PC is one of the most common and lethal malignancies in men in the world[1]. Treatment strategies for prostate cancer have made significant progress in the past few decades [2]. Curcumin has been shown to treat a variety of chronic diseases, including inflammation, arthritis, metabolic syndrome, liver disease, obesity, neurodegeneration, and especially in cancers ([19–21]. In this study, prostate cancer cells were treated with different concentration curcumin to explore new therapeutic strategies..
Curcumin demonstrates cytotoxic activity by inhibiting or blocking mitosis and growth of cancer cells. The specific focus of this study was to investigate its cytotoxicity on prostate cell lines. The IC50 of curcumin in LnCap and PC-3 cell lines is 16.9 µM and 47 µM, respectively. Additionally, the findings indicate that curcumin inhibits cell proliferation and induces changes in cell morphology.
Abnormal cell proliferation and differentiation, as well as an imbalance in apoptosis, are also important causes of tumorigenesis. Many chemotherapeutic drugs can inhibit the proliferation of cancer cells and induce their apoptosis. Major morphological changes of apoptotic cells, such as cell contraction, cytoplasmic vacuolation, chromatin condensation, nuclear fragmentation, and vesicular cells, ultimately lead to the appearance of apoptotic bodies [22–24]. Hoechst 333258 staining showed that the two cell lines treated with curcumin exhibited typical apoptosis. These results were also confirmed by flow cytometry and mitochondrial membrane potential analysis.
BCL-2 family is a class of anti-apoptotic proteins, mainly involved in the endogenous pathway of apoptosis. It could inhibit apoptosis mainly by binding to and inhibiting pro-apoptotic proteins such as Bax and Bak. Cytokine C and other apoptosis-related factors play key roles in the mitochondrial apoptosis pathway and can activate the caspase pathway in cancer cells. However, by investigating the mechanism by which curcumin induces apoptosis, the results revealed that prostate cancer cells treated with curcumin for 24 h could significantly reduce expression of Bcl-2 while enhanced expression of Bax and cleaved Caspase-3 .
Glycolysis is the process of converting glucose to pyruvate and producing energy, which is the main way for producing important metabolite precursors. Under aerobic conditions, glycolysis still uased to provide energy called the Warburg effectt [25]. This function is used by cancer cells to support the metabolic reprogramming process of their high energy demands and high rate of macromolecule synthesis. The Warburg effect is regulated by several glycolytic enzymes, including HK2, PFKP, PKM2, and LDH [26]. Our results suggest that curcumin treatment may inhibit glucose uptake and extracellular lactate production in prostate cancer cells. Glycolytic enzymes were downregulated in the curcumin treatment group.
In previous studies, the PI3K/Akt signaling pathway has been associated with hypoxia. However, phosphorylation of Akt could promote hypoxia-induced HIF-1 α expression and promote intracellular glucose utilization as well as angiogenesis, which in turn promotes intracellular environmental stabilization; This can ultimately promote the growth of tumor cells [27, 28]. Our results suggest that curcumin could decrease the phosphorylation of Akt and the expression of HIF-1 α in prostate cancer cells.
As a member of ETS transcription factor family, ETS-related gene (Erg) is the most frequently expressed proto-oncogene in PCA. [18]. The protein encoded by this gene acts as an activator or inhibitor of transcription and plays a regulatory role in proliferation, differentiation, apoptosis and other cellular processes [29]. ERG is one of the most highly expressed genes in prostate cancer, and it influences cancer progression by regulating FZD4 expression. The TMPRSS2-ERG gene fusion is the most common type of genetic alteration in prostate cancer. It mainly due to chromosomal translocation or intergenic deletion, and most TMPRSS2-ERG fusions are frequently accompanied by deletion of PTEN, there was an association between prostate cancer and the diagnosis of prostate cancer.[30–31] .
A recent study demonstrated that TMPRSS2-ERG fusion-positive prostate cancers can be effectively targeted by peptide-mimicking inhibitors of TMPRSS2-ERG[32].,while Zhang et,al also demonstrated that ERG was a prognostic biomarker for survival and was associated with aerobic glycolysis in cervical cance[33]. In this study, curcumin was found to be more effective on LnCap cells than on PC-3 cells.. We also found that LnCap cells were highly expressing ERG gene. Therefore, we speculate that the results we obtained are related to the expression of ERG. To test our hypothesis, we performed several experiments. The results showed that curcumin could downregulate the expression of full-length ERG and truncated ERG.
In conclusion, the results of this study show that curcumin can inhibit the proliferation of prostate cancer cells and induce apoptosis. The possible mechanism is that curcumin reduces glycolysis by downregulating the expression of the oncogene ERG, which in turn downregulates HIF-1 α protein by inhibiting the intracellular PI3K/AKT pathway. In the future, we will futher focus on the role of ERG in curcumin treated prostate cancer cells