AUTHOR=Ma Chao , Taghour Mohammed S. , Belal Amany , Mehany Ahmed B. M. , Mostafa Naglaa , Nabeeh Ahmed , Eissa Ibrahim H. , Al-Karmalawy Ahmed A. 

TITLE=Design and Synthesis of New Quinoxaline Derivatives as Potential Histone Deacetylase Inhibitors Targeting Hepatocellular Carcinoma: In Silico, In Vitro, and SAR Studies

JOURNAL=Frontiers in Chemistry

VOLUME=Volume 9 - 2021

YEAR=2021

URL=https://www.frontiersin.org/journals/chemistry/articles/10.3389/fchem.2021.725135

DOI=10.3389/fchem.2021.725135

ISSN=2296-2646

ABSTRACT=Guided by the structural optimization principle and the promising anticancer effect of the 
quinoxaline nucleus, a new series of novel HDAC inhibitors were designed and synthesized. The 
synthesized compounds were designed to bear the reported pharmacophoric features of the HDAC 
inhibitors in addition to an extra moiety to occupy the non-used vacant deep pocket of the HDAC 
receptor. The newly prepared compounds were evaluated for their in vitro anti-proliferative 
activities against HepG-2 and HuH-7 liver cancer cell lines. The tested compounds showed 
promising anti-proliferative activities against both cell lines. The most active ten candidates (6c, 
6d, 6f, 6g, 6k, 6l, 7b, 8, 10h, and 12) were further evaluated for their effect on the gene expression 
levels of Bax as an apoptotic marker and Bcl-2 as an antiapoptotic one. Moreover, they were 
evaluated for their ability to inhibit histone deacetylase (HDAC4) activity. Compound 6c achieved 
the best cytotoxic activities on both HepG-2 and HuH-7 cell lines with IC50 values of 1.53 and 
3.06 µM, respectively, and also it showed the most inhibitory activity on HDAC4 with an IC50
value of 1.39 µM compared to valproic acid as a reference drug (IC50 = 1.42 µM). Furthermore, it 
achieved a more characteristic arrest in the growth of cell population of HepG-2 at both G0/G1 
and S phases with 1.23-, and 1.18- fold, respectively, compared to that of the control, as determined 
by cell cycle analysis. Also, compound 6c showed a marked elevation in the AnxV-FITC apoptotic 
HepG-2 cells percentage in both early and late phases increasing the total apoptosis percentage by 
9.98-, and 10.81- fold, respectively, compared to the control. Furthermore, docking studies were 
carried out to identify the proposed binding mode of the synthesized compounds towards the 
prospective target (HDAC4). In silico ADMET and toxicity studies revealed that most of the 
synthesized compounds have accepted profile of drug-likeness with low toxicity. Finally, an 
interesting SAR analysis was concluded to help the future design of more potent HDACIs in the 
future by medicinal chemists.