Date Published: December 27, 2018
Author(s): Subhankar Biswas, Neetinkumar D. Reddy, B. S. Jayashree, C. Mallikarjuna Rao.
Alteration of epigenetic enzymes is associated with the pathophysiology of colon cancer with an overexpression of histone deacetylase 8 (HDAC8) enzyme in this tissue. Numerous reports suggest that targeting HDAC8 is a viable strategy for developing new anticancer drugs. Flavonols provide a rich source of molecules that are effective against cancer; however, their clinical use is limited. The present study investigated the potential of quercetin and synthetic 3-hydroxyflavone analogues to inhibit HDAC8 enzyme and evaluated their anticancer property. Synthesis of the analogues was carried out, and cytotoxicity was determined using MTT assay. Nonspecific and specific HDAC enzyme inhibition assays were performed followed by the expression studies of target proteins. Induction of apoptosis was studied through annexin V and caspase 3/7 activation assay. Furthermore, the analogues were assessed against in vivo colorectal cancer. Among the synthesized analogues, QMJ-2 and QMJ-5 were cytotoxic against HCT116 cells with an IC50 value of 68 ± 2.3 and 27.4 ± 1.8 µM, respectively. They inhibited HDAC enzyme in HCT116 cells at an IC50 value of 181.7 ± 22.04 and 70.2 ± 4.3 µM, respectively, and inhibited human HDAC8 and 1 enzyme at an IC50 value of <50 µM with QMJ-5 having greater specificity towards HDAC8. A reduction in the expression of HDAC8 and an increase in acetyl H3K9 expression were observed with the synthesized analogues. Both QMJ-2 and QMJ-5 treatment induced apoptosis through the activation of caspase 3/7 evident from 55.70% and 83.55% apoptotic cells, respectively. In vivo studies revealed a significant decrease in colon weight to length ratio in QMJ-2 and QMJ-5 treatment groups compared to DMH control. Furthermore, a reduction in aberrant crypt foci formation was observed in the treatment groups. The present study demonstrated the potential of novel 3-hydroxyflavone analogues as HDAC8 inhibitors with anticancer property against colorectal cancer.
Cancer is a multifactorial disease and the second largest cause of death globally . Over the years, knowledge about the pathophysiology of cancer has increased radically owing to the emergence of drug resistance and through the identification of newer hallmarks of cancer. Genetic predisposition was thought be one of the prime concerns in understanding the etiological background of cancer; however, the treatment modalities were still not successful based on either biochemically mediated or targeting genetically predisposed factors. This has created an arousal of interest in the field of epigenetic research. Researchers are earnestly attempting to develop newer therapies for cancer to improve the quality of life of patients. To support the continuous efforts made in developing anticancer agents, epidemiological survey shows that the overall mortality rate caused due to cancer has decreased by 25% from 1991 to 2014 .
Colorectal cancer (CRC) is one of the lethal forms of malignancy and is a global burden both in terms of morbidity and economic expenditure. Various factors are associated with the pathogenesis of CRC among which numerous studies have highlighted the role of epigenetics. The epigenetic enzyme HDACs are overexpressed in colorectal cancer leading to cellular proliferation and differentiation . Among the various HDAC enzymes, HDAC8 is an emerging target in cancer research. Genomic analysis of colon cancer cells shows an increased expression of HDAC8 compared to normal cells . Studies have reported that HDAC8 inhibits apoptosis in colon cancer cells by repressing Bcl-2-modifying factor (BMF) transcription . Interestingly, the deacetylase activity of HDAC8 is exhibited by the enzyme without being associated with any multiprotein complex . These features provide rationale for developing inhibitors against HDAC8 that could be beneficial towards CRC. Natural molecules, especially polyphenols, have been widely studied and are found to be valuable for the treatment of cancer. Among the diverse polyphenolic compounds, flavonols exhibit beneficial property in cancer. The structural feature of flavonols including C2=C3 unsaturation and the presence of the 3-hydroxy group is a crucial determinant for their antitumor property. Exploiting this feature, the polyphenol quercetin and a series of 3-hydroxyflavone analogues were evaluated for their HDAC8 inhibitory potential and anticancer property against colorectal cancer.
The present study revealed that both analogues QMJ-2 and QMJ-5 and the polyphenol quercetin were found to be cytotoxic and inhibited HDAC enzyme, where QMJ-5 showed greater specificity towards HDAC8. Induction of apoptosis by QMJ-2 and QMJ-5 in colon cancer cells was mediated through the activation of caspase 3/7 along with the cell cycle arrest at the G0/G1 phase through the expression of p21Waf1/Cip1. The synthesized analogues reduced the formation of ACF and adenocarcinoma in the animal model of colorectal cancer. Thus, the present study identified the potentials of novel 3-hydroxyflavone analogues as HDAC8 inhibitors with anticancer property against colorectal cancer providing a lead for new drug development.