The role of Bcl-2 family members in the progression of cutaneous melanoma

Directly targeting BAX for drug discovery: Therapeutic opportunities and challenges

For over two decades, the development of B-cell lymphoma-2 (Bcl-2) family therapeutics has primarily focused on anti-apoptotic proteins, resulting in the first-in-class drugs called BH3 mimetics, especially for Bcl-2 inhibitor Venetoclax. The pro-apoptotic protein Bcl-2-associated X protein (BAX) plays a crucial role as the executioner protein of the mitochondrial regulated cell death, contributing to organismal development, tissue homeostasis, and immunity. The dysregulation of BAX is closely associated with the onset and progression of diseases characterized by pathologic cell survival or death, such as cancer, neurodegeneration, and heart failure. In addition to conducting thorough investigations into the physiological modulation of BAX, research on the regulatory mechanisms of small molecules identified through biochemical screening approaches has prompted the identification of functional and potentially druggable binding sites on BAX, as well as diverse all-molecule BAX modulators. This review presents recent advancements in elucidating the physiological and pharmacological modulation of BAX and in identifying potentially druggable binding sites on BAX. Furthermore, it highlights the structural and mechanistic insights into small-molecule modulators targeting diverse binding surfaces or conformations of BAX, offering a promising avenue for developing next-generation apoptosis modulators to treat a wide range of diseases associated with dysregulated cell death by directly targeting BAX.

Correlation of ultrasound features with Bcl-2 protein expression in basal cell carcinomas (BCCs)

BACKGROUND

The expression of the Bcl-2 protein is frequently observed in basal cell carcinomas (BCCs), making it a significant biological marker and potential therapeutic target. Skin ultrasonography offers a noninvasive means of obtaining anatomical information about cutaneous tumors.

OBJECTIVES

The purpose of this study was to investigate the correlation between ultrasound features and Bcl-2 expression in BCCs, to provide a reference for developing pharmacological treatment plans.

METHODS

According to the Bcl-2 protein expression, 74 BCCs confirmed by surgical pathology were divided into high Bcl-2 expression BCCs (HB-BCCs) and low Bcl-2 expression BCCs (LB-BCCs). Preoperative lesion ultrasound features were analyzed retrospectively based on Liang's criteria, which included the following features: shape, surface, keratinization, base, infiltration level, internal echogenicity, distribution of hyperechoic spots, posterior echogenic changes, internal Doppler signal, and lesion size (maximum diameter and infiltration depth). The differences of two groups were compared using a chi-square test or a paired t-test.

RESULTS

Based on ultrasound features, cystic areas were more frequent in LB-BCCs (χ2  = 7.015, P = .008). Furthermore, LB-BCCs exhibited greater infiltration depth than HB-BCCs (4.86 ± 2.12 mm vs. 2.72 ± 1.40 mm, P = .000), had a higher propensity to infiltrate the subcutaneous tissue (χ2  = 12.422, P = .002), and displayed a more abundant internal Doppler signal within the lesions (χ2  = 24.696, P = .000). Conversely, maximum diameter of the lesions, shape, surface, keratinization, base, hyperechoic spots distribution, and posterior echogenic changes of the lesions did not differ significantly between the two groups.

CONCLUSIONS

Ultrasound features are correlated with Bcl-2 protein expression level in BCCs. LB-BCCs show greater infiltration depth, subcutaneous infiltration, more cystic changes and more abundant internal Doppler signal than HB-BCCs, which may suggest a potential basis for drug selection in BCC chemotherapy.

Trojan horse treatment based on PEG-coated extracellular vesicles to deliver doxorubicin to melanoma in vitro and in vivo

Tailoring extracellular vesicles (EVs) as targeted drug delivery systems to enhance the therapeutic efficacy showed superior advantage over liposomal therapies. Herein, we developed a novel nanotool for targeting B16.F10 murine melanoma, based on EVs stabilized with Polyethylene glycol (PEG) and loaded with doxorubicin (DOX). Small EVs were efficiently enriched from melanoma cells cultured under metabolic stress by ultrafiltration coupled with size exclusion chromatography (UF-SEC) and characterized by size, morphology, and proteome. To reduce their clearance in vivo, EVs were PEGylated and passively loaded with DOX (PEG-EV-DOX). Our data suggested that the low PEG coverage of EVs might still favor EV surface protein interactions with target proteins from intratumor cells, ensuring their use as "Trojan horses" to deliver DOX to the tumor tissue. Moreover, our results showed a superior antitumor activity of PEG-EV-DOX in B16.F10 murine melanoma models in vivo compared to that exerted by clinically applied liposomal DOX in the same tumor model. The PEG-EV-DOX administration in vivo reduced NF-κB activation and increased BAX expression, suggesting better prognosis of EV-based therapy than liposomal DOX treatment. Collectively, our results highlight the promising potential of EVs as optimal tools for systemic delivery of DOX to solid tumors.

Risk stratification of cutaneous melanoma reveals carcinogen metabolism enrichment and immune inhibition in high-risk patients

Cutaneous melanoma (CM) is the most lethal form of skin cancer. Risk assessment should facilitate stratified surveillance and guide treatment selection. Here, based on the mRNA-seq data from 419 CM patients in the Cancer Genome Atlas (TCGA), we developed a prognostic 21-gene signature to distinguish the outcomes of high- and low-risk patients, which was further validated in two external cohorts. The signature achieved a higher C-index as compared with other known biomarkers and clinical characteristics in both the TCGA and validation cohorts. Notably, in high-risk patients the expression levels of three driver genes, BRAF, NRAS, and NF1 in the MAPK pathway, were lower but exhibited a stronger positive correlation as compared with low-risk patients. Moreover, the genes involved in nicotinamide adenine dinucleotide metabolism were negatively correlated with the expression of BRAF in the high-risk group. Function analysis revealed that the upregulated genes in the high-risk group were enriched in the cytochrome P450-mediated metabolism of chemical carcinogens. Furthermore, the low-risk group had high levels of gamma delta T cells infiltration, while regulatory T cells were accumulated in the high-risk group. The present study offers a promising new prognostic signature for CM, and provides insight into the mechanisms of melanoma progression.

Interleukin 8 mediates bcl-xL-induced enhancement of human melanoma cell dissemination and angiogenesis in a zebrafish xenograft model

The protein bcl-xL is able to enhance the secretion of the proinflammatory chemokine interleukin 8 (CXCL8) in human melanoma lines. In this study, we investigate whether the bcl-xL/CXCL8 axis is important for promoting melanoma angiogenesis and aggressiveness in vivo, using angiogenesis and xenotransplantation assays in zebrafish embryos. When injected into wild-type embryos, bcl-xL-overexpressing melanoma cells showed enhanced dissemination and angiogenic activity compared with control cells. Human CXCL8 protein elicited a strong proangiogenic activity in zebrafish embryos and zebrafish Cxcr2 receptor was identified as the mediator of CXCL8 proangiogenic activity using a morpholino-mediated gene knockdown. However, human CXCL8 failed to induce neutrophil recruitment in contrast to its zebrafish homolog. Interestingly, the greater aggressiveness of bcl-xL-overexpressing melanoma cells was mediated by an autocrine effect of CXCL8 on its CXCR2 receptor, as confirmed by an shRNA approach. Finally, correlation studies of gene expression and survival analyses using microarray and RNA-seq public databases of human melanoma biopsies revealed that bcl-xL expression significantly correlated with the expression of CXCL8 and other markers of melanoma progression. More importantly, a high level of co-expression of bcl-xL and CXCL8 was associated with poor prognosis in melanoma patients. In conclusion, these data demonstrate the existence of an autocrine CXCL8/CXCR2 signaling pathway in the bcl-xL-induced melanoma aggressiveness, encouraging the development of novel therapeutic approaches for high bcl-xL-expressing melanoma.

Targeting the intrinsic apoptosis pathway as a strategy for melanoma therapy

Melanoma drug resistance is often attributed to abrogation of the intrinsic apoptosis pathway. Targeting regulators of apoptosis is thus considered a promising approach to sensitizing melanomas to treatment. The development of small-molecule inhibitors that mimic natural antagonists of either antiapoptotic members of the BCL-2 family or the inhibitor of apoptosis proteins (IAPs), known as BH3- or SMAC-mimetics, respectively, are helping us to understand the mechanisms behind apoptotic resistance. Studies using BH3-mimetics indicate that the antiapoptotic BCL-2 protein MCL-1 and its antagonist NOXA are particularly important regulators of BCL-2 family signaling, while SMAC-mimetic studies show that both XIAP and the cIAPs must be targeted to effectively induce apoptosis of cancer cells. Although most solid tumors, including melanoma, are insensitive to these mimetic drugs as single agents, combinations with other therapeutics have yielded promising results, and tests combining them with BRAF-inhibitors, which have already revolutionized melanoma treatment, are a clear priority.

Melatonin combined with endoplasmic reticulum stress induces cell death via the PI3K/Akt/mTOR pathway in B16F10 melanoma cells

This study investigated B16F10 melanoma cell death induced by melatonin combined with endoplasmic reticulum (ER) stress through the PI3K/Akt/mTOR pathway. Cell viability was significantly decreased after treatment with melatonin combined with ER stress from thapsigargin or tunicamycin compared to no treatment or treatment with melatonin only. Combined melatonin and ER stress also significantly reduced expression of p85β, p-Akt (Ser473, Thr308), and p-mTOR (Ser2448, Ser2481) compared to treatment with melatonin only. The ER stress protein p-PERK and p-eIF2α were significantly increased under combined melatonin and ER stress treatment compared to no treatment or treatment with melatonin only. Combined melatonin and ER stress significantly reduced Bcl-2 protein and augmented Bax protein compared to melatonin-only treatment. Also, the combined treatment significantly lowered expression of catalase, Cu/Zn-SOD, and Mn-SOD proteins compared to melatonin only. Expression of p85β was significantly more decreased under treatment with melatonin and thapsigargin or tunicamycin plus the PI3K inhibitors LY294002 or wortmannin than under treatment with only melatonin or a PI3K inhibitor. The PI3K downstream target p-Akt (Ser473, Thr308) showed significantly decreased expression under treatment with melatonin and thapsigargin or tunicamycin plus PI3K inhibitors than under treatment with melatonin or PI3K inhibitors only. These results indicate that survival of B16F10 melanoma cells after combined treatment with melatonin and ER stress inducers is suppressed through regulation of the PI3K/Akt/mTOR pathway. Melatonin combined with thapsigargin or tunicamycin appears to be a promising strategy for effective melanoma treatment.

Dioscin-induced apoptosis of human LNCaP prostate carcinoma cells through activation of caspase-3 and modulation of Bcl-2 protein family

Dioscin is a natural steroid saponin derived from several plants, showing potent anti-cancer effect against a variety of tumor cell lines. In the present study, we investigated the anti-cancer activity of dioscin against human LNCaP cells, and evaluated the possible mechanism involved in its antineoplastic action. It was found that dioscin (1, 2 and 4 μmol/L) could significantly inhibit the viability of LNCaP cells in a time- and concentration-dependent manner. Flow cytometry revealed that the apoptosis rate was increased after treatment of LNCaP cells with dioscin for 24 h, indicating that apoptosis was an important mechanism by which dioscin inhibited cancer. Western blotting was employed to detect the expression of caspase-3, Bcl-2 and Bax in LNCaP cells. The expression of cleaved caspase-3 was significantly increased, and meanwhile procaspase-3 was markedly decreased. The expression of anti-apoptotic protein Bcl-2 was down-regulated, whereas the pro-apoptotic protein Bax was up-regulated. Moreover, the Bcl-2/Bax ratio was drastically decreased. These results suggested that dioscin possessed potential anti-tumor activity in human LNCaP cells through the apoptosis pathway, which might be associated with caspase-3 and Bcl-2 protein family.

Proteasomal degradation of Mcl-1 by maritoclax induces apoptosis and enhances the efficacy of ABT-737 in melanoma cells

Background and purpose

Metastatic melanoma remains one of the most invasive and highly drug resistant cancers. The over expression of anti-apoptotic protein Mcl-1 has been associated with inferior survival, poor prognosis and chemoresistance of malignant melanoma. A BH3 mimetic, ABT-737, has demonstrated efficacy in several forms of cancers. However, the efficacy of ABT-737 depends on Mcl-1. Because the over expression of Mcl-1 is frequently observed in melanoma, specifically targeting of Mcl-1 may overcome the resistance of ABT-737. In this study, we investigated the effects of Maritoclax, a novel Mcl-1-selective inhibitor, alone and in combination with ABT-737, on the survival of human melanoma cells.

Experimental approach

For cell viability assessment we performed MTT assay. Apoptosis was determined using western blot and flow cytometric analysis.

Key results

The treatment of Maritoclax reduced the cell viability of melanoma cells with an IC₅₀ of between 2.2–5.0 µM. Further, treatment of melanoma cells with Maritoclax showed significant decrease in Mcl-1 expression. We found that Maritoclax was able to induce apoptosis in melanoma cells in a caspase-dependent manner. Moreover, Maritoclax induced Mcl-1 degradation via the proteasome system, which was associated with its pro-apoptotic activity. We also found that Maritoclax treatment increased mitochondrial translocation of Bim and Bmf. Importantly, Maritoclax markedly enhanced the efficacy of ABT-737 against melanoma cells in both two- and three-dimensional spheroids.

Conclusions and implications

Taken together, these results suggest that targeting of Mcl-1 by Maritoclax may represent a new therapeutic strategy for melanoma treatment that warrants further investigation as a single therapy or in combination with other agents such as Bcl-2 inhibitors.

Changes of PI3K/AKT/BCL2 signaling proteins in congenital Giant Nevi: melanocytes contribute to their increased survival and integrity

Congenital Giant Nevi (CGN) are rare melanocytic lesions with the potential to regress into malignant melanoma. Simultaneous up-regulation and cooperative interactions of signaling pathways are crucial events in the pathogenesis of melanocytes. Our study aimed to identify changes in the expression and activation of proteins controlling survival and/or apoptosis of the key signaling pathways PI3K/AKT/BCL2 and Wnt/β-catenin of CGN melanocytes. We applied a model of cultured melanocytes from paired CGN and normal appearing skin, and Western blot (WB) analyzed the expression and activation profile of survival and anti-apoptotic proteins of these signaling pathways, growth pattern, cell cycle and apoptosis. WB analysis demonstrated a significant higher expression level of activated AKT and of BCL2 proteins in the CGN melanocytes compared with paired melanocytes from normal appearing skin. A relative increase in the level of GSK3 and FOXO1 proteins, down stream targets of AKT, as well as of pβ-catenin was also detected in the CGN melanocytes compared with the controls. These changes were not affected by growth of the CGN melanocytes in reduced serum (starvation). Both cell populations shared a similar growth pattern, with no significant differences in the proportion of apoptotic cells and in cell cycle fractions. These data demonstrate for the first time, changes in signaling proteins of cultured CGN melanocytes. Further, suggesting that the changes in AKT/BCL2 signaling molecules might mediate growth and anti-apoptosis processes at least in part, thus increasing the survival potential of CGN melanocytes and maintaining their integrity.

Oblimersen in combination with temozolomide and albumin-bound paclitaxel in patients with advanced melanoma: a phase I trial

PURPOSE

The combination of oblimersen, a bcl-2 antisense oligonucleotide, and dacarbazine lead to superior progression-free survival in advanced melanoma patients. Albumin-bound paclitaxel (nab-paclitaxel) has single-agent activity in melanoma.

METHODS

In a phase I trial, chemotherapy-naïve patients with metastatic melanoma and normal LDH levels were enrolled on 3 cohorts. The treatment regimen consisted of 56-day cycles of oblimersen (7 mg/kg/day continuous IV infusion on day 1-7 and 22-28 in cohort 1 and 2; 900 mg fixed dose, twice weekly in weeks 1-2, 4-5 for cohort 3), temozolomide (75 mg/m(2), days 1-42), and nab-paclitaxel (175 mg/m(2) in cohort 1 and 3, 260 mg/m(2) in cohort 2 on day 7 and 28). Apoptosis markers were tested in pre- and post-treatment specimens of a subset of patients.

RESULTS

Six grade 3 events (neutropenia, renal insufficiency, hyponatremia, elevated creatinine, allergic reaction, and neuropathy) and 2 grade 4 events (neutropenia and thrombocytopenia) were seen in 32 patients. The objective response rate was 40.6% (2 complete responses and 11 partial responses) and 11 patients had stable disease, for a disease control rate of 75%.

CONCLUSIONS

The combination of oblimersen, temozolomide, and nab-paclitaxel was well tolerated and demonstrated encouraging activity in patients with advanced melanoma.

MicroRNAs: molecular features and role in cancer

microRNAs (miRNAs) are small noncoding endogenously produced RNAs that play key roles in controlling the expression of many cellular proteins. Once they are recruited and incorporated into a ribonucleoprotein complex miRISC, they can target specific mRNAs in a miRNA sequence-dependent process and interfere in the translation into proteins of the targeted mRNAs via several mechanisms. Consequently, miRNAs can regulate many cellular pathways and processes. Dysregulation of their physiological roles may largely contribute to disease. In particular, in cancer, miRNAs can be involved in the deregulation of the expression of important genes that play key roles in tumorigenesis, tumor development, and angiogenesis and have oncogenic or tumor suppressor roles. This review focuses on the biogenesis and maturation of miRNAs, their mechanisms of gene regulation, and the way their expression is deregulated in cancer. The involvement of miRNAs in several oncogenic pathways such as angiogenesis and apoptosis, and in the inter-cellular dialog mediated by miRNA-loaded exosomes as well as the development of new therapeutical strategies based on miRNAs will be discussed.

Selective induction of cell death in melanoma cell lines through targeting of Mcl-1 and A1

Melanoma is an often fatal form of skin cancer which is remarkably resistant against radio- and chemotherapy. Even new strategies that target RAS/RAF signaling and display unprecedented efficacy are characterized by resistance mechanisms. The targeting of survival pathways would be an attractive alternative strategy, if tumor-specific cell death can be achieved. Bcl-2 proteins play a central role in regulating survival of tumor cells. In this study, we systematically investigated the relevance of antiapoptotic Bcl-2 proteins, i.e., Bcl-2, Bcl-xL, Bcl-w, Mcl-1, and A1, in melanoma cell lines and non-malignant cells using RNAi. We found that melanoma cells required the presence of specific antiapoptotic Bcl-2 proteins: Inhibition of Mcl-1 and A1 strongly induced cell death in some melanoma cell lines, whereas non-malignant cells, i.e., primary human fibroblasts or keratinocytes were not affected. This specific sensitivity of melanoma cells was further enhanced by the combined inhibition of Mcl-1 and A1 and resulted in 60% to 80% cell death in all melanoma cell lines tested. This treatment was successfully combined with chemotherapy, which killed a substantial proportion of cells that survived Mcl-1 and A1 inhibition. Together, these results identify antiapoptotic proteins on which specifically melanoma cells rely on and, thus, provide a basis for the development of new Bcl-2 protein-targeting therapies.

Glutathione and Bcl-2 targeting facilitates elimination by chemoradiotherapy of human A375 melanoma xenografts overexpressing bcl-xl, bcl-2, and mcl-1

BACKGROUND

Bcl-2 is believed to contribute to melanoma chemoresistance. However, expression of Bcl-2 proteins may be different among melanomas. Thus correlations among expression of Bcl-2-related proteins and in vivo melanoma progression, and resistance to combination therapies, was investigated.

METHODS

Human A375 melanoma was injected s.c. into immunodeficient nude mice. Protein expression was studied in tumor samples obtained by laser microdisection. Transfection of siRNA or ectopic overexpression were applied to manipulate proteins which are up- or down-regulated, preferentially, during melanoma progression. Anti-bcl-2 antisense oligonucleotides and chemoradiotherapy (glutathione-depleting agents, paclitaxel protein-binding particles, daunorubicin, X rays) were administered in combination.

RESULTS

In vivo A375 cells down-regulated pro-apoptotic bax expression; and up-regulated anti-apoptotic bcl-2, bcl-xl, and mcl-1, however only Bcl-2 appeared critical for long-term tumor cell survival and progression in vivo. Reduction of Bcl-2, combined with partial therapies, decreased melanoma growth. But only Bcl-2 targeting plus the full combination of chemoradiotherapy eradicated A375 melanoma, and led to long-term survival (> 120 days) without recurrence in 80% of mice. Tumor regression was not due to immune stimulation. Hematology and clinical chemistry data were within accepted clinical toxicities.

CONCLUSION

Strategies to target Bcl-2, may increase the effectiveness of antitumor therapies against melanomas overexpressing Bcl-2 and likely other Bcl-2-related antiapoptotic proteins.

Modulation of NOXA and MCL-1 as a strategy for sensitizing melanoma cells to the BH3-mimetic ABT-737

PURPOSE

Drug resistance in melanoma is commonly attributed to ineffective apoptotic pathways. Inhibiting antiapoptotic BCL-2 and its relatives is an attractive strategy for sensitizing lymphoid malignancies to drugs but it has been largely unsuccessful for melanoma and other solid tumors. ABT-737, a small-molecule BH3-mimetic, selectively inhibits BCL-2, BCL-XL, and BCL-w and shows promise for treating leukemia, lymphoma, and small-cell lung cancer. Melanoma cells are insensitive to ABT-737, but MCL-1 inhibition reportedly increases the sensitivity of other tumors to the compound.

EXPERIMENTAL DESIGN

The efficacy of MCL-1 and BFL-1 inhibition for sensitizing melanoma cells to ABT-737 was investigated by short hairpin RNA-mediated knockdown or overexpression of their antagonist NOXA in two-dimensional cell culture, a three-dimensional organotypic spheroid model, and an in vivo model.

RESULTS

MCL-1 downregulation or NOXA overexpression strongly sensitized melanoma cells to ABT-737 in vitro. NOXA-inducing cytotoxic drugs also strongly sensitized melanomas to ABT-737 but, surprisingly, not vice versa. The drugs most suitable are not necessarily those normally used to treat melanoma. Resistance to ABT-737 occurred quickly in three-dimensional melanoma spheroids through reduced NOXA expression, although experiments with both xenografts and three-dimensional spheroids suggest that penetration of ABT-737 into tumor masses may be the principal limitation, which may be obviated through use of more diffusible BH3-mimetics.

CONCLUSION

Sensitization of tumors to BH3-mimetics by cytotoxic drugs that induce NOXA is a therapeutic strategy worth exploring for the treatment of melanoma and other solid cancers.

Towards new therapeutic approaches for malignant melanoma

Recent progress in understanding the molecular mechanisms of the initiation and progression of melanoma has created new opportunities for developing novel therapeutic modalities to manage this potentially lethal disease. Although at first glance, melanoma carcinogenesis appears to be a chaotic system, it is indeed, arguably, a deterministic multistep process involving sequential alterations of proto-oncogenes, tumour suppressors and miRNA genes. The scope of this article is to discuss the most recent and significant advances in melanoma molecular therapeutics. It is apparent that using single agents targeting solely individual melanoma pathways might be insufficient for long-term survival. However, the outstanding results on melanoma survival observed with novel selective inhibitors of B-RAF, such as PLX4032 give hope that melanoma can be cured. The fact that melanoma develops acquired resistance to PLX4032 emphasises the importance of simultaneously targeting several pathways. Because the most striking feature of melanoma is its unsurpassed ability to metastasise, it is important to implement newer systems for drug delivery adapted from research on stem cells and nanotechnology.

Bioinformatic prediction of ultraviolet light mutagenesis sensitivity of human genes and a method for genetically engineering UVB resistance

Living on earth, we are exposed to ultraviolet (UV) light as part of the solar radiation. UVB spectrum light exposure contributes to the development of skin cancer by interacting with pyrimidine pairs to create lesions called cyclobutane pyrimidine dimers. If these lesions are not removed by nucleotide excision repair, they often give rise to C to T transition mutations. Based on these observations, a bioinformatics approach was used to predict the vulnerability of human protein coding genes to UVB induced loss of function mutations. This data was used to evaluate in depth those genes associated with malignant melanoma. In addition, we demonstrate a method of genetically engineering genes that significantly improves resistance to UVB loss of function mutations.

Oligonucleotide Therapeutics

The idea of sequence-specific gene silencing by synthetic oligonucleotides targeting mRNA is at least 40 years old, but it was only in the mid-1980s when technical advances made the chemical synthesis of oligonucleotides possible that practical steps could be taken toward its implementation. The result was a deluge of experimental data in a variety of systems [1], most of which employed the phosphorothioate (PS) backbone modification, and much of which was ultimately, and unfortunately, uninterpretable.

Molecular mechanism of MART-1+/A*0201+ human melanoma resistance to specific CTL-killing despite functional tumor-CTL interaction

Durable responses in metastatic melanoma patients remain generally difficult to achieve. Adoptive cell therapy (ACT) with ex vivo engineered lymphocytes expressing high affinity T-cell receptors (TCRα/β) for the melanoma antigen MART-1₂₇₋₃₅/HLA-A*0201 [recognized by F5 cytotoxic T lymphocytes (F5 CTL)] has been found to benefit certain patients. However, many other patients are inherently unresponsive and/or relapse for unknown reasons. To analyze the basis for the acquired resistance and strategies to reverse it, we established F5 CTL-resistant (R) human melanoma clones from relatively sensitive parental lines under selective F5 CTL pressure. Surface MART-1₂₇₋₃₅/HLA-A*0201 in these clones was unaltered and F5 CTLs recognized and interacted with them similar to the parental lines. Nevertheless, the R clones were resistant to F5 CTL killing, exhibited hyperactivation of the NF-κB survival pathway, and overexpression of the antiapoptotic genes B cell lymphoma protein 2 (Bcl-2), Bcl-2 related gene (long alternatively spliced variant of Bcl-x gene; Bcl-(xL)), and myeloid cell differentiation 1 (Mcl-1). Sensitivity to F5 CTL-killing could be increased by pharmacological inhibition of the NF-κB pathway, Bcl-2 family members, or the proteasome, the latter of which reduced NF-κB activity and diminished antiapoptotic gene expression. Specific gene-silencing (by siRNA) confirmed the protective role of antiapoptotic factors by reversing R clone resistance. Together, our findings suggest that long-term immunotherapy may impose a selection for the development of resistant cells that are unresponsive to highly avid and specific melanoma-reactive CTLs, despite maintaining expression of functional peptide:MHC complexes, due to activation of antiapoptotic signaling pathways. Though unresponsive to CTL, our results argue that resistant cells can be resensitized to immunotherapy with coadministration of targeted inhibitors to antiapoptotic survival pathways.

Interface of signal transduction inhibition and immunotherapy in melanoma

Food and Drug Administration-approved treatment for metastatic melanoma, including interferon alpha and interleukin-2, offer a modest benefit. Immunotherapy, although has not enjoyed high overall response rates, is capable of providing durable responses in a subset of patients. In recent years, new molecular-targeted therapies have become available and offer promise of clinical benefit, although low durability of response. It is not yet clear how best to integrate these 2 novel modalities that target the immune response to melanoma (immune therapy) or that target molecular signaling pathways in the melanoma cells (targeted therapy). Many signal transduction pathways are important in both tumor cell and T-cell proliferation and survival, which generate risk in combining targeted therapy and immunotherapy. This review focuses on the role of targeted therapy and immunotherapy in melanoma, and discusses how to combine the 2 modalities rationally for increased duration and response.

A new era: melanoma genetics and therapeutics

We have recently witnessed an explosion in our understanding of melanoma. Knowledge of the molecular basis of melanoma and the successes of targeted therapies have pushed melanoma care to the precipice of a new era. Identification of significant pathways and oncogenes has translated to the development of targeted therapies, some of which have produced major clinical responses. In this review, we provide an overview of selected key pathways and melanoma oncogenes as well as the targeted agents and therapeutic approaches whose successes suggest the promise of a new era in melanoma and cancer therapy. Despite these advances, the conversion of transient remissions to stable cures remains a vital challenge. Continued progress towards a better understanding about the complexity and redundancy responsible for melanoma progression may provide direction for anti-cancer drug development.

Functional and biological analysis of Bcl-xL expression in human osteosarcoma

Bcl-xL, a member of Bcl-2 protein family functioned as dominant regulators of apoptotic cell death, has been reported to play important roles in malignant transformation and tumor development. In the present study, our aim was to explore the roles of Bcl-xL overexpression and determine its possibility as a therapeutic target in human osteosarcoma. Real-time quantitative RT-PCR and Western blot or immunohistochemistry assays were performed to detect the expression of Bcl-xL mRNA and protein in human osteosarcoma cell lines or tissue samples. The expression of other Bcl-2 family proteins (Bcl-2, Mcl-1, Bim and Bik) in osteosarcoma tissues was also detected by immunohistochemistry. The associations of Bcl-xL mRNA expression with clinicopathologic factors and prognosis of osteosarcoma patients were evaluated. RNA interference or gene overexpression technologies were employed to downregulate or upregulate endogenous Bcl-xL expression in osteosarcoma cells and the effects of Bcl-xL downregulation or upregulation on phenotypes and chemo- or radiosensitivity of human osteosarcoma cells were analyzed. Finally, the mechanism of synergistic effects of Bcl-xL downregulation and chemo- or radiotherapy was explored by detecting the activity of caspase-3. The expression levels of Bcl-xL mRNA and protein in high metastatic osteosarcoma cells showed higher than those in low metastatic osteosarcoma cells. Moreover, the levels of Bcl-xL mRNA expression were significantly higher in osteosarcoma tissues than those in chondroma or corresponding non-tumor tissues (P<0.01), and osteosarcoma tissues showed stronger immunostaining of Bcl-xL protein than non-tumor tissues. The stronger staining of Bcl-2 and Mcl-1 proteins was also observed, while the staining of pro-apoptotic proteins (Bim and Bik) was significantly weaker or not detected in osteosarcoma tissues. The higher levels of Bcl-xL mRNA expression were significantly correlated with advanced clinical stage (P=0.005) or hematogenous metastasis (P=0.001) of osteosarcoma patients. Osteosarcoma patients with higher Bcl-xL mRNA expression showed a poorer survival compared with those with lower expression (P=0.039). Bcl-xL downregulation or upregulation could significantly reduce or increase the proliferation capacity of osteosarcoma cells. Furthermore, Bcl-xL downregulation could significantly enhance in vitro chemo- or radiosensitivity of osteosarcoma cells, which might be associated with elevated activity of caspase-3. Taken together, overexpression of Bcl-xL may play important roles in osteosarcoma progression and this molecule will be a potential chemo- or radiotherapeutic molecular target for osteosarcoma therapy.

Inhibition of p38 MAPK enhances ABT-737-induced cell death in melanoma cell lines: novel regulation of PUMA

The mitogen-activated protein kinase (MAPK) pathway is constitutively activated in the majority of melanomas, promoting cell survival, proliferation and migration. In addition, anti-apoptotic Bcl-2 family proteins Mcl-1, Bcl-xL and Bcl-2 are frequently overexpressed, contributing to melanoma's well-documented chemoresistance. Recently, it was reported that the combination of MAPK pathway inhibition by specific MEK inhibitors and Bcl-2 family inhibition by BH3-mimetic ABT-737 synergistically induces apoptotic cell death in melanoma cell lines. Here we provide the first evidence that inhibition of another key MAPK, p38, synergistically induces apoptosis in melanoma cells in combination with ABT-737. We also provide novel mechanistic data demonstrating that inhibition of p38 increases expression of pro-apoptotic Bcl-2 protein PUMA. Furthermore, we demonstrate that PUMA can be cleaved by a caspase-dependent mechanism during apoptosis and identify what appears to be the PUMA cleavage product. Thus, our findings suggest that the combination of ABT-737 and inhibition of p38 is a promising, new treatment strategy that acts through a novel PUMA-dependent mechanism.

RNA silencing of Mcl-1 enhances ABT-737-mediated apoptosis in melanoma: role for a caspase-8-dependent pathway

BACKGROUND

Malignant melanoma is resistant to almost all conventional forms of chemotherapy. Recent evidence suggests that anti-apoptotic proteins of the Bcl-2 family are overexpressed in melanoma and may contribute to melanoma's striking resistance to apoptosis. ABT-737, a small-molecule inhibitor of Bcl-2, Bcl-xl and Bcl-w, has demonstrated efficacy in several forms of leukemia, lymphoma as well as solid tumors. However, overexpression of Mcl-1, a frequent observance in melanoma, is known to confer ABT-737 resistance.

METHODOLOGY/PRINCIPAL FINDINGS

Here we report that knockdown of Mcl-1 greatly reduces cell viability in combination with ABT-737 in six different melanoma cell lines. We demonstrate that the cytotoxic effect of this combination treatment is due to apoptotic cell death involving not only caspase-9 activation but also activation of caspase-8, caspase-10 and Bid, which are normally associated with the extrinsic pathway of apoptosis. Caspase-8 (and caspase-10) activation is abrogated by inhibition of caspase-9 but not by inhibitors of the death receptor pathways. Furthermore, while caspase-8/-10 activity is required for the full induction of cell death with treatment, the death receptor pathways are not. Finally, we demonstrate that basal levels of caspase-8 and Bid correlate with treatment sensitivity.

CONCLUSIONS/SIGNIFICANCE

Our findings suggest that the combination of ABT-737 and Mcl-1 knockdown represents a promising, new treatment strategy for malignant melanoma. We also report a death receptor-independent role for extrinsic pathway proteins in treatment response and suggest that caspase-8 and Bid may represent potential markers of treatment sensitivity.

Molecular pathogenesis of cutaneous melanocytic neoplasms

Melanoma is the deadliest form of skin cancer without an effective treatment. An understanding of the genetic basis of melanoma has recently shed light on some of the mechanisms of melanomagenesis. This review explores the major genes involved in familial and sporadic cutaneous melanoma with an emphasis on CDKN2A, CDK4, MC1R, and MAPK pathway targets (e.g., RAS and BRAF), apoptosis regulators (e.g., BCL-2, AKT, and APAF-1), and the tumor-suppressor genes TP53 and PTEN. New directions for therapeutics based on our current knowledge of the genes implicated in melanoma are also discussed.

Peptides and peptide mimics as modulators of apoptotic pathways

Programmed cell death is an important and stringently controlled process. Aberrancies in its control mechanisms can lead to disease; overactive apoptosis can cause neurodegenerative disorders, whereas deficient apoptotic activity can lead to cancer. Therefore, controlling apoptotic pathways with peptides is showing increasing promise as a strategy in drug development.Programmed cell death or apoptosis is a noninvasive and strictly regulated cellular process required for organism development and tissue homeostasis. Deficiencies in apoptotic pathways are the source of many diseases such as cancer, neurodegenerative and autoimmune diseases, and disorders related to an inappropriate loss of cells such as heart failure, stroke, and liver injury. Validation of the various points of intervention as targets for drug development has been the subject of a vast number of studies. Peptides are essential tools for drug discovery, as well as preclinical and pharmaceutical drug development.

Expression and function of bcl-2 proteins in melanoma

Bcl-2 proteins are critical regulators of mitochondrial membrane permeability and the proapoptotic mitochondrial pathway. The family encloses pro- and antiapoptotic factors encoded by over 15 genes, which frequently give rise to alternative splice products. Antiapoptotic, proapoptotic multidomain, and proapoptotic BH3-only proteins are characterized by the presence of at least one of four Bcl-2 homology domains (BH 1-4). Their expression and activities are controlled by survival pathways as MAP kinases and protein kinase B/Akt, which are in touch with a number of transcription factors. In melanoma, the mitochondrial apoptosis pathways and Bcl-2 proteins appear of particular importance for apoptosis resistance, which has been addressed in clinical trials applying antisense-Bcl-2. Overexpression or induction of proapoptotic Bcl-2 proteins as well as the use of small molecule mimetics for the proapoptotic BH3 domain are further promising strategies.

Molecular predictors of human nervous system cancer responsiveness to enediyne chemotherapy

PURPOSE

To identify and mathematically model molecular predictors of response to the enediyne chemotherapeutic agent, neocarzinostatin, in nervous system cancer cell lines.

METHODS

Human neuroblastoma, breast cancer, glioma, and medulloblastoma cell lines were maintained in culture. Content of caspase-3 and Bcl-2, respectively, was determined relative to actin content for each cell line by Western blotting and optical densitometry. For each cell line, sensitivity to neocarzinostatin was determined. Brain tumor cell lines were stably transfected with human Bcl-2 cDNA cloned into the pcDNA3 plasmid vector.

RESULTS

In human tumor cell lines of different tissue origins, sensitivity to neocarzinostatin is proportional to the product of the relative contents of Bcl-2 and caspase-3 (r (2) = 0.9; P < 0.01). Neuroblastoma and brain tumor cell lines are particularly sensitive to neocarzinostatin; the sensitivity of brain tumor lines to neocarzinostatin is enhanced by transfection with an expression construct for Bcl-2 and is proportional in transfected cells to the product of the relative contents of Bcl-2 and caspase-3 (r (2) = 0.7).

CONCLUSION

These studies underscore the potential of molecular profiling in identifying effective chemotherapeutic paradigms for cancer in general and tumors of the nervous system in particular.

Down-regulation of mcl-1 by small interfering RNA sensitizes resistant melanoma cells to fas-mediated apoptosis

Resistance of malignant melanoma cells to Fas-mediated apoptosis is among the mechanisms by which they escape immune surveillance. However, the mechanisms contributing to their resistance are not completely understood, and it is still unclear whether antiapoptotic Bcl-2-related family proteins play a role in this resistance. In this study, we report that treatment of Fas-resistant melanoma cell lines with cycloheximide, a general inhibitor of de novo protein synthesis, sensitizes them to anti-Fas monoclonal antibody (mAb)-induced apoptosis. The cycloheximide-induced sensitization to Fas-induced apoptosis is associated with a rapid down-regulation of Mcl-1 protein levels, but not that of Bcl-2 or Bcl-xL. Targeting Mcl-1 in these melanoma cell lines with specific small interfering RNA was sufficient to sensitize them to both anti-Fas mAb-induced apoptosis and activation of caspase-9. Furthermore, ectopic expression of Mcl-1 in a Fas-sensitive melanoma cell line rescues the cells from Fas-mediated apoptosis. Our results further show that the expression of Mcl-1 in melanoma cells is regulated by the mitogen-activated protein kinase/extracellular signal-regulated kinase (ERK) and not by phosphatidylinositol 3-kinase/AKT signaling pathway. Inhibition of ERK signaling with the mitogen-activated protein/ERK kinase-1 inhibitor or by expressing a dominant negative form of mitogen-activated protein/ERK kinase-1 also sensitizes resistant melanoma cells to anti-Fas mAb-induced apoptosis. Thus, our study identifies mitogen-activated protein kinase/ERK/Mcl-1 as an important survival signaling pathway in the resistance of melanoma cells to Fas-mediated apoptosis and suggests that its targeting may contribute to the elimination of melanoma tumors by the immune system.

Apoptosis pathways and oncolytic adenoviral vectors: promising targets and tools to overcome therapy resistance of malignant melanoma

In the last decades melanoma incidence has been increasing worldwide, while mortality remained on a high level. Until now, there is no suitable therapy for metastasized melanoma, which could lead to a significant increase in overall survival. Apoptosis deficiency is supposed to be a critical factor for therapy resistance, and previous work has characterized the basic mechanisms of apoptosis regulation in melanoma. Genes and strategies suitable for efficient induction of apoptosis in melanoma cells were identified, which are based on proapoptotic Bcl-2 proteins (Bcl-x(S), Bcl-x(AK), Bik/Nbk and Bax) as well as on tumor necrosis factor (TNF)-related death ligands (CD95L/Fas ligand and TNF-related apoptosis-inducing ligand, TRAIL). Proapoptotic genes may be employed in improved gene therapeutic strategies, based on conditional oncolytic adenoviral vectors.

Bim Expression Is Reduced in Human Cutaneous Melanomas

Bim is a BH3-only protein belonging to the Bcl-2 family of apoptotic regulators. Upon activation, Bim can antagonize all the prosurvival Bcl-2 proteins, leading to apoptosis. To investigate whether Bim plays a role in melanoma progression, we used tissue microarray and immunohistochemistry to measure Bim expression in 52 cases of dysplastic nevi, 159 cases of primary melanomas and 52 cases of melanoma metastases, and evaluated the prognostic value of Bim expression. Our results showed that Bim expression is reduced as melanoma progresses. Significant differences for Bim staining pattern were observed between dysplastic nevi and metastatic melanomas (P<0.001, chi2 test), and between primary melanomas and metastatic melanomas (P<0.001, chi2 test). Moreover, reduced Bim expression is significantly correlated with poor 5-year survival of melanoma patients but failed to be an independent prognostic factor by Cox regression analysis. Our data suggest that Bim loss may play an important role in melanoma progression.

Overcoming apoptosis deficiency of melanoma-hope for new therapeutic approaches

The increased incidence of malignant melanoma in the last decades, its high mortality and pronounced therapy resistance pose an enormous challenge. Important therapeutic targets for melanoma are the induction of apoptosis and suppression of survival pathways. Preclinical studies have demonstrated the efficacy of pro-apoptotic Bcl-2 proteins and of death receptor ligands to trigger apoptosis in melanoma cells. In the clinical setting, BH3 domain mimics and death receptor agonists are therefore considered as promising, specific novel treatments to add to the conventional pro-apoptotic strategies such as chemo- or radiotherapy. However, constitutively activated survival pathways, in particular the mitogen-activated protein kinases, protein kinase B/Akt and nuclear factor (NF)-kappaB, all may work in concert to prevent effective therapy. Thus, selective biologicals developed with the aim to inhibit pro-survival signaling are currently tested in melanoma. For highly therapy-resistant tumors such as melanoma, development of novel drug combinations will be essential, and combinations of survival inhibitors and pro-apoptotic mediators appear most promising. The challenge of the near future will be to make a rational choice of the multiple possible combinations and protocols. This review gives a critical overview of proteins involved in melanoma chemoresistance, which are targets for current drug development leading to the best choice for future trials.

Modulation of bcl-xL in tumor cells regulates angiogenesis through CXCL8 expression

In this paper, we investigated whether bcl-xL can be involved in the modulation of the angiogenic phenotype of human tumor cells. Using the ADF human glioblastoma and the M14 melanoma lines, and their derivative bcl-xL-overexpressing clones, we showed that the conditioned medium of bcl-xL transfectants increased in vitro endothelial cell functions, such as proliferation and morphogenesis, and in vivo vessel formation in Matrigel plugs, compared with the conditioned medium of control cells. Moreover, the overexpression of bcl-xL induced an increased expression of the proangiogenic interleukin-8 (CXCL8), both at the protein and mRNA levels, and an enhanced CXCL8 promoter activity. The role of CXCL8 on bcl-xL-induced angiogenesis was validated using CXCL8-neutralizing antibodies, whereas down-regulation of bcl-xL through antisense oligonucleotide or RNA interference strategies confirmed the involvement of bcl-xL on CXCL8 expression. Transient overexpression of bcl-xL led to extend this observation to other tumor cell lines with different origin, such as colon and prostate carcinoma. In conclusion, our results showed that CXCL8 modulation by bcl-xL regulates tumor angiogenesis, and they point to elucidate an additional function of bcl-xL protein.

Targeting Bcl-X(L) for prevention and therapy of skin cancer

Apoptosis plays an important role in skin carcinogenesis. Bcl-X(L), an antiapoptotic Bcl-2 family member, is a key regulator in the process. Aberrant expression of Bcl-X(L) allows cells carrying mutations to survive and propagate. Overexpression of Bcl-X(L) is correlated with tumor malignancy and invasion. Importantly, deregulation of Bcl-X(L) confers drug resistance to chemotherapy. Therefore, targeting Bcl-X(L) in combination with conventional chemotherapy is a promising way to pursue cancer chemotherapy. Several compounds targeting Bcl-X(L) expression or function have shown their potential in chemoprevention and of chemotherapy of cancer.

Oblimersen in the treatment of metastatic melanoma

Oblimersen (Genasense is a Bcl-2 antisense compound that selectively targets Bcl-2 RNA for degradation by RNase H and thereby decreases Bcl-2 protein production. Bcl-2 protein plays a major role in preventing apoptosis and has been linked to chemotherapy resistance in melanoma. Preclinical studies with oblimersen in melanoma cell lines and xenograft models of melanoma have demonstrated downregulation of Bcl-2 protein, induction of apoptosis and enhanced tumor response when combined with chemotherapy. Results of a Phase I/II study have shown that reducing Bcl-2 with oblimersen coincident with the administration of dacarbazine may amplify apoptosis and improve therapeutic outcome. A subsequent Phase III trial showed that the addition of oblimersen to dacarbazine significantly improved multiple clinical outcomes relative to dacarbazine alone based on an intent-to-treat analysis of progression-free survival and response rate (overall, complete and durable), as well as overall survival in patients with normal lactate dehydrogenase. This article reviews the biochemistry, pharmacodynamics and pharmacokinetics, safety and efficacy data related to oblimersen in melanoma.

Specific amino acid dependency regulates the cellular behavior of melanoma

Relative specific amino acid dependency is one of the metabolic abnormalities of melanoma cells and metabolic studies of this dependency are in their infancy. Herein, we review the current studies in this area and present new information that adds to the understanding of how tyrosine (Tyr) and phenylalanine (Phe) dependency as well as other amino acids regulate the cell behaviors of melanoma cells. Amino acid dependency of human melanoma cells is multifactorial and restricting Tyr and Phe to melanoma triggers a series of alterations in metabolic and signaling pathways in a time-ordered fashion to alter different cellular behaviors. For example, at early time points, the reduction of Tyr and Phe alters metabolic reactions quantitatively or qualitatively. The alterations include modulation of integrin/focal adhesion kinase (FAK)/G protein pathways and the plasminogen activator (PA)/PA inhibitor pathways to inhibit tumor cell invasion. At later time periods, a further drop in intracellular amino acids induces more metabolic alterations to impact the FAK/Ras/Raf and Bcl-2 pathways leading to apoptosis. The threshold effects and the targeting of multiple pathways by restriction of specific amino acids provide a connection between the metabolic alterations and signaling pathways that modulate the cellular behaviors of melanoma cells. Decoding the metabolic alterations that connect amino acid concentration to the crucial step(s) in signaling is important and an exciting area of cancer research.

Melanoma biology and new targeted therapy

Melanoma is a cancer that arises from melanocytes, specialized pigmented cells that are found predominantly in the skin. The incidence of melanoma is rising steadily in western populations--the number of cases worldwide has doubled in the past 20 years. In its early stages malignant melanoma can be cured by surgical resection, but once it has progressed to the metastatic stage it is extremely difficult to treat and does not respond to current therapies. Recent discoveries in cell signalling have provided greater understanding of the biology that underlies melanoma, and these advances are being exploited to provide targeted drugs and new therapeutic approaches.

Update on therapy for melanoma: opportunities for patient selection and overcoming tumor resistance

The incidence of malignant melanoma is rising faster than any other malignancy. Although earlier stage patients can be cured with surgical resection with or without adjuvant therapy, a significant number of patients go on to develop disseminated disease. Currently, limited therapeutic options exist for patients with metastatic melanoma. Recent studies suggest that patient selection is feasible and may enable the restriction of treatment to those most likely to benefit. Additionally, several potential mechanisms of tumor resistance have been identified creating opportunities for circumventing them. This article will review current strategies for patient selection and overcoming therapeutic resistance. These strategies hold the promise of extending the clinical benefits of current therapies as well as facilitating the development of additional and more active treatments.

Malignant melanoma: genetics and therapeutics in the genomic era

Cell for cell, probably no human cancer is as aggressive as melanoma. It is among a handful of cancers whose dimensions are reported in millimeters. Tumor thickness approaching 4 mm presents a high risk of metastasis, and a diagnosis of metastatic melanoma carries with it an abysmal median survival of 6-9 mo. What features of this malignancy account for such aggressive behavior? Is it the migratory history of its cell of origin or the programmed adaptation of its differentiated progeny to environmental stress, particularly ultraviolet radiation? While the answers to these questions are far from complete, major strides have been made in our understanding of the cellular, molecular, and genetic underpinnings of melanoma. More importantly, these discoveries carry profound implications for the development of therapies focused directly at the molecular engines driving melanoma, suggesting that we may have reached the brink of an unprecedented opportunity to translate basic science into clinical advances. In this review, we attempt to summarize our current understanding of the genetics and biology of this disease, drawing from expanding genomic information and lessons from development and genetically engineered mouse models. In addition, we look forward toward how these new insights will impact on therapeutic options for metastatic melanoma in the near future.

Relative Bcl-2 independence of drug-induced cytotoxicity and resistance in 518A2 melanoma cells

PURPOSE

Inhibition of the function of Bcl-2 protein has been postulated to sensitize cells to cytotoxic chemotherapy. G3139 (Genasense) is a phosphorothioate anti-Bcl-2 antisense oligonucleotide, but its mechanism of action is uncertain. The aim of the present work is to investigate inhibition of Bcl-2 expression in 518A2 melanoma cells, the cell line on which recent phase II and phase III clinical trials employing this agent were based.

EXPERIMENTAL DESIGN

We down-regulated the expression of Bcl-2 protein by two different strategies in these cells: one employing G3139 and controls, and the other using a small interfering RNA approach. Cell viability after treatment with oligonucleotides or small interfering RNA and cytotoxic agents including gemcitibine, DDP, docetaxel, and thapsigargin was measured by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay. A 518A2 melanoma cell line stably overexpressing Bcl-2 protein was constructed and treated with either these cytotoxic agents or G3139.

RESULTS

The cytotoxic effects of either G3139 or small interfering RNA treatment of 518A2 melanoma cells are Bcl-2 independent. In addition, in the Bcl-2-overexpressing cells, only a modest increment in chemoresistance was observed, and treatment with G3139 not only did not down-regulate Bcl-2 expression but produced essentially identical toxicity as was observed in the wild-type or mock-transfected cells.

CONCLUSIONS

Our results suggest that the mechanism whereby G3139 produces drug-induced cytotoxicity in the 518A2 melanoma line is not dependent on levels of Bcl-2. These findings emphasize the nonsequence specific effects of this phosphorothioate oligonucleotide and call into question the validity of Bcl-2 as a target in this cell line.

Enhanced antitumour efficacy of gimatecan in combination with Bcl-2 antisense oligonucleotide in human melanoma xenografts

The anti-apoptotic protein Bcl-2 has been implicated in the intrinsic resistance of melanoma to chemotherapy. The aim of this study was to investigate the effects of anti-Bcl-2 oligonucleotide oblimersen on the antitumour activity of gimatecan, a novel lipophilic camptothecin currently undergoing clinical phase II studies. Results showed a reduced sensitivity of melanoma cells to gimatecan following Bcl-2 transfection and inversely, increased cell sensitivity to gimatecan in combination with oblimersen. In in vivo studies performed in two melanoma xenografts expressing different Bcl-2 levels, the antitumour activity of oblimersen itself was modest, but the combination with gimatecan produced a significant therapeutic advantage. The combination therapy inhibited tumour growth and delayed regrowth of the two tumours tested. The enhancement of antitumour activity was observed at doses that were tolerated well. The effects of oblimersen on antitumour activity and toxicity of gimatecan were dose-dependent. The capability of oblimersen to improve the efficacy of gimatecan supports the therapeutic potential of the drug combination in the treatment of human melanoma.

The novel tumor suppressor p33ING2 enhances UVB-induced apoptosis in human melanoma cells

The roles of p33ING2 as a tumor suppressor candidate have been shown through regulation of gene transcription, induction of cell cycle arrest, and apoptosis. As p33ING2 shares 58.9% homology with p33ING1b, we hypothesized that p33ING2 shares functional similarities with p33ING1b. We previously found that p33ING1b cooperates with p53 to enhance UVB-induced apoptosis. Here, we report that overexpression of p33ING2 enhanced apoptosis in UVB-irradiated and non-irradiated melanoma MMRU cells. We demonstrate that enhancement of apoptosis by p33ING2 requires the presence of functional p53. Furthermore, we found that overexpression of p33ING2 significantly downregulated the expression of Bcl-2 after UVB irradiation, resulting in an increased Bax/Bcl-2 ratio. Moreover, we found that p33ING2 promoted Bax translocation to mitochondria, altered the mitochondrial membrane potential, and induced cytochrome c release and thus the activation of caspases 9 and 3. In addition, we showed that under non-stress conditions p33ING2 upregulates Fas expression and activates caspase 8. Taken together, we demonstrate that p33ING2 cooperates with p53 to regulate apoptosis via activation of both the mitochondrial/intrinsic and death-receptor/extrinsic apoptotic pathways.

Apoptosis pathway-targeted drugs--from the bench to the clinic

It is an exciting time for cancer researchers in the field of apoptotic cell death. The avalanche of discoveries over the past decade or so regarding how apoptosis is regulated begins to be exploited for therapeutic benefit as the first apoptosis-targeted drugs enter early clinical trials. This chapter provides a selective review on the development of such drugs. We also outline issues regarding the regulation and design of early clinical trials of this type of molecularly targeted agent. Finally, we discuss the biomarkers and surrogate pharmacodynamic endpoint assays currently available to chart the efficacy of apoptosis-inducing anticancer therapy.

Phosphorothioate oligodeoxynucleotides and G3139 induce apoptosis in 518A2 melanoma cells

In a previous study, we showed that G3139, an antisense phosphorothioate oligonucleotide that down-regulates the expression of Bcl-2 protein, did not cause chemosensitization of 518A2 melanoma cells. In this work, we show that G3139, and the 2-base mismatch, G4126, can initiate apoptosis in this and other melanoma cell lines as shown by increased cell surface Annexin V expression, typical nuclear phenotypic changes as assessed by 4′,6-diamidino-2-phenylindole staining, activation of caspase-3 (but not caspase-8) and Bid, appearance of DEVDase (but not IETDase) activity, and cleavage of poly(ADP-ribose)-polymerase 1. Depolarization of the mitochondrial membrane occurs as a relatively late event. All of these processes seem to be substantially, but perhaps not totally, Bcl-2 independent as shown by experiments employing an anti-Bcl-2 small interfering RNA, which as shown previously down-regulated Bcl-2 protein expression but did not produce apoptosis or chemosensitization in melanoma cells. In fact, these G3139-induced molecular events were not dramatically altered in cells that forcibly overexpressed high levels of Bcl-2 protein. Addition of irreversible caspase inhibitors (e.g., the pan-caspase inhibitor zVAD-fmk) to G3139-treated cells almost completely blocked cytotoxicity. Examination of the time course of the appearance of caspase-3 and cleaved poly(ADP-ribose)-polymerase 1 showed that this could be correlated with the release of cytochrome c from the mitochondria, an event that begins only ∼4 hours after the end of the oligonucleotide/LipofectAMINE 2000 5-hour transfection period. Thus, both G3139 and cytotoxic chemotherapy activate the intrinsic pathway of apoptosis in these cells, although Bcl-2 expression does not seem to contribute strongly to chemoresistance. These findings suggest that the attainment of G3139-induced chemosensitization in these cells will be difficult.