Expression of the cancer stem cell marker OCT4 is associated with worse prognosis and survival in cutaneous melanoma

Generation of 3D melanoma models using an assembloid-based approach

While 3D tumor models have greatly evolved over the past years, there is still a strong requirement for more biosimilar models which are capable of recapitulating cellular crosstalk within the tumor microenvironment while equally displaying representative levels of tumor aggressiveness and invasion. Herein, we disclose an assembloid melanoma model based on the fusion of individual stromal multicellular spheroids (MCSs). In contrast to more traditional tumor models, we show that it is possible to develop self-organizing, heterotypic melanoma models where tumor cells present stem-cell like features like up-regulated pluripotency master regulators SOX2, POU5F1 and NANOG. Additionally, these assembloids display high levels of invasiveness while embedded in 3D matrices as evidenced by stromal cell promotion of melanoma cell invasion via metalloproteinase production. Furthermore, sensitivity to anticancer drug doxorubicin was demonstrated for the melanoma assembloid model. These findings suggest that melanoma assembloids may play a significant role in the field of 3D cancer models as they more closely mimic the tumor microenvironment when compared to more traditional MCSs, opening the doors to a better understanding of the role of tumor microenvironment in supporting tumor progression. STATEMENT OF SIGNIFICANCE: The development of complex 3D tumor models that better recapitulate the tumor microenvironment is crucial for both an improved comprehension of intercellular crosstalk and for more efficient drug screening. We have herein developed a self-organizing heterotypic assembloid-based melanoma model capable of closely mimicking the tumor microenvironment. Key features recapitulated were the preservation of cancer cell stemness, sensitivity to anti-cancer agents and tumor cell invasion promoted by stromal cells. The approach of pre-establishing distinct stromal domains for subsequent combination into more complex tumor constructs provides a route for developing superior tumor models with a higher degree of similarity to native cancer tissues.

Reactive Oxygen Species Regulation of Chemoresistance and Metastatic Capacity of Melanoma: Role of the Cancer Stem Cell Marker CD271

BRAF mutations are present in 30-50% of cases of cutaneous melanoma, and treatment with selective BRAF and MEK inhibitors has been introduced. However, the development of resistance to these drugs often occurs. Chemo-resistant melanoma cells show increased expression of CD271, a stem cell marker that features increased migration. Concordantly, resistance to the selective inhibitor of oncogenic BRAFV600E/K, vemurafenib, is mediated by the increased expression of CD271. It has recently been shown that the BRAF pathway leads to an overexpression of the NADPH oxidase Nox4, which produces reactive oxygen species (ROS). Here, we examined in vitro how Nox-derived ROS in BRAF-mutated melanoma cells regulates their drug sensitivity and metastatic potential. We demonstrated that DPI, a Nox inhibitor, reduced the resistance of a melanoma cell line (SK-MEL-28) and a primary culture derived from a BRAFV600E-mutated biopsy to vemurafenib. DPI treatment affected the expression of CD271 and the ERK and Akt signaling pathways, leading to a drop in epithelial-mesenchymal transition (EMT), which undoubtedly promotes an invasive phenotype in melanoma. More importantly, the scratch test demonstrated the efficacy of the Nox inhibitor (DPI) in blocking migration, supporting its use to counteract drug resistance and thus cell invasion and metastasis in BRAF-mutated melanoma.

Methods for assessing the effect of microRNA on stemness genes

According to the latest concepts, for micrometastasis to develop into macrometastasis, differentiated cancer cells must revert to a dedifferentiated state. Activation of stemness genes plays a key role in this transition. Suppression of stemness gene expression using microRNAs can become the basis for the development of effective anti-metastatic drugs. This article provides an overview of the existing methods for assessing the effect of microRNAs on stemness genes and cancer cell dedifferentiation.

Dexamethasone Promotes a Stem-Like Phenotype in Human Melanoma Cells via Tryptophan 2,3 Dioxygenase

In addition to its well-established immunosuppressive actions, tryptophan 2,3-dioxygenase (TDO) appears to elicit direct effects on tumor cell function. Although TDO has been associated with cancer stemness, its involvement in melanoma stem cell biology remains largely unknown. Since we showed that by upregulating TDO, dexamethasone (dex) promotes proliferation and migration of SK-Mel-28 human melanoma cells, we sought to investigate dex effects on melanoma spherogenesis and stemness, and whether these events are mediated by TDO. We demonstrate here that dex significantly upregulates TDO in A375, a more aggressive melanoma cell line, confirming that dex effects are not limited to SK-Mel-28 cells. Moreover, dex stimulates spherogenesis of both cell lines, which is mediated by TDO, evident by its suppression with 680C91, a TDO inhibitor. The formed melanospheres appear to be enriched with embryonic stem cell marker mRNAs, the expression of which is potentiated by dex. Expression of cancer stem cell markers (CD133, CD44, ganglioside GD2) was significantly increased in A375 spheres, as detected by flow cytometry. Taken together, our results suggest that TDO could represent a promising target in the management of melanoma and that dex, routinely used as a co-medication also in advanced melanoma, may stimulate melanoma cell function/tumor-supporting properties, a rather debilitating and undesired side effect.