Aldehyde dehydrogenase isozymes: markers of cancer stem cells in human melanoma

Oxidative Stress-Related Mechanisms in Melanoma and in the Acquired Resistance to Targeted Therapies

Melanoma is a highly aggressive cancer with the poorest prognosis, representing the deadliest form of skin cancer. Activating mutations in BRAF are the most frequent genetic alterations, present in approximately 50% of all melanoma cases. The use of specific inhibitors towards mutant BRAF variants and MEK, a downstream signaling target of BRAF in the MAPK pathway, has significantly improved progression-free and overall survival in advanced melanoma patients carrying BRAF mutations. Nevertheless, despite these improvements, resistance still develops within the first year of therapy in around 50% of patients, which is a significant problem in managing BRAF-mutated advanced melanoma. Understanding these mechanisms is one of the mainstreams of the research on BRAFi/MEKi acquired resistance. Both genetic and epigenetic mechanisms have been described. Moreover, in recent years, oxidative stress has emerged as another major force involved in all the phases of melanoma development, from initiation to progression until the onsets of the metastatic phenotype and chemoresistance, and has thus become a target for therapy. In the present review, we discuss the current knowledge on oxidative stress and its signaling in melanoma, as well as the oxidative stress-related mechanisms in the acquired resistance to targeted therapies.

Isolation and Characterization of a Distinct Subpopulation from the WM115 Cell Line That Resembles In Vitro Properties of Melanoma Cancer Stem Cells

Despite key advances in cancer therapies, malignant tumors, such as melanoma, continue to be one of the leading causes of mortality. Recent debate on whether cancer can originate from a tumor-initiating subpopulation has permeated oncology and stem cell research. It has been well established that primary and immortalized tumor cells consist of heterogeneous cell populations. The profound effect of tumor heterogeneity on tumor growth and drug resistance remains elusive, but it is highly likely that subpopulations of cancer cells have different capabilities of self-renewal and drug resistance. Discrepancies between excellent in vitro potency and efficacy and poor patient response have been observed on multiple cancer therapeutics. Although this observation can be attributed to many factors, a better understanding of the contribution from subpopulations within a cancer will help bridge the gap between in vitro assay results and patient prognosis. To comprehend this impact, it is critical to isolate and characterize cancer subpopulations that possess higher growth and drug resistance properties so that novel therapeutics can be developed to eventually eradicate all cancer cells. In this article, we describe a method to enrich a subpopulation, CB4, from the melanoma cell line WM115. CB4 exhibited higher anchorage-independent growth, higher survival under serum starvation condition, and lower drug sensitivity to commonly used melanoma treatment compared with WM115. Details of functional properties and gene expression of CB4 compared with WM115 are reported. Our study demonstrates that it is feasible to isolate and enrich a subpopulation that exhibits higher growth capacity and treatment resistance from an immortalized tumor cell line.