Bioisosteres of Indomethacin as Inhibitors of Aldo-Keto Reductase 1C3

Abstract

Aldo-keto reductase 1C3 (AKR1C3) is an attractive target in drug design for its role in resistance to anticancer therapy. Several nonsteroidal anti-inflammatory drugs such as indomethacin are known to inhibit AKR1C3 in a nonselective manner because of COX-off target effects. Here we designed two indomethacin analogues by proposing a bioisosteric connection between the indomethacin carboxylic acid function and either hydroxyfurazan or hydroxy triazole rings. Both compounds were found to target AKR1C3 in a selective manner. In particular, hydroxyfurazan derivative is highly selective for AKR1C3 over the 1C2 isoform (up to 90-times more) and inactive on COX enzymes. High-resolution crystal structure of its complex with AKR1C3 shed light onto the binding mode of the new inhibitors. In cell-based assays (on colorectal and prostate cancer cells), the two indomethacin analogues showed higher potency than indomethacin. Therefore, these two AKR1C3 inhibitors can be used to provide further insight into the role of AKR1C3 in cancer.

Figure 1

Chemical structures of AKR1C3 inhibitors: FLU, hydroxytriazoles bioisosteres of FLU (structures A and B), INDO and the INDO bioisosteres studied in this work (compounds 1 and 2).

Scheme 1. Synthesis of Target Compounds 1 and 2

Reagents and conditions: (a) Dry pyridine, dry toluene, rt; (b) HCl (gas), dry toluene, dry MeOH, 10 °C; (c) NaH (60% w/w), dry THF; (d) PTSA, dry toluene, 90 °C; (e) CH₃COOH, 80 °C; (f) H₂, Pd/C, dry THF.

Figure 2

AKR1C3 cocrystallized with compound 1 (orange sticks) (PDB ID 6GXK), superimposed with the AKR1C3 structure in complex with INDO (green sticks). NADP⁺ is represented in purple sticks. Molecular graphics and analyses were performed using the UCSF Chimera package.

Figure 3

Effect of 1, 2, and INDO on selected cell lines. Compounds were utilized at 10–200 μM. Cell viability was estimated by determining ATP content in three replicate wells. Results are normalized to the growth of cells that were treated with dimethyl sulfoxide (DMSO) and are represented as mean ± SEM of at least three independent experiments.