Selective HDAC inhibitors with potent oral activity against leukemia and colorectal cancer: Design, structure-activity relationship and anti-tumor activity study

Abstract

Previously, we reported the discovery of a series of N-hydroxycinnamamide-based HDAC inhibitors, among which compound 11y exhibited high HDAC1/3 selectivity. In this current study, structural derivatization of 11y led to a new series of benzamide based HDAC inhibitors. Most of the compounds exhibited high HDACs inhibitory potency. Compound 11a (with 4-methoxybenzoyl as N-substituent in the cap and 4-(aminomethyl) benzoyl as the linker group) exhibited selectivity against HDAC1 to some extent, and showed potent antiproliferative activity against several tumor cell lines. In vivo studies revealed that compound 11a displayed potent oral antitumor activity in both hematological tumor cell U937 xenograft model and solid tumor cell HCT116 xenograft model with no obvious toxicity. Further modification of benzamide 3, 11a and 19 afforded new thienyl and phenyl compounds (50a, 50b, 63a, 63b and 63c) with dramatic HDAC1 and HDAC2 dual selectivity, and the fluorine containing compound 56, with moderate HDAC3 selectivity.

Keywords: Anti-tumor drugs; Benzamides; HDACIs; HDACs; In vivo oral activity.

Fig. 1

Design of benzamides bearing HDACIs.

Fig. 2

Antitumor activity comparison of 11a and MS275 against U937 human tumor xenografts implanted in mice. (a) Picture of dissected U937 tumor tissues; (b) Tumor weight in different mice group; (c) Mean tumor volume during mice treatment; (d) Mice body weight change after administration.

Fig. 3

Antitumor activity comparison of 11a, SAHA and MS275 against HCT116 human tumor xenografts implanted in mice. (a) Picture of dissected HCT116 tumor tissues; (b) Mean tumor volume during mice treatment.

Fig. 4

Design of the new series compounds.

Fig. 5

Western blot analysis of acetylated histone H3 (AcHH3), acetylated histone H4 (AcHH4), procaspase-3, cleaved caspase-3 and cleaved PARP in HL60 cell lines after 48 h treatment with compounds using MS275 as positive control. β-actin was used as a loading control.

Scheme 1

Synthesis of Compound 3. Reagents and conditions: (a) CH₃OH/H₂O, KOH, reflux, 85% yield; (b) TBTU, Et₃N, anhydrous THF, 30–33% yield.

Scheme 2

Synthesis of Compounds 11a-11g. Reagents and conditions: (a) CH₃COCl, CH₃OH, 95% yield; (b) TBTU, Et₃N, anhydrous CH₂Cl₂, 60–65% yield; (c) AcOEt/HCl, 80% yield; (d) ROOH, TBTU, Et₃N, anhydrous CH₂Cl₂, 60–65% yield; (e) CH₃OH/H₂O, KOH, reflux, 80% yield; (f) TBTU, Et₃N, anhydrous THF, 30–33% yield.

Scheme 3

Synthesis of Compound 19. Reagents and conditions: (a) TBTU, Et₃N, anhydrous CH₂Cl₂, 60–65% yield; (b) CH₃OH/H₂O, KOH, reflux, 80% yield; (c) CH₃COCl, CH₃OH, 95% yield; (d) TBTU, Et₃N, anhydrous THF, 30–33% yield.

Scheme 4

Synthesis of Compound 22. Reagents and conditions: (a) CH₃OH/H₂O, KOH, reflux, 90% yield; (b) TBTU, Et₃N, anhydrous THF, 30–33% yield.

Scheme 5

Synthesis of Compounds 30a, 30b. Reagents and conditions: (a) CH₃COCl, CH₃OH, 95% yield; (b) PPh₃, DEAD, anhydrous THF, 57% yield; (c) AcOEt/HCl, 80% yield; (d) TBTU, Et₃N, anhydrous CH₂Cl₂, 60–65% yield; (e) CH₃OH/H₂O, KOH, reflux, 80% yield; (f) TBTU, Et₃N, anhydrous THF, 30–33% yield.

Scheme 6

Synthesis of Compound 37. Reagents and conditions: (a) TBTU, Et₃N, anhydrous CH₂Cl₂, 60–65% yield; (b) LiAlH₄, 2 h, 70% yield; (c) NaBH₃CN, AcOH, Et₃N, CH₃OH, 53% yield; (d) (Boc)₂O, Et₃N, CH₂Cl₂, 90% yield; (e) CH₃OH/H₂O, KOH, reflux, 80% yield; (f) TBTU, Et₃N, anhydrous THF, 48% yield; (g) AcOEt/HCl, 65% yield.

Scheme 7

Synthesis of Compounds 43a and 43b. Reagents and conditions: (a) (Boc)₂O, Et₃N, CH₂Cl₂, DMAP, 90% yield; (b) Thiophene-2-boronic acid or phenylboronic acid, Pd(OAc)₂, PPh₃, Na₂CO₃, H₂O, DMSO, 48% yield; (c) Pd/C, H₂, CH₃OH, 85% yield; (d) TBTU, Et₃N, anhydrous THF, 60–65% yield; (e) CF₃COOH, 68% yield.

Scheme 8

Synthesis of Compound 49. Reagents and conditions: (a) (Boc)₂O, Et₃N, CH₂Cl₂, DMAP, 90% yield; (b) CF₃COOH, CH₂Cl₂, 78% yield; (c) Pd/C, H₂, ethyl alcohol, 85% yield; (d) TBTU, Et₃N, anhydrous CH₂Cl₂, 60–65% yield; (e) CF₃COOH, 65% yield.

Scheme 9

Synthesis of Compounds 56a-56c. Reagents and conditions: (a) (CF₃CO)₂O, 95% yield; (b) SOCl₂, reflex, 83% yield; (c) pyridine, 78% yield; (d) K₂CO₃, CH₃OH/H₂O, 67% yield; (e) TBTU, Et₃N, anhydrous CH₂Cl₂, 60–65% yield; (f) CF₃COOH, 65% yield.

Scheme 10

Synthesis of Compounds 60a and 60b. Reagents and conditions: (a) pyridine, 78% yield; (b) K₂CO₃, CH₃OH/H₂O, 67% yield; (c) TBTU, Et₃N, anhydrous CH₂Cl₂, 60–65% yield; (d) CF₃COOH, 65% yield.