New benzothiazole hybrids as potential VEGFR-2 inhibitors: design, synthesis, anticancer evaluation, and in silico study

Abstract

A new series of 2-aminobenzothiazole hybrids linked to thiazolidine-2,4-dione 4a-e, 1,3,4-thiadiazole aryl urea 6a-d, and cyanothiouracil moieties 8a-d was synthesised. The in vitro antitumor effect of the new hybrids was assessed against three cancer cell lines, namely, HCT-116, HEPG-2, and MCF-7 using Sorafenib (SOR) as a standard drug. Among the tested compounds, 4a was the most potent showing IC50 of 5.61, 7.92, and 3.84 µM, respectively. Furthermore, compounds 4e and 8a proved to have strong impact on breast cancer cell line with IC50 of 6.11 and 10.86 µM, respectively. The three compounds showed a good safety profile towards normal WI-38 cells. Flow cytometric analysis of the three compounds in MCF-7 cells revealed that compounds 4a and 4c inhibited cell population in the S phase, whereas 8a inhibited the population in the G1/S phase. The most promising compounds were subjected to a VEGFR-2 inhibitory assay where 4a emerged as the best active inhibitor of VEGFR-2 with IC50 91 nM, compared to 53 nM for SOR. In silico analysis showed that the three new hybrids succeeded to link to the active site like the co-crystallized inhibitor SOR.

Keywords: 134-thiadiazoles; 2-Aminobenzothiazole; VEGFR-2 inhibition; cyanothiouracils; thiazolidine-24-diones.

Figure 1.

The necessary pharmacophoric properties of some FDA and clinically approved VEGFR-2 inhibitors.

Figure 2.

Representative examples of some reported anticancer VEGFR-2 inhibitors carrying 2-aminobenzothiazole scaffold, thiazolidine-2,4-dione, cyanothiouracil, and thiadiazole-urea pharmacophores.

Figure 3.

The fundamental structural requirements for SOR and rational of design of the novel postulated VEGFR-2 inhibitors.

Scheme 1.

Preparation of benzothiazole/thiazolidine-2,4-dione hybrids 4a–e; reagents and conditions: (i) CH₂Cl₂/Et₃N 0 °C, rt; (ii) AcOH, NaOAc, reflux 14 h; (iii) EtOH, KOH, reflux 2 h; and (iv) DMF, K₂CO₃, reflux overnight.

Scheme 2.

Synthesis of benzothiazole/1,3,4-thiadiazole-aryl urea hybrids 6a–d; reagents and conditions: (i) CS₂, EtOH, reflux overnight; (ii) CH₃CN, reflux overnight; and (iii) acetone, K₂CO₃, reflux overnight.

Scheme 3.

Synthesis of benzothiazole/cyanothiouracil hybrids 8a–d; reagents and conditions: (i) EtOH, K₂CO₃, reflux 12 h and (ii) acetone, K₂CO₃, reflux overnight.

Figure 4.

Cytotoxic effect of the most active compounds 4a, 4e, 8e, and SOR on human normal WI-38 cell line.

Figure 5.

Effect of compounds 4a, 4e, and 8a on DNA-ploidy flow cytometric analysis of MCF-7 cells. The cells were treated with DMSO as control and 4a, 4e, and 8a for 24 h.

Figure 6.

Effect of compounds 4a, 4e, and 8a on the percentage of annexin V-FITC-positive staining in MCF-7 cells. The cells were treated with DMSO as control and 4a, 4e, and 8a for 24 h. Q1 quadrant represents dead (necrotic) cells; Q2 quadrant represents late apoptosis; Q3 quadrant represent live cells; Q4 quadrant represents early apoptosis.

Figure 7.

Compound 4a compound 4e compound 8a docked in the active site and aligned to the co-crystallized ligand SOR. Please refer to the online version for colored figure.