Parthenolide reduces the frequency of ABCB5-positive cells and clonogenic capacity of melanoma cells from anchorage independent melanospheres

Abstract

Growing evidence suggests that the cancer stem cell phenotype in melanoma is dynamically regulated. Therefore, effective therapies have to target simultaneously bulk tumor cells and melanoma stem-like cells. The aim of the present study was to investigate the effects of parthenolide on heterogeneous cancer cell populations from anchorage-independent melanospheres. Cells derived from nodular melanoma specimens were grown under serum-free sphere-forming conditions. The effects of parthenolide on cellular viability, immunophenotype and self-renewing capacity were assessed with cells from dissociated melanospheres. Its penetration capacity was evaluated with intact melanospheres. In melanoma cells that survived treatment with parthenolide, a different immunophenotype than that in untreated control was found. The frequency of cells expressing the ABCB5 transporter was markedly reduced. Most importantly, melanoma cells that survived parthenolide treatment lost their self-renewing capacity. Significantly lower influence of drug on cellular viability and frequency of ABCB5-positive cells was observed in intact melanospheres. The potential clinical significance of our findings is based on the ability of parthenolide to affect both bulk and melanoma stem-like cells with clonogenic capacity and high expression of the ABCB5 transporter. Its low penetration capacity, however, may limit its action to easily accessible melanoma cells, either circulating in the blood or those in the vicinity to blood vessels within the tumor. Because of limited penetration capacity of parthenolide, this drug should be further explored as a part of multimodal therapies rather than as a stand-alone therapeutic agent.

Phenotypic diversity of patient-derived melanoma populations in stem cell medium

“…For many markers including CD133, Oct3/4, gp100, and Melan-A, an extensive phenotypic diversity was observed between populations derived from different specimens. Therefore, the present results and those obtained previously 14,15,23,25 suggest that the marker expression profile seems to be an intrinsic characteristics of a particular melanoma sample. No correlation between the frequency of cells expressing a given marker and the capability of forming melanospheres was found.…”

“…Expression of Oct3/4 also displayed variable pattern. The present results and those obtained previously 23,25 revealed a high immunophenotypic heterogeneity within cell populations cultured in SCM and a remarkable variability among cultures derived from different NM specimens. As all populations exerted unlimited proliferative potential, but the cells expressing CD133, CD90, CD20, or Tra1-81 were undetectable in at least one of investigated populations, it could be speculated that this unlimited growth was not dependent on the presence of cells expressing any of those antigens.…”

“…Melanoma specimens classified histopathologically as clinical stages III and IV and various TNM staging 23,25 were obtained during surgical procedures. The study was approved by Ethical Commission of Medical University of Lodz.…”

“…Results of this analysis are shown in Table 1 and in our previous reports. 23,25 From markers considered previously as cancer stem cell markers, only CD133 seemed to correlate well with the ability to form melanospheres. The populations containing CD133-positive cells exerted a high melanosphere-forming capacity, whereas those lacking CD133-positive cells formed either aggregates (DMBC12) or single-cell culture (DMBC9) (Figure 2).…”

“…23,25 Using transcriptome analyses we have identified MITF and DKK1 as key regulators of microenvironment-dependent phenotypic heterogeneity in vitro. 24 We observed that the ability to form melanospheres in SCM depends on the sample, and cell aggregates and single-cell culture can arise instead of melanospheres.…”