Phase I Trial of G3139, a bcl-2 antisense oligonucleotide, combined with doxorubicin and cyclophosphamide in children with relapsed solid tumors: a Children's Oncology Group Study

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.

Mitochondrial Dysfunction at the Center of Cancer Therapy

Significance: Mitochondria undergo constant morphological changes through fusion, fission, and mitophagy. As the key organelle in cells, mitochondria are responsible for numerous essential cellular functions such as metabolism, regulation of calcium (Ca²⁺), generation of reactive oxygen species, and initiation of apoptosis. Unsurprisingly, mitochondrial dysfunctions underlie many pathologies including cancer. Recent Advances: Currently, the gold standard for cancer treatment is chemotherapy, radiation, and surgery. However, the efficacy of these treatments varies across different cancer cells. It has been suggested that mitochondria may be at the center of these diverse responses. In the past decade, significant advances have been made in understanding distinct types of mitochondrial dysfunctions in cancer. Through investigations of underlying mechanisms, more effective treatment options are developed. Critical Issues: We summarize various mitochondria dysfunctions in cancer progression that have led to the development of therapeutic options. Current mitochondrial-targeted therapies and challenges are discussed. Future Directions: To address the "root" of cancer, utilization of mitochondrial-targeted therapy to target cancer stem cells may be valuable. Investigation of other areas such as mitochondrial trafficking may offer new insights into cancer therapy. Moreover, common antibiotics could be explored as mitocans, and synthetic lethality screens can be utilized to overcome the plasticity of cancer cells.

Destined to Die: Apoptosis and Pediatric Cancers

Apoptosis (programmed cell death) is a systematic and coordinated cellular process that occurs in physiological and pathophysiological conditions. Sidestepping or resisting apoptosis is a distinct characteristic of human cancers including childhood malignancies. This review dissects the apoptosis pathways implicated in pediatric tumors. Understanding these pathways not only unraveled key molecules that may serve as potential targets for drug discovery, but also molecular nodes that integrate with other signaling networks involved in processes such as development. This review presents current knowledge of the complex regulatory system that governs apoptosis with respect to other processes in pediatric cancers, so that fresh insights may be derived regarding treatment resistance or for more effective treatment options.

RNA-targeted therapeutics in cancer clinical trials: Current status and future directions

Recent advances in RNA delivery and target selection provide unprecedented opportunities for cancer treatment, especially for cancers that are particularly hard to treat with existing drugs. Small interfering RNAs, microRNAs, and antisense oligonucleotides are the most widely used strategies for silencing gene expression. In this review, we summarize how these approaches were used to develop drugs targeting RNA in human cells. Then, we review the current state of clinical trials of these agents for different types of cancer and outcomes from published data. Finally, we discuss lessons learned from completed studies and future directions for this class of drugs.

Outcomes of Patients With Relapsed Hepatoblastoma Enrolled on Children's Oncology Group (COG) Phase I and II Studies

Data are limited regarding outcomes of patients treated for relapsed hepatoblastoma. We reviewed enrollment patterns and outcomes of patients with hepatoblastoma on Children's Oncology Group (COG) phase I/II studies. The medical literature was searched for reports of COG phase I/II studies using PUBMED as well as an inventory from the COG publications office searching manuscripts published from 2000 to 2014. Seventy-one patients with relapsed hepatoblastoma were enrolled on 23 separate COG phase I/II studies. Four studies collected α-fetoprotein (AFP) data, but none utilized AFP decline in assessing response. Most studies enrolled few patients with relapsed hepatoblastoma: 7 studies enrolled 1 patient, and another 7 studies enrolled 2 patients each. Only 9 studies enrolled 3 or more patients with relapsed hepatoblastoma. Four responses were reported. Dedicated strata and/or focus on 1 or 2 studies with compelling biological or clinical rationale for hepatoblastoma may improve accrual (and statistical significance of response data) of patients with relapsed hepatoblastoma. Prospective study of AFP decline versus RECIST response could help determine the optimal method of assessing response to identify potentially beneficial treatments in hepatoblastoma.

Killing Two Cells with One Stone: Pharmacologic BCL-2 Family Targeting for Cancer Cell Death and Immune Modulation

A crucial component of regulating organismal homeostasis is maintaining proper cell number and eliminating damaged or potentially malignant cells. Apoptosis, or programed cell death, is the mechanism responsible for this equilibrium. The intrinsic apoptotic pathway is also especially important in the development and maintenance of the immune system. Apoptosis is essential for proper positive and negative selection during B- and T-cell development and for efficient contraction of expanded lymphocytes following an immune response. Tight regulation of the apoptotic pathway is critical, as excessive cell death can lead to immunodeficiency while apoptotic resistance can lead to aberrant lymphoproliferation and autoimmune disease. Dysregulation of cell death is implicated in a wide range of hematological malignancies, and targeting various components of the apoptotic machinery in these cases is an attractive chemotherapeutic strategy. A wide array of compounds has been developed with the purpose of reactivating the intrinsic apoptotic pathway. These compounds, termed BH3 mimetics are garnering considerable attention as they gain greater clinical oncologic significance. As their use expands, it will be imperative to understand the effects these compounds have on immune homeostasis. Uncovering their potential immunomodulatory activity may allow for administration of BH3 mimetics for direct tumor cell killing as well as novel therapies for a wide range of immune-based directives. This review will summarize the major proteins involved in the intrinsic apoptotic pathway and define their roles in normal immune development and disease. Clinical and preclinical BH3 mimetics are described within the context of what is currently known about their ability to affect immune function. Prospects for future antitumor immune amplification and immune modulation are then proposed.

Molecular profiling of childhood cancer: Biomarkers and novel therapies

BACKGROUND

Technological advances including high-throughput sequencing have identified numerous tumor-specific genetic changes in pediatric and adolescent cancers that can be exploited as targets for novel therapies.

SCOPE OF REVIEW

This review provides a detailed overview of recent advances in the application of target-specific therapies for childhood cancers, either as single agents or in combination with other therapies. The review summarizes preclinical evidence on which clinical trials are based, early phase clinical trial results, and the incorporation of predictive biomarkers into clinical practice, according to cancer type.

MAJOR CONCLUSIONS

There is growing evidence that molecularly targeted therapies can valuably add to the arsenal available for treating childhood cancers, particularly when used in combination with other therapies. Nonetheless the introduction of molecularly targeted agents into practice remains challenging, due to the use of unselected populations in some clinical trials, inadequate methods to evaluate efficacy, and the need for improved preclinical models to both evaluate dosing and safety of combination therapies.

GENERAL SIGNIFICANCE

The increasing recognition of the heterogeneity of molecular causes of cancer favors the continued development of molecularly targeted agents, and their transfer to pediatric and adolescent populations.

Potential molecular targets for Ewing's sarcoma therapy

Ewing's sarcoma (ES) is a highly malignant tumor of children and young adults. Modern therapy for Ewing's sarcoma combines high-dose chemotherapy for systemic control of disease, with advanced surgical and/or radiation therapeutic approaches for local control. Despite optimal management, the cure rate for localized disease is only approximately 70%, whereas the cure rate for metastatic disease at presentation is less than 30%. Patients who experience long-term disease-free survival are at risk for significant side-effects of therapy, including infertility, limb dysfunction and an increased risk for second malignancies. The identification of new targets for innovative therapeutic approaches is, therefore, strongly needed for its treatment. Many new pharmaceutical agents have been tested in early phases of clinical trials in ES patients who have recurrent disease. While some agents led to partial response or stable disease, the percentages of drugs eliciting responses or causing an overall effect have been minimal. Furthermore, of the new pharmaceuticals being introduced to clinical practice, the most effective agents also have dose-limiting toxicities. Novel approaches are needed to minimize non-specific toxicity, both for patients with recurrence and at diagnosis. This report presents an overview of the potential molecular targets in ES and highlights the possibility that they may serve as therapeutic targets for the disease. Although additional investigations are required before most of these approaches can be assessed in the clinic, they provide a great deal of hope for patients with Ewing's sarcoma.

Relapsed hepatoblastoma

Successful treatment of recurrent hepatoblastoma (HB) relies largely on surgical resection. When tumors are responsive, chemotherapy can be used to render patients resectable. Various chemotherapeutic regimens studied in small numbers of patients on phase I/II trials have shown few responses. The best available data indicate that doxorubicin, if not given during intial treatment, and irinotecan are the most active agents in recurrent HB. Stem cell transplantation and radiation therapy have been reported in several patients with unclear successes. Advances in therapy for relapsed patients require concentrating enrollment in one or two phase I/II trials utilizing agents with promising preclinical data.

Target mRNA inhibition by oligonucleotide drugs in man

Oligonucleotide delivery in vivo is commonly seen as the principal hurdle to the successful development of oligonucleotide drugs. In an analysis of 26 oligonucleotide drugs recently evaluated in late-stage clinical trials we found that to date at least half have demonstrated suppression of the target mRNA and/or protein levels in the relevant cell types in man, including those present in liver, muscle, bone marrow, lung, blood and solid tumors. Overall, this strongly implies that the drugs are being delivered to the appropriate disease tissues. Strikingly we also found that the majority of the drug targets of the oligonucleotides lie outside of the drugable genome and represent new mechanisms of action not previously investigated in a clinical setting. Despite the high risk of failure of novel mechanisms of action in the clinic, a subset of the targets has been validated by the drugs. While not wishing to downplay the technical challenges of oligonucleotide delivery in vivo, here we demonstrate that target selection and validation are of equal importance for the success of this field.

Pediatric sarcomas: translating molecular pathogenesis of disease to novel therapeutic possibilities

Pediatric sarcomas represent a diverse group of rare bone and soft tissue malignancies. Although the molecular mechanisms that propel the development of these cancers are not well understood, identification of tumor-specific translocations in many sarcomas has provided significant insight into their tumorigenesis. Each fusion protein resulting from these chromosomal translocations is thought to act as a driving force in the tumor, either as an aberrant transcription factor (TF), constitutively active growth factor, or ligand-independent receptor tyrosine kinase. Identification of transcriptional targets or signaling pathways modulated by these oncogenic fusions has led to the discovery of potential therapeutic targets. Some of these targets have shown considerable promise in preclinical models and are currently being tested in clinical trials. This review summarizes the molecular pathology of a subset of pediatric sarcomas with tumor-associated translocations and how increased understanding at the molecular level is being translated to novel therapeutic advances.

New therapeutic targets in soft tissue sarcoma

Soft tissue sarcomas are an uncommon and diverse group of more than 50 mesenchymal malignancies. The pathogenesis of many of these is poorly understood, but others have begun to reveal the secrets of their underlying mechanisms. With considerable effort over recent years, soft tissue sarcomas have increasingly been classified on the basis of underlying molecular alterations. In turn, this has allowed the development and application of targeted agents in several specific, molecularly defined, sarcoma subtypes. This review will focus on the rationale for targeted therapy in sarcoma, with emphasis on the relevance of specific molecular factors and pathways in both translocation-associated sarcomas and in genetically complex tumors. In addition, we will address some of the early successes in sarcoma-targeted therapy as well as a few challenges and disappointments in this field. Finally, we will discuss several possible opportunities represented by poorly understood, but potentially promising new therapeutic targets, as well as several novel biological agents currently in preclinical and early phase I/II trials. This will provide the reader with the context for understanding the current state of this field and a sense of where it may be headed in the coming years.

Neuroblastoma therapy: what is in the pipeline?

Despite the expansion of knowledge about neuroblastoma (NB) in recent years, the therapeutic outcome for children with a high-risk NB has not significantly improved. Therefore, more effective therapies are needed. This might be achieved by aiming future efforts at recently proposed but not yet developed targets for NB therapy. In this review, we discuss the recently proposed molecular targets that are in clinical trials and, in particular, those that are not yet explored in the clinic. We focus on the selection of these molecular targets for which promising in vitro and in vivo results have been obtained by silencing/inhibiting them. In addition, these selected targets are involved at least in one of the NB tumorigenic processes: proliferation, anti-apoptosis, angiogenesis and/or metastasis. In particular, we will review a recently proposed target, the microtubule-associated proteins (MAPs) encoded by doublecortin-like kinase gene (DCLK1). DCLK1-derived MAPs are crucial for proliferation and survival of neuroblasts and are highly expressed not only in NB but also in other tumours such as gliomas. Additionally, we will discuss neuropeptide Y, its Y2 receptor and cathepsin L as examples of targets to decrease angiogenesis and metastasis of NB. Furthermore, we will review the micro-RNAs that have been proposed as therapeutic targets for NB. Detailed investigation of these not yet developed targets as well as exploration of multi-target approaches might be the key to a more effective NB therapy, i.e. increasing specificity, reducing toxicity and avoiding long-term side effects.

Long-term survival of a child with refractory anaplastic large cell lymphoma following therapy with an antisense oligonucleotide, topotecan, and vinblastine

Anaplastic large cell lymphoma includes a subset of highly aggressive tumours and has a relapse rate of 30% at 2 years. Relapsed patients often have poor clinical outcome. The use of antisense oligonucleotides to down-regulate Bcl-2 protein can reverse chemotherapy resistance. The authors describe an 11-year-old boy with recurrent anaplastic large cell lymphoma who had received double high-dose chemotherapy followed by autologous haematopoietic stem-cell transplantation, had refractory disease and then had achieved long-term remission with the use of an antisense oligonucleotides in combination with vinblastine and topotecan.

Pharmacokinetic evaluation of oblimersen sodium for the treatment of chronic lymphocytic leukemia

INTRODUCTION

Chronic lymphocytic leukemia (CLL) is the most common form of leukemia in the western hemisphere. Developing new therapies remains a priority as present treatment options do not offer a cure. BCL-2 overexpression in CLL is associated with aggressive disease features and resists chemotherapy. Oblimersen sodium (G3139) is a phosphorothioate oligonucleotide antisense drug targeting the BCL-2 mRNA and is the first antisense to reach advanced clinical testing in oncology. Preclinical evaluation has demonstrated good antineoplastic effect in B-cell cancers; several clinical trials have confirmed its safety and efficacy both alone and in combination with other therapeutics.

AREAS COVERED

This review focuses on the chemistry, pharmacodynamics, pharmacokinetics and clinical evaluation of oblimersen in CLL. PubMed and MEDLINE searches assisted in data collection.

EXPERT OPINION

Bcl-2 is an important target in CLL. Antisense therapy is a novel approach to target oncoproteins; this can be beneficial in the clinical setting. Oblimersen sodium demonstrates the clinical safety of the antisense therapeutic approach and, with chemotherapy, shows survival advantage in a subset of CLL patients. However, future approval of oblimersen sodium in CLL remains uncertain. Nevertheless, BCL-2 remains a critical target in drug development and is an area of high-priority research.

Targeting apoptosis pathways in childhood malignancies

Evasion of apoptosis (programmed cell death) is a characteristic feature of human cancers including childhood malignancies. Since cytotoxic therapies such as chemotherapy or radiotherapy trigger apoptosis as a primary mechanism of action, resistance to apoptosis can also lead to treatment resistance. Studies on apoptosis pathways in childhood malignancies yielded a series of key molecules that can now be exploited as molecular targets for the development of targeted therapies. This strategy is anticipated to open novel perspectives for more effective treatment options for children with cancer.

Pharmacotherapy of neuroblastoma

IMPORTANCE OF THE FIELD

Neuroblastoma, a tumor of the sympathetic nervous system, is the most common extracranial solid tumor of early life. High risk disease in older children remains a therapeutic challenge, despite high-intensity therapy with correspondingly significant short- and long-term toxicities.

AREAS COVERED IN THIS REVIEW

We have reviewed therapy for neuroblastoma over the last three decades. This includes cytotoxic chemotherapy, immunotherapy, radionuclides, antiangiogenic compounds, and molecularly targeted agents. We provide a perspective on the incorporation of these drugs into therapy for neuroblastoma.

WHAT THE READER WILL GAIN

The reader will gain a better understanding of these novel agents and their targets in neuroblastoma. The reader will also gain insight into the need to define through sequential, carefully designed clinical trials, the roles and toxicities of these therapies, especially if the combination of targeted and conventional cytotoxic agents is used.

TAKE HOME MESSAGE

Advanced-stage neuroblastoma in older infants and children remains a disease that is difficult to cure. New, targeted agents may improve both the therapeutic index and the outcome, but are, for the most part, in early development and present a challenge for clinical trial design given both the rarity of this disease and its responsiveness (albeit incomplete) to currently used cytotoxic agents.

Targeting mitochondria for cancer therapy

Mitochondria are the cells' powerhouse, but also their suicidal weapon store. Dozens of lethal signal transduction pathways converge on mitochondria to cause the permeabilization of the mitochondrial outer membrane, leading to the cytosolic release of pro-apoptotic proteins and to the impairment of the bioenergetic functions of mitochondria. The mitochondrial metabolism of cancer cells is deregulated owing to the use of glycolytic intermediates, which are normally destined for oxidative phosphorylation, in anabolic reactions. Activation of the cell death machinery in cancer cells by inhibiting tumour-specific alterations of the mitochondrial metabolism or by stimulating mitochondrial membrane permeabilization could therefore be promising therapeutic approaches.

Exploiting apoptosis pathways for the treatment of pediatric cancers

Resistance to apoptosis (programmed cell death) is a characteristic feature of human cancers including childhood malignancies. Further, evasion of apoptosis is a frequent cause of treatment resistance, since most anti-cancer therapies, for example chemo- or radiotherapy act primarily by inducing apoptosis in cancer cells. Over the last two decades, the dissection of apoptosis pathways in pediatric tumors has resulted in the identification of many key molecules that may serve as molecular targets for drug discovery. Accordingly, components of the apoptotic cascade are currently exploited for the development of rationally designed molecular targeted therapies. This approach is expected to open new and more effective approaches for the treatment of childhood cancers.

Targeting the apoptotic pathway with BCL-2 inhibitors sensitizes primary chronic lymphocytic leukemia cells to vesicular stomatitis virus-induced oncolysis

Chronic lymphocytic leukemia (CLL) is characterized by clonal accumulation of CD5(+) CD19(+) B lymphocytes that are arrested in the G(0)/G(1) phase of the cell cycle and fail to undergo apoptosis because of overexpression of the antiapoptotic B-cell CLL/lymphoma 2 (BCL-2) protein. Oncolytic viruses, such as vesicular stomatitis virus (VSV), have emerged as potential anticancer agents that selectively target and kill malignant cells via the intrinsic mitochondrial pathway. Although primary CLL cells are largely resistant to VSV oncolysis, we postulated that targeting the apoptotic pathway via inhibition of BCL-2 may sensitize CLL cells to VSV oncolysis. In the present study, we examined the capacity of EM20-25--a small-molecule antagonist of the BCL-2 protein--to overcome CLL resistance to VSV oncolysis. We demonstrate a synergistic effect of the two agents in primary ex vivo CLL cells (combination index of 0.5; P < 0.0001). In a direct comparison of peripheral blood mononuclear cells from healthy volunteers with primary CLL, the two agents combined showed a therapeutic index of 19-fold; furthermore, the combination of VSV and EM20-25 increased apoptotic cell death in Karpas-422 and Granta-519 B-lymphoma cell lines (P < 0.005) via the intrinsic mitochondrial pathway. Mechanistically, EM20-25 blocked the ability of the BCL-2 protein to dimerize with proapoptotic BAX protein, thus sensitizing CLL to VSV oncolytic stress. Together, these data indicate that the use of BCL-2 inhibitors may improve VSV oncolysis in treatment-resistant hematological malignancies, such as CLL, with characterized defects in the apoptotic response.

Abundant anti-apoptotic BCL-2 is a molecular target in leukaemias with t(4;11) translocation

Chemotherapy resistance from imbalanced apoptosis regulation may contribute to poor outcome in leukaemias with t(4;11). Anti-apoptotic BCL-2 expression and target modulation were characterized in cell lines with t(4;11) and BCL-2 expression was examined in MLL and non-MLL infant/paediatric leukaemia cases by Western blot analysis and/or real-time polymerase chain reaction. Cytotoxicity of Genasensetrade mark (Oblimersen Sodium, G3139) alone or combined with cytotoxic drugs was assessed by MTT [(3-4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide] assays of the cell lines, applying pharmacostatistical response surface modelling of drug interactions. Apoptosis and cell cycle were evaluated by flow cytometry in RS4:11 cells. Primary leukaemias and cell lines with t(4;11) expressed abundant BCL2 mRNA and protein. Variable, sometimes substantial BCL2 mRNA was detected in other leukaemia subtypes. G3139 reduced BCL2 mRNA and protein in RS4:11 cells. The most sensitive cell line to single-agent G3139 was RS4:11. Low G3139 concentrations sensitized RS4:11 and MV4-11 cells to select anti-leukaemia cytotoxic drugs. In RS4:11 cells, combining G3139 with doxorubicin (ADR) increased active caspase 3 and TUNEL staining compared to ADR alone, indicating greater apoptosis, and G3139 increased S-phase progression. The abundant BCL-2 affords a molecular target in leukaemias with t(4;11). G3139 exhibits preclinical activity and synergy with select cytotoxic agents in RS4:11 and MV4-11 cells, and these effects occur through apoptosis.

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.