Assessment of potential anti-cancer stem cell activity of marine algal compounds using an in vitro mammosphere assay

Abstract

BackgroundThe cancer stem cell (CSC) theory proposes that tumours arise from and are sustained by a subpopulation of cells with both cancer and stem cell properties. One of the key hallmarks of CSCs is the ability to grow anchorage-independently under serum-free culture conditions resulting in the formation of tumourspheres. It has further been reported that these cells are resistant to traditional chemotherapeutic agents.MethodsIn this study, the tumoursphere assay was validated in MCF-7 cells and used to screen novel marine algal compounds for potential anti-cancer stem cell (CSC) activity in vitro.ResultsMCF-7 breast cancer cells were observed to generate tumourspheres or mammospheres after 3-5 days growth in anchorage-independent conditions and an apparent enrichment in potential CSCs was observed by an increase in the proportion of CD44high/CD24low marker-bearing cells and Oct4 expression compared to those in the bulk population grown in regular adherent conditions. Using this assay, a set of algal metabolites was screened for the ability to inhibit mammosphere development as a measure of potential anti-CSC activity. We report that the polyhalogenated monoterpene stereoisomers RU017 and RU018 isolated from the red alga Plocamium cornutum, both of which displayed no cytotoxicity against either adherent MCF-7 breast cancer or MCF-12A non-transformed breast epithelial cells, were able to prevent MCF-7 mammosphere formation in vitro. On the other hand, neither the brown algal carotenoid fucoxanthin nor the chemotherapeutic paclitaxel, both of which were toxic to adherent MCF-7 and MCF-12A cells, were able to inhibit mammosphere formation. In fact, pre-treatment with paclitaxel appeared to enhance mammosphere formation and development, a finding which is consistent with the reported resistance of CSCs to traditional chemotherapeutic agents.ConclusionDue to the proposed clinical significance of CSC in terms of tumour initiation and metastasis, the identification of agents able to inhibit this subpopulation has clinical significance.

Vitamin D compounds reduce mammosphere formation and decrease expression of putative stem cell markers in breast cancer

“…The shapes and MFE of MCF10A were unchanged with treatment from vitamin D compounds supporting the notion that these compounds do not significantly affect normal mammary cells. Although the change from irregular spheres to more round spheres has not traditionally been linked to stem cells phenotype, it has recently been reported with the chemotherapeutic drug, paclitaxel, in MCF-7 mammospheres (36). The overall effects on mammospheres indicate that treatment with vitamin D compounds could alter the characteristics of the stem cell population to that of a less malignant cell type.…”

Novel insights into ion channels in cancer stem cells (Review)

“…The novel concept of CSCs was introduced in the late 1990s, and numerous research efforts have aimed to elucidate its role over the past decades (72,73). This concept may influence all approaches of cancer biology, since CSCs have an important role in tumorigenesis, drug resistance (74,75), invasion, metastasis and recurrence. The function of CSCs is predominantly regulated by microenvironmental factors that provide an adaptive landscape for relapsed tumor cells (76)(77)(78).…”

Isolation, Characterization and Antiproliferative Activity of New Metabolites from the South African Endemic Red Algal Species Laurencia alfredensis

“…The antiproliferative effects of the compounds were assessed using the WST-1 assay (Sigma-Aldrich, Johannesburg, South Africa) as previously described [ 35 , 36 ]. Briefly, cells were seeded at a density of 6000 cells per well into 96-well plates and incubated overnight, followed by treatment with a range of concentrations (0.32, 1.6, 8, 40, 200 and 1000 μM) of the compounds or dimethyl sulfoxide (DMSO) vehicle control (0.02% v / v DMSO) for 96 h. Thereafter 2.5 µL of WST-1 Cell Proliferation Reagent was added per well and the absorbance at 450 nm after 8 h recorded using a Synergy Mx spectrophotometer (BioTek).…”