Jasplakinolide: interaction with radiation and hyperthermia in human prostate carcinoma and Lewis lung carcinoma

Therapeutic Potential of Marine-Derived Cyclic Peptides as Antiparasitic Agents

Parasitic diseases still compromise human health. Some of the currently available therapeutic drugs have limitations considering their adverse effects, questionable efficacy, and long treatment, which have encouraged drug resistance. There is an urgent need to find new, safe, effective, and affordable antiparasitic drugs. Marine-derived cyclic peptides have been increasingly screened as candidates for developing new drugs. Therefore, in this review, a systematic analysis of the scientific literature was performed and 25 marine-derived cyclic peptides with antiparasitic activity (1-25) were found. Antimalarial activity is the most reported (51%), followed by antileishmanial (27%) and antitrypanosomal (20%) activities. Some compounds showed promising antiparasitic activity at the nM scale, being active against various parasites. The mechanisms of action and targets for some of the compounds have been investigated, revealing different strategies against parasites.

The Potential for Targeting AVIL and Other Actin-Binding Proteins in Rhabdomyosarcoma

Rhabdomyosarcoma (RMS) is the most common pediatric soft-tissue cancer with a survival rate below 27% for high-risk children despite aggressive multi-modal therapeutic interventions. After decades of research, no targeted therapies are currently available. Therapeutically targeting actin-binding proteins, although promising, has historically been challenging. Recent advances have made this possibility more salient, including our lab's identification of advillin (AVIL), a novel oncogenic actin-binding protein that plays a role in many cytoskeletal functions. AVIL is overexpressed in many RMS cell lines, patient-derived xenograft models, and a cohort of 30 clinical samples of both the alveolar (ARMS) and embryonal (ERMS) subtypes. Overexpression of AVIL in mesenchymal stem cells induces neoplastic transformation both in vitro and in vivo, and reversing overexpression through genetic modulation reverses the transformation. This suggests a critical role of AVIL in RMS tumorigenesis and maintenance. As an actin-binding protein, AVIL would not traditionally be considered a druggable target. This perspective will address the feasibility of targeting differentially expressed actin-binding proteins such as AVIL therapeutically, and how critical cell infrastructure can be damaged in a cancer-specific manner.

Therapeutic Potential of Marine Peptides in Prostate Cancer: Mechanistic Insights

Prostate cancer (PCa) is the leading cause of cancer death in men, and its treatment is commonly associated with severe adverse effects. Thus, new treatment modalities are required. In this context, natural compounds have been widely explored for their anti-PCa properties. Aquatic organisms contain numerous potential medications. Anticancer peptides are less toxic to normal cells and provide an efficacious treatment approach via multiple mechanisms, including altered cell viability, apoptosis, cell migration/invasion, suppression of angiogenesis and microtubule balance disturbances. This review sheds light on marine peptides as efficacious and safe therapeutic agents for PCa.

GAGE mediates radio resistance in cervical cancers via the regulation of chromatin accessibility

Radiotherapy (RT) resistance is a major cause of treatment failure in cancers that use definitive RT as their primary treatment modality. This study identifies the cancer/testis (CT) antigen G antigen (GAGE) as a mediator of radio resistance in cervical cancers. Elevated GAGE expression positively associates with de novo RT resistance in clinical samples. GAGE, specifically the GAGE12 protein variant, confers RT resistance through synemin-dependent chromatin localization, promoting the association of histone deacetylase 1/2 (HDAC1/2) to its inhibitor actin. This cumulates to elevated histone 3 lysine 56 acetylation (H3K56Ac) levels, increased chromatin accessibility, and improved DNA repair efficiency. Molecular or pharmacological disruption of the GAGE-associated complex restores radiosensitivity. Molecularly, this study demonstrates the role of GAGE in the regulation of chromatin dynamics. Clinically, this study puts forward the utility of GAGE as a pre-screening biomarker to identify poor responders at initial diagnosis and the therapeutic potential of agents that target GAGE and its associated complex in combination with radiotherapy to improve outcomes.

Bcl-3 promotes multi-modal tumour cell migration via NF-κB1 mediated regulation of Cdc42

A key challenge in the implementation of anti-metastatics as cancer therapies is the multi-modal nature of cell migration, which allows tumour cells to evade the targeted inhibition of specific cell motility pathways. The nuclear factor-kappaB (NF-κB) co-factor B-cell lymphoma 3 (Bcl-3) has been implicated in breast cancer cell migration and metastasis, yet it remains to be determined exactly which cell motility pathways are controlled by Bcl-3 and whether migrating tumour cells are able to evade Bcl-3 intervention. Addressing these questions and the mechanism underpinning Bcl-3's role in this process would help determine its potential as a therapeutic target. Here we identify Bcl-3 as an upstream regulator of the two principal forms of breast cancer cell motility, involving collective and single-cell migration. This was found to be mediated by the master regulator Cdc42 through binding of the NF-κB transcription factor p50 to the Cdc42 promoter. Notably, Bcl-3 depletion inhibited both stable and transitory motility phenotypes in breast cancer cells with no evidence of migratory adaptation. Overexpression of Bcl-3 enhanced migration and increased metastatic tumour burden of breast cancer cells in vivo, whereas overexpression of a mutant Bcl-3 protein, which is unable to bind p50, suppressed cell migration and metastatic tumour burden suggesting that disruption of Bcl-3/NF-κB complexes is sufficient to inhibit metastasis. These findings identify a novel role for Bcl-3 in intrinsic and adaptive multi-modal cell migration mediated by its direct regulation of the Rho GTPase Cdc42 and identify the upstream Bcl-3:p50 transcription complex as a potential therapeutic target for metastatic disease.

Impairment of nuclear F-actin formation and its relevance to cellular phenotypes in Hutchinson-Gilford progeria syndrome

Hutchinson-Gilford progeria syndrome (HGPS) is a premature aging disorder caused by a mutation of lamin A, which contributes to nuclear architecture and the spatial organization of chromatin in the nucleus. The expression of a lamin A mutant, named progerin, leads to functional and structural disruption of nuclear organization. Since progerin lacks a part of the actin-binding site of lamin A, we hypothesized that nuclear actin dynamics and function are altered in HGPS cells. Nuclear F-actin is required for the organization of nuclear shape, transcriptional regulation, DNA damage repair, and activation of Wnt/β-catenin signaling. Here we show that the expression of progerin decreases nuclear F-actin and impairs F-actin-regulated transcription. When nuclear F-actin levels are increased by overexpression of nuclear-targeted actin or by using jasplakinolide, a compound that stabilizes F-actin, the irregularity of nuclear shape and defects in gene expression can be reversed. These observations provide evidence for a novel relationship between nuclear actin and the etiology of HGPS.

Jasplakinolide Attenuates Cell Migration by Impeding Alpha-1-syntrophin Protein Phosphorylation in Breast Cancer Cells

BACKGROUND

Alpha-1-syntrophin (SNTA1) is emerging as a novel modulator of the actin cytoskeleton. SNTA1 binds to F-actin and regulates intracellular localization and activity of various actin organizing signaling molecules. Aberration in syntrophin signaling has been closely linked with deregulated growth connected to tumor development/metastasis and its abnormal over expression has been observed in breast cancer. In the present work the effect of jasplakinolide, an actin-binding cyclodepsipeptide, on the SNTA1 protein activity and SNTA1 mediated downstream cellular events was studied in MDA-MB-231 breast cancer cell line.

METHODS

SNTA1 protein levels and phosphorylation status were determined in MDA-MB-231 cells post jasplakinolide exposure using western blotting and immunoprecipitation techniques respectively. MDA-MB-231 cells were transfected with WT SNTA1 and DM SNTA1 (Y^215/229 phospho mutant) and simultaneously treated with jasplakinolide. The effect of jasplakinolide and SNTA1 protein on cell migration was determined using the boyden chamber assay.

RESULTS

Jasplakinolide treatment decreases proliferation of MDA-MB-231 cells in both dose and time dependent manner. Results suggest that subtoxic doses of jasplakinolide induce morphological changes in MDA-MB-231 cells from flat spindle shape adherent cells to round weakly adherent forms. Mechanistically, jasplakinolide treatment was found to decrease SNTA1 protein levels and its tyrosine phosphorylation status. Moreover, migratory potential of jasplakinolide treated cells was significantly inhibited in comparison to control cells.

CONCLUSION

Our results demonstrate that jasplakinolide inhibits cell migration by impairing SNTA1 functioning in breast cancer cells.

Targeting the cytoskeleton against metastatic dissemination

Cancer is a pathology characterized by a loss or a perturbation of a number of typical features of normal cell behaviour. Indeed, the acquisition of an inappropriate migratory and invasive phenotype has been reported to be one of the hallmarks of cancer. The cytoskeleton is a complex dynamic network of highly ordered interlinking filaments playing a key role in the control of fundamental cellular processes, like cell shape maintenance, motility, division and intracellular transport. Moreover, deregulation of this complex machinery contributes to cancer progression and malignancy, enabling cells to acquire an invasive and metastatic phenotype. Metastasis accounts for 90% of death from patients affected by solid tumours, while an efficient prevention and suppression of metastatic disease still remains elusive. This results in the lack of effective therapeutic options currently available for patients with advanced disease. In this context, the cytoskeleton with its regulatory and structural proteins emerges as a novel and highly effective target to be exploited for a substantial therapeutic effort toward the development of specific anti-metastatic drugs. Here we provide an overview of the role of cytoskeleton components and interacting proteins in cancer metastasis with a special focus on small molecule compounds interfering with the actin cytoskeleton organization and function. The emerging involvement of microtubules and intermediate filaments in cancer metastasis is also reviewed.

Cell Softness Prevents Cytolytic T-cell Killing of Tumor-Repopulating Cells

Biomechanics is a fundamental feature of a cell. However, the manner by which actomysin tension affects tumor immune evasion remains unclear. Here we show that although cytotoxic T lymphocytes (CTL) can effectively destroy stiff differentiated tumor cells, they fail to kill soft tumor-repopulating cells (TRC). TRC softness prevented membrane pore formation caused by CTL-released perforin. Perforin interacting with nonmuscle myosin heavy-chain 9 transmitted forces to less F-actins in soft TRC, thus generating an inadequate contractile force for perforin pore formation. Stiffening TRC allowed perforin the ability to drill through the membrane, leading to CTL-mediated killing of TRC. Importantly, overcoming mechanical softness in human TRC also enhanced TRC cell death caused by human CTL, potentiating a mechanics-based immunotherapeutic strategy. These findings reveal a mechanics-mediated tumor immune evasion, thus potentially providing an alternative approach for tumor immunotherapy. SIGNIFICANCE: Tumor-repopulating cells evade CD8⁺ cytolytic T-cell killing through a mechanical softness mechanism, underlying the impediment of perforin pore formation at the immune synapse site.

Targeting actin inhibits repair of doxorubicin-induced DNA damage: a novel therapeutic approach for combination therapy

Severe side effects often restrict clinical application of the widely used chemotherapeutic drug doxorubicin. In order to decrease required substance concentrations, new concepts for successful combination therapy are needed. Since doxorubicin causes DNA damage, combination with compounds that modulate DNA repair could be a promising strategy. Very recently, a role of nuclear actin for DNA damage repair has been proposed, making actin a potential target for cancer therapy in combination with DNA-damaging therapeutics. This is of special interest, since actin-binding compounds have not yet found their way into clinics. We find that low-dose combination treatment of doxorubicin with the actin polymerizer chondramide B (ChB) synergistically inhibits tumor growth in vivo. On the cellular level we demonstrate that actin binders inhibit distinctive double strand break (DSB) repair pathways. Actin manipulation impairs the recruitment of replication factor A (RPA) to the site of damage, a process crucial for homologous recombination. In addition, actin binders reduce autophosphorylation of DNA-dependent protein kinase (DNA-PK) during nonhomologous end joining. Our findings substantiate a direct involvement of actin in nuclear DSB repair pathways, and propose actin as a therapeutic target for combination therapy with DNA-damaging agents such as doxorubicin.

Migrastatics-Anti-metastatic and Anti-invasion Drugs: Promises and Challenges

In solid cancers, invasion and metastasis account for more than 90% of mortality. However, in the current armory of anticancer therapies, a specific category of anti-invasion and antimetastatic drugs is missing. Here, we coin the term ‘migrastatics’ for drugs interfering with all modes of cancer cell invasion and metastasis, to distinguish this class from conventional cytostatic drugs, which are mainly directed against cell proliferation. We define actin polymerization and contractility as target mechanisms for migrastatics, and review candidate migrastatic drugs. Critical assessment of these antimetastatic agents is warranted, because they may define new options for the treatment of solid cancers.

Local invasion and metastasis, rather than clonal proliferation, are the dominant features of solid cancer. However, a specific category of anti-invasion and antimetastatic drugs is missing for treatment of solid cancer

We propose the term ‘migrastatics’ for drugs interfering with all modes of cancer cell invasiveness and, consequently, with their ability to metastasize (e.g., inhibiting not only local invasion, but also extravasation and metastatic colonization).

In solid cancer, drug resistance is the main cause of treatment failure, and is attributed to mutations of the target. Since targeting the cause, although academically desirable, may be futile, a pragmatic and near-term option is to move downstream, to common denominators of cell migration and/or invasion, such as actin polymerization and actomyosin-mediated contractility.

Bioactive Peptide of Marine Origin for the Prevention and Treatment of Non-Communicable Diseases

Non-communicable diseases (NCD) are the leading cause of death and disability worldwide. The four main leading causes of NCD are cardiovascular diseases, cancers, respiratory diseases and diabetes. Recognizing the devastating impact of NCD, novel prevention and treatment strategies are extensively sought. Marine organisms are considered as an important source of bioactive peptides that can exert biological functions to prevent and treatment of NCD. Recent pharmacological investigations reported cardio protective, anticancer, antioxidative, anti-diabetic, and anti-obesity effects of marine-derived bioactive peptides. Moreover, there is available evidence supporting the utilization of marine organisms and its bioactive peptides to alleviate NCD. Marine-derived bioactive peptides are alternative sources for synthetic ingredients that can contribute to a consumer's well-being, as a part of nutraceuticals and functional foods. This contribution focus on the bioactive peptides derived from marine organisms and elaborates its possible prevention and therapeutic roles in NCD.

The actin depolymerizing factor (ADF)/cofilin signaling pathway and DNA damage responses in cancer

The actin depolymerizing factor (ADF)/cofilin protein family is essential for actin dynamics, cell division, chemotaxis and tumor metastasis. Cofilin-1 (CFL-1) is a primary non-muscle isoform of the ADF/cofilin protein family accelerating the actin filamental turnover in vitro and in vivo. In response to environmental stimulation, CFL-1 enters the nucleus to regulate the actin dynamics. Although the purpose of this cytoplasm-nucleus transition remains unclear, it is speculated that the interaction between CFL-1 and DNA may influence various biological responses, including DNA damage repair. In this review, we will discuss the possible involvement of CFL-1 in DNA damage responses (DDR) induced by ionizing radiation (IR), and the implications for cancer radiotherapy.

Exploiting the cytoskeletal filaments of neoplastic cells to potentiate a novel therapeutic approach

Although cytoskeletal-directed agents have been a mainstay in chemotherapeutic protocols due to their ability to readily interfere with the rapid mitotic progression of neoplastic cells, they are all microtubule-based drugs, and there has yet to be any microfilament- or intermediate filament-directed agents approved for clinical use. There are many inherent differences between the cytoskeletal networks of malignant and normal cells, providing an ideal target to attain preferential damage. Further, numerous microfilament-directed agents, and an intermediate filament-directed agent of particular interest (withaferin A) have demonstrated in vitro and in vivo efficacy, suggesting that cytoskeletal filaments may be exploited to supplement chemotherapeutic approaches currently used in the clinical setting. Therefore, this review is intended to expose academics and clinicians to the tremendous variety of cytoskeletal filament-directed agents that are currently available for further chemotherapeutic evaluation. The mechanisms by which microfilament directed- and intermediate filament-directed agents damage malignant cells are discussed in detail in order to establish how the drugs can be used in combination with each other, or with currently approved chemotherapeutic agents to generate a substantial synergistic attack, potentially establishing a new paradigm of chemotherapeutic agents.

Peptide-based cancer therapy: opportunity and challenge

Cancer is one of the leading causes of death worldwide. Conventional cancer therapies mainly focus on mass cell killing without high specificity and often cause severe side effects and toxicities. Peptides are a novel class of anticancer agents that could specifically target cancer cells with lower toxicity to normal tissues, which will offer new opportunities for cancer prevention and treatment. Anticancer peptides face several therapeutic challenges. In this review, we present the sources and mechanisms of anticancer peptides and further discuss modification strategies to improve the anticancer effects of bioactive peptides.

Synthetic chondramide A analogues stabilize filamentous actin and block invasion by Toxoplasma gondii

Apicomplexan parasites such as Toxoplasma gondii rely on actin-based motility to cross biological barriers and invade host cells. Key structural and biochemical differences in host and parasite actins make this an attractive target for small-molecule inhibitors. Here we took advantage of recent advances in the synthesis of cyclic depsipeptide compounds that stabilize filamentous actin to test the ability of chondramides to disrupt growth of T. gondii in vitro. Structural modeling of chondramide A (2) binding to an actin filament model revealed variations in the binding site between host and parasite actins. A series of 10 previously synthesized analogues (2b-k) with substitutions in the β-tyrosine moiety blocked parasite growth on host cell monolayers with EC₅₀ values that ranged from 0.3 to 1.3 μM. In vitro polymerization assays using highly purified recombinant actin from T. gondii verified that synthetic and natural product chondramides target the actin cytoskeleton. Consistent with this, chondramide treatment blocked parasite invasion into host cells and was more rapidly effective than pyrimethamine, a standard therapeutic agent. Although the current compounds lack specificity for parasite vs host actin, these studies provide a platform for the future design and synthesis of synthetic cyclic peptide inhibitors that selectively disrupt actin dynamics in parasites.

Novel small-molecule compounds that affect cellular morphogenesis in yeast and mammalian cells

Drugs affecting cellular morphological changes leading to tumor cell migration and invasion are desirable for cancer therapy. In the present study, we screened for small-molecule compounds that affect the cellular morphology of both unicellular yeast and mammalian HEK293 cells to identify drug candidates. The yeast formin protein Bni1 and Src homology 3 (SH3)-pleckstrin homology (PH) domain protein Boi1, which are required for proper morphogenesis, cause growth defects when overexpressed in yeast. Using this system, we screened a chemical library consisting of ～8000 compounds to identify drug candidates that suppress these growth defects. None of the screened compounds induced morphological changes in vegetatively growing yeast cells, but several compounds had inhibitory effects on pheromone-induced projection formation and actin localization, suggesting that these compounds affected a specific stage of morphogenesis. Five of the compounds also induced morphological changes in mammalian HEK293 cells. Among the identified compounds, BTB03156, 2-[(4-chlorophenyl)sulfonyl]-1-methyl-3,5-dinitrobenzene, and BTB02467, 1-[(4-chlorophenyl)sulfonyl]-2-nitro-4-(trifluoromethyl)benzene, although they have similar structures, displayed differing effects on the yeast growth defects caused by latrunculin A, an actin polymerization inhibitor. The chemical library compounds identified using this in vivo screening approach are simple, cell-permeable molecules, and therefore may be useful in the development of therapeutic drugs for cancer metastasis and other actin-related diseases.

The effects of jaspamide on human cardiomyocyte function and cardiac ion channel activity

Jaspamide (jasplakinolide; NSC-613009) is a cyclodepsipeptide that has antitumor activity. A narrow margin of safety was observed between doses required for efficacy in mouse tumor models and doses that caused severe acute toxicity in rats and dogs. We explored the hypothesis that the observed toxicity was due to cardiotoxicity. Jaspamide was tested in a patch clamp assay to determine its effect on selected cardiac ion channels. Jaspamide (10 μM) inhibited Kv1.5 activity by 98.5%. Jaspamide also inhibited other channels including Cav1.2, Cav3.2, and HCN2; however, the Kv11.1 (hERG) channel was minimally affected. Using spontaneously contracting human cardiomyocytes derived from induced pluripotent stem cells, effects on cardiomyocyte contraction and viability were also examined. Jaspamide (30 nM to 30 μM) decreased cardiomyocyte cell indices and beat amplitude, putative measurements of cell viability and cardiac contractility, respectively. Concentration-dependent increases in rhythmic beating rate were noted at ≤ 6 h of treatment, followed by dose-dependent decreases after 6 and 72 h exposure. The toxic effects of jaspamide were compared with that of the known cardiotoxicant mitoxantrone, and confirmed by multiparameter fluorescence imaging analysis. These results support the hypothesis that the toxicity observed in rats and dogs is due to toxic effects of jaspamide on cardiomyocytes.

Total synthesis and configurational assignment of chondramide A

The first total synthesis of the cyclodepsipeptide chondramide A (2 b) is described. This depsipeptide is composed of four subunits, namely L-alanine, N-Me-D-tryptophan, 3-amino-2-methoxy-propionic acid (beta-tyrosine derivative), and a 7-hydroxy-alkenoic acid. While the configuration of the stereogenic centers in the 7-hydroxy-alkenoic acid were known, the configuration of the tyrosine derivative required clarification and turned out to be (2S,3R) or (2L,3L), respectively. The synthesis of the 3-amino-2-methoxy-3-arylpropanoic ester 20 b relied on an asymmetric dihydroxylation yielding diol ent-15 a followed by a regioselective Mitsunobu substitution leading to 3-azido-2-hydroxypropanoate 18 b. We could also show that the ester bond in the seco compound 26 b can be fashioned by a Mitsunobu esterification by using hydroxy ester (7S)-7 and the tripeptide acid 25 b. This synthesis should allow for the preparation of various analogues.

Jasplakinolide: an actin-specific reagent that promotes actin polymerization

Jasplakinolide, a cyclo-depsipeptide is a commonly used actin filament polymerizing and stabilizing drug. The substance has originally been isolated from a marine sponge, and can now be synthesized and has become commercially available. This, together with the benefit that jasplakinolide is membrane permeable has made it a commonly used tool in cell biology, when actin filament stabilization or polymerization has to be achieved. This may either be the case in studies on morphogenesis, motility, organelle movement, or when apoptosis has to be induced. Its use as a potent anticancer drug is discussed. The direct action on actin filaments may have further consequences in golgi body and membrane raft protein organization. In this chapter, the visualization of jasplaklinolide effects by different fluorescent and transmission electron microscopic methods is described. As competitive binding capacities of jasplakinolide and phalloidin make the detection of actin filaments by fluorescently labeled phalloidin problematic, alternatives are given here.

Antimitotic chemotherapeutics promote adhesive responses in detached and circulating tumor cells

In the clinical treatment of breast cancer, antimitotic cytotoxic agents are one of the most commonly employed chemotherapies, owing largely to their antiproliferative effects on the growth and survival of adherent cells in studies that model primary tumor growth. Importantly, the manner in which these chemotherapeutics impact the metastatic process remains unclear. Furthermore, since dissemination of tumor cells through the systemic circulation and lymphatics necessitates periods of detached survival, it is equally important to consider how circulating tumor cells respond to such compounds. To address this question, we exposed both nontumorigenic and tumor-derived epithelial cell lines to two antitumor compounds, jasplakinolide and paclitaxel (Taxol), in a series of attached and detached states. We report here that jasplakinolide promoted the extension of microtubule-based projections and microtentacle protrusions in adherent and suspended cells, respectively. These protrusions were specifically enriched by upregulation of a stable post-translationally modified form of alpha-tubulin, and this occurred prior to, and independently of any reductions in cellular viability. Microtubule stabilization with Taxol significantly enhanced these effects. Additionally, Taxol promoted the attachment and spreading of suspended tumor cell populations on extracellular matrix. While the antiproliferative effects of these compounds are well recognized and clinically valuable, our findings that microfilament and microtubule binding chemotherapeutics rapidly increase the mechanisms that promote endothelial adhesion of circulating tumor cells warrant caution to avoid inadvertently enhancing metastatic potential, while targeting cell division.

Synthesis and structure-activity relationship of cytotoxic marine cyclodepsipeptide IB-01212 analogues

Several recently discovered marine products have remarkable in vitro and in vivo anticancer profiles against a wide range of tumor cell lines. Some of these compounds are currently in clinical trials. These compounds show complex structures and mechanisms of action of interest. Herein, we describe the preparation of a series of totally synthetic molecules that are structurally related to the natural marine product IB-01212 and evaluated them as antitumor agents. For this, total solid-phase syntheses of the products were performed in parallel by two distinct routes: linear synthesis and convergent synthesis. Structural modifications were introduced in several residue positions to afford 21 IB-01212 analogues for structure-relationship studies. An increase in the number of methyl groups in the macrocycle enhanced cytotoxic activity. Also, the replacement of an ester bond by an amide bond favored antitumor activity against several human cell lines. In addition, the L configuration analogues were more active against all the tumor cell lines than those containing the D configuration. A significant increase in the size and asymmetry of the macrocycle diminished biological activity with respect to that of IB-01212. These results are of great value for the discovery of new and more effective anticancer agents.

Bioactive Molecules from Sea Hares

Sea hares, belonging to the order Opisthobranchia, subclass Gastropoda, are mollusks that have attracted many researchers who are interested in the chemical defense mechanisms of these soft and "shell-less" snails. Numbers of small molecules of dietary origin have been isolated from sea hares and some have ecologically relevant activities, such as fish deterrent activity or toxicity. Recently, however, greater attention has been paid to biomedically interesting sea hare isolates such as dolastatins, a series of antitumor peptide/macrolides isolated from Dolabella auricularia. Another series of bioactive peptide/macrolides, as represented by aplyronines, have been isolated from sea hares in Japanese waters. Although earlier studies indicated the potent antitumor activity of aplyronines, their clinical development has never been conducted because of the minute amount of compound available from the natural source. Recent synthetic studies, however, have made it possible to prepare these compounds and analogs for a structure-activity relationship study, and started to uncover their unique action mechanism towards their putative targets, microfilaments. Here, recent findings of small antitumor molecules isolated from Japanese sea hares are reviewed. Sea hares are also known to produce cytotoxic and antimicrobial proteins. In contrast to the small molecules of dietary origin, proteins are the genetic products of sea hares and they are likely to have some primary physiological functions in addition to ecological roles in the sea hare. Based on the biochemical properties and phylogenetic analysis of these proteins, we propose that they belong to one family of molecule, the "Aplysianin A family," although their molecular weights are apparently divided into two groups. Interestingly, the active principles in Aplysia species and Dolabella auricularia were shown to be L-amino acid oxidase (LAAO), a flavin enzyme that oxidizes an alpha-amino group of the substrate with molecular oxygen and liberates hydrogen peroxide, with a sequence similar to other known LAAOs, including snake venom. Possible antibacterial activity and cytotoxic activity mechanisms of these proteins are also discussed.

Synthesis, solution structure, and bioactivity of six new simplified analogues of the natural cyclodepsipeptide jaspamide

Recently, we described the synthesis and the biological evaluation of three modified analogues of jaspamide (1), a natural cyclodepsipeptide possessing a potent antitumor activity as a consequence of its ability to interfere with actin cytoskeleton. To obtain additional information on the potential pharmacophoric core of the target molecule, which is of fundamental importance to discover new and more effective anticancer products, we decided to explore the biological effects of further structural modifications carried out on the parent molecule. The synthesis and the chemical characterization of six jaspamide analogues (2-7) are reported and their conformational and biological properties are described.

Jasplakinolide induces apoptosis in various transformed cell lines by a caspase-3-like protease-dependent pathway

To clarify the mechanisms underlying the antiproliferative effects of jasplakinolide, a cyclic depsipeptide from marine sponges, we examined whether jasplakinolide induces apoptosis in a variety of transformed and nontransformed cells. Jasplakinolide inhibited proliferation of human Jurkat T cells, resulting in cell death. This was accompanied by chromatin condensation and DNA cleavage at the linker regions between the nucleosomes. When caspase-3-like activity in the cytosolic extracts of Jurkat T cells was examined with a fluorescent substrate, DEVD-MAC (N-acetyl-Asp-Glu-Val-Asp-4-methyl-coumaryl-7-amide), the activity in the cells treated with jasplakinolide was remarkably increased in a time-dependent manner. Pretreatment of Jurkat T cells with the caspase inhibitor zVAD [benzyloxycarbonyl(Cbz)-Val-Ala-beta-Asp(OMe)-fluoromethylketone] or DEVD-CHO (N-acetyl-Asp-Glu-Val-Asp-1-aldehyde) prevented the induction of apoptosis by jasplakinolide. Moreover, exposure of various murine transformed cell lines to jasplakinolide resulted in cell death, which was inhibited by zVAD. Although it has been well established that murine immature thymocytes are sensitive to apoptosis when exposed to various apoptotic stimuli, these cells as well as mature T lymphocytes were resistant to jasplakinolide-induced apoptosis. The results suggest that jasplakinolide induces apoptotic cell death through a caspase-3-like protease-dependent pathway. Another important outcome is that transformed cell lines were more susceptible to jasplakinolide-induced apoptosis than normal nontransformed cells.

Microfilament stabilization by jasplakinolide arrests oocyte maturation, cortical granule exocytosis, sperm incorporation cone resorption, and cell-cycle progression, but not DNA replication, during fertilization in mice

Jasplakinolide (JAS), which induces microfilament polymerization and stabilization, inhibits microfilament-mediated events in murine oocyte maturation and fertilization in a fashion unlike the effects of cytochalasin B (CCB) and latranculin A (LAT A). JAS prevents egg polar body emission at a much lower concentration than either CCB or LAT A. Microfilament bundles were detected on the entire egg cortex after JAS exposure. Conversely, microfilament patterns did not change after exposure to CCB, and few microfilaments were observed after exposure to LAT A. Eggs that were allowed to recover from JAS were unable to recover normal microfilament organization. During oocyte maturation, JAS prevented both spindle migration to the oocyte cortex and first polar body emission. During in vitro fertilization, sperm head entered the eggs and formed pronuclei, but sperm tail entry, pronuclear centration, and second polar body emission were not detected. DNA synthesis occurs in these JAS-treated zygotes. JAS inhibited not only the formation, but also the disassembly, of incorporation cones. JAS was also found to prevent cortical granule exocytosis following artificial activation, and cortical granules were still beneath the plasma membrane even after activation. Finally, incorporation of microinjected nonmuscle actin into the microfilament network of mice eggs was delayed by JAS. We conclude that JAS acts as a microfilament inhibitor during maturation and fertilization and is more powerful than other inhibitors. Its mechanism differs in that it promotes assembly and stabilization of microfilaments. JAS is a novel cell permeable tool for the investigation of microfilament-dependent events in early mammalian development.

Actin stabilization by jasplakinolide enhances apoptosis induced by cytokine deprivation

Participation of the actin cytoskeleton in the transduction of proliferative signals has been established through the use of compounds that disrupt the cytoskeleton. To address the possibility that actin also participates in the transduction of an apoptotic signal, we have studied the response of the murine interleukin 2 (IL-2)-dependent T cell line CTLL-20 to treatment with the actin-binding compound jasplakinolide upon IL-2 deprivation. Like phalloidin, jasplakinolide stabilizes F-actin and promotes actin polymerization. Treatment of CTLL-20 cells with jasplakinolide, in the presence or absence of recombinant human IL-2, altered actin morphology as assessed by confocal fluorescence microscopy. Jasplakinolide was not toxic to CTLL-20 cells, nor was apoptosis induced in the presence of exogenous recombinant human IL-2. However, actin stabilization at the time of IL-2 deprivation enhanced apoptosis by changing the time at which CTLL-20 cells committed to the apoptotic pathway. This effect of jasplakinolide correlated with its ability to stabilize polymerized actin, as treatment with a synthetic analog of jasplakinolide with a greatly reduced ability to bind actin, jasplakinolide B, did not enhance apoptosis. The enhancement occurred upstream of the induction of caspase-3-like activity and could be inhibited by the overexpression of the anti-apoptotic protein Bcl-xL. These data suggest that the actin cytoskeleton plays an active role in modulating lymphocyte apoptosis induced by cytokine deprivation.