The prognosis of metastatic melanoma is very poor, due to the development of drug resistance.,Cancer stem cells (CSCs) may play a crucial role in this mechanism, contributing to disease relapse.,We first characterized CSCs in melanoma cell lines.,We observed that A375 (but not BLM) cells are able to form melanospheres and show CSCs traits: expression of the pluripotency markers SOX2 and KLF4, higher invasiveness and tumor formation capability in vivo with respect to parental adherent cells.,We also showed that a subpopulation of autofluorescent cells expressing the ABCG2 stem cell marker is present in the A375 spheroid culture.,Based on these data, we investigated whether δ-TT might target melanoma CSCs.,We demonstrated that melanoma cells escaping the antitumor activity of δ-TT are completely devoid of the ability to form melanospheres.,In contrast, cells that escaped vemurafenib treatment show a higher ability to form melanospheres than control cells. δ-TT also induced disaggregation of A375 melanospheres and reduced the spheroidogenic ability of sphere-derived cells, reducing the expression of the ABCG2 marker.,These data demonstrate that δ-TT exerts its antitumor activity by targeting the CSC subpopulation of A375 melanoma cells and might represent a novel chemopreventive/therapeutic strategy against melanoma.
Tumor blood vessels play an important role in tumor progression and metastasis.,It has been reported that tumor endothelial cells (TECs) exhibit highly angiogenic phenotypes compared with those of normal endothelial cells (NECs).,TECs show higher proliferative and migratory abilities than those NECs, together with upregulation of vascular endothelial growth factor (VEGF) and VEGF receptor 2 (VEGFR2).,Furthermore, compared with NECs, stem cell markers such as Sca-1, CD90, and multidrug resistance 1 are upregulated in TECs, suggesting that stem-like cells exist in tumor blood vessels.,In this study, to reveal the biological role of stem-like TECs, we analyzed expression of the stem cell marker aldehyde dehydrogenase (ALDH) in TECs and characterized ALDHhigh TECs.,TECs and NECs were isolated from melanoma-xenografted nude mice and normal dermis, respectively.,ALDH mRNA expression and activity were higher in TECs than those in NECs.,Next, ALDHhigh/low TECs were isolated by fluorescence-activated cell sorting to compare their characteristics.,Compared with ALDHlow TECs, ALDHhigh TECs formed more tubes on Matrigel-coated plates and sustained the tubular networks longer.,Furthermore, VEGFR2 expression was higher in ALDHhigh TECs than that in ALDHlow TECs.,In addition, ALDH was expressed in the tumor blood vessels of in vivo mouse models of melanoma and oral carcinoma, but not in normal blood vessels.,These findings indicate that ALDHhigh TECs exhibit an angiogenic phenotype.,Stem-like TECs may have an essential role in tumor angiogenesis.