Allosteric Glutaminase Inhibitors Based on a 1,4-Di(5-amino-1,3,4-thiadiazol-2-yl)butane Scaffold

Abstract

A series of allosteric kidney-type glutaminase (GLS) inhibitors were designed and synthesized using 1,4-di(5-amino-1,3,4-thiadiazol-2-yl)butane as a core scaffold. A variety of modified phenylacetyl groups were incorporated into the 5-amino group of the two thiadiazole rings in an attempt to facilitate additional binding interactions with the allosteric binding site of GLS. Among the newly synthesized compounds, 4-hydroxy-N-[5-[4-[5-[(2-phenylacetyl)amino]-1,3,4-thiadiazol-2-yl]butyl]-1,3,4-thiadiazol-2-yl]-benzeneacetamide, 2m, potently inhibited GLS with an IC50 value of 70 nM, although it did not exhibit time-dependency as seen with CB-839. Antiproliferative effects of 2m on human breast cancer lines will be also presented in comparison with those observed with CB-839.

Keywords: Glutaminase; allosteric inhibition; cancer metabolism.

Figure 1

Representative glutaminase inhibitors.

Scheme 1. Synthesis of 2a–o

Conditions: (a) DIPEA, HATU, DMF, 0 °C; (b) 2 N NaOH, MeOH, rt; (c) 2 N NaOH, THF, rt; (d) 4 N HCl, 1,4-dioxane, rt.

Scheme 2. Synthesis of 2p–u

Conditions: (a) DIPEA, HATU, DMF, 0 °C; (b) 2 N NaOH, THF, rt; (c) for 4r to 6r, DIPEA, HATU, DMF, 0 °C; (d) for 4s to 6s, T₃P, NEt₃, DMF, RT; (e) 2.5% LiOH, THF, RT; (f) NH₂CSN₂H₃, POCl₃, 90 °C; (g) DIPEA, HATU, DMF, 0 °C; (h) 2 N NaOH, THF, rt.

Figure 2

Effect of preincubation time on GLS inhibitory potency of CB-839 and compound 2m.

Figure 3

Effects of BPTES, CB-839, and compound 2m on (A) MDA-MB-231 and (B) HCC1806 cell growth. Cell viability assays were performed in quadruplicate, and error bars represent standard deviation. Live cell viability was determined using CellTiter-Glo Luminescent Cell Viability Assay daily. *P < 0.05 compared to the controls.