Evaluation of SHetA2 Analogs as Anti‐Cancer Agents on Human Prostate Cancer Cells

Abstract

BackgroundSHetA2 is a flexible heteroarotinoid compound that has shown potential anticancer effects on many cancer cell lines as well as animal models of cancer. However, due to its high lipophilicity, poor target specificity and low bioavailability, it may not be an ideal drug candidate. To overcome these limitations, over twenty thiochroman analogs of SHetA2 were synthesized and screened for their growth inhibitory effects in three different human prostate cancer cells. The screening yielded three analogs, SL‐01‐18, SL‐01‐30 and SL‐01‐39 that showed growth inhibitory effects comparable to SHetA2. All three analogs were more potent in inhibiting the growth of androgen receptor (AR) positive cell line, LNCaP, than the AR negative cell lines, DU145 and PC3. Here, we further evaluated the mechanism of action of these three analogs in LNCaP cell line.ObjectiveThe aim of the study was to evaluate the mechanism of action of the three SHetA2 analogs and compare their effects to SHetA2 in androgen receptor positive cell line, LNCaP.MethodsApoTox‐Glo assay was performed on LNCaP cells after 24 hours exposure to SHetA2 and its three analogs to determine the cell viability, cytotoxicity and caspase 3/7 activity. Bromodeoxyuridine (BrdU) incorporation assay was performed to measure the proportion of LNCaP cells in S‐phase of the cell cycle after drug treatments. Western blot analysis was performed on LNCaP cells treated with the SHetA2 analogs to analyze the effect on the expression of androgen receptor (AR) protein. Finally, prostate specific antigen (PSA)‐ELISA assay was performed to determine PSA concentration on LNCaP supernatants upon treatment with SHetA2 and its analogs.ResultsApoTox‐Glo assay results showed decreased cell viability, increased caspase activity and very little cytotoxicity in LNCaP cells treated with SHetA2 and its analogs. BrdU incorporation assay in LNCaP cells revealed a significant reduction in the proportion of cells in the S‐phase of the cell cycle with all four drug treatments, Finally, Western blot analysis revealed time and concentration‐dependent decrease in AR expression in treated cells while PSA‐ELISA assay indicated significant decrease in PSA secretion from LNCaP cells treated with SHetA2 and its analogs for 72 hours.ConclusionSHetA2 and its thiochroman analogs, SL‐01‐18, SL‐01‐30 and SL‐01‐39 inhibited cell growth of AR positive LNCaP cells while not being cytotoxic to these cells. In addition to stalling the cells from entering the S‐phase of the cell cycle, these agents also raised the likelihood of the cells to undergo apoptosis by activating the executioner caspase 3/7. A decrease in secreted PSA levels as well as concentration‐dependent decrease in AR protein expression suggests that the SHetA2 analogs may elicit their action by interfering with androgen receptor signaling. However, understanding how exactly are the analogs affecting androgen receptor signaling, inducing cell cycle arrest and/or causing programmed cell death requires further investigation.Support or Funding InformationTouro CA COP‐MS Program for funding this research.This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.