A phase I study of intravenous bryostatin 1 in patients with advanced cancer

Harnessing bacterial metabolites for enhanced cancer chemotherapy: unveiling unique therapeutic potentials

Cancer poses a serious threat to health globally, with millions diagnosed every year. According to Global Cancer Statistics 2024, about 20 million new cases were reported in 2022, and 9.7 million people worldwide died of this condition. Advanced therapies include combination of one or more treatment procedures, depending on the type, stage, and particular genetic constitution of the cancer, which may include surgery, radiotherapy, chemotherapy, immunotherapy, hormone therapy, targeted therapy, and stem cell transplant. Also, awareness about lifestyle changes, preventive measures and screening at early stages has reduced the incidence of the disease; still, there is a major failure in controlling the incidence of cancer because of its complex and multifaceted nature. With increasing interest in bacterial metabolites as possible novel and effective treatment options in cancer therapy, their main benefits include not only direct anticancer effects but also the modulation of the immune system and potential for targeted and combination therapies. They can therefore be used in combination with chemotherapy, radiotherapy, or immunotherapy to improve outcomes or reduce side effects. Furthermore, nanoparticle-based delivery systems have the potential to enhance the potency and safety of anticancer drugs by providing improved stability, targeted release, and controlled delivery.

Destroying the Shield of Cancer Stem Cells: Natural Compounds as Promising Players in Cancer Therapy

In a scenario where eco-sustainability and a reduction in chemotherapeutic drug waste are certainly a prerogative to safeguard the biosphere, the use of natural products (NPs) represents an alternative therapeutic approach to counteract cancer diseases. The presence of a heterogeneous cancer stem cell (CSC) population within a tumor bulk is related to disease recurrence and therapy resistance. For this reason, CSC targeting presents a promising strategy for hampering cancer recurrence. Increasing evidence shows that NPs can inhibit crucial signaling pathways involved in the maintenance of CSC stemness and sensitize CSCs to standard chemotherapeutic treatments. Moreover, their limited toxicity and low costs for large-scale production could accelerate the use of NPs in clinical settings. In this review, we will summarize the most relevant studies regarding the effects of NPs derived from major natural sources, e.g., food, botanical, and marine species, on CSCs, elucidating their use in pre-clinical and clinical studies.

Thomas O, Barraja P, Gaudêncio SP, Bertoni F. Marine Anticancer Agents: An Overview with a Particular Focus on Their Chemical Classes

The marine environment is a rich source of biologically active molecules for the treatment of human diseases, especially cancer. The adaptation to unique environmental conditions led marine organisms to evolve different pathways than their terrestrial counterparts, thus producing unique chemicals with a broad diversity and complexity. So far, more than 36,000 compounds have been isolated from marine micro- and macro-organisms including but not limited to fungi, bacteria, microalgae, macroalgae, sponges, corals, mollusks and tunicates, with hundreds of new marine natural products (MNPs) being discovered every year. Marine-based pharmaceuticals have started to impact modern pharmacology and different anti-cancer drugs derived from marine compounds have been approved for clinical use, such as: cytarabine, vidarabine, nelarabine (prodrug of ara-G), fludarabine phosphate (pro-drug of ara-A), trabectedin, eribulin mesylate, brentuximab vedotin, polatuzumab vedotin, enfortumab vedotin, belantamab mafodotin, plitidepsin, and lurbinectedin. This review focuses on the bioactive molecules derived from the marine environment with anticancer activity, discussing their families, origin, structural features and therapeutic use.

Unlocking the Drug Potential of the Bryostatin Family: Recent Advances in Product Synthesis and Biomedical Applications

Bryostatins are a class of naturally occurring macrocyclic lactones with a unique fast developing portfolio of clinical applications, including treatment of AIDS, Alzheimer's disease, and cancer. This comprehensive account summarizes the recent progress (2014-present) in the development of bryostatins, including their total synthesis and biomedical applications. An emphasis is placed on the discussion of bryostatin 1, the most-studied analogue to date. This review highlights the synthetic and biological challenges of bryostatins and provides an outlook on their future development.

Cancer Biomarkers for Integrative Oncology

PURPOSE OF REVIEW

There has been an increasing interest in using complementary and alternative medicine (CAM) approaches to treat cancer. It is therefore relevant and timely to determine if CAM biomarkers can be identified and developed to guide cancer diagnosis and treatment. Herein, we review the status of cancer biomarkers in CAM research and treatment to stimulate further research in this area.

RECENT FINDINGS

Studies on promising anti-cancer natural products, such as PHY906, honokiol, bryostatin-1, and sulforaphane have demonstrated the existence of potential cancer biomarker(s). Additional studies are required to further develop and ultimately validate these biomarkers that can predict clinical activity of the anti-cancer natural products used alone or in combination with chemotherapeutic agents. A systematic approach is needed to identify and develop CAM treatment associated biomarkers and to define their role in facilitating clinical decision-making. The expectation is to use these biomarkers in determining potential options for CAM treatment, examining treatment effects and toxicity and/or clinical efficacy in patients with cancer.

Recent Advances in the Development of Anticancer Drugs that Act against Signalling Pathways

Cancer can be considered a disease of deranged intracellular signalling. The intracellular signalling pathways that mediate the effects of oncogenes on cell growth and transformation present attractive targets for the development of new classes of drugs for the prevention and treatment of cancer. This is a new approach to developing anticancer drugs and the potential, as well as some of the problems, inherent in the approach are discussed. Anticancer drugs that produce their effects by disrupting signalling pathways are already in clinical trial. Some properties of these drugs, as well as other inhibitors of signalling pathways under development as potential anticancer drugs, are reviewed.

Which therapeutic strategy will achieve a cure for HIV-1?

Strategies to achieve a cure for HIV-1 infection can be broadly classified into three categories: eradication cure (elimination of all viral reservoirs), functional cure (immune control without reservoir eradication), or a hybrid cure (reservoir reduction with improved immune control). The many HIV-1 cure strategies being investigated include modification of host cells to resist HIV-1, engineered T cells to eliminate HIV-infected cells, broadly HIV-1 neutralizing monoclonal antibodies, and therapeutic vaccination, but the 'kick and kill' strategy to expose latent HIV-1 with latency reversing agents (LRAs) and kill the exposed cells through immune effector functions is currently the most actively pursued. It is unknown, however, whether LRAs can deplete viral reservoirs in vivo or whether current LRAs are sufficiently safe for clinical use.

Bryostatin-1 causes radiosensitization of BMG-1 malignant glioma cells through differential activation of protein kinase-Cδ not evident in the non-malignant AA8 fibroblasts

Bryostatin-1 (bryo-1), a non-phorbol ester, is known to sensitize mammalian cells against certain chemotherapeutic drugs. We assessed its ability to modify radiation response of mammalian cells using Chinese hamster fibroblasts AA8 cells and human malignant glioma BMG-1 cells. In the malignant glioma BMG-1 cell line, bryo-1 pre-treatment significantly enhanced radiation-induced growth inhibition and cytogenetic damage, and further reduced the clonogenic cell survival as compared to cells irradiated at the clinically relevant dose of 2 Gy. PKCδ expression increased significantly when bryo-1 pre-treated BMG-1 glioma cells were irradiated at 2 Gy and induced prolonged ERK-1/2 activation associated with p21 overexpression. Silencing PKCδ resulted in inhibition of bryo-1-induced radiosensitization. In contrast, bryo-1 failed to alter radiosensitivity (cell survival; growth inhibition; cytogenetic damage) or activate ERK1/2 pathway in the AA8 fibroblasts despite PKCδ phosphorylation at its regulatory (Y155) domain, indicating alternate mechanisms in these non-malignant cells as compared to the glioma cells. This study suggests that bryo-1 may effectively enhance the radiosensitivity of malignant cells and warrants further in-depth investigations to evaluate its radiosensitizing potential in various cell types.

Marine natural products: bryostatins in preclinical and clinical studies

CONTEXT

Bryostatins represent an important group of pharmaceutically promising substances. These compounds are produced by commensal microorganisms naturally occurring in marine invertebrates, mainly in bryozoans. The most frequently investigated substance is bryostatin-1, which is a highly oxygenated macrolide with a polyacetate backbone.

OBJECTIVE

The aim of this work was to summarize documented preclinical and clinical effects of bryostatin-class compounds.

METHODS

A literature search was made of Medline and Web of Science databases in 2012.

RESULTS AND CONCLUSION

Our review showed that bryostatins are potent agonists of protein kinase C. In addition to this, their significant antineoplastic activity against several tumor types has also been established and described. Bryostatin's anticancer activity has been proved against various cancer types. Moreover, significant results have been achieved by using bryostatin-1 in combination with other therapies, including combination with vaccine testing. Concerning other important properties that bryostatins possess, their ability to sensitize some resistant cells to chemotherapy agents, or immunoactivity and further stimulating growth of new neural connections, and enhancing effect on long-term memory are worth mentioning. In particular, some new bryostatin analogs could represent potential therapeutic agent for the treatment of cancer and other diseases in future.

Phase II study of bryostatin 1 and vincristine for aggressive non-Hodgkin lymphoma relapsing after an autologous stem cell transplant

Bryostatin 1, isolated from a marine bryozoan, enhances the efficacy of cytotoxic agents through modulation of the protein kinase C pathway and is active in combination with vincristine for diffuse large B-cell lymphoma. Further, the apoptotic frequency of peripheral blood T lymphocytes as determined by flow cytometry may predict which patients will respond to this combination. We tested the efficacy and safety of bryostatin 1 50 microg/m(2) given over 24 hr and vincristine 1.4 mg/m(2) on days 1 and 15 every 28 days in aggressive B-cell non-Hodgkin lymphoma (NHL) relapsing after autologous stem cell transplantation. End points included tumor response, toxicity, and survival. Responses were correlated with an increase in apoptotic frequency of CD5+ cells by flow cytometry using annexin V staining. Fourteen patients were enrolled with 13 being evaluable for a response. The overall response rate was 31% with two patients achieving a complete response. The most common toxicities were Grade 3 lymphopenia (seven patients), Grade 3 to 4 neutropenia (two patients), and Grade 3 hypophosphatemia (two patients). Median progression-free and overall survivals for all patients were 5.7 and 21.4 months, respectively. One patient demonstrated an increase in T-cell apoptotic frequency, also achieving a complete response. Bryostatin 1 and vincristine have efficacy in select patients with aggressive NHL. Future investigations of agents targeting the protein kinase C pathway may benefit from early response assessment using flow cytometry to evaluate T-cell apoptosis.

Beyond monoclonal antibodies: new therapeutic agents in non-Hodgkin's lymphomas

The availability of active monoclonal antibodies, either as single agents or in combination with cytotoxic agents, has improved treatment results in non-Hodgkin's lymphoma (NHL). Despite this and the increasing number of available active monoclonal antibodies, alone or conjugated with radioisotopes, not all types of lymphoma are sensitive to these biological agents and often they become resistant because of different molecular mechanisms. New molecular targets in neoplastic cells are emerging and provide the rationale for novel discovery initiatives. In fact, a greater knowledge of the biology of lymphoma and the identification of compounds selectively active against a potential therapeutic pathway have already improved the time to progression and survival time of patients with some subtypes of NHL. The growing list of new drugs provides the exciting prospect of developing disease-specific and even patient-specific therapies. The aim of this review is to identify and discuss non-monoclonal antibody new therapeutic agents in terms of mechanism of action and clinical results. The preclinical and clinical features of proteasome inhibitors, histone deacetylase inhibitors, thalidomide and lenalidomide, mammalian target of rapamycin inhibitors, antisense oligonucleotides, heat shock protein inhibitors, protein kinase C inhibitors, antiangiogenic agents, and new cytotoxics are reviewed.

Phase I study of bryostatin 1, a protein kinase C modulator, preceding cisplatin in patients with refractory non-hematologic tumors

PURPOSE

Preclinical data suggested that bryostatin-1 (bryo) could potentiate the cytotoxicity of cisplatin when given prior to this drug. We designed a phase I study to achieve tolerable doses and schedules of bryo and cisplatin in combination and in this sequence.

METHODS

Patients with non-hematologic malignancies received bryo followed by cisplatin in several schedules. Bryo was given as an 1 and a 24 h continuous infusion, while cisplatin was always given over 1 h at 50 and 75 mg/m(2); the combined regimen was repeated on an every 3-week and later on an every 2-week schedule. Bryo doses were escalated until recommended phase II doses were defined for each schedule. Patients were evaluated with computerized tomography every 2 cycles.

RESULTS

Fifty-three patients were entered. In an every 2-week schedule, the 1-h infusion of bryo became limited by myalgia that was clearly cumulative. With cisplatin 50 mg/m(2) its recommended phase II dose was 30 microg/m(2). In the 3-week schedule, dose-limiting toxicities were mostly related to cisplatin effects while myalgias were tolerable. Pharmacokinetics unfortunately proved to be unreliable due to bryo's erratic extraction. Consistent inhibition of PKC isoform eta (eta) in peripheral blood mononuclear cells was observed following bryo.

CONCLUSIONS

Bryo can be safely administered with cisplatin with minimal toxicity; however, only four patients achieved an objective response. Modulation of cisplatin cytotoxicity by bryo awaits further insight into the molecular pathways involved.

Targeting the protein kinase C family: are we there yet?

Protein kinase C (PKC) comprises a family of serine/threonine kinases that are involved in the transduction of signals for cell proliferation, differentiation, apoptosis and angiogenesis. Unsurprisingly, disruption of PKC regulation is implicated in tumorigenesis and drug resistance. PKC function is complex in this context owing to the differing roles of individual isozymes within the cell and across tumour types. Therapeutically targeting PKC isozymes is not new; however, with many of the early PKC inhibitor cytotoxic drug combinations being discarded at the phase II level, and recent phase III studies in non-small-cell lung cancer proving negative, what's going wrong?

Phase I Study of Bryostatin 1 and Fludarabine in Patients with Chronic Lymphocytic Leukemia and Indolent (Non-Hodgkin's) Lymphoma

PURPOSE

Preclinical studies suggested that bryostatin 1 might potentiate the therapeutic effects of fludarabine in the treatment of hematologic malignancies. We undertook a phase I study to identify appropriate schedules and doses of bryostatin 1 and fludarabine to be used in phase II studies.

EXPERIMENTAL DESIGN

Patients with chronic lymphocytic leukemia (CLL) or indolent lymphoma received fludarabine daily for 5 days and a single dose of bryostatin 1 via a 24-hour continuous infusion either before or after the fludarabine course. Doses were escalated in successive patients until recommended phase II doses for each sequence were identified on the basis of dose-limiting toxic events.

RESULTS

Bryostatin 1 can be administered safely and tolerably with full dose fludarabine (25 mg/m(2)/d x 5). The recommended bryostatin 1 phase II dose is 50 microg/m(2) for both sequences, bryostatin 1 --> fludarabine and fludarabine --> bryostatin 1. The combination is active against both CLL and indolent lymphomas with responses seen in patients who had been previously treated with fludarabine. Correlative studies do not support the hypothesis that bryostatin 1 potentiates fludarabine activity through down-regulation of protein kinase C in target cells.

CONCLUSIONS

Bryostatin 1 can be administered with full dose fludarabine, and the combination is moderately active in patients with persistent disease following prior treatment. In view of the activity of monoclonal antibodies such as the anti-CD20 monoclonal antibody rituximab in the treatment of CLL and indolent lymphomas, the concept of combining bryostatin 1 and fludarabine with rituximab warrants future consideration.

Targeting the cell cycle: a new approach to cancer therapy

The cell cycle represents a series of tightly integrated events that allow the cell to grow and proliferate. Critical parts of the cell cycle machinery are the cyclin-dependent kinases (CDKs), which, when activated, provide a means for the cell to move from one phase of the cell cycle to the next. The CDKs are regulated positively by cyclins and regulated negatively by naturally occurring CDK inhibitors (CDKIs). Cancer represents a dysregulation of the cell cycle such that cells that overexpress cyclins or do not express the CDKIs continue to undergo unregulated cell growth. The cell cycle also serves to protect the cell from DNA damage. Thus, cell cycle arrest, in fact, represents a survival mechanism that provides the tumor cell the opportunity to repair its own damaged DNA. Thus, abrogation of cell cycle checkpoints, before DNA repair is complete, can activate the apoptotic cascade, leading to cell death. Now in clinical trials are a series of targeted agents that directly inhibit the CDKs, inhibit unrestricted cell growth, and induce growth arrest. Recent attention has also focused on these drugs as inhibitors of transcription. In addition, there are now agents that abrogate the cell cycle checkpoints at critical time points that make the tumor cell susceptible to apoptosis. An understanding of the cell cycle is critical to understanding how best to clinically develop these agents, both as single agents and in combination with chemotherapy.

Pediatric Phase I Trials in Oncology: An Analysis of Study Conduct Efficiency

Purpose

To determine the efficacy and safety of pediatric phase I oncology trials in the era of dose-intensive chemotherapy and to analyze how efficiently these trials are conducted.

Methods

Phase I pediatric oncology trials published from 1990 to 2004 and their corresponding adult phase I trials were reviewed. Dose escalation schemes using fixed 30% dose increments were studied to theoretically determine whether trials could be completed utilizing fewer patients and dose levels.

Results

Sixty-nine pediatric phase I oncology trials enrolling 1,973 patients were identified. The pediatric maximum-tolerated dose (MTD) was strongly correlated with the adult MTD (r = 0.97). For three-fourths of the trials, the pediatric and adult MTD differed by no more than 30%, and for more than 85% of the trials, the pediatric MTD was less than or equal to 1.6 times the adult MTD. The median number of dose levels studied was four (range, two to 13). The overall objective response rate was 9.6%, the likelihood of experiencing a dose-limiting toxicity was 24%, and toxic death rate was 0.5%.

Conclusion

Despite the strong correlation between the adult and pediatric MTDs, more than four dose levels were studied in 40% of trials. There appeared to be little value in exploring dose levels greater than 1.6 times the adult MTD. Limiting pediatric phase I trials to a maximum of four doses levels would significantly shorten the timeline for study conduct without compromising safety.

New cytotoxic agents: a review of the literature

The goal of treatment for patients with advanced cancer is to prolong survival, control symptoms, and reduce disease-related complications. Despite the introduction of many cytotoxic agents during the past decade, only modest improvement in survival has been achieved. In order to urgently improve these situations, new cytotoxic agents as well as molecular-targeted agents are now under investigation. In this article, we reviewed the latest information regarding antitumor activity, toxicity, pharmacokinetics, and clinical application of the new cytotoxic agents.

Capacity building for the clinical investigation of AIDS malignancy in East Africa

PURPOSE

To build capacity in the resource-poor setting to support the clinical investigation and treatment of AIDS-related malignancies in a region of the world hardest hit by the AIDS pandemic.

METHODS

An initial MEDLINE database search for international collaborative partnerships dedicated to AIDS malignancies in developing countries failed to identify any leads. This search prompted us to report progress on our collaboration in this aspect of the epidemic. Building on the formal Uganda-Case Western Reserve University (Case) Research Collaboration dating back to 1987, established NIH-supported centers of research excellence at Case, and expanding activities in Kenya, scientific and training initiatives, research capital amongst our institutions are emerging to sustain a international research enterprise focused on AIDS and other viral-related malignancies.

RESULTS

A platform of clinical research trials with pragmatic design has been developed to further enhance clinical care and sustain training initiatives with partners in East Africa and the United States. An oral chemotherapy feasibility trial in AIDS lymphoma is near completion; a second lymphoma trial of byrostatin and vincristine is anticipated and a feasibility trial of indinavir for endemic Kaposi's sarcoma is planned.

CONCLUSIONS

In the absence of published reports of evolving international partnerships dedicated to AIDS malignancy in resource constrained settings, we feel it important for such progress on similar or related international collaborative pursuits to be published. The success of this effort is realized by the long-term international commitment of the collaborating investigators and institutions to sustain this effort in keeping with ethical and NIH standards for the conduct of research; the provision of formal training of investigators and research personnel on clinical problems our East African partners are faced with in practice and the development of pragmatic clinical trials and therapeutic intervention to facilitate technology transfer and enhance clinical practice.

A randomized phase II evaluation of bryostatin-1 (NSC #339555) in recurrent or persistent platinum-sensitive ovarian cancer: a Gynecologic Oncology Group Study

OBJECTIVES

The Gynecologic Oncology Group (GOG) performed a randomized phase II study to determine the antitumor activity and toxicity of two different schedules of bryostatin-1 administration in patients with recurrent or persistent platinum-sensitive epithelial ovarian cancer or primary peritoneal carcinoma.

METHODS

Eligible patients were randomized to receive either bryostatin-1 25 microg/m2 as a 1h infusion weekly for 3 weeks followed by a 1-week rest (Regimen I) or bryostatin-1 120 microg/m2 as a 72 h continuous infusion every 2 weeks (Regimen II).

RESULTS

Fifty-five patients were enrolled on this study. There was one durable response among 27 eligible patients (response rate=3.7%) on Regimen II and no responses in the 27 eligible patients on Regimen I. Nineteen patients (eleven on Regimen I and eight on Regimen II) had stable disease. The most common adverse event was myalgia, with 12 of 27 patients (44%) on each regimen experiencing some degree of myalgia. There were no other significant toxicities on either treatment arm.

CONCLUSIONS

Both of these schedules and doses of bryostatin-1 are inactive as single agents in previously treated epithelial ovarian cancer.

A randomized phase II evaluation of bryostatin-1 (NSC #339555) in persistent or recurrent squamous cell carcinoma of the cervix: A Gynecologic Oncology Group Study

OBJECTIVES

The Gynecologic Oncology Group performed a randomized phase II study to determine the antitumor activity and toxicity of two different schedules of administration of bryostatin-1 in patients with persistent or recurrent squamous cell carcinoma of the cervix.

METHODS

Eligible patients were randomized to receive either bryostatin-1 25 mug/m(2) as a 1-h infusion weekly for 3 weeks followed by a 1-week rest (Regimen I) or bryostatin-1 120 mug/m(2) as a 72-h continuous infusion every 2 weeks (Regimen II).

RESULTS

A total of 70 patients were enrolled on this study. There were 32 eligible patients on Regimen I and 33 eligible patients on Regimen II; all but 4 had had prior chemotherapy. There were two partial responses (one on each treatment arm) among the 65 eligible patients (response rates = 3.1 and 3.0%, respectively). Ten patients on each regimen had stable disease. The most common adverse event was myalgia; 8 of 32 patients (25%) on Regimen I and 16 of 33 patients (48%) on Regimen II had any grade of myalgia. There was no significant myelosuppression on either treatment arm.

CONCLUSIONS

Both of these schedules and doses of bryostatin-1 are inactive as single agents in the second-line treatment of squamous cell carcinoma of the cervix.

Bryostatin-1: a novel PKC inhibitor in clinical development

Modulation of PKC represents a novel approach to cancer therapy. Bryostatin-1 is a macrocyclic lactone derived from a marine invertebrate that binds to the regulatory domain of protein kinase C. Short-term exposure to bryostatin-1 promotes activation of PKC, whereas prolonged exposure promotes significant downregulation of PKC. In numerous hematological and solid tumor cell lines, bryostatin-1 inhibits proliferation, induces differentiation, and promotes apoptosis. Furthermore, preclinical studies indicate that bryostatin-1 potently enhances the effect of chemotherapy. In many cases, this effect is sequence specific. Bryostatin-1 is currently in phase I and phase II clinical trials. The major toxicities are myalgias, nausea, and vomiting. Although there is minimal single-agent activity, combinations with standard chemotherapy are providing very encouraging results and indicate a new direction in cancer therapy.

A phase II trial of bryostatin-1 administered by weekly 24-hour infusion in recurrent epithelial ovarian carcinoma

Bryostatin-1 is a macrocyclic lactone whose main mechanism of action is protein kinase C modulation. We investigated its activity as a weekly 24-h infusion in recurrent ovarian carcinoma. In all, 17 patients were recruited and 11 had chemotherapy-resistant disease as defined by disease progression within 4 months of last cytotoxic therapy. All were evaluable for toxicity and 14 for response. There were no disease responses and the main toxicity was myalgia.

A multicentre phase II trial of bryostatin-1 in patients with advanced renal cancer

Protein kinase C (PKC) has a critical role in several signal transduction pathways, and is involved in renal cancer pathogenesis. Bryostatin-1 modulates PKC activity and has antitumour effects in preclinical studies. We conducted a multicentre phase II clinical trial in patients with advanced renal cancer to determine the response rate, immunomodulatory activity and toxicity of bryostatin-1 given as a continuous 24 h infusion weekly for 3 out of 4 weeks at a dose of 25 μg m⁻². In all, 16 patients were recruited (11 males and five females). The median age was 59 years (range 44–68). Patients had been treated previously with nephrectomy (8) and/or interferon therapy (9) and/or hormone therapy (4) and/or radiotherapy (6). Eight, five and three patients had performance statuses of 0, 1 and 2, respectively. A total of 181 infusions were administered with a median of 12 infusions per patient (range 1–29). Disease response was evaluable in 13 patients. Three patients achieved stable disease lasting for 10.5, 8 and 5.5 months, respectively. No complete responses or partial responses were seen. Myalgia, fatigue, nausea, headache, vomiting, anorexia, anaemia and lymphopenia were the commonly reported side effects. Assessment of biological activity of bryostatin-1 was carried out using the whole–blood cytokine release assay in six patients, two of whom had a rise in IL-6 levels 24 h after initiating bryostatin-1 therapy compared to pretreatment values. However, the IL-6 level was found to be significantly lower at day 28 compared to the pretreatment level in all six patients analysed.

Signal transduction--directed cancer treatments

The pathogenic mechanisms giving rise to cancer frequently involve altered signal transduction pathways. Therefore therapeutic agents that directly address signal transduction molecules are being explored as cancer treatments. Inhibitors of protein tyrosine and threonine kinases including STI-571, ZD-1839, OSI-774, and flavopiridol are ATP-site antagonists that have completed initial phase I and phase II evaluations. Herceptin and C225 are monoclonal antibodies also directed against signaling targets. Numerous other kinase antagonists are in clinical evaluation, including UCN-01 and PD184352. Alternative strategies to downmodulate kinase-driven signaling include 17-allyl-amino-17-demethoxygeldanamycin and rapamycin derivatives, and phospholipase-directed signaling may be modulated by alkylphospholipids. Farnesyltransferase inhibitors were originally developed as inhibitors of ras-driven signals but may have activity by affecting other or additional targets. Signal transduction will remain a fertile basis for suggesting cancer treatments of the future, the evaluation of which should include monitoring effects of the drugs on their intended target signaling molecules in preclinical and early clinical studies.

Marine-derived anticancer agents in clinical trials

Anticancer agents may be derived either from the isolation of an active lead compound occurring spontaneously in nature or by novel chemical synthesis in the laboratory. There are examples of successful drugs being derived from both sources, which have had a profound impact on the natural history of various types of cancer. The treatment of lymphomas and acute leukaemias with the use of combination chemotherapy, including anthracyclines and vinca alkaloids, are examples of the contribution of nature. In contrast, agents such as 5-fluorouracil, methotrexate and more recently, the humanised anti-CD20 antibody rituximab and the tyrosine kinase inhibitor imatinib are examples of synthetic compounds, which were designed with a clear rationale, that are routinely used in patients with solid tumours and haematological malignancies. Until recently, the tradition in natural product-derived anticancer drug development was to rely almost exclusively on the screening of terrestrial sources (plant extracts and fermentation products) for their cytotoxic properties. Although C-nucleosides obtained from Caribbean sponge were the initial inspiration for the synthesis of antiviral substituted nucleosides and the successful anticancer agent citarabine, active against leukaemias and lymphomas, the contribution of marine compounds as a source of anticancer agents was modest. In recent years, the improvements in the technology of deep-sea collection and aquaculture added to the growing recognition of the tremendous biodiversity present in the marine world, and has contributed to the growing interest of exploring the oceans as a potential source of new anticancer candidates. This is reflected in the number of marine-derived compounds undergoing preclinical and early clinical development. In this paper, the authors discuss the available literature on anticancer agents that have reached clinical trials, such as didemnin B, aplidine, dolastatin-10, bryostatin-1 and ecteinascidin-743 (ET-743, trabectedin), as well as other promising compounds still undergoing tests in the laboratory.

Targeted therapy for lung cancer

Lung cancer remains the leading cause of death in men and women in the United States. This status is attributed to late diagnosis and lack of effective chemotherapy for metastatic lung cancer. Understanding of the mechanism by which mutated genes confer a neoplastic phenotype on cells has resulted in the development of many potential targeted cancer therapies. This article briefly discusses the work being done with some of these targeted agents in the treatment of lung cancer.

Cyclin-dependent kinases as targets for cancer therapy

Cell cycle perturbations are commonly observed in human malignancies. Exploiting this finding is the rationale for the development of CDK inhibitors as anti-tumor agents. Single-agent evaluation of several CDKIs has demonstrated limited clinical activity. The combination of CDKIs with standard cytotoxic agents is an emerging, alternative approach to anticancer therapy that also exploits the cell cycle perturbations of malignancy. Pre-clinical studies demonstrate the concept of cell cycle mediated drug resistance, and suggest that the combination of standard cytotoxic agents with CDKIs will require thoughtful sequencing and scheduling. With this in mind, there are presently several clinical investigations underway examining the combination of a standard cytotoxic with a novel CDKI, with particular attention to sequence and scheduling. Although phase II evaluation of these combination studies will provide initial evidence of anti-tumor activity, definitive phase III studies will be needed to establish this class of agents in the care of patients with cancer.

The clinical development of the bryostatins

The bryostatins are a group of novel macrocyclic lactones derived from the marine bryozoan, Bugula neritina. In vitro evidence indicates that their main mechanism of action is modulation of protein kinase C (PKC) activity. Phase I studies suggested significant antineoplastic activity against several tumor types and defined the main dose-limiting toxicity as myalgia. Bryostatin-1 has subsequently been investigated extensively in phase II clinical trials as a single agent, although trial design has been hampered by lack of human pharmacokinetic data. Results have been generally disappointing but in vitro and animal data suggests an important role for bryostatin-1 in combination with cytotoxic agents. Preliminary results of phase I studies support these observations but further work needs to be done to define the future role of the bryostatins in the clinic.

Novel targets for lung cancer therapy: part I

Lung cancer is the second most common form of cancer in the United States, and although it accounts for 15% of all cancers, it is the most lethal, accounting for approximately 28% of cancer deaths. In 2002, it is estimated that 177,000 new cases of lung cancer will be diagnosed in the United States, and an estimated 160,000 men and women will die from the disease. This mortality rate is greater than that attributable to colorectal, breast, and prostate cancer combined. Systemic treatments for lung cancer with standard chemotherapy agents are still relatively ineffective. Agents targeting novel proliferative and survival pathways in lung cancer are needed to improve treatment outcomes. In recent years, numerous agents inhibiting aberrant processes in tumor cells have undergone clinical evaluation. This review is the first of a two-part series that summarizes pertinent preclinical and clinical information on novel drugs that target critical abnormalities in lung cancer. In this article, agents inhibiting growth factor receptors and various molecules downstream of activated signaling cascades, such as cytoplasmic second messengers, are described.

Signaling inhibitors in the treatment of prostate cancer

Inhibiting androgen receptor (AR) activation through medical or surgical castration and blockade of AR-androgen binding is the cornerstone of treatment for advanced prostate cancer. However, in most cases tumor growth eventually becomes androgen independent. Alternative mechanisms of AR activation, some of which involve growth factor receptor signaling, have been demonstrated in prostate cancer models, and it is likely that a number of autocrine and paracrine growth factor ligand-receptor interactions such as those of epidermal growth factors, fibroblast growth factors, and insulin-like growth factors contribute to the androgen independent phenotype by promoting cell proliferation and survival. Blocking activation and signaling through growth factor receptors and upstream signaling proteins has emerged as a credible approach to cancer treatment. Successful application of this approach in prostate cancer using a growing array of small molecule kinase inhibitors, antibodies, and antisense oligonucleotides will be greatly accelerated by elucidation of the key signaling pathways that maintain the androgen independent phenotype.

Use of marine toxins in combination with cytotoxic drugs for induction of apoptosis in acute myelogenous leukaemia cells

Intensive chemotherapy for acute myelogenous leukaemia (AML) results in an overall long-term disease-free survival of < 50%. This percentage reflects an improved survival for certain subsets of patients with low-risk cytogenetic abnormalities after treatment with high-dose cytarabine, whereas lower long-term survival is seen for other patients and especially for the large group of elderly patients. New treatment strategies are therefore considered in AML and one approach is to target the regulation of apoptosis in AML cells with new pharmacological agents. Regulation of apoptosis seems to be clinically important in AML as intracellular levels of apoptosis-regulating mediators can be used as predictors of prognosis in AML. It is also well documented that cytotoxic drugs exert important antileukaemic effects through induction of apoptosis. Marine toxins represent new pharmacological agents with proapoptotic effects and should be considered for combination therapy with cytotoxic drugs. These agents are already useful laboratory tools for in vitro studies of AML cells but it is still too early to conclude whether they will become useful in clinical therapy. One of the major problems to be investigated is the toxicity of combination therapy, although this may be solved by the coupling of toxins to antibodies or growth factors with a preferential binding to AML cells. Other problems that have to be addressed are the possible effect of the toxins' tumour promoting effects on chemosensitivity in relapsed AML and the possibility of cross-resistance between cytotoxic drugs and toxins.

A phase II trial of bryostatin-1 in patients with metastatic or recurrent squamous cell carcinoma of the head and neck

Bryostatin-1 is a macrocyclic lactone that has been shown to modulate Protein Kinase C activity and has demonstrated antitumor activity in vitro and in vivo. Fifteen patients with metastatic or recurrent squamous cell carcinoma of the head and neck were treated with bryostatin-1 at a dose of 25 mcg/m2 by continuous intravenous infusion over 24 hours once weekly for three weeks followed by a break week to complete a four-week cycle. There were no major objective responses in the 14 evaluable patients. One patient with nasopharynx cancer had disease stabilization for 4 months prior to being removed from the study due to medical issues. This clinical benefit corresponded to a radiographic decrease in metabolic activity on positron emission tomograpy (PET) scan as well as molecular evidence of tumor apoptosis in a poly[ADP-ribose] polymerase (PARP) cleavage assay. Bryostatin-1 is not recommended for use as a single agent for the treatment of squamous cell head and neck cancer. Further investigation is warranted to determine the strength of the correlation between bryostatin-1 activity and PARP cleavage as a surrogate molecular marker of apoptosis.

Protein kinase C inhibitors

Protein kinase C (PKC) is a family of serine-threonine protein kinases that are involved in signal transduction pathways that regulate growth factor response, proliferation, and apoptosis. Its central role in these processes, which are closely involved in tumor initiation, progression, and response to antitumor agents, makes it an attractive therapeutic target in cancer. Despite initial activity seen in melanoma (bryostatin and UCN-01), non-Hodgkin's lymphoma (ISIS 3521, bryostatin, and UCN-01), and ovarian carcinoma (ISIS 3521 and bryostatin) in phase I studies, single-agent activity in those phase II studies reported to date has been limited. Preclinical data highlight a role for PKC in modulation of drug resistance and synergy with conventional cytotoxic drugs. A randomized phase III study of ISIS 3521 in combination with carboplatin and paclitaxel, compared with chemotherapy alone, in advanced non-small-cell lung cancer is underway. This paper reviews the rationale for using PKC inhibitors in cancer therapy, the challenges for clinical trial design, and the recent clinical experience with modulators of PKC activity.

Different levels of TGFbeta, IL-10, IFNgamma and gelatinase A occur in experimental white and black metastases induced by bryostatin 1 or by phorbol ester-treated BL6T murine melanoma cells

Bryostatin 1 and phorbol esters reduce the intracellular melanin level in high metastatic overexpressing nPKCdelta BL6 (BL6T) cells, thereby inducing white experimental metastasis in syngeneic mice. We evaluate here the possible differences between white and black metastases induced by both treatments on the proliferative and metastatic potential as well as on the expression of some cytokines involved in the metastatic process such as TGFbeta, IL-10 and IFNgamma. The level of expression of gelatinase A is also considered. White and black metastases induced after the injection of bryostatin 1- or phorbol ester-treated cells into the tail vein of syngenic mice were isolated and analysed for the levels of LDH usually used as markers of cytotoxicity, for the levels of cytokines and gelatinase A or dissociated and cultured in vitro for a few passages. The cultured cells were analysed in vitro for the proliferative capacity and the melanin synthesis. The same cells were also re-injected into syngeneic mice and the number of experimental metastases were counted after 17 days or injected with matrigel in order to quantify the proliferative capacity in vivo. The results show only one significant difference between bryostatin I and phorbol ester, namely the cells obtained from white bryostatin 1-treated cells return to a black phenotype after a few passages in culture. This suggests that PKC mediates many of the biological effects of bryostatin 1 but that its effect is lost in vitro. On the other hand, white and black metastases (at least for metastases induced by BL6T cells treated with phorbol ester) do appear significantly different. In vivo white metastases show lower levels of LDH, lower levels of proliferative capacity into matrigel, higher levels of TGFbeta and IFNgamma and, when re-injected into syngeneic mice, give big black metastases. Therefore, in murine melanoma cells, the treatment with bryostatin I induces the appearance of a white population expressing different levels of TGFbeta, IFNgamma, IL-10 and gelatinase A. Such a white population is more difficult to diagnose and is capable of turning into a more aggressive phenotype under suitable environmental conditions.

Differentiation therapy of human cancer: basic science and clinical applications

Current cancer therapies are highly toxic and often nonspecific. A potentially less toxic approach to treating this prevalent disease employs agents that modify cancer cell differentiation, termed 'differentiation therapy.' This approach is based on the tacit assumption that many neoplastic cell types exhibit reversible defects in differentiation, which upon appropriate treatment, results in tumor reprogramming and a concomitant loss in proliferative capacity and induction of terminal differentiation or apoptosis (programmed cell death). Laboratory studies that focus on elucidating mechanisms of action are demonstrating the effectiveness of 'differentiation therapy,' which is now beginning to show translational promise in the clinical setting.

A phase II trial of bryostatin 1 in patients with non-Hodgkin's lymphoma

Bryostatin 1 is a naturally occurring macrocyclic lactone with promising antitumour and immunomodulatory function in preclinical and phase I clinical investigations. In this phase II study, 17 patients with progressive non-Hodgkin's lymphoma of indolent type (NHL), previously treated with chemotherapy, received a median of 6 (range 1-9) intravenous infusions of 25 microg/m(2) bryostatin 1 given once weekly over 24 hours. In 14 evaluable patients no responses were seen. Stable disease was attained in one patient for 9 months. The principal toxicities were myalgia and phlebitis. Treatment was discontinued early because of toxicity alone (phlebitis) in 2 patients, toxicity in addition to progressive disease in 3 patients (myalgia and phlebitis n = 2; thrombocytopenia n = 1) and progressive disease in 5 patients. The results fail to demonstrate efficacy of this regimen of bryostatin 1 in the treatment of NHL. In light of preclinical data that demonstrate synergy between bryostatin 1 and several cytotoxic agents and cytokines, clinical studies to investigate bryostatin 1 in combination are warranted. We also present data to demonstrate that central venous lines may be used in future studies to avoid phlebitis.

Marine organisms as a source of new anticancer agents

Various active anticancer agents are derived from plants and terrestrial microorganisms. The isolation of C-nucleosides from the Caribbean sponge, Cryptotheca crypta, four decades ago, provided the basis for the synthesis of cytarabine, the first marine-derived anticancer agent to be developed for clinical use. Cytarabine is currently used in the routine treatment of patients with leukaemia and lymphoma. Gemcitabine, one of its fluorinated derivatives, has also been approved for use in patients with pancreatic, breast, bladder, and non-small-cell lung cancer. Over the past decade, several new experimental anticancer agents derived from marine sources have entered preclinical and clinical trials. This field has expanded significantly as a result of improvements in the technology of deep-sea collection, extraction, and large-scale production through aquaculture and synthesis. In this paper, examples of marine-derived experimental agents that are currently undergoing preclinical and early clinical evaluation are briefly discussed. A summary of the available information on the results of phase I and II trials of agents such as aplidine, ecteinascidin-734 (ET-734), dolastatin 10 and bryostatin 1 is also presented.

Phase II evaluation of bryostatin-1 in metastatic melanoma

In this phase II study we assessed the efficacy of bryostatin-1 (NSC 339555) in metastatic melanoma patients when given intravenously either once a week at a dose of 25 microg/m2 per day over 24 h for 3 weeks or at 40 microg/m2 per day over 72 h every 2 weeks. Treatment courses were repeated every 4 weeks. Patients who had received one prior chemotherapy regimen for advanced melanoma, with or without biotherapy, were randomized to one or the other bryostatin-1 dose schedules until 12 patients were registered to each arm. Because there was one confirmed response among the 12 patients who received the 72 h dose schedule, 25 more patients were added to that arm. No prophylactic medications were given. Objective tumour measurements were used to assess the efficacy of the regimen. The National Cancer Institutes common toxicity criteria were used to grade reactions. In total, 49 patients with metastatic melanoma, none having symptomatic brain metastasis, were studied. Of these, 12 patients received the 24 h bryostatin-1 regimen, while the remaining 37 received the 72 h regimen. One patient receiving the 72 h regimen had a partial response lasting over 7 months. Muscle pain occurred in over 90% of the patients and was the dose-limiting side effect of the 72 h regimen. Grade 3/4 nausea and vomiting were more common on the 24 h regimen than on the 72 h one (35% versus 5% of patients). There was no therapy-related thrombocytopenia. Neutropenia was mild and mainly limited to patients receiving the 72 h regimen. Bryostatin-1 has limited activity against melanoma when given by 72 h intravenous infusion.

Modulation of protein kinase C in antitumor treatment

PKC isoenzymes were found to be involved in proliferation, antitumor drug resistance and apoptosis. Therefore, it has been tried to exploit PKC as a target for antitumor treatment. PKC alpha activity was found to be elevated, for example, in breast cancers and malignant gliomas, whereas it seems to be underexpressed in many colon cancers. So it can be expected that inhibition of PKC activity will not show similar antitumor activity in all tumors. In some tumors it seems to be essential to inhibit PKC to reduce growth. However, for inhibition of tumor proliferation it may be an advantage to induce apoptosis. In this case an activation of PKC delta should be achieved. The situation is complicated by the facts that bryostatin leads to the activation of PKC and later to a downmodulation and that the PKC inhibitors available to date are not specific for one PKC isoenzyme. For these reasons, PKC modulation led to many contradicting results. Despite these problems, PKC modulators such as miltefosine, bryostatin, safingol, CGP41251 and UCN-01 are used in the clinic or are in clinical evaluation. The question is whether PKC is the major or the only target of these compounds, because they also interfere with other targets. PKC may also be involved in apoptosis. Oncogenes and growth factors can induce cell proliferation and cell survival, however, they can also induce apoptosis, depending on the cell type or conditions in which the cells or grown. PKC participates in these signalling pathways and cross-talks. Induction of apoptosis is also dependent on many additional factors, such as p53, bcl-2, mdm2, etc. Therefore, there are also many contradicting results on PKC modulation of apoptosis. Similar controversial data have been reported about MDR1-mediated multidrug resistance. At present it seems that PKC inhibition alone without direct interaction with PGP will not lead to successful reversal of PGP-mediated drug efflux. One possibility to improve chemotherapy would be to combine established antitumor drugs with modulators of PKC. However, here also very contrasting results were obtained. Many indicate that inhibition, others, that activation of PKC enhances the antiproliferative activity of anticancer drugs. The problem is that the exact functions of the different PKC isoenzymes are not clear at present. So further investigations into the role of PKC isoenzymes in the complex and interacting signalling pathways are essential. It is a major challenge in the future to reveal whether modulation of PKC can be used for the improvement of cancer therapy.

A phase II trial of bryostatin 1 in patients with non-Hodgkin's lymphoma

Bryostatin 1 is a naturally occurring macrocyclic lactone with promising antitumour and immunomodulatory function in preclinical and phase I clinical investigations. In this phase II study, 17 patients with progressive non-Hodgkin's lymphoma of indolent type (NHL), previously treated with chemotherapy, received a median of 6 (range 1-9) intravenous infusions of 25 microg/m(2) bryostatin 1 given once weekly over 24 hours. In 14 evaluable patients no responses were seen. Stable disease was attained in one patient for 9 months. The principal toxicities were myalgia and phlebitis. Treatment was discontinued early because of toxicity alone (phlebitis) in 2 patients, toxicity in addition to progressive disease in 3 patients (myalgia and phlebitis n = 2; thrombocytopenia n = 1) and progressive disease in 5 patients. The results fail to demonstrate efficacy of this regimen of bryostatin 1 in the treatment of NHL. In light of preclinical data that demonstrate synergy between bryostatin 1 and several cytotoxic agents and cytokines, clinical studies to investigate bryostatin 1 in combination are warranted. We also present data to demonstrate that central venous lines may be used in future studies to avoid phlebitis.

Pharmaceutical development of anticancer agents derived from marine sources

The marine ecosystem is more and more acknowledged as a source of potential anticancer agents. After the identification of a potential substance several hurdles have to be overcome before a marine candidate can enter the clinic. Amongst these are the establishment of a method which ensures sufficient supply and, which is the focus of this review, the development of a clinically useful pharmaceutical formulation. General issues with respect to the pharmaceutical development of marine anticancer agents will be discussed, which will be illustrated by highlighting aspects of the pharmaceutical development and clinical use of some representative compounds.