoxy group was important at either position C-5 or C-6 [22].…”

“…A shown in Table 1, we noticed a slight decrease in potency for the 8b derivative bearing a leucine residue, while a valine residue in 8a had no effect. Finally, mono methylation at one of the two nitrogen atoms or dimethylation of MBL-II-141 altered the inhibitory activity (results not shown here, in agreement with previous observations on other derivatives [22]). Cell cytotoxicity assays were performed on control, untransfected, HEK293 cells.…”

“…When ABCG2-transfected HEK293 cells were used (not shown here), the same cytotoxicity values as in control cells were observed for all compounds, suggesting that none of these chromone derivatives was transported by ABCG2. This confirms the lack of transport previously reported for MBL-II-141 [19] and other derivatives [22].…”

“…Pursuing our efforts to develop effective modulators of ABC proteins, we recently reported that a chromone-derived compound, namely MBL-II-141 ( Fig. 1) was an excellent in vivo ABCG2 inhibitor, based on its potency, high selectivity, lack of transport and very low toxicity [19,22].…”

The linker region of breast cancer resistance protein ABCG2 is critical for coupling of ATP-dependent drug transport

“…The first type concerned the ATPase activity, for which a decrease in both Vmax and Km for ATP hydrolysis was observed; this suggested a role of the C2-sequence in either ATP binding or in ADP release, which is known to be often a rate-limiting step of ATP hydrolysis for various ATPases. In addition, the complete abolition of drug-induced stimulated ATP hydrolysis, recognized as coupling ATPase activity, was consistent with the strong catalytic impairment observed upon C-motif point-mutations in various ABC transporters, such as the second glycine in either only P-glycoprotein NBD1 [13] or both MRP1 NBD1 and NBD2 [15], the two serines in both P-glycoprotein NBD1 and NBD2 [14], and either 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 primary, alteration of coupled ATP hydrolysis, the alterations observed on drug efflux might be considered as consequences, or secondary effects, rather than a direct contribution of mutated residues; ii) the strong alteration of the potent, selective, and noncompetitive Ko143 and chromone 1 inhibitors [34], known to inhibit basal …”