Dual targeting of androgen receptor and mTORC1 by salinomycin in prostate cancer

AMPK's double-faced role in advanced stages of prostate cancer

Prostate cancer (PCa) is the second leading cause of cancer deaths in men. Unfortunately, a very limited number of drugs are available for the relapsed and advanced stages of PCa, adding only a few months to survival; therefore, it is vital to develop new drugs. 5´ AMP-activated protein kinase (AMPK) is a master regulator of cell metabolism. It plays a significant role in the metabolism of PCa; hence, it can serve well as a treatment option for the advanced stages of PCa. However, whether this pathway contributes to cancer cell survival or death remains unknown. The present study reviews the possible pathways by which AMPK plays role in the advanced stages of PCa, drug resistance, and metastasis: (1) AMPK has a contradictory role in promoting glycolysis and the Warburg effect which are correlated with cancer stem cells (CSCs) survival and advanced PCa. It exerts its effect by interacting with hypoxia-induced factor 1 (HIF1) α, pyruvate kinase 2 (PKM2), glucose transporter (GLUT) 1 and pyruvate dehydrogenase complex (PDHC), which are key regulators of glycolysis; however, whether it promotes or discourage glycolysis is not conclusive. It can also exert an anti-CSC effect by negative regulation of NANOG and epithelial-mesenchymal transition (EMT) transcription factors, which are the major drivers of CSC maintenance; (2) the regulatory effect of AMPK on autophagy is also noticeable. Androgen receptors' expression increases AMPK activation through Calcium/calmodulin-dependent protein kinase 2 (CaMKK2) and induces autophagy. In addition, AMPK itself increases autophagy by downregulating the mammalian target of rapamycin complex (mTORC). However, whether increased autophagy inhibits or promotes cell death and drug resistance is contradictory. This study reveals that there are numerous pathways other than cell metabolism by which AMPK exerts its effects in the advanced stages of PCa, making it a priceless treatment target. Finally, we mention some drugs developed to treat the advanced stages of PCa by acting on AMPK.

Precision Targets for Intercepting the Lethal Progression of Prostate Cancer: Potential Avenues for Personalized Therapy

Organ-confined prostate cancer of low-grade histopathology is managed with radiation, surgery, active surveillance, or watchful waiting and exhibits a 5-year overall survival (OS) of 95%, while metastatic prostate cancer (PCa) is incurable, holding a 5-year OS of 30%. Treatment options for advanced PCa-metastatic and non-metastatic-include hormone therapy that inactivates androgen receptor (AR) signaling, chemotherapy and genome-targeted therapy entailing synthetic lethality of tumor cells exhibiting aberrant DNA damage response, and immune checkpoint inhibition (ICI), which suppresses tumors with genomic microsatellite instability and/or deficient mismatch repair. Cancer genome sequencing uncovered novel somatic and germline mutations, while mechanistic studies are revealing their pathological consequences. A microRNA has shown biomarker potential for stratifying patients who may benefit from angiogenesis inhibition prior to ICI. A 22-gene expression signature may select high-risk localized PCa, which would not additionally benefit from post-radiation hormone therapy. We present an up-to-date review of the molecular and therapeutic aspects of PCa, highlight genomic alterations leading to AR upregulation and discuss AR-degrading molecules as promising anti-AR therapeutics. New biomarkers and druggable targets are shaping innovative intervention strategies against high-risk localized and metastatic PCa, including AR-independent small cell-neuroendocrine carcinoma, while presenting individualized treatment opportunities through improved design and precision targeting.

Inhibitors of the PI3K/Akt/mTOR Pathway in Prostate Cancer Chemoprevention and Intervention

The phosphatidylinositol 3-kinase (PI3K)/serine-threonine kinase (Akt)/mammalian target of the rapamycin (mTOR)-signaling pathway has been suggested to have connections with the malignant transformation, growth, proliferation, and metastasis of various cancers and solid tumors. Relevant connections between the PI3K/Akt/mTOR pathway, cell survival, and prostate cancer (PC) provide a great therapeutic target for PC prevention or treatment. Recent studies have focused on small-molecule mTOR inhibitors or their usage in coordination with other therapeutics for PC treatment that are currently undergoing clinical testing. In this study, the function of the PI3K/Akt/mTOR pathway, the consequence of its dysregulation, and the development of mTOR inhibitors, either as an individual substance or in combination with other agents, and their clinical implications are discussed. The rationale for targeting the PI3K/Akt/mTOR pathway, and specifically the application and potential utility of natural agents involved in PC treatment is described. In addition to the small-molecule mTOR inhibitors, there are evidence that several natural agents are able to target the PI3K/Akt/mTOR pathway in prostatic neoplasms. These natural mTOR inhibitors can interfere with the PI3K/Akt/mTOR pathway through multiple mechanisms; however, inhibition of Akt and suppression of mTOR 1 activity are two major therapeutic approaches. Combination therapy improves the efficacy of these inhibitors to either suppress the PC progression or circumvent the resistance by cancer cells.

Combined Anticancer Effect of Plasma-Activated Infusion and Salinomycin by Targeting Autophagy and Mitochondrial Morphology

Non-thermal atmospheric pressure plasma (NTAPP)-activated liquids have emerged as new promising anticancer agents because they preferentially injure malignant cells. Here, we report plasma-activated infusion (PAI) as a novel NTAPP-based anti-neoplastic agent. PAI was prepared by irradiating helium NTAP to form a clinically approved infusion fluid. PAI dose-dependently killed malignant melanoma and osteosarcoma cell lines while showing much lower cytotoxic effects on dermal and lung fibroblasts. We found that PAI and salinomycin (Sal), an emerging anticancer stem cell agent, mutually operated as adjuvants. The combined administration of PAI and Sal was much more effective than single-agent application in reducing the growth and lung metastasis of osteosarcoma allografts with minimal adverse effects. Mechanistically, PAI explicitly induced necroptosis and increased the phosphorylation of receptor-interacting protein 1/3 rapidly and transiently. PAI also suppressed the ambient autophagic flux by activating the mammalian target of the rapamycin pathway. PAI increased the phosphorylation of Raptor, Rictor, and p70-S6 kinase, along with decreased LC3-I/II expression. In contrast, Sal promoted autophagy. Moreover, Sal exacerbated the mitochondrial network collapse caused by PAI, resulting in aberrant clustering of fragmented mitochondrial in a tumor-specific manner. Our findings suggest that combined administration of PAI and Sal is a promising approach for treating these apoptosis-resistant cancers.

ASC-J9® suppresses prostate cancer cell proliferation and invasion via altering the ATF3-PTK2 signaling

Background

Early studies indicated that ASC-J9®, an androgen receptor (AR) degradation enhancer, could suppress the prostate cancer (PCa) progression. Here we found ASC-J9® could also suppress the PCa progression via an AR-independent mechanism, which might involve modulating the tumor suppressor ATF3 expression.

Methods

The lentiviral system was used to modify gene expression in C4–2, CWR22Rv1 and PC-3 cells. Western blot and Immunohistochemistry were used to detect protein expression. MTT and Transwell assays were used to test the proliferation and invasion ability.

Results

ASC-J9® can suppress PCa cell proliferation and invasion in both PCa C4–2 and CWR22Rv1 cells via altering the ATF3 expression. Further mechanistic studies reveal that ASC-J9® can increase the ATF3 expression via decreasing Glutamate-cysteine ligase catalytic (GCLC) subunit expression, which can then lead to decrease the PTK2 expression. Human clinical studies further linked the ATF3 expression to the PCa progression. Preclinical studies using in vivo mouse model also proved ASC-J9® could suppress AR-independent PCa cell invasion, which could be reversed after suppressing ATF3.

Conclusions

ASC-J9® can function via altering ATF3/PTK2 signaling to suppress the PCa progression in an AR-independent manner.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13046-020-01760-2.

Inhibitory Interplay of SULT2B1b Sulfotransferase with AKR1C3 Aldo-keto Reductase in Prostate Cancer

SULT2B1b (SULT2B) is a prostate-expressed hydroxysteroid sulfotransferase, which may regulate intracrine androgen homeostasis by mediating 3β-sulfation of dehydroepiandrosterone (DHEA), the precursor for 5α-dihydrotestosterone (DHT) biosynthesis. The aldo-keto reductase (AKR)1C3 regulates androgen receptor (AR) activity in castration-resistant prostate cancer (CRPC) by promoting tumor tissue androgen biosynthesis from adrenal DHEA and also by functioning as an AR-selective coactivator. Herein we report that SULT2B-depleted CRPC cells, arising from stable RNA interference or gene knockout (KO), are markedly upregulated for AKR1C3, activated for ERK1/2 survival signal, and induced for epithelial-to-mesenchymal (EMT)-like changes. EMT was evident from increased mesenchymal proteins and elevated EMT-inducing transcription factors SNAI1 and TWIST1 in immunoblot and single-cell mass cytometry analyses. SULT2B KO cells showed greater motility and invasion in vitro; growth escalation in xenograft study; and enhanced metastatic potential predicted on the basis of decreased cell stiffness and adhesion revealed from atomic force microscopy analysis. While AR and androgen levels were unchanged, AR activity was elevated, since PSA and FKBP5 mRNA induction by DHT-activated AR was several-fold higher in SULT2B-silenced cells. AKR1C3 silencing prevented ERK1/2 activation and SNAI1 induction in SULT2B-depleted cells. SULT2B was undetectable in nearly all CRPC metastases from 50 autopsy cases. Primary tumors showed variable and Gleason score (GS)-independent SULT2B levels. CRPC metastases lacking SULT2B expressed AKR1C3. Since AKR1C3 is frequently elevated in advanced prostate cancer, the inhibitory influence of SULT2B on AKR1C3 upregulation, ERK1/2 activation, EMT-like induction, and on cell motility and invasiveness may be clinically significant. Pathways regulating the inhibitory SULT2B-AKR1C3 axis may inform new avenue(s) for targeting SULT2B-deficient prostate cancer.

Dairy Products: Is There an Impact on Promotion of Prostate Cancer? A Review of the Literature

This review of the literature aims to study potential associations between high consumption of milk and/or dairy products and prostate cancer (PC). Literature is scarce, yet there is a direct relationship between mTORC1 activation and PC; several ingredients in milk/dairy products, when in high concentrations, increase signaling of the mTORC1 pathway. However, there are no studies showing an unequivocal relationship between milk products PC initiation and/or progression. Three different reviews were conducted with articles published in the last 5 years: (M1) PC and intake of dairy products, taking into account the possible mTORC1signaling mechanism; (M2) Intake of milk products and incidence/promotion of PC; (M3) mTORC1 activation signaling pathway, levels of IGF-1 and PC; (M4) mTORC pathway and dairy products. Of the 32 reviews identified, only 21 met the inclusion criteria and were analyzed. There is little scientific evidence that directly link the three factors: incidence/promotion of PC, intake of dairy products and PC, and PC and increased mTORC1 signaling. Persistent hyper-activation of mTORC1 is associated with PC promotion. The activity of exosomal mRNA in cellular communication may lead to different impacts of different types of milk and whether or not mammalian milks will have their own characteristics within each species. Based on this review of the literature, it is possible to establish a relationship between the consumption of milk products and the progression of PC; we also found a possible association with PC initiation, hence it is likely that the intake of dairy products should be reduced or minimized in mens' diet.

Salinomycin and its derivatives - A new class of multiple-targeted "magic bullets"

The history of drug development clearly shows the scale of painstaking effort leading to a finished product - a highly biologically active agent that would be at the same time no or little toxic to human organism. Moreover, the aim of modern drug discovery can move from "one-molecule one-target" concept to more promising "one-molecule multiple-targets" one, particularly in the context of effective fight against cancer and other complex diseases. Gratifyingly, natural compounds are excellent source of potential drug leads. One of such promising naturally-occurring drug candidates is a polyether ionophore - salinomycin (SAL). This compound should be identified as multi-target agent for two reasons. Firstly, SAL combines a broad spectrum of bioactivity, including antibacterial, antifungal, antiviral, antiparasitic and anticancer activity, with high selectivity of action, proving its significant therapeutic potential. Secondly, the multimodal mechanism of action of SAL has been shown to be related to its interactions with multiple molecular targets and signalling pathways that are synergistic for achieving a therapeutic anticancer effect. On the other hand, according to the Paul Ehrlich's "magic bullet" concept, invariably inspiring the scientists working on design of novel target-selective molecules, a very interesting direction of research is rational chemical modification of SAL. Importantly, many of SAL derivatives have been found to be more promising as chemotherapeutics than the native structure. This concise review article is focused both on the possible role of SAL and its selected analogues in future antimicrobial and/or cancer therapy, and on the potential use of SAL as a new class of multiple-targeted "magic bullet" because of its multimodal mechanism of action.

Stimulation of Prostate Cells by the Senescence Phenotype of Epithelial and Stromal Cells: Implication for Benign Prostate Hyperplasia

Hyperproliferation of prostate transition‐zone epithelial and stromal cells leads to benign prostate hyperplasia (BPH), a prevalent pathology in elderly men. Senescent cells in BPH tissue induce a senescence‐associated secretory phenotype (SASP) which, by generating inflamed microenvironment and reactive stroma, promotes leukocyte infiltration, cellular hyperproliferation, and nodular prostate growth. We examined human prostate epithelial (BPH‐1, PNT‐1α) and stromal (HPS‐19I) cells for SASP induction by ionizing radiation and assessed SASP's impacts on cell proliferation and on signal transducers that promote cellular growth, proliferation, and survival. Radiation‐induced DNA damage led to cellular senescence, evident from elevated expression of senescence‐associated β‐galactosidase and the cell‐cycle inhibitor p16/INK4a. Clinical BPH tissue showed p16 accumulation. SASP induced mRNA expression for inflammatory cytokines (IL‐1α, IL‐6, IL‐8, TNF‐α); chemokines (GM‐CSF, CXCL12); metalloproteases (MMP‐1, MMP‐3, MMP‐10); growth factor binding IGFBP‐3. Media from irradiated epithelial or stromal cells enhanced BPH‐1 proliferation. ERK1/2 and AKT, which enhance cell growth/survival and STAT5, which facilitates cell cycle progression and leukocyte recruitment to epithelial microenvironment, were activated by SASP components. The radiation‐induced cellular senescence model can be a platform for identification of individual SASP components and pathways that drive BPH etiology/progression in vivo and targeting them may form the basis for novel BPH therapy.

Enhanced targeting of prostate cancer-initiating cells by salinomycin-encapsulated lipid-PLGA nanoparticles linked with CD44 antibodies

Prostate cancer is the fifth most common cause of cancer-associated mortality in males worldwide. The survival of prostate cancer-initiating cells (CICs) is an important factor behind the metastasis and recurrence of prostate cancer. The cluster of differentiation (CD) 44 antigen is considered an important marker for prostate CICs. Salinomycin is a potent therapeutic drug against CICs. The present study demonstrated that salinomycin exerts potent activity against CD44⁺ prostate CICs. To further enhance this anticancer effect, salinomycin-encapsulated lipid-poly(lactic-co-glycolic acid) nanoparticles linked with CD44 antibodies (SM-LPN-CD44) were generated. The anticancer effect of the nanoparticles was investigated in a series of assays, including a cytotoxicity assay, flow cytometry and anticancer assay in prostate cancer-bearing mice in vivo. The results revealed that SM-LPN-CD44 could efficiently and specifically promote the delivery of salinomycin to CD44⁺ prostate CICs, and there by achieve greater inhibition of the cells compared with that achieved by salinomycin and non-targeted nanoparticles. To the best of our knowledge, this is the first study to report improved therapeutic effects against prostate CICs achieved by the enhancement of targeted drug delivery via nanoparticles conjugated with CD44 antibodies. Therefore, SM-LPN-CD44 nanoparticle-based therapy represents a novel approach to eliminate prostate CICs and is a promising potential treatment strategy for prostate cancer.

Dichloroacetate and Salinomycin Exert a Synergistic Cytotoxic Effect in Colorectal Cancer Cell Lines

In the present study, we examined a hypothesis that dichloroacetate, a metabolic inhibitor, might efficiently potentiate the cytotoxic effect of salinomycin, an antibiotic ionophore, on two human colorectal cancer derived cell lines DLD-1 and HCT116. First, we performed a series of dose response experiments in the 2D cell culture by applying mono- and combination therapy and by using the Chou-Talalay method found that salinomycin in combination with dichloroacetate acted synergistically in both cell lines. Secondly, in order to recapitulate the in vivo tumor architecture, we tested various doses of these compounds, alone and in combination, in the 3D multicellular spheroid culture. The effect of combination of dichloracetate and salinomycin on multicellular spheroid size was stronger than the sum of both monotherapies, particularly in HCT116 cells. Further, we demonstrate that the synergistic effect of compounds may be related to the inhibitory effect of dichloroacetate on multidrug resistance proteins, and in contrast, it is not related to dichloroacetate-induced reduction of intracellular pH. Our findings indicate that the combination therapy of salinomycin and dichloroacetate could be an effective option for colorectal cancer treatment and provide the first mechanistic explanation of the synergistic action of these compounds.

Salinomycin, as an autophagy modulator-- a new avenue to anticancer: a review

Since Salinomycin (Sal) emerged its ability to target breast cancer stem cells in 2009, numerous experiments have been carried out to test Sal’s anticancer effects. What deserve to be mentioned is that Sal can efficiently induce proliferation inhibition, cell death and metastasis suppression against human cancers from different origins both in vivo and in vitro without causing serious side effects as the conventional chemotherapeutical drugs on the body. There may be novel cell death pathways involving the anticancer effects of Sal except the conventional pathways, such as autophagic pathway. This review is focused on how autophagy involves the effects of Sal, trying to describe clearly and systematically why autophagy plays a vital role in predominant anticancer effects of Sal, including its distinctive characteristic. Based on recent advances, we present evidence that a dual role of Sal involving in autophagy may account for its unique anticancer effects - the preference for cancer cells. Further researches are required to confirm the authenticity of this suppose in order to develop an ideal anticancer drug.

Functional analysis of Cullin 3 E3 ligases in tumorigenesis

Cullin 3-RING ligases (CRL3) play pivotal roles in the regulation of various physiological and pathological processes, including neoplastic events. The substrate adaptors of CRL3 typically contain a BTB domain that mediates the interaction between Cullin 3 and target substrates to promote their ubiquitination and subsequent degradation. The biological implications of CRL3 adaptor proteins have been well described where they have been found to play a role as either an oncogene, tumor suppressor, or can mediate either of these effects in a context-dependent manner. Among the extensively studied CRL3-based E3 ligases, the role of the adaptor protein SPOP (speckle type BTB/POZ protein) in tumorigenesis appears to be tissue or cellular context dependent. Specifically, SPOP acts as a tumor suppressor via destabilizing downstream oncoproteins in many malignancies, especially in prostate cancer. However, SPOP has largely an oncogenic role in kidney cancer. Keap1, another well-characterized CRL3 adaptor protein, likely serves as a tumor suppressor within diverse malignancies, mainly due to its specific turnover of its downstream oncogenic substrate, NRF2 (nuclear factor erythroid 2-related factor 2). In accordance with the physiological role the various CRL3 adaptors exhibit, several pharmacological agents have been developed to disrupt its E3 ligase activity, therefore blocking its potential oncogenic activity to mitigate tumorigenesis.

Cucurbitacin E induces apoptosis of human prostate cancer cells via cofilin-1 and mTORC1

Cucurbitacin E is an important member of the cucurbitacin family and exhibits inhibitory effects in various types of cancer. Cucurbitacin is a potential antineoplastic drug; however, its anticancer effect in human prostate cancer (PC) remains unknown. The aim of the present study was to determine whether the effect of cucurbitacin E on the cell viability and apoptosis of the human PC cell line, LNCaP, was mediated by cofilin-1- and mammalian target of rapamycin (mTOR). The results of the present study demonstrated that cucurbitacin E significantly exhibited cytotoxicity, suppressed cell viability (P<0.0001) and induced apoptosis (P=0.0082) in LNCaP cells. In addition, it was demonstrated that treatment with cucurbitacin E significantly induced cofilin-1 (P=0.0031), p-mTOR (P=0.0022), AMP-activated protein kinase (AMPK; P=0.0048), cellular tumor antigen p53 (p53; P=0.0018) and caspase-9 (P=0.0026) protein expression in LNCaP cells, suggesting that cucurbitacin E exerts its effects on LNCaP cells through cofilin-1, mTOR, AMPK, p53 and caspase-9 signaling. These results suggested that cucurbitacin E maybe used as a therapeutic agent in the treatment of human PC.