Safety and biologic activity of intravenous BCL-2 antisense oligonucleotide (G3139) and taxane chemotherapy in patients with advanced cancer

Antisense Oligonucleotide-Mediated Splice Switching: Potential Therapeutic Approach for Cancer Mitigation

Splicing is an essential process wherein precursor messenger RNA (pre-mRNA) is reshaped into mature mRNA. In alternative splicing, exons of any pre-mRNA get rearranged to form mRNA variants and subsequently protein isoforms, which are distinct both by structure and function. On the other hand, aberrant splicing is the cause of many disorders, including cancer. In the past few decades, developments in the understanding of the underlying biological basis for cancer progression and therapeutic resistance have identified many oncogenes as well as carcinogenic splice variants of essential genes. These transcripts are involved in various cellular processes, such as apoptosis, cell signaling and proliferation. Strategies to inhibit these carcinogenic isoforms at the mRNA level are promising. Antisense oligonucleotides (AOs) have been developed to inhibit the production of alternatively spliced carcinogenic isoforms through splice modulation or mRNA degradation. AOs can also be used to induce splice switching, where the expression of an oncogenic protein can be inhibited by the induction of a premature stop codon. In general, AOs are modified chemically to increase their stability and binding affinity. One of the major concerns with AOs is efficient delivery. Strategies for the delivery of AOs are constantly being evolved to facilitate the entry of AOs into cells. In this review, the different chemical modifications employed and delivery strategies applied are discussed. In addition to that various AOs in clinical trials and their efficacy are discussed herein with a focus on six distinct studies that use AO-mediated exon skipping as a therapeutic strategy to combat cancer.

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.

PIAS1 is a crucial factor for prostate cancer cell survival and a valid target in docetaxel resistant cells

Occurrence of an inherent or acquired resistance to the chemotherapeutic drug docetaxel is a major burden for patients suffering from different kinds of malignancies, including castration resistant prostate cancer (PCa). In the present study we address the question whether PIAS1 targeting can be used to establish a basis for improved PCa treatment. The expression status and functional relevance of PIAS1 was evaluated in primary tumors, in metastatic lesions, in tissue of patients after docetaxel chemotherapy, and in docetaxel resistant cells. Patient data were complemented by functional studies on PIAS1 knockdown in vitro as well as in chicken chorioallantoic membrane and mouse xenograft in vivo models. PIAS1 was found to be overexpressed in local and metastatic PCa and its expression was further elevated in tumors after docetaxel treatment as well as in docetaxel resistant cells. Furthermore, PIAS1 knockdown experiments revealed an increased expression of tumor suppressor p21 and declined expression of anti-apoptotic protein Mcl1, which caused diminished cell proliferation and tumor growth in vitro and in vivo. In summary, the presented data indicate that PIAS1 is crucial for parental and docetaxel resistant PCa cell survival and is therefore a promising new target for treatment of primary, metastatic, and chemotherapy resistant PCa.

A Phase II Study of AT-101 to Overcome Bcl-2--Mediated Resistance to Androgen Deprivation Therapy in Patients With Newly Diagnosed Castration-Sensitive Metastatic Prostate Cancer

In a phase II multicenter study, men with castration sensitive metastatic prostate cancer were treated with AT-101, a small molecule Bcl-2 inhibitor, and androgen deprivation therapy. At the end of 7 cycles of therapy in 55 patients, an undetectable PSA was achieved in 31%. However, the combination did not meet the pre-specified level of activity for further development.

BACKGROUND

We conducted a phase II study in men with castration-sensitive metastatic prostate cancer to test the hypothesis that AT-101, a small molecule Bcl-2 inhibitor, has clinical activity in patients initiating androgen deprivation therapy (ADT) for metastatic prostate cancer.

MATERIALS AND METHODS

Patients with metastatic prostate cancer scheduled to start, or who had recently (within 6 weeks) initiated, ADT were enrolled. ADT with a luteinizing hormone-releasing hormone agonist and bicalutamide was started 6 weeks before initiation of oral AT-101, 20 mg/day for 21 days of a 28-day cycle. The primary endpoint of the study was the percentage of patients with an undetectable prostate-specific antigen (PSA) level (≤ 0.2 ng/mL) after 7.5 months (1.5 months of ADT alone plus 6 months of combined ADT and AT-101). To assess for an association between chromodomain helicase DNA binding protein 1 (CHD1) and drug sensitivity, fluorescence in situ hybridization with confocal microscopy was assessed in a subgroup of patients.

RESULTS

A total of 55 patients were enrolled, with median age of 61 years and a median PSA level of 27.6 ng/dL. Of the 55 patients, 72% had a Gleason score ≥ 8. Three patients had visceral metastases, and the remaining patients had bone or nodal metastasis. An undetectable PSA level was achieved in 31% of the patients. Of the 31 patients, 12 experienced serious adverse events, 7 of which were considered related to study therapy. Most of the related adverse events were gastrointestinal and nervous system disorders. CHD1 assessment was feasible, with a nonsignificant association with therapeutic sensitivity in a small number of patients.

CONCLUSION

The combination of ADT and AT-101 did not meet the prespecified level of activity for further development of this combination.

Pathways of chemotherapy resistance in castration-resistant prostate cancer

Chemotherapy remains the major treatment option for castration-resistant prostate cancer (CRPC) and limited cytotoxic options are available. Inherent chemotherapy resistance occurs in half of all patients and inevitably develops even in those who initially respond. Docetaxel has been the mainstay of therapy for 6 years, providing a small survival benefit at the cost of significant toxicity. Cabazitaxel is a promising second-line agent; however, it is no less toxic, whereas mitoxantrone provides only symptomatic benefit. Multiple cellular pathways involving apoptosis, inflammation, angiogenesis, signalling intermediaries, drug efflux pumps and tubulin are implicated in the development of chemoresistance. A thorough understanding of these pathways is needed to identify biomarkers that predict chemotherapy resistance with the aim to avoid unwarranted toxicities in patients who will not benefit from treatment. Until recently, the search for predictive biomarkers has been disappointing; however, the recent discovery of macrophage inhibitory cytokine 1 as a marker of chemoresistance may herald a new era of biomarker discovery in CRPC. Understanding the interface between this complex array of chemoresistance pathways rather than their study in isolation will be required to effectively predict response and target the late stages of advanced disease. The pre-clinical evidence for these resistance pathways and their progress through clinical trials as therapeutic targets is reviewed in this study.

Emerging Bcl-2 inhibitors for the treatment of cancer

INTRODUCTION

Bcl-2 family proteins are a component of the antiapoptotic machinery and are overexpressed in different malignancies. Accordingly, their enhanced expression has been attributed to the observed chemoresistance in most of the cancers. Therefore, targeting Bcl-2 family members becomes an important and attractive approach towards cancer therapy and is currently a very rapidly evolving area of research. This article highlights the numerous advancements that have been made in the design and synthesis of small molecule inhibitors (SMI) of pro-survival Bcl-2 proteins.

AREAS COVERED

This review comprehensively describes the progress made over the last 2 decades on this subject, including the clinical status of SMIs of Bcl-2 family proteins. Newer insights on the status of our knowledge on SMIs of Bcl-2 family proteins, their most beneficial application as well as current and future directions in this field are discussed.

EXPERT OPINION

Targeting Bcl-2 family proteins using SMI strategies is gaining momentum, with the emergence of certain new classes of inhibitors in Phase I and II clinical settings. In view of the tremendous progress toward the development of such inhibitors, this innovative approach certainly holds promise and has the potential to become a future mainstay for cancer therapy. The stage is set for the next generation of SMIs, for not only Bcl-2 proteins but also for Mcl-1. Other emerging molecules in the apoptotic machinery will also be explored and targeted.

Targeted nanoparticles deliver siRNA to melanoma

Melanoma is a severe skin cancer that often leads to death. To examine the potential of small interfering RNA (siRNA) therapy for melanoma, we have developed anisamide-targeted nanoparticles that can systemically deliver siRNA into the cytoplasm of B16F10 murine melanoma cells, which express the sigma receptor. A c-Myc siRNA delivered by the targeted nanoparticles effectively suppressed c-Myc expression in the tumor and partially inhibited tumor growth. More significant tumor growth inhibition was observed with nanoparticles composed of N,N-distearyl-N-methyl-N-2-(N'-arginyl) aminoethyl ammonium chloride (DSAA), a guanidinium-containing cationic lipid, than with a commonly used cationic lipid, 1,2-dioleoyl-3-trimethylammonium-propane (DOTAP). Three daily injections of c-Myc siRNA formulated in the targeted nanoparticles containing DSAA could impair tumor growth, and the ED(50) of c-Myc siRNA was about 0.55  mg  kg(-1). The targeted DSAA nanoparticles containing c-Myc siRNA sensitized B16F10 cells to paclitaxel (Taxol), resulting in a complete inhibition of tumor growth for 1 week. Treatments of c-Myc siRNA in the targeted nanoparticles containing DSAA also showed significant inhibition on the growth of MDA-MB-435 tumor. The enhanced anti-melanoma activity is probably related to the fact that DSAA, but not DOTAP, induced reactive oxygen species, triggered apoptosis, and downregulated antiapoptotic protein Bcl-2 in B16F10 melanoma cells. Thus, the targeted nanoparticles containing c-Myc siRNA may serve as an effective therapeutic agent for melanoma.

Bcl-2 modulation to activate apoptosis in prostate cancer

Apoptosis resistance is a hallmark of cancer linked to disease progression and treatment resistance, which has led to the development of anticancer therapeutics that restore apoptotic function. Antiapoptotic Bcl-2 is frequently overexpressed in refractory prostate cancer and increased following standard hormonal therapy and chemotherapy; however, the rationally designed Bcl-2 antagonist, ABT-737, has not shown single agent apoptosis-promoting activity against human prostate cancer cell lines. This is likely due to the coordinate expression of antiapoptotic, Bcl-2-related Mcl-1 that is not targeted by ABT-737. We developed a mouse model for prostate cancer in which apoptosis resistance and tumorigenesis were conferred by Bcl-2 expression. Combining ABT-737 with agents that target Mcl-1 sensitized prostate cancer cell lines with an apoptotic block to cell death in vitro. In mice in vivo, ABT-737 showed single agent efficacy in prostate tumor allografts in which tumor cells are under hypoxic stress. In human prostate cancer tissue, examined using a novel tumor explant system designated Tumor Tissue Assessment for Response to Chemotherapy, combination chemotherapy promoted efficient apoptosis. Thus, rational targeting of both the Bcl-2 and Mcl-1 mechanisms of apoptosis resistance may be therapeutically advantageous for advanced prostate cancer.

Sphingolipids and the sphingosine kinase inhibitor, SKI II, induce BCL-2-independent apoptosis in human prostatic adenocarcinoma cells

BACKGROUND

Elevated BCL-2 is one mechanism of therapeutic resistance in prostate cancer (PC), and new approaches are needed to overcome such resistance.

METHODS

We evaluated the effects of BCL-2 over-expression in human prostatic adenocarcinoma cells on their susceptibility to sphingolipids (SLs) and to the sphingosine kinase (SpK) inhibitor, SKI II.

RESULTS

In survival assays, no significant differences were observed in the responses to sphingosine or ceramide among parental PC-3 cells lacking detectable BCL-2 and BCL-2 over-expressing PC-3 transfectants; similarly, the responses to dimethyl-sphingosine (DMSP) of parental LNCaP cells and a BCL-2 over-expressing LNCaP transfectant were equivalent. SKI II induced protracted, BCL-2-independent survival loss in both PC-3 and LNCaP parental/transfectant pairs; in contrast, DMSP induced rapid cell shrinkage, caspase activation and caspase-dependent DNA fragmentation. DMSP-induced DNA fragmentation and loss of mitochondrial membrane potential were equivalent in BCL-2 transfectants and parental PC-3 cells and were not associated with BCL-2 downregulation. DMSP-mediated cytotoxicity was not associated with the enhanced production of reactive oxygen intermediates. SL analyses of parental and transfectant PC-3 cells did not reveal increased levels of sphingosine-1-phosphate in the BCL-2 transfectants; further, there only a modest early shift, corresponding to apoptotic onset, in pro- versus anti-apoptotic SLs in response to DMSP treatment.

CONCLUSIONS

Thus, in contrast to the inhibitory effects of BCL-2 on apoptosis induced by various agents in tumor cells, SKI II and selected pro-apoptotic SLs appear atypical in their independence from such inhibition, and may have merits as new candidates for treatment of AI PC.

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.

Taxane refractory prostate cancer

PURPOSE

Although docetaxel based therapy has become established as a front line therapy choice based on large, randomized studies, published studies of second line therapy for taxane refractory disease are limited.

MATERIAL AND METHODS

The literature on the biology of taxane resistance and studies applied to prostate cancer were reviewed using a PubMed(R) search and proceedings from recent symposia.

RESULTS

Although taxane resistance invariably emerges in the treatment of prostate cancer, a consensus working definition or classification does not exist. Although there is a body of knowledge on the mechanisms of action of taxanes and resistance pathways, there are few clinical or translational studies in prostate cancer adequately assessing the modulation of these mechanisms. Results of additional clinical trials are needed to define and improve the standard of care in the second line setting for castration resistant prostate cancer after docetaxel failure.

CONCLUSIONS

The validation of the microtubule as a target in prostate cancer implies that a finer understanding of specific mechanisms of efficacy and resistance may yield novel strategies. Taxane analogues that have greater antitumor activity and/or are less susceptible to drug resistance mechanisms than their prototypes are in development, as are nontaxane microtubule targeting agents and other agents directed against the mitotic spindle. Combinations of such agents may yield added efficacy but potentially added neurotoxicity. In contrast, combinations with drugs that inhibit cellular mechanisms of taxane resistance and vascular endothelial or tumor-stromal prosurvival interactions may have lower neurotoxic profiles. Although alternate classes of cytotoxic agents, eg satraplatin, are being studied, there is a strong imperative for translational studies in this setting.

Circulating tumor cell analysis in patients with progressive castration-resistant prostate cancer

PURPOSE

To better direct targeted therapies to the patients with tumors that express the target, there is an urgent need for blood-based assays that provide expression information on a consistent basis in real time with minimal patient discomfort. We aimed to use immunomagnetic-capture technology to isolate and analyze circulating tumor cells (CTC) from small volumes of peripheral blood of patients with advanced prostate cancer.

EXPERIMENTAL DESIGN

Blood was collected from 63 patients with metastatic prostate cancer. CTCs were isolated by the Cell Search system, which uses antibodies to epithelial cell adhesion marker and immunomagnetic capture. CTCs were defined as nucleated cells positive for cytokeratins and negative for CD45. Captured cells were analyzed by immunofluorescence, Papanicolau staining, and fluorescence in situ hybridization.

RESULTS

Most patients (65%) had 5 or more CTCs per 7.5 mL blood sample. Cell counts were consistent between laboratories (c = 0.99) and did not change significantly over 72 or 96 h of storage before processing (c = 0.99). Their identity as prostate cancer cells was confirmed by conventional cytologic analysis. Molecular profiling, including analysis of epidermal growth factor receptor (EGFR) expression, chromosome ploidy, and androgen receptor (AR) gene amplification, was possible for all prostate cancer patients with >or=5 CTCs.

CONCLUSIONS

The analysis of cancer-related alterations at the DNA and protein level from CTCs is feasible in a hospital-based clinical laboratory. The alterations observed in EGFR and AR suggest that the methodology may have a role in clinical decision making.

Down-regulation of Polo-like kinase 1 elevates drug sensitivity of breast cancer cells in vitro and in vivo

Human polo-like kinase 1 (Plk1) is a key player in different stages of mitosis and modulates the spindle checkpoint at the metaphase-anaphase transition. Overexpression of Plk1 is observed in various human tumors and it is a negative prognostic factor in patients suffering from diverse cancers. We used phosphorothioate antisense oligonucleotides (ASO) targeted against Plk1, together with paclitaxel, carboplatin, and Herceptin, for the treatment of breast cancer cells to identify conditions for enhanced drug sensitivity. After transfection of the breast cancer cell lines BT-474, MCF-7, and MDA-MB-435 with Plk1-specific ASOs, paclitaxel, carboplatin, or Herceptin was added and cell proliferation, cell cycle distribution, and apoptosis were measured. Whereas the dual treatment of breast cancer cells with Plk1-specific ASOs with carboplatin or Herceptin caused only a limited antiproliferative effect in breast cancer cells, we observed synergistic effects after combination of low doses of Plk1-specific ASOs with paclitaxel, which is used in a variety of clinical anticancer regimens. Plk1-specific ASOs also acted synergistically with paclitaxel in the arrest of the cell cycle at the G(2)-M phase and in the induction of apoptosis. Interestingly, in a human xenograft experiment using MDA-MB-435 cells, the combination of Plk1 ASOs with paclitaxel led to synergistic reduction of tumor growth after 3 weeks of treatment compared with either agent alone. This study suggests that antisense inhibitors against Plk1 at well-tolerated doses may be considered as highly efficient promoters for the antineoplastic potential of taxanes, such as paclitaxel, causing synergistic effects in breast cancer cells.

PTEN expression in melanoma: relationship with patient survival, Bcl-2 expression, and proliferation

PURPOSE

Inactivation of the tumor suppressor gene, phosphatase and tensin homologue (PTEN), is a major alteration in preclinical melanoma models. We investigated the clinical relevance of PTEN expression in the primary melanoma patients with extended follow-up.

EXPERIMENTAL DESIGN

We correlated PTEN expression with clinicopathologic variables and outcome in 127 primary melanomas (median follow-up, 12.8 years). We evaluated the associations between PTEN expression and proliferation and resistance to apoptosis (assessed by Ki-67 and Bcl-2, respectively). We also examined the effect of a favorable phenotype, defined as retained PTEN, low proliferative index, and low expression of Bcl-2 on disease-free survival and overall survival.

RESULTS

Altered PTEN, Bcl-2, and Ki-67 expressions were observed in 55 of 127 (43.3%), 61 of 127 (48%), and 43 of 114 (37.7%) of cases, respectively. Decreased PTEN expression correlated significantly with the ulceration (P = 0.01). Rates of disease-free survival and overall survival in patients with favorable phenotype were 72% and 74% at 5 years versus 64% and 64% in patients with an unfavorable phenotype. At 10 years, the rates of disease-free survival and overall survival were 72% and 68% for patients with a favorable phenotype but declined to 60% and 55% in patients with an unfavorable phenotype. However, relationships between both PTEN and Bcl2 and patient survival were not significant as well as the associations between PTEN and Bcl-2 or Ki-67.

CONCLUSIONS

Our data suggest that altered PTEN expression is common in primary melanomas and is associated with aggressive tumor behavior. However, PTEN alone provided limited prognostic value. Our findings show the need to examine molecular alterations identified in preclinical studies using an adequately large cohort of patients with extended follow-up to better assess the magnitude of their clinical relevance.

Actualización del tratamiento del cáncer de próstata avanzado y de sus complicaciones

Prostate adenocarcinoma is the leading cause of cancer in Spain, among men older than 65. 1,200 new cases out of every 100,000 males are diagnosed with prostate cancer on an annual basis. In the United States, this illness represents the second leading cause of death due to cancer in males. In those patients whose prostate tumors progress after surgery or radiotherapy, or have metastatic disease when diagnosed, a systemic approach in order to improve their quality of life and overall survival is mandatory. First line hormone therapies usually reach a proper control of the tumor maintaining an acceptable quality of life. However, most of these tumors becomes androgen-independent over time and behave as a more aggressive cancer type. In these patients, combination therapy protocols have recently demonstrated a benefit not only in terms of symptoms control and response rates but also in improving survival. In addition, several new molecules are currently under study. The accurate knowledge of the symptoms due to disease spreading as well as treatment's side effects is necessary to provide an appropriate palliative management that contributes to an improvement of the quality of life in advanced prostate cancer patients.