BH3 Mimetics for the Treatment of Prostate Cancer

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.

The Role of BCL-2 Proteins in the Development of Castration-resistant Prostate Cancer and Emerging Therapeutic Strategies

The development of androgen resistance in advanced prostate cancer remains a challenging clinical problem. Because androgen deprivation therapy constitutes the backbone of first-line treatments for metastatic prostate cancer, the phenotypic switch from an androgen-dependent to an androgen-independent growth state limits the treatment options for these patients. This critical change from an androgen-dependent to an androgen-independent growth state can be regulated by the B-cell lymphoma gene 2 (BCL-2) family of apoptotic proteins. While the roles of BCL-2 protein family members in the carcinogenesis of prostate cancer have been well-studied, emerging data also delineates their modulation of disease progression to castration-resistant prostate cancer (CRPC). Over the past 2 decades, investigators have sought to describe the mechanisms that underpin this development at the molecular level, yet no recent literature has consolidated these findings in a dedicated review. As new classes of BCL-2 family inhibitors are finding indications for other cancer types, it is time to evaluate how such agents might find stable footing for the treatment of CRPC. Several trials to date have investigated BCL-2 inhibitors as therapeutic agents for CRPC. These therapies include selective BCL-2 inhibitors, pan-BCL-2 inhibitors, and novel inhibitors of MCL-1 and BCL-XL. This review details the research regarding the role of BCL-2 family members in the pathogenesis of prostate cancer and contextualizes these findings within the contemporary landscape of prostate cancer treatment.

2-Deoxy-d-glucose Promotes Buforin IIb-Induced Cytotoxicity in Prostate Cancer DU145 Cells and Xenograft Tumors

Inhibition of the glycolytic pathway is a critical strategy in anticancer therapy because of the role of aerobic glycolysis in cancer cells. The glycolytic inhibitor 2-Deoxy-d-glucose (2-DG) has shown potential in combination with other anticancer agents. Buforin IIb is an effective antimicrobial peptide (AMP) with broad-spectrum anticancer activity and selectivity. The efficacy of combination treatment with 2-DG and buforin IIb in prostate cancer remains unknown. Here, we tested the efficacy of buforin IIb as a mitochondria-targeting AMP in the androgen-independent human prostate cancer cell line DU145. Combining 2-DG with buforin IIb had a synergistic toxic effect on DU145 cells and mouse xenograft tumors. Combination treatment with 2-DG and buforin IIb caused stronger proliferation inhibition, greater G1 cell cycle arrest, and higher apoptosis than either treatment alone. Combination treatment dramatically decreased L-lactate production and intracellular ATP levels, indicating severe inhibition of glycolysis and ATP production. Flow cytometry and confocal laser scanning microscopy results indicate that 2-DG may increase buforin IIb uptake by DU145 cells, thereby increasing the mitochondria-targeting capacity of buforin IIb. This may partly explain the effect of combination treatment on enhancing buforin IIb-induced apoptosis. Consistently, 2-DG increased mitochondrial dysfunction and upregulated Bax/Bcl-2, promoting cytochrome c release to initiate procaspase 3 cleavage induced by buforin IIb. These results suggest that 2-DG sensitizes prostate cancer DU145 cells to buforin IIb. Moreover, combination treatment caused minimal hemolysis and cytotoxicity to normal WPMY-1 cells. Collectively, the current study demonstrates that dual targeting of glycolysis and mitochondria by 2-DG and buforin IIb may be an effective anticancer strategy for the treatment of some advanced prostate cancer.

Mechanisms of Taxane Resistance

The taxane family of chemotherapy drugs has been used to treat a variety of mostly epithelial-derived tumors and remain the first-line treatment for some cancers. Despite the improved survival time and reduction of tumor size observed in some patients, many have no response to the drugs or develop resistance over time. Taxane resistance is multi-faceted and involves multiple pathways in proliferation, apoptosis, metabolism, and the transport of foreign substances. In this review, we dive deeper into hypothesized resistance mechanisms from research during the last decade, with a focus on the cancer types that use taxanes as first-line treatment but frequently develop resistance to them. Furthermore, we will discuss current clinical inhibitors and those yet to be approved that target key pathways or proteins and aim to reverse resistance in combination with taxanes or individually. Lastly, we will highlight taxane response biomarkers, specific genes with monitored expression and correlated with response to taxanes, mentioning those currently being used and those that should be adopted. The future directions of taxanes involve more personalized approaches to treatment by tailoring drug-inhibitor combinations or alternatives depending on levels of resistance biomarkers. We hope that this review will identify gaps in knowledge surrounding taxane resistance that future research or clinical trials can overcome.

An Anti-PSMA Immunotoxin Reduces Mcl-1 and Bcl2A1 and Specifically Induces in Combination with the BAD-Like BH3 Mimetic ABT-737 Apoptosis in Prostate Cancer Cells

Background: Upregulation of anti-apoptotic Bcl-2 proteins in advanced prostate cancer leads to therapeutic resistance by prevention of cell death. New therapeutic approaches aim to target the Bcl-2 proteins for the restoration of apoptosis. Methods: The immunotoxin hD7-1(VL-VH)-PE40 specifically binds to the prostate specific membrane antigen (PSMA) on prostate cancer cells and inhibits protein biosynthesis. It was tested with respect to its effects on the expression of anti-apoptotic Bcl-2 proteins. Combination with the BAD-like mimetic ABT-737 was examined on prostate cancer cells and 3D spheroids and in view of tumor growth and survival in the prostate cancer SCID mouse xenograft model. Results: The immunotoxin led to a specific inhibition of Mcl-1 and Bcl2A1 expression in PSMA expressing target cells. Its combination with ABT-737, which inhibits Bcl-2, Bcl-xl, and Bcl-w, led to an induction of the intrinsic apoptotic pathway and to a synergistic cytotoxicity in prostate cancer cells and 3D spheroids. Furthermore, combination therapy led to a significantly prolonged survival of mice bearing prostate cancer xenografts based on an inhibition of tumor growth. Conclusion: The combination therapy of anti-PSMA immunotoxin plus ABT-737 represents the first tumor-specific therapeutic approach on the level of Bcl-2 proteins for the induction of apoptosis in prostate cancer.

Prediction of risk scores for colorectal cancer patients from the concentration of proteins involved in mitochondrial apoptotic pathway

One of the major challenges in managing the treatment of colorectal cancer (CRC) patients is to predict risk scores or level of risk for CRC patients. In past, several biomarkers, based on concentration of proteins involved in type-2/intrinsic/mitochondrial apoptotic pathway, have been identified for prognosis of colorectal cancer patients. Recently, a prognostic tool DR_MOMP has been developed that can discriminate high and low risk CRC patients with reasonably high accuracy (Hazard Ratio, HR = 5.24 and p-value = 0.0031). This prognostic tool showed an accuracy of 59.7% when used to predict favorable/unfavorable survival outcomes. In this study, we developed knowledge based models for predicting risk scores of CRC patients. Models were trained and evaluated on 134 stage III CRC patients. Firstly, we developed multiple linear regression based models using different techniques and achieved a maximum HR value of 6.34 with p-value = 0.0032 for a model developed using LassoLars technique. Secondly, models were developed using a parameter optimization technique and achieved a maximum HR value of 38.13 with p-value 0.0006. We also predicted favorable/unfavorable survival outcomes and achieved maximum prediction accuracy value of 71.64%. A further enhancement in the performance was observed if clinical factors are added to this model. Addition of age as a variable to the model improved the HR to 40.11 with p-value as 0.0003 and also boosted the accuracy to 73.13%. The performance of our models were evaluated using five-fold cross-validation technique. For providing service to the community we also developed a web server ‘CRCRpred’, to predict risk scores of CRC patients, which is freely available at https://webs.iiitd.edu.in/raghava/crcrpred.

Dual role of Endoplasmic Reticulum Stress-Mediated Unfolded Protein Response Signaling Pathway in Carcinogenesis

Cancer constitutes a grave problem nowadays in view of the fact that it has become one of the main causes of death worldwide. Poor clinical prognosis is presumably due to cancer cells metabolism as tumor microenvironment is affected by oxidative stress. This event triggers adequate cellular response and thereby creates appropriate conditions for further cancer progression. Endoplasmic reticulum (ER) stress occurs when the balance between an ability of the ER to fold and transfer proteins and the degradation of the misfolded ones become distorted. Since ER is an organelle relatively sensitive to oxidative damage, aforementioned conditions swiftly cause the activation of the unfolded protein response (UPR) signaling pathway. The output of the UPR, depending on numerous factors, may vary and switch between the pro-survival and the pro-apoptotic branch, and hence it displays opposing effects in deciding the fate of the cancer cell. The role of UPR-related proteins in tumorigenesis, such as binding the immunoglobulin protein (BiP) and inositol-requiring enzyme-1α (IRE1α), activating transcription factor 6 (ATF6) or the protein kinase R (PKR)-like endoplasmic reticulum kinase (PERK), has already been specifically described so far. Nevertheless, due to the paradoxical outcomes of the UPR activation as well as gaps in current knowledge, it still needs to be further investigated. Herein we would like to elicit the actual link between neoplastic diseases and the UPR signaling pathway, considering its major branches and discussing its potential use in the development of a novel, anti-cancer, targeted therapy.

Para-Toluenesulfonamide Induces Anti-tumor Activity Through Akt-Dependent and -Independent mTOR/p70S6K Pathway: Roles of Lipid Raft and Cholesterol Contents

Castration-resistant prostate cancer (CRPC) cells can resist many cellular stresses to ensure survival. There is an unmet medical need to fight against the multiple adaptive mechanisms in cells to achieve optimal treatment in patients. Para-toluenesulfonamide (PTS) is a small molecule that inhibited cell proliferation of PC-3 and DU-145, two CRPC cell lines, through p21- and p27-independent G1 arrest of cell cycle in which cyclin D1 was down-regulated and Rb phosphorylation was inhibited. PTS also induced a significant loss of mitochondrial membrane potential that was attributed to up-regulation of both Bak and PUMA, two pro-apoptotic Bcl-2 family members, leading to apoptosis. PTS inhibited the phosphorylation of m-TOR, 4E-BP1, and p70S6K in both cell lines. Overexpression of constitutively active Akt rescued the inhibition of mTOR/p70S6K signaling in PC-3 cells indicating an Akt-dependent pathway. In contrast, Akt-independent effect was observed in DU-145 cells. Lipid rafts serve as functional platforms for multiple cellular signaling and trafficking processes. Both cell lines expressed raft-associated Akt, mTOR, and p70S6K. PTS induced decreases of expressions in both raft-associated total and phosphorylated forms of these kinases. PTS-induced inhibitory effects were rescued by supplement of cholesterol, an essential constituent in lipid raft, indicating a key role of cholesterol contents. Moreover, the tumor xenograft model showed that PTS inhibited tumor growth with a T/C (treatment/control) of 0.44 and a 56% inhibition of growth rate indicating the in vivo efficacy. In conclusion, the data suggest that PTS is an effective anti-tumor agent with in vitro and in vivo efficacies through inhibition of both Akt-dependent and -independent mTOR/p70S6K pathways. Moreover, disturbance of lipid raft and cholesterol contents may at least partly explain PTS-mediated anti-tumor mechanism.