New potential anti-cancer agents synergize with bortezomib and ABT-737 against prostate cancer

Oncogenic role of FOXM1 in human prostate cancer (Review)

Prostate cancer is the leading cause of cancer‑related mortality among men worldwide. In particular, castration‑resistant prostate cancer presents a formidable clinical challenge and emphasizes the need to develop novel therapeutic strategies. Forkhead box M1 (FOXM1) is a multifaceted transcription factor that is implicated in the acquisition of the multiple cancer hallmark capabilities in prostate cancer cells, including sustaining proliferative signaling, resisting cell death and the activation of invasion and metastasis. Elevated FOXM1 expression is frequently observed in prostate cancer, and in particular, FOXM1 overexpression is closely associated with poor clinical outcomes in patients with prostate cancer. In the present review, recent advances in the understanding of the oncogenic role of deregulated FOXM1 expression in prostate cancer were highlighted. In addition, the molecular mechanisms by which FOXM1 regulates prostate cancer development and progression were described, thereby providing knowledge and a conceptual framework for FOXM1. The present review also provided valuable insight into the inherent challenges associated with translating biomedical knowledge into effective therapeutic strategies for prostate cancer.

Small-molecule inhibitors targeting FOXM1: Current challenges and future perspectives in cancer treatments

Forkhead box (FOX) protein M1 (FOXM1) is a critical proliferation-associated transcription factor (TF) that is aberrantly overexpressed in the majority of human cancers and has also been implicated in poor prognosis. A comprehensive understanding of various aspects of this molecule has revealed its role in, cell proliferation, cell migration, invasion, angiogenesis and metastasis. The FOXM1 as a TF directly or indirectly regulates the expression of several target genes whose dysregulation is associated with almost all hallmarks of cancer. Moreover, FOXM1 expression is associated with chemoresistance to different anti-cancer drugs. Several studies have confirmed that suppression of FOXM1 enhanced the drug sensitivity of various types of cancer cells. Current data suggest that small molecule inhibitors targeting FOXM1 in combination with anticancer drugs may represent a novel therapeutic strategy for chemo-resistant cancers. In this review, we discuss the clinical utility of FOXM1, further, we summarize and discuss small-molecule inhibitors targeting FOXM1 and categorize them according to their mechanisms of targeting FOXM1. Despite great progress, small-molecule inhibitors targeting FOXM1 face many challenges, and we present here all small-molecule FOXM1 inhibitors in different stages of development. We discuss the current challenges and provide insights on the future application of FOXM1 inhibition to the clinic.

Comprehensive Analysis of Cell Cycle-Related Genes in Patients With Prostate Cancer

This study aimed to identify critical cell cycle-related genes (CCRGs) in prostate cancer (PRAD) and to evaluate the clinical prognostic value of the gene panel selected. Gene set variation analysis (GSVA) of dysregulated genes between PRAD and normal tissues demonstrated that the cell cycle-related pathways played vital roles in PRAD. Patients were classified into four clusters, which were associated with recurrence-free survival (RFS). Moreover, 200 prognostic-related genes were selected using the Kaplan-Meier (KM) survival analysis and univariable Cox regression. The prognostic CCRG risk score was constructed using random forest survival and multivariate regression Cox methods, and their efficiency was validated in Memorial Sloan Kettering Cancer Center (MSKCC) and GSE70770. We identified nine survival-related genes: CCNL2, CDCA5, KAT2A, CHTF18, SPC24, EME2, CDK5RAP3, CDC20, and PTTG1. Based on the median risk score, the patients were divided into two groups. Then the functional enrichment analyses, mutational profiles, immune components, estimated half-maximal inhibitory concentration (IC50), and candidate drugs were screened of these two groups. In addition, the characteristics of nine hub CCRGs were explored in Oncomine, cBioPortal, and the Human Protein Atlas (HPA) datasets. Finally, the expression profiles of these hub CCRGs were validated in RWPE-1 and three PRAD cell lines (PC-3, C4-2, and DU-145). In conclusion, our study systematically explored the role of CCRGs in PRAD and constructed a risk model that can predict the clinical prognosis and immunotherapeutic benefits.

The bacterial thiopeptide thiostrepton. An update of its mode of action, pharmacological properties and applications

The bacterial thiopeptide thiostrepton (TS) is used as a veterinary medicine to treat bacterial infections. TS is a protein translation inhibitor, essentially active against Gram-positive bacteria and some Gram-negative bacteria. In procaryotes, TS abrogates binding of GTPase elongation factors to the 70S ribosome, by altering the structure of rRNA-L11 protein complexes. TS exerts also antimalarial effects by disrupting protein synthesis in the apicoplast genome of Plasmodium falciparum. Interestingly, the drug targets both the infectious pathogen (bacteria or parasite) and host cell, by inducing endoplasmic reticulum stress-mediated autophagy which contributes to enhance the host cell defense. In addition, TS has been characterized as a potent chemical inhibitor of the oncogenic transcription factor FoxM1, frequently overexpressed in cancers or other diseases. The capacity of TS to crosslink FoxM1, and a few other proteins such as peroxiredoxin 3 (PRX3) and the 19S proteasome, contributes to the anticancer effects of the thiopeptide. The anticancer activities of TS evidenced using diverse tumor cell lines, in vivo models and drug combinations are reviewed here, together with the implicated targets and mechanisms. The difficulty to formulate TS is a drag on the pharmaceutical development of the natural product. However, the design of hemisynthetic analogues and the use of micellar drug delivery systems should facilitate a broader utilization of the compound in human and veterinary medicines. This review shed light on the many pharmacological properties of TS, with the objective to promote its use as a pharmacological tool and medicinal product.

BH3-mimetics: recent developments in cancer therapy

The hopeful outcomes from 30 years of research in BH3-mimetics have indeed served a number of solid paradigms for targeting intermediates from the apoptosis pathway in a variety of diseased states. Not only have such rational approaches in drug design yielded several key therapeutics, such outputs have also offered insights into the integrated mechanistic aspects of basic and clinical research at the genetics level for the future. In no other area of medical research have the effects of such work been felt, than in cancer research, through targeting the BAX-Bcl-2 protein-protein interactions. With these promising outputs in mind, several mimetics, and their potential therapeutic applications, have also been developed for several other pathological conditions, such as cardiovascular disease and tissue fibrosis, thus highlighting the universal importance of the intrinsic arm of the apoptosis pathway and its input to general tissue homeostasis. Considering such recent developments, and in a field that has generated so much scientific interest, we take stock of how the broadening area of BH3-mimetics has developed and diversified, with a focus on their uses in single and combined cancer treatment regimens and recently explored therapeutic delivery methods that may aid the development of future therapeutics of this nature.

Dual Akt and Bcl-2 inhibition induces cell-type specific modulation of apoptotic and autophagic signaling in castration resistant prostate cancer cell lines

BACKGROUND

Cancer cell survival depends on the cross-regulation between apoptosis and autophagy which share common signaling pathways including PI3K/Akt/mTOR and Bcl-2. The aim of this study was to elucidate the modulation patterns between apoptosis and autophagy following dual inhibition by Akt inhibitor erufosine and Bcl-2 inhibitor ABT-737 in castration-resistant prostate cancer (CRPC) cell lines, PC-3 (Bax+) and DU-145 (Bax-).

METHODS AND RESULTS

Cell cycle progression, apoptotic and autophagic signaling were examined by flow cytometry, multi-caspase assay, Hoechst staining, acridine orange staining of acidic vesicular organelles (AVOs), qRT-PCR and Western Blot. Dual inhibition increased G2/M arrest in PC-3 and DU-145, but not in the healthy prostate epithelium cells, PNT-1A. Only in PC-3, dual inhibition induced synergistic apoptotic and additive autophagic effects. In DU-145 and PNT-1A cells, ABT-737 did not display any remarkable effect on multicaspase activity and erufosine and ABT-737, neither alone nor in combination induced AVOs. By dual inhibition, AKT, BCL-2 and NF-κB gene expressions were downregulated in PC-3, both ATG-5 and BECLIN-1 gene expressions were upregulated in DU-145 but Beclin-1 protein expression was substantially reduced in both CRPC cells. Dual inhibition-induced synergistic multicaspase activation in PC-3 degrades and disrupts autophagic activity of Beclin-1, enhancing caspase-dependent apoptosis. However, in DU-145, following dual inhibition, rate of multicaspase induction and apoptosis are lower but autophagy is completely abolished despite markedly increased BECLIN-1 gene expression.

CONCLUSION

In conclusion, antineoplastic drug combinations may display cell-type specific modulation of apoptotic and autophagic signaling and lack of protective autophagy may not necessarily indicate increased chemotherapeutic sensitivity in heterogenous tumor subpopulations.

Novel Therapeutic Strategies for CDK4/6 Inhibitors in Metastatic Castrate-Resistant Prostate Cancer

The majority of patients with castrate-resistant prostate cancer will have metastatic disease at the time of diagnosis. Investigative efforts on new therapeutics for this patient population have improved with the development of androgen signaling inhibitors, such as abiraterone and enzalutamide, and PARP inhibitors, such as rucaparib and olaparib, to accompany the previously FDA-approved docetaxel, cabazitaxel, sipuleucel-T, and Radium 223. However, new therapeutic strategies are necessary to prolong survival as progression after these agents is inevitable. CDK4/6 inhibitors have advanced the field of estrogen receptor positive breast cancer treatment and are being investigated in prostate cancer given the role of androgen receptor signaling effects on the cell cycle. Response to CDK4/6 inhibitors may be predicted by the tumors' genomic profile and may provide insight into combinatory therapy with CDK4/6 inhibitors in order to delay resistance or provide synergistic effects. Here, we review the use of CDK4/6 inhibitors in prostate cancer and potential combinations based on known resistance mechanisms to CDK4/6 inhibitors, prostate cancer regulatory pathways, and prostate-cancer-specific genomic alterations.

ABT-737 and erufosine combination against castration-resistant prostate cancer: a promising but cell-type specific response associated with the modulation of anti-apoptotic signaling

A deeper understanding of the molecular basis of castration-resistant prostate cancer (CRPC) paved the way for the rational design and development of targeted therapies, which yielded promising preclinical results. However, translation of these potentially promising agents into clinics has usually failed, partly because of tumor heterogeneity. In this study, anticancer activities of the Bcl-2 inhibitor ABT-737 and the Akt-inhibitor erufosine (ErPC3) alone and in combination were compared between CRPC (PC-3 and DU-145) and healthy (PNT-1A) cell lines. The combination of ABT-737 and ErPC3 showed synergistic antiproliferative, antimigratory, and apoptotic effects in PC-3 cells. In DU-145 cells, ErPC3 showed a resistant profile, with half-maximal inhibitory concentration (IC50) values more than two-fold of PC-3, and combining ErPC3 with ABT-737 yielded no added benefit for all the incubation periods compared with ErPC3 alone. In PNT-1A cells, ABT-737 and ErPC3 alone and in combination reduced cell survival slightly and only at the highest concentrations. Apoptosis analysis showed that ABT-737 induced increased Akt expression and ErPC3 induced increased Mcl-1 expression in DU-145 cells. In conclusion, the ABT-737 and ErPC3 combination seems to be promising against CRPC, with a favorable safety profile in healthy cells. However, CRPC cell-type-specific resistance may be induced by enhancement of antiapoptotic signaling.

Single and dual target inhibitors based on Bcl-2: Promising anti-tumor agents for cancer therapy

B-cell lymphoma-2 (Bcl-2) proteins family is an essential checkpoint in apoptosis. Extensive evidences suggested that overexpression of anti-apoptotic Bcl-2 proteins can be observed in multiple cancer cell lines and primary tumor biopsy samples, which is an important reason for tumor cells to evade apoptosis and further acquire drug resistance for chemotherapy. Hence, down-regulation of anti-apoptotic Bcl-2 proteins is effective for the treatment of cancers. In view that Bcl-2 inhibitors and some other anti-tumor agents, such as HDAC inhibitors and Mdm2 inhibitors, exert synergy effects in tumor cells, it is pointed out that dual-targeting therapies based on these targets are regarded as rational strategies to enhance the effectiveness of single target agents for cancer treatment. This review briefly introduces the apoptosis, the structure of Bcl-2 family proteins, and focuses on the current status and recent advances of Bcl-2 inhibitors and the corresponding SARs of them. Moreover, we discuss the synergisms between Bcl-2 and other anti-tumor targets, and summarize the current dual-target agents.

TRIM6 promotes colorectal cancer cells proliferation and response to thiostrepton by TIS21/FoxM1

BACKGROUND

Tripartite motif-containing proteins (TRIM) play a crucial role in carcinogenesis. Little attention has been focused on the possible functions of TRIM6 on carcinogenesis.

METHODS

The expression levels of TRIM6 were assessed in colorectal cancer (CRC) samples. TRIM6 expression was knocked down in CRC cell lines, and subjected to Cell counting kit-8 (CCK-8), bromodeoxyuridine (BrdU) incorporation and cell cycle assays. Immunoprecipitation and proteomics analysis was performed to identify potential associated proteins of TRIM6.

RESULTS

TRIM6 expression was up-regulated in CRC samples and TRIM6 expression may be an independent prognostic marker for CRC. Knocking down TRIM6 expression suppressed CRC cell proliferation, induced cell cycle arrested at G2/M phase and increased sensitivity to 5-fluorouracil and oxaliplatin. TIS21, an anti-proliferative protein involved in the regulation of G2/M arrest, was identified as an interaction partner of TRIM6. Moreover, CRC cells with TRIM6 overexpression showed decreased TIS21 protein stability. TIS21 ubiquitination was increased in CRC cells overexpressing TRIM6, but not in those overexpressing TRIM6 E3 catalytic mutant (C15A). Further, Lys5 was essential for TRIM6 mediated TIS21 ubiquitination. TIS21 overexpression reversed the induced effects of TRIM6 overexpression on CRC cell proliferation, and the levels of forkhead box M1 (FoxM1), phosphorylated FoxM1, Cyclin B1 and c-Myc. Thiostrepton, a specific inhibitor for FoxM1, was less effective in anti-proliferative activity against CRC cells with lower level of TRIM6 in vitro and in vivo.

CONCLUSIONS

Our study suggests that TRIM6 promotes the progression of CRC via TIS21/FoxM1.

Discovery of therapeutic agents for prostate cancer using genome-scale metabolic modeling and drug repositioning

BACKGROUND

Genome-scale metabolic models (GEMs) offer insights into cancer metabolism and have been used to identify potential biomarkers and drug targets. Drug repositioning is a time- and cost-effective method of drug discovery that can be applied together with GEMs for effective cancer treatment.

METHODS

In this study, we reconstruct a prostate cancer (PRAD)-specific GEM for exploring prostate cancer metabolism and also repurposing new therapeutic agents that can be used in development of effective cancer treatment. We integrate global gene expression profiling of cell lines with >1000 different drugs through the use of prostate cancer GEM and predict possible drug-gene interactions.

FINDINGS

We identify the key reactions with altered fluxes based on the gene expression changes and predict the potential drug effect in prostate cancer treatment. We find that sulfamethoxypyridazine, azlocillin, hydroflumethiazide, and ifenprodil can be repurposed for the treatment of prostate cancer based on an in silico cell viability assay. Finally, we validate the effect of ifenprodil using an in vitro cell assay and show its inhibitory effect on a prostate cancer cell line.

INTERPRETATION

Our approach demonstate how GEMs can be used to predict therapeutic agents for cancer treatment based on drug repositioning. Besides, it paved a way and shed a light on the applicability of computational models to real-world biomedical or pharmaceutical problems.

BH3 Mimetics for the Treatment of Prostate Cancer

Despite improved diagnostic and therapeutic intervention, advanced prostate cancer (PC) remains incurable. The acquired resistance of PC cells to current treatment protocols has been traced to apoptosis resistance based on the upregulation of anti-apoptotic proteins of the Bcl-2 family. The use of BH3 mimetics, mimicking pro-apoptotic activator or sensitizer proteins of the intrinsic apoptotic pathway, is therefore a promising treatment strategy. The present review gives an overview of preclinical and clinical studies with pan- and specific BH3 mimetics as sensitizers for cell death and gives an outlook how they could be effectively used for the therapy of advanced PC in future.

MLN2238 synergizes BH3 mimetic ABT-263 in castration-resistant prostate cancer cells by induction of NOXA

Patients undergoing androgen blockade therapy develop castration-resistant prostate cancer (CRPC), which is associated with Bcl-2 upregulation and results in disease progression and death. In recent years, promising therapeutic agents, such as the BH3-only mimetic ABT-263 and proteasome inhibitors, have been developed and widely evaluated against a broad spectrum of cancer types, including prostate cancer, alone or in combination with other chemotherapeutic agents. In this study, the antitumor efficacy of ABT-263 and MLN2238 were evaluated as single agents and in combination in four CRPC cell lines: PC3, C4-2B, C4-2, and DU145. The viability of the treated cells and markers of apoptosis were assayed. Protein-protein interactions were analyzed by co-immunoprecipitation in drug-treated cells. Lentivirus-mediated short hairpin RNA was used to knockdown Bax, Mcl-1, and NOXA expressions. We found that ABT-263 and MLN2238 alone exhibited a mild cytotoxicity, and in combination, they elicited a synergistic cytotoxic effect in CRPC cells. The cell apoptosis induced by the combination drug treatment was evidenced by enhanced caspase-3 and Poly (ADP-ribose) polymerase (PARP) cleavage, and annexin-V-positive staining was significantly depleted by Bax knockdown. MLN2238 treatment upregulated NOXA and Mcl-1 expression, leading NOXA/Mcl-1 complexes to disassociate Bak from its complexes with Mcl-1 and enhancing ABT263-triggered Bax activation. NOXA knockdown by short hairpin RNA significantly attenuated the cytotoxicity of ABT-263 and MLN2238 co-administration. In conclusion, MLN2238 and ABT-263 synergistically triggered apoptosis in CRPC cells by upregulating NOXA and activating Bax, indicating a promising therapeutic strategy for the treatment of CRPC.

Suppression of the Oncogenic Transcription Factor FOXM1 by Proteasome Inhibitors

The oncogenic transcription factor FOXM1 is one of the key regulators of tumorigenesis. We found that FOXM1 upregulates its own transcription and its protein stability depends on its interaction with the chaperone nucleophosmin. We also determined that FOXM1 is negatively regulated by the tumor suppressor p53. We identified the thiazole antibiotics Siomycin A and thiostrepton as inhibitors of transcriptional activity and FOXM1 expression via proteasome inhibition. In addition, we found that all tested proteasome inhibitors target FOXM1. We showed synergy between thiostrepton and bortezomib in different human cancer cell lines and in vivo. We generated isogenic human cancer cell lines of different origin with wild-type p53 or p53 knockdown and we demonstrated that proteasome inhibitors induce p53-independent apoptosis in these cells. Using RNA-interference or proteasome inhibitors to inhibit FOXM1 we found that suppression of FOXM1 sensitized human cancer cells to apoptosis induced by DNA-damaging agents or oxidative stress. We encapsulated thiostrepton into micelle-nanoparticles and after injection we detected accumulation of nanoparticles in tumors and in the livers of treated mice. This treatment led to inhibition of human xenograft tumor growth in nude mice. Our data indicate that targeting FOXM1 increases apoptosis and inhibits tumor growth.

Targeting CDK9 by wogonin and related natural flavones potentiates the anti-cancer efficacy of the Bcl-2 family inhibitor ABT-263

Tumor initiation, progression and resistance to therapies are tightly associated with over-expression of anti-apoptotic proteins Bcl-2, Bcl-x(L), Bcl-w and Mcl-1. ABT-263 (Navitoclax), an orally bio-available small-molecule mimetic of the Bcl-2 homology domain 3, inhibits Bcl-2, Bcl-x(L), and Bcl-w and has shown anti-cancer effects mainly on lymphomas and lymphocytic leukemia. Despite promising results obtained from the clinical trials, the use of ABT-263 in patients is dose-limited due to causing thrombocytopenia via inhibition of Bcl-x(L) in platelets. ABT-199 specifically inhibits Bcl-2; however, its use is limited to tumors over-expressing only Bcl-2. Besides, many tumors resist treatment due to high levels of Mcl-1 expression or develop resistance via up-regulation of Mcl-1 during long-term exposure. These obstacles highlight the demand to improve the ABT-263-based therapy. In this study, we show that anti-cancer flavones, e.g., wogonin, baicalein, apigenin, chrysin and luteolin enhance ABT-263-induced apoptosis in different cancer cell lines and in primary AML and ALL cells by down-regulation of Mcl-1 expression. Importantly, wogonin does not enhance the toxicity of ABT-263 to proliferating normal T cells and thrombocytes. Wogonin also potentiates the lethality of ABT-263 in cancer cells which have acquired resistance to ABT-263. Furthermore, we show that combination of wogonin with ABT-263 promotes in vivo tumor regression in a human T-cell leukemia xenograft mouse model. Our study demonstrates that wogonin (and related flavones) reduce the effective dose of ABT-263 thereby possibly decreasing the risk of adverse side effects.

FOXM1 and androgen receptor co-regulate CDC6 gene transcription and DNA replication in prostate cancer cells

CDC6 is a key component of the DNA replication initiation machinery, and its transcription is regulated by E2F or androgen receptor (AR) alone or in combination in prostate cancer (PCa) cells. Through both overexpression and knockdown approaches, we found that in addition to its effects on the E2F pathway, the cell proliferation specific transcription factor FOXM1 stimulated CDC6 transcription in cooperation with AR. We have identified a forkhead box motif in the CDC6 proximal promoter that is occupied by FOXM1 and is sufficient to drive FOXM1-regulated transcription. Indirectly, FOXM1 elevated AR protein levels and AR dependent transcription. Furthermore, FOXM1 and AR proteins physically interact. Using synchronized cultures, we observed that CDC6 expression is elevated near S phase of the cell cycle, at a time coinciding with elevated FOXM1 and AR expression and CDC6 promoter occupancy by both AR and FOXM1 proteins. Androgen increased the binding of AR protein to CDC6 promoter, and AR and FOXM1 knockdown decreased AR binding. These results provided new evidence for the regulatory mechanism of aberrant CDC6 oncogene transcription by FOXM1 and AR, two highly expressed transcription factors in PCa cells. Functionally, the cooperation of FOXM1 and AR accelerated DNA synthesis and cell proliferation by affecting CDC6 gene expression. Furthermore, siomycin A, a proteasome inhibitor known to inhibit FOXM1 expression and activity, inhibited PCa cell proliferation and its effect was additive to that of bicalutamide, an antiandrogen commonly used to treat PCa patients.

The dual inhibitory effect of thiostrepton on FoxM1 and EWS/FLI1 provides a novel therapeutic option for Ewing's sarcoma

The poor prognosis of Ewing’s sarcoma (EWS), together with its high lethal recurrence rate and the side-effects of current treatments, call for novel targeted therapies with greater curative effectiveness and substantially reduced side-effects. The oncogenic chimeric protein EWS/FLI1 is the key malignancy driver in most EWSs, regulating numerous target genes, many of which influence cell cycle progression. It has often been argued that targeting proteins regulated directly or indirectly by EWS/FLI1 may provide improved therapeutic options for EWS. In this context, our study examined FoxM1, a key cell cycle regulating transcription factor, reported to be expressed in EWS and influenced by EWS/FLI1. Thiostrepton, a naturally occurring small molecule, has been shown to selectively inhibit FoxM1 expression in cancer cells. We demonstrate that in EWS, in addition to inhibiting FoxM1 expression, thiostrepton downregulates the expression of EWS/FLI1, both at the mRNA and protein levels, leading to cell cycle arrest and, ultimately, to apoptotic cell death. We also show that thiostrepton treatment reduces the tumorigenicity of EWS cells, significantly delaying the growth of nude mouse xenograft tumors. Results from this study demonstrate a novel action of thiostrepton as inhibitor of the expression of the EWS/FLI1 oncoprotein in vitro and in vivo, and that it shows greater efficacy against EWS than against other tumor types, as it is active on EWS cells and tumors at concentrations lower than those reported to have effective inhibitory activity on tumor cells derived from other cancers. Owing to the dual action of this small molecule, our findings suggest that thiostrepton may be particularly effective as a novel agent for the treatment of EWS patients.

FOXM1 (Forkhead box M1) in tumorigenesis: overexpression in human cancer, implication in tumorigenesis, oncogenic functions, tumor-suppressive properties, and target of anticancer therapy

FOXM1 (Forkhead box M1) is a typical proliferation-associated transcription factor and is also intimately involved in tumorigenesis. FOXM1 stimulates cell proliferation and cell cycle progression by promoting the entry into S-phase and M-phase. Additionally, FOXM1 is required for proper execution of mitosis. In accordance with its role in stimulation of cell proliferation, FOXM1 exhibits a proliferation-specific expression pattern and its expression is regulated by proliferation and anti-proliferation signals as well as by proto-oncoproteins and tumor suppressors. Since these factors are often mutated, overexpressed, or lost in human cancer, the normal control of the foxm1 expression by them provides the basis for deregulated FOXM1 expression in tumors. Accordingly, FOXM1 is overexpressed in many types of human cancer. FOXM1 is intimately involved in tumorigenesis, because it contributes to oncogenic transformation and participates in tumor initiation, growth, and progression, including positive effects on angiogenesis, migration, invasion, epithelial-mesenchymal transition, metastasis, recruitment of tumor-associated macrophages, tumor-associated lung inflammation, self-renewal capacity of cancer cells, prevention of premature cellular senescence, and chemotherapeutic drug resistance. However, in the context of urethane-induced lung tumorigenesis, FOXM1 has an unexpected tumor suppressor role in endothelial cells because it limits pulmonary inflammation and canonical Wnt signaling in epithelial lung cells, thereby restricting carcinogenesis. Accordingly, FOXM1 plays a role in homologous recombination repair of DNA double-strand breaks and maintenance of genomic stability, that is, prevention of polyploidy and aneuploidy. The implication of FOXM1 in tumorigenesis makes it an attractive target for anticancer therapy, and several antitumor drugs have been reported to decrease FOXM1 expression.

Targeting FOXM1 in cancer

Oncogenic transcription factor FOXM1 is overexpressed in the majority of human cancers. In addition, FOXM1 has been implicated in cell migration, invasion, angiogenesis and metastasis. The important role of FOXM1 in cancer affirms its significance for therapeutic intervention. Current data suggest that targeting FOXM1 in mono- or combination therapy may have promising therapeutic benefits for the treatment of cancer. However, challenges with the delivery of anti-FOXM1 siRNA to tumors and the absence of small molecules, which specifically inhibit FOXM1, are delaying the development of FOXM1 inhibitors as feasible anticancer drugs. In this review, we describe and summarize the efforts that have been made to target FOXM1 in cancer and the consequences of FOXM1 suppression in human cancer cells.

Bcl-2 family of proteins as therapeutic targets in genitourinary neoplasms

INTRODUCTION

Overexpression of antiapoptotic B-cell lymphoma (Bcl-2) proteins confers the dysregulation of apoptosis and results in drug resistance in a variety of cancers, including those of the genitourinary tract. Inhibitors that target prosurvival Bcl-2 proteins are in preclinical and clinical development. The objective of this review is to assess the involvement of Bcl-2 proteins as well as the preclinical and clinical activity of Bcl-2 inhibitors under evaluation for genitourinary neoplasms.

MATERIALS AND METHODS

PubMed was used with both medical subject heading terms and free search to identify the relevant literature. Information on clinical trials was obtained using http://Clincaltrials.gov, EU Clinical Trials Register, and meeting abstracts of the American Society of Clinical Oncology.

RESULTS

To date, 2 Bcl-2 inhibitors have been evaluated in clinical trials for genitourinary tumors (oblimersen and AT-101 (R-(-)-gossypol)). Both agents demonstrated some success in early stages of development, but their clinical activity did not meet expectations. Preclinical studies are under way for other Bcl-2 inhibitors including ABT-737, HA14-1, and Bcl-2 homology 3 inhibitors.

CONCLUSION

Antiapoptotic Bcl-2 proteins are potential molecular targets in genitourinary cancers. Bcl-2 inhibitors might be effective as single agents or in combination with conventional therapies. However, the biology of the Bcl-2 family in genitourinary cancers remains poorly understood and robust preclinical studies are needed to inform clinical development. Such studies should aim to identify: (1) pharmacodynamic markers that could help guide patient selection for treatment with Bcl-2 inhibitors, and (2) optimal combinations of Bcl-2 inhibitors with other anticancer agents for future clinical investigation.

The maternal embryonic leucine zipper kinase (MELK) is upregulated in high-grade prostate cancer

Loss of cell cycle control is a prerequisite for cancer onset and progression. In prostate cancer, increased activity of cell cycle genes has been associated with prognostic parameters such as biochemical relapse and survival. The identification of novel oncogenic and druggable targets in patient subgroups with poor prognosis may help to develop targeted therapy approaches. We analyzed prostate cancer and corresponding benign tissues (n = 98) using microarrays. The comparison of high- and low-grade tumors (Gleason score ≥ 4 + 3 vs. ≤ 3 + 4) revealed 144 differentially expressed genes (p < 0.05). Out of these, 15 genes were involved in the cell cycle process. The gene maternal embryonic leucine zipper kinase (MELK) was identified to be highly correlated with cell cycle genes like UBE2C, TOP2A, CCNB2, and AURKB. Increased MELK gene expression in high-risk prostate cancer was validated by qPCR in an independent patient cohort (p < 0.005, n = 79). Immunohistochemistry analysis using a tissue microarray (n = 94) revealed increased MELK protein expression in prostate cancer tissues of high Gleason scores. RNAi-based inhibition of MELK in PC3 and LNCaP cells suggested putative function in chromatin modification, embryonic development and cell migration. The concerted inhibition of MELK and other cell cycle targets by the antibiotic siomycin A strongly impaired cell viability of prostate cancer cells, and may point to a novel therapy approach for a subset of high-risk prostate cancer patients.

Combination with bortezomib enhances the antitumor effects of nanoparticle-encapsulated thiostrepton

Bortezomib is well-known for inducing cell death in cancer cells, specifically through the mechanism of proteasome inhibition. Thiostrepton, a thiazole antibiotic, has also been described for its proteasome inhibitory action, although differing slightly to bortezomib in the proteasomal site to which it is active. Previously we had shown the synergic effect of bortezomib and thiostrepton in breast cancer cells in vitro, where sub-apoptotic concentrations of both proteasome inhibitors resulted in synergic increase in cell death when combined as a treatment. Here, we administered such a combination to MDA-MB-231 xenograft tumors in vivo, and found that the effect of complementary proteasome inhibitors reduced tumor growth rates more efficiently than compared with when administered alone. Increased induction of apoptotic activity in tumors was found be associated with the growth inhibitory activity of combination treatment. Further examination additionally revealed that combination-treated tumors exhibited reduced proteasome activity, compared with non-treated and single drug-treated tumors. These data suggest that this drug combination may be useful as a therapy for solid tumors.

Targeting Mcl-1 for the therapy of cancer

INTRODUCTION

Human cancers are genetically and epigenetically heterogeneous and have the capacity to commandeer a variety of cellular processes to aid in their survival, growth and resistance to therapy. One strategy is to overexpress proteins that suppress apoptosis, such as the Bcl-2 family protein Mcl-1. The Mcl-1 protein plays a pivotal role in protecting cells from apoptosis and is overexpressed in a variety of human cancers.

AREAS COVERED

Targeting Mcl-1 for extinction in these cancers, using genetic and pharmacological approaches, represents a potentially effectual means of developing new efficacious cancer therapeutics. Here we review the multiple strategies that have been employed in targeting this fundamental protein, as well as the significant potential these targeting agents provide in not only suppressing cancer growth, but also in reversing resistance to conventional cancer treatments.

EXPERT OPINION

We discuss the potential issues that arise in targeting Mcl-1 and other Bcl-2 anti-apoptotic proteins, as well problems with acquired resistance. The application of combinatorial approaches that involve inhibiting Mcl-1 and manipulation of additional signaling pathways to enhance therapeutic outcomes is also highlighted. The ability to specifically inhibit key genetic/epigenetic elements and biochemical pathways that maintain the tumor state represent a viable approach for developing rationally based, effective cancer therapies.

Down-regulation of Notch-1 is associated with Akt and FoxM1 in inducing cell growth inhibition and apoptosis in prostate cancer cells

Although many studies have been done to uncover the mechanisms by which down-regulation of Notch-1 exerts its anti-tumor activity against a variety of human malignancies, the precise molecular mechanisms remain unclear. In the present study, we investigated the cellular consequence of Notch-1 down-regulation and also assessed the molecular consequence of Notch-1-mediated alterations of its downstream targets on cell viability and apoptosis in prostate cancer (PCa) cells. We found that the down-regulation of Notch-1 led to the inhibition of cell growth and induction of apoptosis, which was mechanistically linked with down-regulation of Akt and FoxM1, suggesting for the first time that Akt and FoxM1 are downstream targets of Notch-1 signaling. Moreover, we found that a "natural agent" (genistein) originally discovered from soybean could cause significant reduction in cell viability and induced apoptosis of PCa cells, which was consistent with down-regulation of Notch-1, Akt, and FoxM1. These results suggest that down-regulation of Notch-1 by novel agents could become a newer approach for the prevention of tumor progression and/or treatment, which is likely to be mediated via inactivation of Akt and FoxM1 signaling pathways in PCa.

Determinants of sensitivity to DZNep induced apoptosis in multiple myeloma cells

The 3-Deazaneplanocin A (DZNep), one of S-adenosylhomocysteine (AdoHcy) hydrolase inhibitors, has shown antitumor activities in a broad range of solid tumors and acute myeloid leukemia. Here, we examined its effects on multiple myeloma (MM) cells and found that, at 500 nM, it potently inhibited growth and induced apoptosis in 2 of 8 MM cell lines. RNA from un-treated and DZNep treated cells was profiled by Affymetrix HG-U133 Plus 2.0 microarray and genes with a significant change in gene expression were determined by significance analysis of microarray (SAM) testing. ALOX5 was the most down-regulated gene (5.8-fold) in sensitive cells and was expressed at low level in resistant cells. The results were corroborated by quantitative RT-PCR. Western-blot analysis indicated ALOX5 was highly expressed only in sensitive cell line H929 and greatly decreased upon DZNep treatment. Ectopic expression of ALOX5 reduced sensitivity to DZNep in H929 cells. Furthermore, down-regulation of ALOX5 by RNA interference could also induce apoptosis in H929. Gene expression analysis on MM patient dataset indicated ALOX5 expression was significantly higher in MM patients compared to normal plasma cells. We also found that Bcl-2 was overexpressed in DZNep insensitive cells, and cotreatment with DZNep and ABT-737, a Bcl-2 family inhibitor, synergistically inhibited growth and induced apoptosis of DZNep insensitive MM cells. Taken together, this study shows one of mechanisms of the DZNep efficacy on MM correlates with its ability to down-regulate the ALOX5 levels. In addition, DZNep insensitivity might be associated with overexpression of Bcl-2, and the combination of ABT-737 and DZNep could synergistically induced apoptosis. These results suggest that DZNep may be exploited therapeutically for a subset of MM.

Synergistic killing of colorectal cancer cells by oxaliplatin and ABT-737

BACKGROUND

Oxaliplatin is frequently used in the treatment of metastatic colorectal cancer (CRC). Our previous work shows that oxaliplatin induces the pro-apoptotic protein Noxa in CRC cells. The Bcl2-inhibitor ABT-737 is particularly effective in cells with high Noxa levels. Therefore, we tested whether oxaliplatin and ABT-737 display synergy in killing CRC cells.

METHODS

A panel of CRC cell lines was treated with oxaliplatin and ABT-737, either alone or in combination. Apoptosis was measured by FACS analysis of sub-G1 DNA content and by Western blot analysis of caspase-3 processing. Noxa expression was suppressed by lentiviral RNA interference.

RESULTS

Oxaliplatin and ABT-737 displayed a strong synergistic apoptotic response, which was dependent on wildtype TP53 and oncogenic KRAS. TP53 and KRAS were required for drug-induced Noxa expression and this was essential for tumor cell apoptosis. Oxaliplatin, but not ABT-737, induced p53 accumulation, but both drugs stimulated Noxa expression. Combination treatment of mice with subcutaneous tumor xenografts drastically reduced tumor volume, while single drug treatment had no effect.

CONCLUSION

ABT-737 synergizes with oxaliplatin to kill colorectal cancer cells. This requires induction of Noxa by wildtype TP53 and oncogenic KRAS. Future studies should explore the anti-tumor efficacy of this drug combination in mouse models for spontaneous CRC development and in patient-derived tumor cell cultures and xenografts.

Thiazole antibiotic thiostrepton synergize with bortezomib to induce apoptosis in cancer cells

Thiazole antibiotic, thiostrepton was recently identified as proteasome inhibitor. We investigated the therapeutic potential of the combination of thiostrepton and proteasome inhibitor bortezomib (Velcade) on various human tumor cell lines. Combination of sub-lethal concentrations of thiostrepton and bortezomib induced potent apoptosis and inhibition of long-term colony formation in a wide variety of human cancer cell lines. The synergistic relationship between thiostrepton and bortezomib combination was also quantitatively demonstrated by calculating their combination index values that were much lower than 1 in all studied cell lines. The synergy between these drugs was based on their proteasome inhibitory activities, because thiostrepton modification, thiostrepton methyl ester, which did not have intact quinaldic acid ring and did not inhibit proteasome activity failed to demonstrate any synergy in combination with bortezomib.

ARC synergizes with ABT-737 to induce apoptosis in human cancer cells

Previously, we reported that the nucleoside analogue/transcriptional inhibitor ARC (4-amino-6-hydrazino-7-beta-D-ribofuranosyl-7H-pyrrolo(2,3-d)-pyrimidine-5-carboxamide) was able to induce p53-independent apoptosis in multiple cancer cell lines of different origins. This occurred, at least in part, by the suppression of short-lived, prosurvival member of the Bcl-2 family, Mcl-1. In contrast, we show here that treatment of human cancer cells with the pan-Bcl-2 inhibitor ABT-737 alone led to upregulation of Mcl-1 protein expression. Combination of subapoptotic concentrations of ABT-737 and ARC induced mitochondrial injury and potent caspase-3/caspase-9-dependent apoptosis in a wide variety of human cancer cell lines. These data suggest that the ABT-737/ARC combination, which simultaneously targets Bcl-2 and Mcl-1, may be efficient against human cancer.