Therapeutic targets for antimetastatic therapy

KISS1 metastasis suppressor in tumor dormancy: a potential therapeutic target for metastatic cancers?

Present therapeutic approaches do not effectively target metastatic cancers, often limited by their inability to eliminate already-seeded non-proliferative, growth-arrested, or therapy-resistant tumor cells. Devising effective approaches targeting dormant tumor cells has been a focus of cancer clinicians for decades. However, progress has been limited due to limited understanding of the tumor dormancy process. Studies on tumor dormancy have picked up pace and have resulted in the identification of several regulators. This review focuses on KISS1, a metastasis suppressor gene that suppresses metastasis by keeping tumor cells in a state of dormancy at ectopic sites. The review explores mechanistic insights of KISS1 and discusses its potential application as a therapeutic against metastatic cancers by eliminating quiescent cells or inducing long-term dormancy in tumor cells.

Microarray Embedding/Sectioning for Parallel Analysis of 3D Cell Spheroids

Three-dimensional cell spheroid models can be used to predict the effect of drugs and therapeutics and to model tissue development and regeneration. The utility of these models is enhanced by high throughput 3D spheroid culture technologies allowing researchers to efficiently culture numerous spheroids under varied experimental conditions. Detailed analysis of high throughput spheroid culture is much less efficient and generally limited to narrow outputs, such as metabolic viability. We describe a microarray approach that makes traditional histological embedding/sectioning/staining feasible for large 3D cell spheroid sample sets. Detailed methodology to apply this technology is provided. Analysis of the technique validates the potential for efficient histological analysis of up to 96 spheroids in parallel. By integrating high throughput 3D spheroid culture technologies with advanced immunohistochemical techniques, this approach will allow researchers to efficiently probe expression of multiple biomarkers with spatial localization within 3D structures. Quantitative comparison of staining will have improved inter- and intra-experimental reproducibility as multiple samples are collectively processed, stained, and imaged on a single slide.

Isolation, purification and characterization of Trichothecinol-A produced by endophytic fungus Trichotheciumsp. and its antifungal, anticancer and antimetastatic activities

Background

A total of 30 endophytic fungi (AAP-PS 1–30) were isolated from the medicinal herb Phyllanthus amarus and screened for the production of Trichothecinol-A. Out of all the endophytic strains screened for Trichothecinol-A production, the culture filtrate of AAP-PS-1 extracted with ethyl acetate yielded Trichothecinol-A extracellularly in appreciable amounts. Trichothecinol-A was purified, quantified and completely characterized by different standard chromatographic and spectroscopic techniques including reverse phase HPLC, 1D and 2D NMR spectroscopy, etc. The compound was tested for antifungal activity against filamentous fungi and yeast, apoptotic activity against B16F10 cells, anticancer activity against MDA-MB-231, HeLa and B16F10 cells as well as antimetastatic activity against MDA-MB-231 cell line.

Results

The endophyte producing Trichothecinol-A was identified as Trichothecium sp. by morphological, cultural and molecular methods. RP-HPLC analyses performed on a Waters model using a C18 symmetry pack column with a flow rate of 0.5 ml/min and the eluting compounds were detected by a dual mode wavelength detector set at 220 nm and 240 nm. The 1D (1H, 13C) and 2D NMR (COSY, NOESY, TOCSY, DEPT, 13C–1H HMBC, 13C–1H HSQC), ESI-MS, HRMS, IR and UV–vis show conclusively that the isolated compound was Trichothecinol–A. One liter of Trichothecium sp. yielded 4.37 mg of Trichothecinol-A. Trichothecinol-A exhibited antifungal activity against Cryptococcus albidus (NCIM 3372) up to 20 μg/ml. Cytotoxicity studies indicate that Trichothecinol-A causes 50% cell death at 500nM concentration in HeLa and B16F10 cells and induces apoptosis in later. Inhibition of wound migration assay performed on MDA-MB-231 cells reveals that 500nM of Trichothecinol-A was able to inhibit wound migration by 50% indicating its remarkable antimetastatic property.

Conclusion

The compound Trichothecinol-A has previously been isolated from Trichothecium roseum and characterized by various standard techniques. Anti-cancer studies conducted on Trichothecinol-A showed that it significantly inhibits cancer cell migration and can thus be developed as a new class of anti-metastatic drug. Here, we for the first time report the anti-metastatic as well as anti-fungal activity exhibited by Trichothecinol-A isolated by us from the endophytic fungus Trichothecium sp. of medicinal plant Phyllanthus amarus. Trichothecinol-A also exhibited apoptotic activity.

A novel o-naphtoquinone inhibits N-cadherin expression and blocks melanoma cell invasion via AKT signaling

The down-regulation or loss of epithelial markers is often accompanied by the up-regulation of mesenchymal markers. E-cadherin generally suppresses invasiveness, whereas N-cadherin promotes invasion and metastasis in vitro. The aim of this work is to investigate the role of biflorin, a naphthoquinone with proven anticancer properties, on the expression of N-cadherin and AKT proteins in MDA-MB-435 invasive melanoma cancer cells after 12h of exposure to 1, 2.5 and 5 μM biflorin. Biflorin inhibited MDA-MB-435 invasion in a dose-dependent manner (p<0.01). Likewise, biflorin down-regulated N-cadherin and AKT-1 expression in a dose-dependent manner. Biflorin did not inhibit the adhesion of MDA-MB-435 cells to any tested substrates. Additionally, biflorin blocked the invasiveness of cells by down-regulating N-cadherin, most likely via AKT-1 signaling. As such, biflorin may be a novel anticancer agent and a new prototype for drug design.

Building on the foundation of daring hypotheses: using the MKK4 metastasis suppressor to develop models of dormancy and metastatic colonization

The identification of a novel metastasis suppressor function for the MAP Kinase Kinase 4 protein established a role for the stress-activated kinases in regulating the growth of disseminated cancer cells. In this review, we describe MKK4's biological mechanism of action and how this information is being used to guide the development of new models to study cancer cell dormancy and metastatic colonization. Specifically, we describe the novel application of microvolume structures, which can be modified to represent characteristics similar to those that cancer cells experience at metastatic sites. Although MKK4 is currently one of many known metastasis suppressors, this field of research started with a single daring hypothesis, which revolutionized our understanding of metastasis, and opened up new areas of exploration for basic research. The combination of our increasing knowledge of metastasis suppressors and such novel technologies provide hope for possible clinical interventions to prevent suffering from the burden of metastatic disease.

Confirmation of the Structures of Synthetic Derivatives of Migrastatin in the Light of Recently Disclosed Crystallographically Based Claims

In the light of recently disclosed crystallographic studies on migrastatin ketone 2 complex with fascin, the structures of migrastatin ketone 2 and migrastatin ether 4 have been re-evaluated by NMR and X-Ray crystallographic techniques. The results of these studies established the correctness of the previously reported structural assignment and confirm that the "small molecule" co-crystallized in complex with fascin is not the migrastatin ketone, which was provided for the infusion experiment, but rather its stereoisomer.

Diverted total synthesis leads to the generation of promising cell-migration inhibitors for treatment of tumor metastasis: in vivo and mechanistic studies on the migrastatin core ether analog

A significantly simpler analog of the natural product migrastatin, termed migrastatin ether (ME), has been prepared and evaluated. Both in vivo and in vitro studies indicate that ME exhibits a concentration-dependent inhibitory effect on migration of breast cancer cells.

Tanshinone IIA inhibits angiogenesis in subcutaneous colorectal cancer xenografts in mice

AIM: To investigate the effects of tanshinone IIA (an active component of traditional Chinese medicine salvia miltiorrhiza) on angiogenesis in subcutaneous colorectal cancer xenografts in mice.

METHODS: An ectopic mouse model of colorectal cancer was established by subcutaneously inoculating colon carcinoma C26 cells into the armpit of mice. The mice were then randomly divided into 5 groups: model control group, low-dose tanshinone IIA group [0.5 mg/(kg•d)], mid-dose tanshinone IIA group [1 mg/(kg•d)], high-dose tanshinone IIA group [2 mg/(kg•d)], and 5-fluorouracil (5-FU) group [1 mg/(kg•d)]. Normal saline (model control group), tanshinone IIA of different doses and 5-FU were injected via the vena caudalis once daily for one week, respectively. Seven days later, the eyeballs were removed to collect blood samples, and the tumors were peeled off to measure tumor size and weight. The microvessel density (MVD) was tested by immunohistochemistry. Tumor necrosis was detected by hematoxylin and eosin staining. Serum VEGF level was assayed by enzyme-linked immunosorbent assay (ELISA).

RESULTS: Compared with the model control group, tumor weight decreased by 45.8%, 60.3% and 84.5% in the low-, mid- and high-dose tanshinone IIA groups, respectively. Corresponding tumor size decreased by 50.5%, 60.7% and 84.2%, respectively. Tumor necrosis was mild in the model control group and low-dose tanshinone IIA group, but moderate to severe in the mid- and high-dose tanshinone IIA groups. The MVD was higher in the model control group and low-dose tanshinone IIA group than in the mid- and high-dose tanshinone IIA groups (86.5 ± 14.6 and 73.5 ± 19.8 vs 48.6 ± 15.2 and 19.4 ± 6.6, respectively). Serum VEGF level was significantly higher in the model control group than in the normal control group. Compared to the model control group, serum VEGF levels decreased by 15.8%, 34.2% and 74.8% in the low-, mid- and high-dose tanshinone IIA groups, respectively.

CONCLUSION: Tanshinone IIA can inhibit tumor angiogenesis and growth of colorectal cancer xenografts in mice perhaps via inhibition of VEGF and MVD.

Linoleic-acid-induced growth suppression induces quiescent cancer cell nests in nude mice

We examined the effect of linoleic acid (LA) on tumor formation. Cell growth was suppressed by LA in a dose-dependent manner in MKN28 and Colo320 cells. Continuous treatment with LA provided growth arrest in both cells at 5-7 weeks after the treatment. LA-pretreated MKN28 and Colo320 cells showed higher tumorigenicity (9/10 and 10/10, respectively) than nontreated cells (2/10 and 3/10, respectively; p < 0.01) in nude mice. In contrast, LA-pretreated MKN28 and Colo320 cells showed more suppressed tumor growth than nontreated cells (p < 0.01). LA-pretreated MKN28 and Colo320 cells with LA administration after the inoculation did not form macroscopic tumors. Histological examination revealed small cancer cell aggregations, which showed no proliferative activity. In LA-treated MKN28 and Colo320 cells, protein production of Bcl-2 was increased, whereas Bak, EGFR and VEGF levels were decreased. These findings suggest that LA might induce quiescence and subsequent dormancy in cancer cells.

Chemistry and biology in search of antimetastatic agents

A recent publication is a great example of the inherent potential of exploring the chemical space inspired by natural products. Expanding access to chemical space through organic synthesis allows the discovery of valuable new small-molecule mediators of biological activity.

Osteopontin: an emerging therapeutic target for anticancer therapy

Distant migration of malignant cells or metastasis is considered one of the hallmarks of tumour progression and makes cancer a most deadly disease. The elevated expression of osteopontin (OPN), a metastasis-associated small integrin-binding ligand N-linked glycoprotein family member has been observed in several cancers and, thus, this protein is considered as a potent prognostic marker during tumour progression. OPN regulates a series of signalling cascades and augments the expression of several oncogenic molecules. Therefore, understanding the molecular mechanism and the signalling pathways by which OPN promotes tumorigenesis may be helpful in designing a novel anticancer therapy. At present, the role of OPN in regulating cancer progression is the subject of intense investigation and targeting OPN might be an appropriate therapeutic strategy for the treatment of cancer. This review is focused on OPN-based anticancer therapy, which may provide a new dimension for the successful treatment of cancer.

Inhibition of VEGFR-3 activation with the antagonistic antibody more potently suppresses lymph node and distant metastases than inactivation of VEGFR-2

Lymph nodes are the first site of metastases for most types of cancer, and lymph node status is a key indicator of patient prognosis. Induction of tumor lymphangiogenesis by vascular endothelial growth factor-C (VEGF-C) has been shown to play an important role in promoting tumor metastases to lymph nodes. Here, we employed receptor-specific antagonist antibodies in an orthotopic spontaneous breast cancer metastasis model to provide direct evidence for the key role of VEGFR-3 activation in metastasis. Inhibition of VEGFR-3 activation more potently suppressed regional and distant metastases than inactivation of VEGFR-2, although VEGFR-2 blockade was more effective in inhibiting angiogenesis and tumor growth. Despite prominent proliferation, metastases were not vascularized in any of the control and treatment groups, indicating that the growth of metastases was not dependent on angiogenesis at the secondary site for the duration of the experiment. Systemic treatment with either VEGFR-2 or VEGFR-3 antagonistic antibodies suppressed tumor lymphangiogenesis, indicating that VEGFR-3 signaling affects the rate of tumor cell entry into lymphatic vessels through both lymphangiogenesis-dependent and independent mechanisms. Combination treatment with the anti-VEGFR-2 and anti-VEGFR-3 antibodies more potently decreased lymph node and lung metastases than each antibody alone. These results validate the concept of targeting the lymphatic dissemination and thereby very early steps of the metastatic process for metastasis control and suggest that a combination therapy with antiangiogenic agents may be a particularly promising approach for controlling metastases.

Maintenance Therapy to Suppress Micrometastasis: The New Challenge for Adjuvant Cancer Treatment

The palliative efficacy of cytotoxic drugs is routinely assessed using tumor shrinkage (response) rates shown in clinical trials. Although adjuvant drug therapy has a goal distinct from that of palliative therapy (i.e., to prolong survival by inhibiting progression of micrometastatic disease), it is widely assumed that the adjuvant efficacy of a drug will parallel its response rate ("activity") in advanced stages of the disease. Reconsideration of this assumption seems timely in view of recent developments: the realization that many predictors of short-term tumor response correlate inversely with long-term survival outcomes; the characterization of tumor progression as a discontinuous process that may include dormant phases; the understanding that micrometastasis is therapeutically suppressible by a variety of mechanisms including direct tumor cell kill, cytotoxic disruption of paracrine growth signals from normal tissues, and targeted inhibition of prometastatic pathways; the recognition that tumor dormancy not only blocks the antimetastatic efficacy of cytotoxic drugs but also represents a therapeutic end point for metastasis-suppressive noncytotoxic drugs such as hormone inhibitors; and the insight that optimal adjuvant drug therapy is likely to include both induction and maintenance components. The traditional view of cytoreductive response as a prerequisite for adjuvant drug efficacy thus merits reappraisal, with a view to accelerating incorporation of novel noncytotoxic maintenance therapies into controlled studies.