Effects of SAHA and RG7388 on p21WAF1/CIP1 and p27KIP1 mediated Pathways in Cancer Cells
Authors: Natarajan Umamaheswari , Venkatesan Thiagarajan , Samuel Shila S , Vijayaraghavan R , Rathinavelu Appu 
Published: June 2021

Epigenetic modifications can lead to significant influence on cancer development, growth and progression. The main epigenetic modifications observed in human are methylation and acetylation. Histone acetylations are largely regulated by histone deacetylases (HDACs) and, several HDAC inhibitors (HDACi) such as SAHA (Vorinostat), which are already approved for human use or currently in different stages of clinical trials, belong to the new class of drugs with promising effects on the cancer growth and metastatic process. The small molecule RG7388 is a newly developed inhibitor that is specific for an oncogene‐derived protein called MDM2, which is also in clinical trials for the treatment of various types of cancers. One of the unique characteristics of these two drugs is their ability to induce p21 expression through distinct mechanisms. A clear understanding related to the molecular mechanism whereby SAHA can induce cell cycle arrest and trigger necrosis, apoptosis or necroptosis is still evolving. Similarly, the ability of RG7388 for producing anticancer effect is undergoing thorough investigation, since it can produce p53 dependent and p53 independent effects. So far, our experiments with MCF‐7 breast cancer cells and LNCaP prostate cancer cells have confirmed the abilities of these two drugs to induce p21 expression through distinct mechanisms. In addition, these two drugs were expected trigger cell cycle arrest and cell death through mechanisms that are similar. Therefore, we performed experiments to measure the cell cycle arrest effects of SAHA and RG7388 by using the MCF‐7 and LNCaP cells. The cytotoxicity, cell cycle arrest and apoptosis/necroptosis effects of the treatments were assessed by using Trypan Blue Dye Exclusion (TBDE) method, and fluorescence assay with caspase 3/7 specific DEVD‐amc fluorogenic substrate. In addition, cell cycle and apoptosis related proteins were analyzed by immunoblotting methods. To this point, our results from MCF‐7 and LNCaP cells suggest that the cell death caused by SAHA treatment in both cell lines are through induction of p21WAF1/CIP1 and p27Kip1 levels, that could be independent of p53. On the other hand, treatment of LNCaP cells with RG7388 was able to induce p21WAF1/CIP1 expression through inhibition of MDM2 that was also causing significant cell death. However, the RG7388 treatment was not able to elevate p21WAF1/CIP1 in MCF‐7 cells, even though there was clear evidence of p53 elevation in these cells. Hence, we are suspecting that, there is some level of uncoupling of p53 mediated transcriptional induction of p21WAF1/CIP1 in MCF‐7 cells. As of now, our studies confirm that two different drugs, which have the ability to induce p21 expression, exhibit distinct mechanisms of cell death through p53 dependent and independent pathways. Since it points to an interesting interplay between multiple pathways, confirmation of the actual cell death mechanism induced by RG7388 in MCF‐7 and LNCaP cancer cells requires additional exploration.Support or Funding InformationThis research was supported by the Royal Dames of Cancer Research Inc., Fort Lauderdale, FloridaThis abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.