Inhibition of proliferation of prostate cancer cell line, PC-3, in vitro and in vivo using (-)-gossypol

Gossypol and Its Natural Derivatives: Multitargeted Phytochemicals as Potential Drug Candidates for Oncologic Diseases

Despite the vast amounts of research and remarkable discoveries that have been made in recent decades, cancer remains a leading cause of death and a major public health concern worldwide. Gossypol, a natural polyphenolic compound derived from the seeds, roots, and stems of cotton (Gossypium hirsutum L.), was first used as a male contraceptive agent. Due to its diverse biological properties, including antifertility, antiviral, antioxidant, antibacterial, antimalarial, and most notably antitumor activities, gossypol has been the subject of numerous studies. Nevertheless, no systematic review has been performed that analyzes the antineoplastic potential of gossypol and related natural compounds in an organ-specific manner while delineating the molecular mechanisms of action. Hence, we have performed an extensive literature search for anticancer properties of gossypol and their natural derivatives against various types of cancer cells utilizing PubMed, ScienceDirect, Google Scholar, and Scopus. The sources, distribution, chemical structure, and toxicity of gossypol and its constituents are briefly reviewed. Based on emerging evidence, gossypol and related compounds exhibit significant antineoplastic effects against various cancer types through the modulation of different cancer hallmarks and signaling pathways. Additionally, the synergistic activity of gossypol and its derivatives with chemotherapeutic agents has been observed. Our evaluation of the current literature suggests the potential of gossypol and its derivatives as multitargeting drug candidates to combat multiple human malignancies.

Structure, properties of gossypol and its derivatives-from physiological activities to drug discovery and drug design

Covering up to 2022Gossypol is a polyphenolic compound isolated from cottonseed. There are two optical enantiomers of gossypol, (-)-gossypol and (+)-gossypol. Gossypol exists as three different tautomers, aldehyde, ketone and lactol. Gossypol is toxic and provides a protective mechanism for cotton plants against pests. Gossypol was used as a male contraceptive in China in the 1970s. It was eventually abandoned due to noticeable side effects, disruption of potassium uptake and incomplete reversibility. Gossypol has gained considerable research interest due to its attractive biological activities, especially antitumor and antivirus. Gossypol derivatives are prepared by a structural modification to reduce toxicity and improve their therapeutic effect. This review depicts the bioactivity and regulation mechanisms of gossypol and its derivatives as drug lead compounds, with emphasis on its antitumor mechanism. The design and synthesis of pharmacologically active derivatives based on the structure of gossypol, such as gossypol Schiff bases, apogossypol, gossypolone, are thoroughly discussed. This review aims to serve as a reference for gossypol-based drug discovery and drug design.

Systematic Review of Gossypol/AT-101 in Cancer Clinical Trials

The potential of gossypol and of its R-(−)-enantiomer (R-(−)-gossypol acetic acid, AT-101), has been evaluated for treatment of cancer as an independent agent and in combination with standard chemo-radiation-therapies, respectively. This review assesses the evidence for safety and clinical effectiveness of oral gossypol/AT-101 in treating various types of cancer. The databases PubMed, MEDLINE, Cochrane, and ClinicalTrials.gov were examined. Phase I and II trials as well as single arm and randomized trials were included in this review. Results were screened to determine if they met inclusion criteria and then summarized using a narrative approach. A total of 17 trials involving 759 patients met the inclusion criteria. Overall, orally applied gossypol/AT-101 at low doses (30 mg daily or lower) was determined as well tolerable either as monotherapy or in combination with chemo-radiation. Adverse events should be strictly monitored and were successfully managed by dose-reduction or treating symptoms. There are four randomized trials, two performed in patients with advanced non-small cell lung cancer, one in subjects with head and neck cancer, and one in patients with metastatic castration-resistant prostate cancer. Thereby, standard chemotherapy (either docetaxel (two trials) or docetaxel plus cisplatin or docetaxel plus prednisone) was tested with and without AT-101. Within these trials, a potential benefit was observed in high-risk patients or in some patients with prolongation in progression-free survival or in overall survival. Strikingly, the most recent clinical trial combined low dose AT-101 with docetaxel, fluorouracil, and radiation, achieving complete responses in 11 of 13 patients with gastroesophageal carcinoma (median duration of 12 months) and a median progression-free survival of 52 months. The promising results shown in subsets of patients supports the need of further specification of AT-101 sensitive cancers as well as for the establishment of effective AT-101-based therapy. In addition, the lowest recommended dose of gossypol and its precise toxicity profile need to be confirmed in further studies. Randomized placebo-controlled trials should be performed to validate these data in large cohorts.

Cyclic RGD-Decorated Liposomal Gossypol AT-101 Targeting for Enhanced Antitumor Effect

Introduction

(-)-Gossypol (AT-101), the (-)-enantiomer of the natural compound gossypol, has shown significant inhibitory effects on various types of cancers such as osteosarcoma, myeloma, glioma, lung cancer, and prostate cancer. However, the clinical application of (-)-gossypol was often hindered by its evident side effects and the low bioavailability via oral administration, which necessitated the development of suitable (-)-gossypol preparations to settle the problems. In this study, injectable cyclic RGD (cRGD)-decorated liposome (cRGD-LP) was prepared for tumor-targeted delivery of (-)-gossypol.

Methods

The cRGD-LP was prepared based on cRGD-modified lipids. For comparison, a non-cRGD-containing liposome (LP) with a similar chemical composition to cRGD-LP was specially designed. The physicochemical properties of (-)-gossypol-loaded cRGD-LP (Gos/cRGD-LP) were investigated in terms of the drug loading efficiency, particle size, morphology, drug release, and so on. The inhibitory effect of Gos/cRGD-LP on the proliferation of tumor cells in vitro was evaluated using different cell lines. The biodistribution of cRGD-LP in vivo was investigated via the near-infrared (NIR) fluorescence imaging technique. The antitumor effect of Gos/cRGD-LP in vivo was evaluated in PC-3 tumor-bearing nude mice.

Results

Gos/cRGD-LP had an average particle size of about 62 nm with a narrow size distribution, drug loading efficiency of over 90%, and sustained drug release for over 96 h. The results of NIR fluorescence imaging demonstrated the enhanced tumor targeting of cRGD-LP in vivo. Moreover, Gos/cRGD-LP showed a significantly enhanced inhibitory effect on PC-3 tumors in mice, with a tumor inhibition rate of over 74% and good biocompatibility.

Conclusion

The incorporation of cRGD could significantly enhance the tumor-targeting effect of the liposomes and improve the antitumor effect of the liposomal (-)-gossypol in vivo, which indicated the potential of Gos/cRGD-LP that warrants further investigation for clinical applications of this single-isomer drug.

Prostate cancer: Therapeutic prospect with herbal medicine

Prostate cancer (PCa) is a major cause of morbidity and mortality in men worldwide. A geographic variation on the burden of the disease suggested that the environment, genetic makeup, lifestyle, and food habits modulate one's susceptibility to the disease. Although it has been generally thought to be an older age disease, and awareness and timely execution of screening programs have managed to contain the disease in the older population over the last decades, the incidence is still increasing in the population younger than 50. Existing treatment is efficient for PCa that is localized and responsive to androgen. However, the androgen resistant and metastatic PCa are challenging to treat. Conventional radiation and chemotherapies are associated with severe side effects in addition to being exorbitantly expensive. Many isolated phytochemicals and extracts of plants used in traditional medicine are known for their safety and diverse healing properties, including many with varying levels of anti-PCa activities. Many of the phytochemicals discussed here, as shown by many laboratories, inhibit tumor cell growth and proliferation by interfering with the components in the pathways responsible for the enhanced proliferation, metabolism, angiogenesis, invasion, and metastasis in the prostate cells while upregulating the mechanisms of cell death and cell cycle arrest. Notably, many of these agents simultaneously target multiple cellular pathways. We analyzed the available literature and provided an update on this issue in this review article.

Bioinformatics Analysis of the Signaling Pathways and Genes of Gossypol Induce Death of Nasopharyngeal Carcinoma Cells

Gossypol has been reported to exhibit antitumor effects against several human cancers. However, the anticancer effects of gossypol on nasopharyngeal carcinoma (NPC) have not been investigated. Against this backdrop, the present study was designed to evaluate the anticancer effects of gossypol against NPC cells and to identify the signaling pathways involved through bioinformatic analysis. Gossypol-inhibited death of NPC cells is concentration-dependent. To explore the underlying mechanism for gossypol's antitumor effect, microarray of gossypol-treated and -untreated NPC cells was performed. A total of 836 differentially expressing genes (DEGs) were identified in gossypol-treated NPC cells, of which 461 genes were upregulated and 375 genes were downregulated. The cellular components, molecular functions, biological processes, and signal pathways, in which the DEGs were involved, were identified by gene ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG). The Gene Set Enrichment Analysis (GSEA) predicted upstream transcription factors (TF) ETS2 and E2F1 that regulate DEGs. Weighted Gene Co-expression Network Analysis (WGCNA) was performed to identify a class of modules and genes related to DNA repair and cell cycle. TNFRSF10B, a receptor for death in NPC cells, was knocked down. The results suggested that the ability of NPC cells to resist gossypol killing was enhanced. In addition, to further investigate the possible molecular mechanisms, we constructed a transcriptional regulatory network of TNFRSF10B containing 109 miRNAs and 47 TFs. Taken together, our results demonstrated that gossypol triggered antitumor effects against NPC cells, indicating its applicability for the management of NPC.

Integrative analysis of clinical and bioinformatics databases to identify anticancer properties of digoxin

Cardiac glycosides, such as digoxin, inhibit Na⁺/K⁺-ATPases and cause secondary activation of Na⁺/Ca²⁺ exchangers. Preclinical investigations have suggested that digoxin may have anticancer properties. In order to clarify the functional mechanisms of digoxin in cancer, we performed an integrative analysis of clinical and bioinformatics databases. The US Food and Drug Administration Adverse Event Reporting System and the Japan Medical Data Center claims database were used as clinical databases to evaluate reporting odds ratios and adjusted sequence ratios, respectively. The BaseSpace Correlation Engine and Connectivity Map bioinformatics databases were used to investigate molecular pathways related to digoxin anticancer mechanisms. Clinical database analyses suggested an inverse association between digoxin and four cancers: gastric, colon, prostate and haematological malignancy. The bioinformatics database analysis suggested digoxin may exert an anticancer effect via peroxisome proliferator-activated receptor α and apoptotic caspase cascade pathways. Our integrative analysis revealed the possibility of digoxin as a drug repositioning candidate for cancers.

Natural Product Gossypol and its Derivatives in Precision Cancer Medicine

Gossypol, a natural product extracted from the seed, roots, and stem of cotton, was initially used as a male contraceptive but was subsequently investigated as a novel antitumor agent. This review depicts the current status of gossypol and its derivatives as novel antitumor agents as well as presents their preparation and characteristics, especially of some gossypol Schiff bases, through quantitative and structural analysis. The main attractive target sites of gossypol and its derivatives are Bcl-2 family proteins containing the anti-apoptosis proteins Bcl-2 and Bcl-XL. The molecular mechanism of gossypol analogs not only involves cell apoptosis but also autophagy, cell cycle arrest, and other abnormal cellular phenomena. Gossypol and its derivatives exert antitumor effects on different cancer types in vitro and in vivo, and demonstrate synergistic effects with other chemo- and radio- therapeutic treatments. In addition, several nanocarriers have been designed to load gossypol or its derivatives in order to expand the range of their applications and evaluate their combination effects with other anti-tumor agents. This review may serve as a reference for the rational application of gossypol analogs as anti-tumor agents.

Effect of the BH3 Mimetic Polyphenol (-)-Gossypol (AT-101) on the in vitro and in vivo Growth of Malignant Mesothelioma

Malignant mesothelioma (MM) is a primary tumor arising from mesothelial cells. The survival of MM patients following traditional chemotherapy is poor, thus innovative treatments for MM are needed. (-)-gossypol (AT-101) is a BH3 mimetic compound which possesses anti-tumoral activity by targeting multiple signaling transduction pathways. Several clinical trials employing AT-101 have been performed and some of them are still ongoing. Accordingly, we investigated the in vitro effects of AT-101 on cell proliferation, cell cycle regulation, pro-survival signaling pathways, apoptosis and autophagy of human (MM-B1, H-Meso-1, and MM-F1) and mouse (#40a) MM cell lines. In addition, we explored the in vivo anti-tumor activities of AT-101 in a mouse model, in which the transplantation of MM cells induces ascites in the peritoneal space. AT-101 inhibited in vitro MM cells survival in a dose- and time-dependent manner and triggered autophagy, but the process was then blocked and was coincident with apoptosis activation. To confirm the effect of AT-101 in inducing the apoptosis of MM cells, MM cells were simultaneously treated with AT-101 and with the caspase inhibitor, Z-VAD-FMK. Z-VAD-FMK was able to significantly reduce the number of cells in the subG1 phase compared to the treatment with AT-101 alone. This result corroborates the induction of cell death by apoptosis following treatment with AT-101. Indeed, Western blotting results showed that AT-101 increases Bax/Bcl-2 ratio, modulates p53 expression, activates caspase 9 and the cleavage of PARP-1. In addition, the treatment with AT-101 was able to: (a) decrease the ErbB2 protein expression; (b) increase the EGFR protein expression; (c) affect the phosphorylation of ERK1/2, p38 and AKT; (d) stimulate JNK1/2 and c-jun phosphorylation. Our in vivo results showed that the intraperitoneal administration of AT-101 increased the median survival of C57BL/6 mice intraperitoneally transplanted with #40a cells and reduced the risk of developing tumors. Our findings may have important implications for the design of MM therapies by employing AT-101 as an anticancer agent in combination with standard therapies.

Natural product derivative Gossypolone inhibits Musashi family of RNA-binding proteins

BACKGROUND

The Musashi (MSI) family of RNA-binding proteins is best known for the role in post-transcriptional regulation of target mRNAs. Elevated MSI1 levels in a variety of human cancer are associated with up-regulation of Notch/Wnt signaling. MSI1 binds to and negatively regulates translation of Numb and APC (adenomatous polyposis coli), negative regulators of Notch and Wnt signaling respectively.

METHODS

Previously, we have shown that the natural product (-)-gossypol as the first known small molecule inhibitor of MSI1 that down-regulates Notch/Wnt signaling and inhibits tumor xenograft growth in vivo. Using a fluorescence polarization (FP) competition assay, we identified gossypolone (Gn) with a > 20-fold increase in Ki value compared to (-)-gossypol. We validated Gn binding to MSI1 using surface plasmon resonance, nuclear magnetic resonance, and cellular thermal shift assay, and tested the effects of Gn on colon cancer cells and colon cancer DLD-1 xenografts in nude mice.

RESULTS

In colon cancer cells, Gn reduced Notch/Wnt signaling and induced apoptosis. Compared to (-)-gossypol, the same concentration of Gn is less active in all the cell assays tested. To increase Gn bioavailability, we used PEGylated liposomes in our in vivo studies. Gn-lip via tail vein injection inhibited the growth of human colon cancer DLD-1 xenografts in nude mice, as compared to the untreated control (P < 0.01, n = 10).

CONCLUSION

Our data suggest that PEGylation improved the bioavailability of Gn as well as achieved tumor-targeted delivery and controlled release of Gn, which enhanced its overall biocompatibility and drug efficacy in vivo. This provides proof of concept for the development of Gn-lip as a molecular therapy for colon cancer with MSI1/MSI2 overexpression.

Dietary gossypol suppressed postprandial TOR signaling and elevated ER stress pathways in turbot (Scophthalmus maximus L.)

Gossypol is known to be a polyphenolic compound toxic to animals. However, its molecular targets are far from fully characterized. To evaluate the physiological and molecular effects of gossypol, we chose turbot (Scophthalmus maximus L.), a carnivorous fish, as our model species. Juvenile turbots (7.83 ± 0.02 g) were fed diets containing gradient levels of gossypol at 0 (G0), 600 (G1), and 1,200 (G2) mg/kg diets for 11 wk. After the feeding trial, fish growth, body protein, and fat contents were significantly reduced in the G2 group compared with those of the G0 group (P < 0.05). Gossypol had little impact on digestive enzyme activities and intestine morphology. However, gossypol caused liver fibrosis and stimulated chemokine and proinflammatory cytokine secretions. More importantly, gossypol suppressed target of rapamycin (TOR) signaling and induced endoplasmic reticulum (ER) stress pathway in both the feeding experiment and cell cultures. Our results demonstrated that gossypol inhibited TOR signaling and elevated ER stress pathways both in vivo and in vitro, thus providing new mechanism of action of gossypol in nutritional physiology.

(±)-Gossypol induces apoptosis and autophagy in head and neck carcinoma cell lines and inhibits the growth of transplanted salivary gland cancer cells in BALB/c mice

Racemic Gossypol [(±)-GOS], composed of both (-)-GOS and (+)-GOS, is a small BH3-mimetic polyphenol derived from cotton seeds. (±)-GOS has been employed and well tolerated by cancer patients. Head and neck carcinoma (HNC) represents one of the most fatal cancers worldwide, and a significant proportion of HNC expresses high levels of antiapoptotic Bcl-2 proteins. In this study, we demonstrate that (±)-GOS inhibits cell proliferation and induces apoptosis and autophagy of human pharynx, tongue, and salivary gland cancer cell lines and of mouse salivary gland cancer cells (SALTO). (±)-GOS was able to: (a) decrease the ErbB2 protein expression; (b) inhibit the phosphorylation of ERK1/2 and AKT; (c) stimulate p38 and JNK1/2 protein phosphorylation. (±)-GOS administration was safe in BALB/c mice and it reduced the growth of transplanted SALTO cells in vivo and prolonged mice median survival. Our results suggest the potential role of (±)-GOS as an antitumor agent in HNC patients.

Broad targeting of resistance to apoptosis in cancer

Apoptosis or programmed cell death is natural way of removing aged cells from the body. Most of the anti-cancer therapies trigger apoptosis induction and related cell death networks to eliminate malignant cells. However, in cancer, de-regulated apoptotic signaling, particularly the activation of an anti-apoptotic systems, allows cancer cells to escape this program leading to uncontrolled proliferation resulting in tumor survival, therapeutic resistance and recurrence of cancer. This resistance is a complicated phenomenon that emanates from the interactions of various molecules and signaling pathways. In this comprehensive review we discuss the various factors contributing to apoptosis resistance in cancers. The key resistance targets that are discussed include (1) Bcl-2 and Mcl-1 proteins; (2) autophagy processes; (3) necrosis and necroptosis; (4) heat shock protein signaling; (5) the proteasome pathway; (6) epigenetic mechanisms; and (7) aberrant nuclear export signaling. The shortcomings of current therapeutic modalities are highlighted and a broad spectrum strategy using approaches including (a) gossypol; (b) epigallocatechin-3-gallate; (c) UMI-77 (d) triptolide and (e) selinexor that can be used to overcome cell death resistance is presented. This review provides a roadmap for the design of successful anti-cancer strategies that overcome resistance to apoptosis for better therapeutic outcome in patients with cancer.

Natural product (-)-gossypol inhibits colon cancer cell growth by targeting RNA-binding protein Musashi-1

Musashi-1 (MSI1) is an RNA-binding protein that acts as a translation activator or repressor of target mRNAs. The best-characterized MSI1 target is Numb mRNA, whose encoded protein negatively regulates Notch signaling. Additional MSI1 targets include the mRNAs for the tumor suppressor protein APC that regulates Wnt signaling and the cyclin-dependent kinase inhibitor P21(WAF-1). We hypothesized that increased expression of NUMB, P21 and APC, through inhibition of MSI1 RNA-binding activity might be an effective way to simultaneously downregulate Wnt and Notch signaling, thus blocking the growth of a broad range of cancer cells. We used a fluorescence polarization assay to screen for small molecules that disrupt the binding of MSI1 to its consensus RNA binding site. One of the top hits was (-)-gossypol (Ki = 476 ± 273 nM), a natural product from cottonseed, known to have potent anti-tumor activity and which has recently completed Phase IIb clinical trials for prostate cancer. Surface plasmon resonance and nuclear magnetic resonance studies demonstrate a direct interaction of (-)-gossypol with the RNA binding pocket of MSI1. We further showed that (-)-gossypol reduces Notch/Wnt signaling in several colon cancer cell lines having high levels of MSI1, with reduced SURVIVIN expression and increased apoptosis/autophagy. Finally, we showed that orally administered (-)-gossypol inhibits colon cancer growth in a mouse xenograft model. Our study identifies (-)-gossypol as a potential small molecule inhibitor of MSI1-RNA interaction, and suggests that inhibition of MSI1's RNA binding activity may be an effective anti-cancer strategy.

Preparation of novel (-)-gossypol nanoparticles and the effect on growth inhibition in human prostate cancer PC-3 cells in vitro

The aim of the present study was to investigate the antitumor effects and possible mechanism of (-)-gossypol nanoparticles, loaded with vv polyethylene glycol-maleimide (mPEG-Mal), in vitro. Emulsification-volatilization was used to prepare the loaded (-)-gossypol nanoparticles. The toxicity of blank nanoparticles on human prostate cancer PC-3 cells and human prostate RWPE-1 cells was measured. The antitumor effects of the nanoparticles on PC-3 cells were evaluated by an MTT assay, acridine orange staining and transmission electron microscopy in vitro, and the results were compared with those of free (-)-gossypol. In addition, the mRNA expression levels of Bcl-2 and Bak were measured using semi-quantitative reverse transcription polymerase chain reaction. The growth inhibition activity of the loaded (-)-gossypol nanoparticles was found to be dose- and time-dependent, and similar to the activity of free (-)-gossypol. The nanoparticles induced apoptotic morphological changes on the PC-3 cells, downregulating the mRNA expression level of Bcl-2 and upregulating the mRNA expression level of Bak. Blank nanoparticles exhibited no evident toxicity on PC-3 and RWPE-1 cells at a high dose. Therefore, the mPEG-Mal loaded (-)-gossypol nanoparticles demonstrated a favorable antitumor activity and no toxicity. The nanoparticles were able to induce the apoptosis of prostate cancer cells; thus, may be a potential antitumor nanodrug.

Apogossypolone inhibits the proliferation of LNCaP cells in vitro and in vivo

The aim of the present study was to investigate the anti-tumor effect of apogossypolone (ApoG2) on human LNCaP cells in vitro and in vivo. Cell viability was evaluated using an MTT assay. Cell autophagy and apoptosis were detected by flow cytometry and using a terminal deoxynucleotidyl transferase dUTP nick end labeling assay, respectively. Morphological autophagy alterations were observed by transmission electron microscopy. The formation of acidic vesicular organelles was assessed by acridine orange staining and fluorescence microscopy. Quantitative polymerase chain reaction (qPCR) was conducted to detect the expression levels of apoptosis-associated protein B-cell lymphoma 2 (Bcl-2) and Bak. The models of transplantation tumors in nude mice were established via subcutaneous injection of LNCaP cells. Growth of LNCaP cells was inhibited by ApoG2 treatment. Flow cytometry demonstrated that ApoG2 induced apoptosis in LNCaP cells. The Bcl-2 expression was decreased while Bak expression was increased. In addition, activation of cysteine aspartate protease (caspase)-3 and -8 was observed and 3-methyladenine (3-MA) enhanced apoptosis of LNCaP cells. Furthermore, nude mice treated with ApoG2 demonstrated a significant decrease in tumor volume and a significant increase in cell viability. Immunohistochemical analysis of tumor tissues demonstrated that ApoG2 enhanced caspase-3, -8, LC-3B and beclin-1 expression and reduced the expression of Bcl-2. ApoG2 was able to effectively suppress the growth of LNCaP cells through the induction of autophagy and apoptosis.

Growth inhibition and apoptosis induction of human umbilical vein endothelial cells by apogossypolone

AIMS AND BACKGROUND

Prostate cancer is one of the most common malignant tumors in the male reproductive system, which causes the second most cancer deaths of males, and control of angiogenesis in prostate lesions is of obvious importance. This study assessed the effect of apogossypolone (ApoG2) on proliferation and apoptosis of human umbilical vein endothelial cells (HUVECs).

SUBJECTS AND METHODS

HUVECs were treated with different concentrations of ApoG2. The survival rate of HUVECs were determined by MTT assay. Utrastructural changes of HUVECs were assessed with transmission electron microscopy. Apoptosis in HUVECs was analyzed by flow cytometry and cell migration by Boyden chamber assay. Matrigel assays were used to quantify the development of tube-like networks.

RESULTS

ApoG2 significantly inhibited HUVEC growth even at 24 h (P<0.05). The inhibitory effect of ApoG2 is more obvious as the concentration and the culture time increased (P<0.05). These results indicate that ApoG2 inhibits the proliferation of HUVECs in a time- and concentration-dependent manner with increase of the apoptosis rate. Besides, ApoG2 reduced the formation of total pseudotubule length and network branches of HUVECs.

CONCLUSIONS

The results suggest that ApoG2 inhibits angiogenesis of HUVECs by growth inhibition and apoptosis induction.

Anti-cancer drug discovery and development: Bcl-2 family small molecule inhibitors

Deregulated apoptosis is a hallmark of cancer, and the B-cell lymphoma-2 (Bcl-2) family of proteins is pivotal to mediating the intrinsic pathway of this process. Recent advances have yielded both pan-Bcl-2 small molecule inhibitors (SMIs) that inhibit both the Bcl-2 and the Mcl-1 arm of the Bcl-2 family anti-apoptotic proteins, as well as selective SMIs to differentially target the two arms. Of these SMIs, ABT-263 (navitoclax), AT-101 [(-)-gossypol], and obatoclax (GX15-070) are currently in clinical trials for multiple cancers. While pan-Bcl-2 inhibitors such as AT-101 and obatoclax can be more toxic for inhibiting all members of the anti-apoptotic Bcl-2 family of proteins, resistance can quickly develop for ABT-263, a selective Bcl-2 inhibitor. In this article, we discuss the current status of Bcl-2 family SMIs in preclinical and clinical development. As Mcl-1 upregulation is a major mechanism of ABT-263 resistance, Mcl-1-specific inhibitors are expected to be efficacious both in combination/sequential treatments and as a single agent against cancers resistant to ABT-263. 

Valproic acid synergistically enhances the cytotoxicity of gossypol in DU145 prostate cancer cells: an iTRTAQ-based quantitative proteomic analysis

Gossypol (GOS), a BH3 mimetic, has been investigated as a sensitizing co-therapy to radiation and chemotherapy in treatment of metastatic prostate cancer. In this study, we found that valproic acid (VPA), a histone deacetylase inhibitor (HDACI), counteracted the suppressive effect of GOS on histone H3 acetylation and enhanced the cytotoxicity of GOS to DU145 prostate cancer cells. Significant synergistic effects were observed in combined GOS and VPA treatment, culminating in more DNA damage and cell death. The iTRAQ-based quantitative proteomic analysis revealed differential proteomic profiles in cells treated with VPA, GOS or their combination. In GOS-treated cells, oxidative phosphorylation-related proteins were depressed and endoplasmic reticulum stress markers were upregulated. In the presence of VPA, the GOS-induced mitochondrial stress was further enhanced since glycolysis- and hypoxia-associated proteins were upregulated, suggesting a disruption of energy metabolism in these cells. Furthermore, the DNA damage repair ability of cells co-treated with GOS and VPA was also decreased, as evidenced by the downregulation of DNA damage repair proteins and the enhancement of DNA fragmentation and cell death. These findings suggest that GOS in combination with an HDACI has the potential to increase its clinical efficacy in the treatment of prostate cancer.

(-)-Gossypol suppresses the growth of human prostate cancer xenografts via modulating VEGF signaling-mediated angiogenesis

(-)-Gossypol, a natural BH3-mimetic and small-molecule Bcl-2 inhibitor, shows promise in ongoing phase II clinical trials for human cancers. However, whether (-)-gossypol plays functional roles in tumor angiogenesis has not been directly elucidated yet. In this study, we showed that (-)-gossypol dose dependently inhibited the expression of VEGF, Bcl-2, and Bcl-xL in human prostate cancer cells (PC-3 and DU 145) and primary cultured human umbilical vascular endothelial cells (HUVEC) in vitro. Notably, the growth of human prostate tumor PC-3 xenografts in mice was significantly suppressed by (-)-gossypol at a dosage of 15 mg/kg/d. This inhibitory action of (-)-gossypol in vivo was largely dependent on suppression of angiogenesis in the solid tumors, where VEGF expression and microvessel density were remarkably decreased. Furthermore, (-)-gossypol inhibited VEGF-induced chemotactic motility and tubulogenesis in HUVECs and human microvascular endothelial cells and suppressed microvessel sprouting from rat aortic rings ex vivo. When examined for the mechanism, we found that (-)-gossypol blocked the activation of VEGF receptor 2 kinase with the half maximal inhibitory concentration of 2.38 μmol/L in endothelial cells. Consequently, the phosphorylation of key intracellular proangiogenic kinases induced by VEGF was all suppressed by the treatment, such as Src family kinase, focal adhesion kinase, extracellular signal-related kinase, and AKT kinase. Taken together, the present study shows that (-)-gossypol potently inhibits human prostate tumor growth through modulating VEGF signaling pathway, which further validates its great potential in clinical practice.