The Combination of Metformin and Valproic Acid Induces Synergistic Apoptosis in the Presence of p53 and Androgen Signaling in Prostate Cancer

Metformin as a Potential Antitumor Agent

Some recent findings suggest that metformin, an oral antidiabetic drug, may have antitumor properties. Studies have shown that metformin can alter cell metabolism, both tumor and immune cells, which can greatly influence disease outcome. In this review, we discuss the potential mechanisms in which metformin can directly induce apoptosis of tumor cells as well as mechanisms in which metformin can elicit or enhance antitumor immune response.

Metformin regulates multiple signaling pathways within castration-resistant human prostate cancer cells

Background

The biguanide metformin has been shown to not only reduce circulating glucose levels but also suppress in vitro and in vivo growth of prostate cancer. However, the mechanisms underlying the anti-tumor effects of metformin in advanced prostate cancers are not fully understood. The goal of the present study was to define the signaling pathways regulated by metformin in androgen-receptor (AR) positive, castration-resistant prostate cancers.

Methods

Our group used RNA sequencing (RNA-seq) to examine genes regulated by metformin within the C4–2 human prostate cancer cell line. Western blot analysis and quantitative RT-PCR were used to confirm alterations in gene expression and further explore regulation of protein expression by metformin.

Results

Data from the RNA-seq analysis revealed that metformin alters the expression of genes products involved in metabolic pathways, the spliceosome, RNA transport, and protein processing within the endoplasmic reticulum. Gene products involved in ErbB, insulin, mTOR, TGF-β, MAPK, and Wnt signaling pathways are also regulated by metformin. A subset of metformin-regulated gene products were genes known to be direct transcriptional targets of p53 or AR. Western blot analyses and quantitative RT-PCR indicated these alterations in gene expression are due in part to metformin-induced reductions in AR mRNA and protein levels.

Conclusions

Together, our results suggest metformin regulates multiple pathways linked to tumor growth and progression within advanced prostate cancer cells.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12885-022-10115-3.

From HDAC to Voltage-Gated Ion Channels: What's Next? The Long Road of Antiepileptic Drugs Repositioning in Cancer

Simple Summary

Although in the last decades the clinical outcome of cancer patients considerably improved, the major drawbacks still associated with chemotherapy are the unwanted side effects and the development of drug resistance. Therefore, a continuous effort in trying to discover new tumor markers, possibly of diagnostic, prognostic and therapeutic value, is being made. This review is aimed at highlighting the anti-tumor activity that several antiepileptic drugs (AEDs) exert in breast, prostate and other types of cancers, mainly focusing on their ability to block the voltage-gated Na⁺ and Ca⁺⁺ channels, as well as to inhibit the activity of histone deacetylases (HDACs), all well-documented tumor markers and/or molecular targets. The existence of additional AEDs molecular targets is highly suspected. Therefore, the repurposing of already available drugs as adjuvants in cancer treatment would have several advantages, such as reductions in dose-related toxicity CVs will be sent in a separate mail to the indicated address of combined treatments, lower production costs, and faster approval for clinical use.

Abstract

Cancer is a major health burden worldwide. Although the plethora of molecular targets identified in the last decades and the deriving developed treatments, which significantly improved patients’ outcome, the occurrence of resistance to therapies remains the major cause of relapse and mortality. Thus, efforts in identifying new markers to be exploited as molecular targets in cancer therapy are needed. This review will first give a glance on the diagnostic and therapeutic significance of histone deacetylase (HDAC) and voltage gated ion channels (VGICs) in cancer. Nevertheless, HDAC and VGICs have also been reported as molecular targets through which antiepileptic drugs (AEDs) seem to exert their anticancer activity. This should be claimed as a great advantage. Indeed, due to the slowness of drug approval procedures, the attempt to turn to off-label use of already approved medicines would be highly preferable. Therefore, an updated and accurate overview of both preclinical and clinical data of commonly prescribed AEDs (mainly valproic acid, lamotrigine, carbamazepine, phenytoin and gabapentin) in breast, prostate, brain and other cancers will follow. Finally, a glance at the emerging attempt to administer AEDs by means of opportunely designed drug delivery systems (DDSs), so to limit toxicity and improve bioavailability, is also given.

Harnessing the Heterogeneity of Prostate Cancer for Target Discovery Using Patient-Derived Explants

Simple Summary

There is a widespread push toward more biologically relevant pre-clinical models of prostate cancer that can improve the discovery and translation of new drugs and biomarkers for this disease. Patient-derived explant culture is an innovative pre-clinical model that utilizes surgical prostate cancer specimens in a way that retains the architecture, microenvironment and heterogeneity of prostate tumors—factors that critically influence cell behavior and response to therapy. With increasing tissue complexity comes increasing complexity of analysis. The aim of this study was to provide critical information for the successful application and analysis of the patient-derived prostate cancer explant model.

Abstract

Prostate cancer is a complex and heterogeneous disease, but a small number of cell lines have dominated basic prostate cancer research, representing a major obstacle in the field of drug and biomarker discovery. A growing lack of confidence in cell lines has seen a shift toward more sophisticated pre-clinical cancer models that incorporate patient-derived tumors as xenografts or explants, to more accurately reflect clinical disease. Not only do these models retain critical features of the original tumor, and account for the molecular diversity and cellular heterogeneity of prostate cancer, but they provide a unique opportunity to conduct research in matched tumor samples. The challenge that accompanies these complex tissue models is increased complexity of analysis. With over 10 years of experience working with patient-derived explants (PDEs) of prostate cancer, this study provides guidance on the PDE method, its limitations, and considerations for addressing the heterogeneity of prostate cancer PDEs that are based on statistical modeling. Using inhibitors of the molecular chaperone heat shock protein 90 (Hsp90) as an example of a drug that induces robust proliferative response, we demonstrate how multi-omics analysis in prostate cancer PDEs is both feasible and essential for identification of key biological pathways, with significant potential for novel drug target and biomarker discovery.

Drug Repurposing Strategies for Non-Cancer to Cancer Therapeutics

Global efforts invested for the prevention and treatment of cancer need to be repositioned to develop safe, effective, and economic anticancer therapeutics by adopting rational approaches of drug discovery. Drug repurposing is one of the established approaches to reposition old, clinically approved off patent noncancer drugs with known targets into newer indications. The literature review suggests key role of drug repurposing in the development of drugs intended for cancer as well as noncancer therapeutics. A wide category of noncancer drugs namely, drugs acting on CNS, anthelmintics, cardiovascular drugs, antimalarial drugs, anti-inflammatory drugs have come out with interesting outcomes during preclinical and clinical phases. In the present article a comprehensive overview of the current scenario of drug repurposing for the treatment of cancer has been focused. The details of some successful studies along with examples have been included followed by associated challenges.

Metformin and Cancer Hallmarks: Molecular Mechanisms in Thyroid, Prostate and Head and Neck Cancer Models

Metformin is the most used drug for type 2 diabetes (T2DM). Its antitumor activity has been described by clinical studies showing reduced risk of cancer development in T2DM patients, as well as management of T2DM compared with those receiving other glucose-lowering drugs. Metformin has a plethora of molecular actions in cancer cells. This review focused on in vitro data on the action mechanisms of metformin on thyroid, prostate and head and neck cancer. AMPK activation regulating specific downstream targets is a constant antineoplastic activity in different types of cancer; however, AMPK-independent mechanisms are also relevant. In vitro evidence makes it clear that depending on the type of tumor, metformin has different actions; its effects may be modulated by different cell conditions (for instance, presence of HPV infection), or it may regulate tissue-specific factors, such as the Na⁺/I⁻ symporter (NIS) and androgen receptors. The hallmarks of cancer are a set of functional features acquired by the cell during malignant development. In vitro studies show that metformin regulates almost all the hallmarks of cancer. Interestingly, metformin is one of these therapeutic agents with the potential to synergize with other chemotherapeutic agents, with low cost, low side effects and high positive consequences. Some questions are still challenging: Are metformin in vitro data able to translate from bench to bedside? Does metformin affect drug resistance? Can metformin be used as a generic anticancer drug for all types of tumors? Which are the specific actions of metformin on the peculiarities of each type of cancer? Several clinical trials are in progress or have been concluded for repurposing metformin as an anticancer drug. The continuous efforts in the field and future in vitro studies will be essential to corroborate clinical trials results and to elucidate the raised questions.

Overcoming Drug Resistance in Advanced Prostate Cancer by Drug Repurposing

Prostate cancer (PCa) is the second most common cancer in men. Common treatments include active surveillance, surgery, or radiation. Androgen deprivation therapy and chemotherapy are usually reserved for advanced disease or biochemical recurrence, such as castration-resistant prostate cancer (CRPC), but they are not considered curative because PCa cells eventually develop drug resistance. The latter is achieved through various cellular mechanisms that ultimately circumvent the pharmaceutical’s mode of action. The need for novel therapeutic approaches is necessary under these circumstances. An alternative way to treat PCa is by repurposing of existing drugs that were initially intended for other conditions. By extrapolating the effects of previously approved drugs to the intracellular processes of PCa, treatment options will expand. In addition, drug repurposing is cost-effective and efficient because it utilizes drugs that have already demonstrated safety and efficacy. This review catalogues the drugs that can be repurposed for PCa in preclinical studies as well as clinical trials.

Inhalation delivery of repurposed drugs for lung cancer: Approaches, benefits and challenges

Lung cancer (LC) is one of the leading causes of mortality accounting for almost 25% of cancer deaths throughout the world. The shortfall of affordable and effective first-line chemotherapeutics, the existence of resistant tumors, and the non-optimal route of administration contribute to poor prognosis and high mortality in LC. Administration of repurposed non-oncology drugs (RNODs) loaded in nanocarriers (NCs) via inhalation may prove as an effective alternative strategy to treat LC. Furthermore, their site-specific release through inhalation route using an appropriate inhalation device would offer improved therapeutic efficacy, thereby reducing mortality and improving patients' quality of life. The current manuscript offers a comprehensive overview on use of RNODs in LC treatment with an emphasis on their inhalation delivery and the associated challenges. The role of NCs to improve lung deposition and targeting of RNODs via inhalation are also elaborated. In addition, information about various RNODs in clinical trials for the treatment of LC, possibility for repurposing phytoceuticals against LC via inhalation and the bottlenecks associated with repurposing RNODs against cancer are also highlighted. Based on the reported studies covered in this manuscript, it was understood that delivery of RNODs via inhalation has emerged as a propitious approach. Hence, it is anticipated to provide effective first-line treatment at an affordable cost in debilitating LC from low and middle-income countries (LMIC).

Anti-cancer potential of some commonly used drugs

Cancer is a global concern leading to millions of deaths every year. A declining trend in new drug discovery and development is becoming one of the major issues among the pharmaceutical, biotechnology industries, and regulatory agencies. New drug development is proven to be a very lengthy and costly process. The launch of a new drug takes 8-12 years and huge investments. The success rate in oncology therapeutics is also low due to toxicities at the pre-clinical and clinical trial levels. Many oncological drugs get rejected at a very promising stage, showing adverse reactions on healthy cells. Thus, exploring new therapeutic benefits of the existing, shelved drugs for their anti-cancerous action could result in a therapeutic approach preventing the toxicities which occur during clinical trials. Drug repurposing has the potential to overcome the challenges faced via conventional way of drug discovery and is becoming an area of interest for researchers and scientists. However, very few in vivo studies are conducted to prove the anti-cancerous activity of the drugs. Insufficient in vivo animal studies and a lack of human clinical trials are the lacunae in the field of drug repurposing. This review focuses on an aspect of drug repurposing for cancer therapeutics. Various studies that show that drugs approved for clinical indications other than cancer have shown promising anti-cancer activities. Some of the commonly used drugs like Benzodiazepines (Diazepam, Midzolam), Antidepressants (Imipramine, Clomipramine, and Citalopram), Antiepileptic (Valporic acid, Phenytoin), Antidiabetics (metformin), etc. have been reported to show potential activity against the cancerous cells.

Regulation of valproic acid induced EMT by AKT/GSK3β/β-catenin signaling pathway in triple negative breast cancer

Valproic acid (VPA) is a selective histone deacetylation (HDAC) inhibitor and exerts anti-cancer properties in different types of cancer. The epithelial-to-mesenchymal transition (EMT) mediating by different signaling cascade can be a potential target in aggressive human cancers. Therefore, we aimed to clarified the unravel relationship between AKT/GSK3β/β-catenin signalling pathway and VPA-induced EMT in triple negative breast cancer (TNBC). The cytotoxicity of VPA in MDA-MB-231 TNBC and MCF-10A control cells was evaluated. Alterations in the expression levels of Snail, E-cadherin, AKT, GSK3β, β-catenin were analyzed by RT-PCR. Additionally, Annexin V, cell cycle and wound healing assays were performed. Our results showed that VPA remarkably inhibited the growth of TNBC cell and triggered apoptotic cell death through G0/G1 arrest. Furthermore, VPA increased cell migration and activated the EMT process through significantly increasing Snail expression and in turn downregulation of E-cadherin and GKS3β levels. However, the level of AKT and β-catenin was reduced after treatment of VPA. Our data showed that VPA induced EMT process and cell migration in TNBC cells. However, AKT/GSK3β/β-catenin signaling pathway did not mediate EMT activation.

Elucidation of the Genomic-Epigenomic Interaction Landscape of Aggressive Prostate Cancer

Background

Majority of prostate cancer (PCa) deaths are attributed to localized high-grade aggressive tumours which progress rapidly to metastatic disease. A critical unmet need in clinical management of PCa is discovery and characterization of the molecular drivers of aggressive tumours. The development and progression of aggressive PCa involve genetic and epigenetic alterations occurring in the germline, somatic (tumour), and epigenomes. To date, interactions between genes containing germline, somatic, and epigenetic mutations in aggressive PCa have not been characterized. The objective of this investigation was to elucidate the genomic-epigenomic interaction landscape in aggressive PCa to identify potential drivers aggressive PCa and the pathways they control. We hypothesized that aggressive PCa originates from a complex interplay between genomic (both germline and somatic mutations) and epigenomic alterations. We further hypothesized that these complex arrays of interacting genomic and epigenomic factors affect gene expression, molecular networks, and signaling pathways which in turn drive aggressive PCa.

Methods

We addressed these hypotheses by performing integrative data analysis combining information on germline mutations from genome-wide association studies with somatic and epigenetic mutations from The Cancer Genome Atlas using gene expression as the intermediate phenotype.

Results

The investigation revealed signatures of genes containing germline, somatic, and epigenetic mutations associated with aggressive PCa. Aberrant DNA methylation had effect on gene expression. In addition, the investigation revealed molecular networks and signalling pathways enriched for germline, somatic, and epigenetic mutations including the STAT3, PTEN, PCa, ATM, AR, and P53 signalling pathways implicated in aggressive PCa.

Conclusions

The study demonstrated that integrative analysis combining diverse omics data is a powerful approach for the discovery of potential clinically actionable biomarkers, therapeutic targets, and elucidation of oncogenic interactions between genomic and epigenomic alterations in aggressive PCa.

New drugs are not enough‑drug repositioning in oncology: An update

Drug repositioning refers to the concept of discovering novel clinical benefits of drugs that are already known for use treating other diseases. The advantages of this are that several important drug characteristics are already established (including efficacy, pharmacokinetics, pharmacodynamics and toxicity), making the process of research for a putative drug quicker and less costly. Drug repositioning in oncology has received extensive focus. The present review summarizes the most prominent examples of drug repositioning for the treatment of cancer, taking into consideration their primary use, proposed anticancer mechanisms and current development status.

Synergistic induction of apoptosis in a cell model of human leukemia K562 by nitroglycerine and valproic acid

Nitroglycerin (NG), a nitric oxide donor, and valproic acid (VPA), an inhibitor of histone deacetylases, have impressive effects on numerous cancer cell lines. This study intended to evaluate synergistic effects of NG and VPA on cell viability and apoptosis in K562 cells. K562 cells were cultured in RPMI-1640 supplemented with 10 % heat-inactivated FBS. They were treated with different doses of NG, VPA and cisplatin for 24, 48, and 72 h, and MTT assay was performed to analyze cell viability. Also, Peripheral blood mononuclear cells (PBMC) were cultured in RPMI-1640 media and incubated with NG (200 μM), VAP (100 μM), NG+VPA (150 μM) and cisplatin (8 μM) to evaluate cytotoxicity. IC₅₀ of the drugs, when they were applied separately and in combination, were calculated using the COMPUSYN software. DNA electrophoresis, TUNEL assay, and Hoechst staining were performed to investigate apoptosis induction. RT-PCR was used for the evaluation of apoptotic genes expression. The results of the MTT assay showed that cell viability decreased at all applied doses of NG and VPA. It was noticed that the cytotoxic effects of these drugs were dose- and time-dependent. Based on the COMPUSYN output, the combination of the drugs (VPA and NG) in a certain ratio concentration synergistically decreased cell viability. Cisplatin significantly decreased cell viability of PBMCs and K562 cells. Also, the combination drug had cytotoxic effect and significantly reduced viability of K562 cells compared with PBMCs and control cells. In the target cells treated with this combination, Bax and caspase-3 expression increased but Bcl-2 expression decreased. These results suggest that NG, VPA, and their combination decreased cell viability and induced apoptosis via the intrinsic apoptotic pathway. This study suggests that this combination therapy can be considered for further evaluation as an effective chemotherapeutic strategy for patients with chronic myeloid leukemia.

Valproic acid-induced amphiregulin secretion confers resistance to temozolomide treatment in human glioma cells

BACKGROUND

Glioblastoma multiforme (GBM) is the most severe type of primary brain tumor with a high mortality rate. Although extensive treatments for GBM, including resection, irradiation, chemotherapy and immunotherapy, have been tried, the prognosis is still poor. Temozolomide (TMZ), an alkylating agent, is a front-line chemotherapeutic drug for the clinical treatment of GBM; however, its effects are very limited because of the chemoresistance. Valproic acid (VPA), an antiepileptic agent with histone deacetylase inhibitor activity, has been shown to have synergistic effects with TMZ against GBM. The mechanism of action of VPA on TMZ combination therapy is still unclear. Accumulating evidence has shown that secreted proteins are responsible for the cross talking among cells in the tumor microenvironment, which may play a critical role in the regulation of drug responses.

METHODS

To understand the effect of VPA on secreted proteins in GBM cells, we first used the antibody array to analyze the cell culture supernatant from VPA-treated and untreated GBM cells. The results were further confirmed by lentivirus-mediated knockdown and exogenous recombinant administration.

RESULTS

Our results showed that amphiregulin (AR) was highly secreted in VPA-treated cells. Knockdown of AR can sensitize GBM cells to TMZ. Furthermore, pretreatment of exogenous recombinant AR significantly increased EGFR activation and conferred resistance to TMZ. To further verify the effect of AR on TMZ resistance, cells pre-treated with AR neutralizing antibody markedly increased sensitivity to TMZ. In addition, we also observed that the expression of AR was positively correlated with the resistance of TMZ in different GBM cell lines.

CONCLUSIONS

The present study aimed to identify the secreted proteins that contribute to the modulation of drug response. Understanding the full set of secreted proteins present in glial cells might help reveal potential therapeutic opportunities. The results indicated that AR may potentially serve as biomarker and therapeutic approach for chemotherapy regimens in GBM.

Metabolomics reveals the effect of valproic acid on MCF-7 and MDA-MB-231 cells

1. Breast cancer is one of the most common malignancies in women worldwide. Metabolomics has been shown to be a promising strategy to elucidate the underlying pathogenesis of cancer and identify new targets for cancer diagnosis and therapy. Valproic acid (VPA), a histone deacetylase inhibitor, is a potential new drug in tumor therapy. This work used metabolomics to examine the effect of VPA on metabolism in breast cancer cells.2. Based on UPLC-MS/MS, we identified 3137 differential metabolites in human breast cancer MCF-7 cells and 2472 differential metabolites in human breast cancer MDA-MB-231 cells after VPA treatment.3. We selected 63 differential metabolites from MCF-7 samples and 61 differential metabolites from MDA-MB-231 cells with the more conspicuous changing trend. Furfural was up-regulated after VPA treatment in both cell lines. In both samples, VPA exerted an effect on the beta-alanine metabolism pathway and the taurine and hypotaurine metabolism pathway.4. This study identified the effect of VPA on metabolites and metabolic pathways in breast cancer cells, and these findings may contribute to the identification of new targets for breast cancer treatment.

Synergistic Effects of Nobiletin and Sorafenib Combination on Metastatic Prostate Cancer Cells

Objective: Herein we, for the first time, investigated a potential synergistic effect of nobiletin (NOB) and sorafenib (SOR) on PC-3 prostate cancer and HUVEC control cell lines. Methods: In order to determine the cytotoxic and apoptotic effects of the combination of NOB and SOR, WST-1, Annexin V, and cell cycle analysis were performed. The potential molecular mechanism of apoptotic cell death was assessed by Bax, Bcl-2, CCDN1, Rb1, and CDKN1A gene expression and acridine orange (AO) and DAPI staining. Results: Our results indicated that NOB and SOR combination had a significant inhibitory effect on the viability of PC-3 cells with less toxicity on HUVEC cells than SOR alone (P < 0.01). NOB and SOR combination significantly caused much more apoptotic cell death and cell cycle arrest at G0/G1 phase by up-regulation of Bax, Rb1, and CDKN1A levels in PC-3 cells (P < 0.01). Therefore, strong synergistic effects between NOB and SOR were analyzed (CI < 1). Conclusion: NOB and SOR combination was more effective than SOR and NOB alone and reduced the exposure time for SOR and NOB in PC-3 cells. Combination strategy is a therapeutic potential to improve efficacy and reduce side-effect of SOR for the treatment of metastatic prostate cancer cells.

Prospects for repurposing CNS drugs for cancer treatment

Drug repurposing is the idea of using an already approved drug for another disease or disorder away from its initial use. This new approach ensures the reduction in high cost required for developing a new drug in addition to the time consumed, especially in the tumor disorders that show an unceasing rising rate with an unmet success rate of new anticancer drugs. In our review, we will review the anti-cancer effect of some CNS drugs, including both therapeutic and preventive, by searching the literature for preclinical or clinical evidence for anticancer potential of central nervous system drugs over the last 8 years period (2010-2018) and including only evidence from Q1 journals as indicated by Scimago website (www.scimagojr.com). We concluded that Some Central Nervous system drugs show a great potential as anti-cancer in vitro, in vivo and clinical trials through different mechanisms and pathways in different types of cancer that reveal a promising evidence for the repurposing of CNS drugs for new indications.

The Combination of Metformin and Valproic Acid Has a Greater Anti-tumoral Effect on Prostate Cancer Growth In Vivo than Either Drug Alone

BACKGROUND/AIM

The hypoglycemic drug metformin (MET) and the anti-epileptic drug valproic acid (VPA) have individually shown anti-tumor effects in prostate cancer in vitro. The present study intended to investigate the efficacy of the combination of MET and VPA in prostate cancer treatment in a pre-clinical xenograft model.

MATERIALS AND METHODS

Prostate cancer cell lines (LNCaP and PC-3) were inoculated under the skin of BALB/c nude mice. The mice were treated with 200 μl/ml MET and/or 0.4% (w/v) VPA diluted in drinking water, or with vehicle control, and were monitored until the tumor volume reached 2,000 mm³ Evaluation of toxicity of the drug combination was determined in liver and kidney by histology.

RESULTS

In both LNCaP and PC-3 xenografts, MET combined with VPA significantly reduced tumor growth during the first 4 weeks following treatment, and delayed the time-to-tumor volume of 2,000 mm³ by 90 days, as compared to MET or to VPA alone, and to vehicle control. There was no significant difference in total mouse weight, liver or kidney morphology in response to combination treatment (MET+VPA) compared to MET or VPA alone and vehicle control.

CONCLUSION

The combination treatment of MET with VPA is more effective at slowing prostate tumor growth in vivo compared to either drug alone, in mouse xenografts. These pre-clinical results support previous in vitro data and also demonstrate the low toxicity of the combination of these drugs, suggesting that this may be a potential new therapy to be investigated in clinical trials for prostate cancer.

The anticancer potential of metformin on prostate cancer

BACKGROUND

Prostate cancer (PCa) is characterized as the most frequent type of cancer in males. Recent research has suggested patients who have diabetes mellitus taking metformin (MF) have a lower risk of PCa. MF has antineoplastic effects such as adenosine monophosphate-activated protein kinase (AMPK)-dependent and independent mechanisms, suppression of androgen signaling pathway, and alterations of insulin-like growth factor-1 (IGF-1) signaling pathways that cause the growth and proliferation of PCa. Based on epidemiological factors, patients with diabetes mellitus may have a protective effect on PCa.

METHODS

A literature search on MEDLINE® was conducted using a combined query of "prostate cancer" and "metformin" to yield publications unveiling the mechanisms of action, biological effects, epidemiological evidence, and research advances of MF with respect to PCa.

RESULTS

Evidence has shown that MF has multiple antineoplastic effects through AMPK-dependent and independent mechanisms, the alteration of IGF-1 signaling pathways, suppression of the androgen receptor pathway, inhibition of the mTOR pathway, and lipogenesis. Conduction of meta-analysis suggests mortality benefit to patients who exhibit PCa when taking MF. Clinical trials have shown evidence, demonstrating MF to improving significantly.

CONCLUSIONS

Herewith we review the literature regarding the numerous mechanisms of action of MF on PCa in order to decrease or repress the growth, proliferation, and differentiation of PCa cells. We analyze the molecular impacts of MF as well as adjunct therapies such as androgen deprivation therapy, aspirin, statin, or chemotherapy, proposing that MF may have a future role in the treatment protocol of PCa whether as a monotherapy or in combination with other drugs.

Metformin alters H2A.Z dynamics and regulates androgen dependent prostate cancer progression

Epigenetic mechanisms involved in prostate cancer include hypermethylation of tumor suppressor genes, general hypomethylation of the genome, and alterations in histone posttranslational modifications (PTMs). In addition, over expression of the histone variant H2A.Z as well as deregulated expression of Polycomb group proteins including EZH2 have been well-documented. Recent evidence supports a role for metformin in prostate cancer (PCa) treatment. However, the mechanism of action of metformin in PCa is poorly understood. We provide data showing that metformin epigenetically targets PCa by altering the levels and gene binding dynamics of histone variant H2A.Z. Moreover, we show that the increase in H2A.Z upon metformin treatment occurs preferentially due to H2A.Z.1 isoform. Chromatin immunoprecipitation (ChIP)-RT PCR analysis indicates that metformin treatment results in an increased H2A.Z occupancy on the androgen receptor (AR) and AR-regulated genes that is more prominent in the androgen dependent AR positive LNCaP cells. Repression of H2A.Z.1 gene by siRNA-mediated knock down identified this H2A.Z isoform to be responsible. Based on preliminary data with an EZH2-specific inhibitor, we suggest that the effects of metformin on the early stages of PCa may involve both EZH2 and H2A.Z through the alteration of different molecular pathways.

Repurposing old drugs in oncology: Opportunities with clinical and regulatory challenges ahead

WHAT IS KNOWN AND OBJECTIVE

In order to expedite the availability of drugs to treat cancers in a cost-effective manner, repurposing of old drugs for oncological indications is gathering momentum. Revolutionary advances in pharmacology and genomics have demonstrated many old drugs to have activity at novel antioncogenic pharmacological targets. We decided to investigate whether prospective studies support the promises of nonclinical and retrospective clinical studies on repurposing three old drugs, namely metformin, valproate and astemizole.

METHODS

We conducted an extensive literature search through PubMed to gather representative nonclinical and retrospective clinical studies that investigated the potential repurposing of these three drugs for oncological indications. We then searched for prospective studies aimed at confirming the promises of retrospective data.

RESULTS AND DISCUSSION

While evidence from nonclinical and retrospective clinical studies with these drugs appears highly promising, large scale prospective studies are either lacking or have failed to substantiate this promise. We provide a brief discussion of some of the challenges in repurposing. Principal challenges and obstacles relate to heterogeneity of cancers studied without considering their molecular signatures, trials with small sample size and short duration, failure consider issues of ethnicity of study population and effective antioncogenic doses of the drug studied.

WHAT IS NEW AND CONCLUSION

Well-designed prospective studies demonstrating efficacy are required for repurposing old drugs for oncology indications, just as they are for new chemical entities for any indication. Early and ongoing interactions with regulatory authorities are invaluable. We outline a tentative framework for a structured approach to repurposing old drugs for novel indications in oncology.

Combination Therapies Using Metformin and/or Valproic Acid in Prostate Cancer: Possible Mechanistic Interactions

Prostate cancer (PCa) is the most frequent cancer in men. The evolution from local PCa to castration-resistant PCa, an end-stage of disease, is often associated with changes in genes such as p53, androgen receptor, PTEN, and ETS gene fusion products. Evidence is accumulating that repurposing of metformin (MET) and valproic acid (VPA) either when used alone, or in combination, with another therapy, could potentially play a role in slowing down PCa progression. This review provides an overview of the application of MET and VPA, both alone and in combination with other drugs for PCa treatment, correlates the responses to these drugs with common molecular changes in PCa, and then describes the potential for combined MET and VPA as a systemic therapy for prostate cancer, based on potential interacting mechanisms.

Metformin-induced apoptosis facilitates degradation of the cellular caspase 8 (FLICE)-like inhibitory protein through a caspase-dependent pathway in human renal cell carcinoma A498 cells

Renal cell carcinoma (RCC) is one of the most common types of cancer in adults. Previous studies have reported that the survival rate was significantly lower for renal cancer patients with diabetes than for those without diabetes. Metformin is a well-known anti-diabetic agent used for the treatment of type 2 diabetes mellitus (T2DM). It also inhibits cell proliferation and angiogenesis and is known to possess antitumor effects. However, the molecular mechanism for metformin-induced apoptosis in renal cell carcinoma is not understood. In the present study, treatment with metformin induced apoptosis in A498 cells in a dose-dependent manner. It was revealed that degradation of cellular caspase 8 (FLICE)-like inhibitory protein (c-FLIP) and activation of procaspase-8 were associated with metformin-mediated apoptosis. By contrast, treatment with metformin did not affect the mRNA level of c-FLIP_L in A498 cells. Treatment with benzyloxycarbonyl-Val-Ala-Asp-fluoromethyl ketone (z-VAD-fmk, a pan-caspase inhibitor) almost completely blocked metformin-induced apoptosis and degradation of c-FLIP_L protein. However, N-acetyl-L-cysteine (NAC), a reactive oxygen species (ROS) scavenger, did not inhibit metformin-mediated apoptosis in A498 cells. Taken together, the results of the present study demonstrated that metformin-induced apoptosis involved degradation of the c-FLIP_L protein and activation of caspase-8 in human renal cell carcinoma A498 cells and suggested that metformin could be potentially used for the treatment of renal cancer.

Drug Repositioning for Effective Prostate Cancer Treatment

Drug repositioning has gained attention from both academia and pharmaceutical companies as an auxiliary process to conventional drug discovery. Chemotherapeutic agents have notorious adverse effects that drastically reduce the life quality of cancer patients so drug repositioning is a promising strategy to identify non-cancer drugs which have anti-cancer activity as well as tolerable adverse effects for human health. There are various strategies for discovery and validation of repurposed drugs. In this review, 25 repurposed drug candidates are presented as result of different strategies, 15 of which are already under clinical investigation for treatment of prostate cancer (PCa). To date, zoledronic acid is the only repurposed, clinically used, and approved non-cancer drug for PCa. Anti-cancer activities of existing drugs presented in this review cover diverse and also known mechanisms such as inhibition of mTOR and VEGFR2 signaling, inhibition of PI3K/Akt signaling, COX and selective COX-2 inhibition, NF-κB inhibition, Wnt/β-Catenin pathway inhibition, DNMT1 inhibition, and GSK-3β inhibition. In addition to monotherapy option, combination therapy with current anti-cancer drugs may also increase drug efficacy and reduce adverse effects. Thus, drug repositioning may become a key approach for drug discovery in terms of time- and cost-efficiency comparing to conventional drug discovery and development process.

Metformin combined with quercetin synergistically repressed prostate cancer cells via inhibition of VEGF/PI3K/Akt signaling pathway

The aim of present study was to examine whether metformin in association with quercetin has any synergistically anti-tumor effects on prostate cancer. Our findings showed that metformin in combination with quercetin synergistically inhibited the growth, migration and invasion of both PC-3 and LNCaP cells. Co-treatment of these two agents induced more apoptosis than single agent treatment. The co-treatment-induced apoptosis was caspase-dependent and accompanied by the down-regulation of Bcl-2 family members. Our data also indicated that co-treatment of metformin and quercetin strongly inhibited the VEGF/Akt/PI3K pathway. Moreover, these two agents acted synergistically to repress the growth of human prostate cancer cell xenograft in vivo in nude mice. In conclusion, our findings indicate that the combination therapy of metformin and quercetin exerted synergistic antitumor effects in prostate cancers via inhibition of VEGF/Akt/PI3K pathway. Thus, combination treatment of metformin and quercetin would be a promising therapeutic strategy for prostate cancer patients.