A major challenge for oncologists and pharmacologists is to develop less toxic drugs that will improve the survival of lung cancer patients. Frondoside A is a triterpenoid glycoside isolated from the sea cucumber, Cucumaria frondosa and was shown to be a highly safe compound. We investigated the impact of Frondoside A on survival, migration and invasion in vitro, and on tumor growth, metastasis and angiogenesis in vivo alone and in combination with cisplatin. Frondoside A caused concentration-dependent reduction in viability of LNM35, A549, NCI-H460-Luc2, MDA-MB-435, MCF-7, and HepG2 over 24 hours through a caspase 3/7-dependent cell death pathway. The IC50 concentrations (producing half-maximal inhibition) at 24 h were between 1.7 and 2.5 µM of Frondoside A. In addition, Frondoside A induced a time- and concentration-dependent inhibition of cell migration, invasion and angiogenesis in vitro. Frondoside A (0.01 and 1 mg/kg/day i.p. for 25 days) significantly decreased the growth, the angiogenesis and lymph node metastasis of LNM35 tumor xenografts in athymic mice, without obvious toxic side-effects. Frondoside A (0.1–0.5 µM) also significantly prevented basal and bFGF induced angiogenesis in the CAM angiogenesis assay. Moreover, Frondoside A enhanced the inhibition of lung tumor growth induced by the chemotherapeutic agent cisplatin. These findings identify Frondoside A as a promising novel therapeutic agent for lung cancer.

Pancreatic cancer cells are resistant to the growth-inhibitory and apoptosis-inducing effects of conventional chemotherapeutic agents. There are multiple genetic and epigenetic events during the process of carcinogenesis that enable the cancer cells to avoid normal growth constraints and apoptosis. Investigation of the mechanisms involved has led to multiple strategies that encourage cell death and apoptosis to occur. The pathways involved are summarized in this review, together with some recently developed strategies to promote cell death in this cancer and with a particular focus on the frondoside A, a novel triterpenoid glycoside isolated from the Atlantic sea cucumber, Cucumaria frondosa. Frondoside A inhibited proliferation of AsPC-1 human pancreatic cancer cells in a concentration- and time-dependent manner, as measured by (3)H-thymidine incorporation and cell counting. In concert with inhibition of cell growth, frondoside A induced significant morphological changes consistent with apoptosis. Propidium iodide DNA staining showed an increase of sub-G0/G1 cell population of apoptotic cells induced by frondoside A. Frondoside A-induced apoptosis was confirmed by annexin V binding and TUNEL assay. Furthermore, western blotting showed a decrease in expression of Bcl-2 and Mcl-1, an increase in Bax expression, activation of caspases 3, 7, and 9, and an increase in the expression of the cyclin-dependent kinase inhibitor, p21. These findings show that frondoside A induced apoptosis in human pancreatic cancer cells through the mitochondrial pathway and activation of the caspase cascade. Finally, a very low concentration of frondoside A (10 mug/kg/day) inhibited growth of AsPC-1 xenografts in athymic mice. In conclusion, new chemotherapeutic agents are desperately needed for pancreatic cancer because of the poor responsiveness to currently available treatment options. Frondoside A has potent growth inhibitory effects on human pancreatic cancer cells, and the inhibition of proliferation is accompanied by marked apoptosis. Frondoside A may be valuable for the treatment or chemoprevention of this devastating disease.

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The cyclooxygenase pathway is strongly implicated in breast cancer progression but the role of this pathway in the biology of breast cancer stem/progenitor cells has not been defined. Recent attention has focused on targeting the cyclooxygenase 2 (COX-2) pathway downstream of the COX-2 enzyme by blocking the activities of individual prostaglandin E (EP) receptors. Prostaglandin E receptor 4 (EP4) is widely expressed in primary invasive ductal carcinomas of the breast and antagonizing this receptor with small molecule inhibitors or shRNA directed to EP4 inhibits metastatic potential in both syngeneic and xenograft models. Breast cancer stem/progenitor cells are defined as a subpopulation of cells that drive tumor growth, metastasis, treatment resistance, and relapse. Mammosphere-forming breast cancer cells of human (MDA-MB-231, SKBR3) or murine (66.1, 410.4) origin of basal-type, Her-2 phenotype and/or with heightened metastatic capacity upregulate expression of both EP4 and COX-2 and are more tumorigenic compared to the bulk population. In contrast, luminal-type or non-metastatic counterparts (MCF7, 410, 67) do not increase COX-2 and EP4 expression in mammosphere culture. Treatment of mammosphere-forming cells with EP4 inhibitors (RQ-15986, AH23848, Frondoside A) or EP4 gene silencing, but not with a COX inhibitor (Indomethacin) reduces both mammosphere-forming capacity and the expression of phenotypic markers (CD44hi/CD24low, aldehyde dehydrogenase) of breast cancer stem cells. Finally, an orally delivered EP4 antagonist (RQ-08) reduces the tumor-initiating capacity and markedly inhibits both the size of tumors arising from transplantation of mammosphere-forming cells and phenotypic markers of stem cells in vivo. These studies support the continued investigation of EP4 as a potential therapeutic target and provide new insight regarding the role of EP4 in supporting a breast cancer stem cell/tumor-initiating phenotype.

Frondoside A, a major triterpene glycoside from North Atlantic commercially harvested sea cucumber Cucumaria frondosa, possesses strong immunomodulatory properties in subtoxic doses. Frondoside A stimulates lysosomal activity of mouse macrophages in vivo at a maximal effective stimulatory dose of 0.2 microg per mouse and is maintained over 10 days. This glycoside also shows a 30% stimulation of lysosomal activity in mouse macrophages in vitro at concentrations of 0.1-0.38 microg/mL. Frondoside A enhances macrophage phagocytosis of the bacterium Staphylococcus aureus in vitro at a maximal effective concentration of 0.001 microg/mL. Frondoside A stimulates reactive oxygen species formation in macrophages in vitro at a maximal effective concentration of 0.001 microg/mL. Frondoside A stimulates an increase in the number of antibody plaque-forming cells (normally B-cells in spleen) in vivo with a maximal stimulatory effect at a concentration of 0.2 microg per mouse (stimulatory index, 1.86). Frondoside A has a weak effect upon immunoglobulin (Ig) M production after immunization with sheep erythrocytes in mice. Frondoside A does not stimulate Ig production in mice and does not significantly enhance the ovalbumin-stimulated IgM and IgG antibody levels in ovalbumin-immunized mice. Hence frondoside A is an immunostimulant of cell-based immunity including phagocytosis without a significant effect on amplification of humoral immune activity or adjuvant properties. Therefore, frondoside A may provide curative and/or preventive treatment options against diseases wherein a depleted immune status contributes to the pathological processes.