title: A combination of photodynamic therapy and chemotherapy displays a differential cytotoxic effect on human metastatic melanoma cells.
abstract: BACKGROUND
  Cutaneous melanoma represents the most lethal form of skin cancer and remains refractory to current therapies. Failure of treatment has been attributed to the over-expression of ABC transporters which efflux the drugs, below their cytotoxic threshold within cells. Therefore, this study set to investigate; the efficacy of a combinatorial approach comprising chemotherapy (Dacarbazine) and photodynamic therapy (PDT) to overcome resistance in pigmented and unpigmented metastatic melanoma and potentially identify resistant mechanisms.
  
  
  METHODS
  The cytotoxic effect of the chemotherapy, PDT and combination therapy treatment (Dacarbazine+PDT) was determined using a cell viability XTT assay. Thereafter, melanoma cells morphology, self-renewal capacity and ABCG2 protein expression, were determined using fluorescence microscopy, clonogenic assay, western blot and flow cytometry. All results were analyzed by t-test and ANOVA, followed by individual comparisons with post-tests.
  
  
  RESULTS
  This study describes possible synergism of PDT+DTIC in reducing melanoma cell viability in vitro. At 24h post-treatment, only the unpigmented melanomas were sensitive to DTIC treatment (20-25% death at 1.25mM). At 48h, a lethal dose of 50% was reached in these cells in contrast to the pigmented melanoma (20% at 48h). The same trend was observed with the combination therapy (DTIC+PDT) at both time points. Furthermore, complete morphological disruption could be observed upon PDT only and PDT+DTIC treatments. Moreover, PDT and DTIC+PDT suppressed the self-renewal capacity of both melanoma cell lines. No significant differences in ABCG2 protein expression was found at 24h post-treatment.
  
  
  CONCLUSIONS
  Overall, these results suggest that human melanomas remain heterogeneous in their phenotypes. Moreover, in our metastatic melanoma cells, ABCG2 transporters did not seem to be involved in resistance to therapies. Significantly though, a combinatorial approach of PDT and chemotherapy significantly decreases the self-renewal capacity of metastatic melanoma cells and could be a suggested adjunctive approach to post-resection treatment regimes.
authors.affiliation: Redox Laboratory, Level 6, Anatomy Building, Department of Human Biology, Faculty of Health Sciences, UCT Medical School, Observatory, 7925 Cape Town, South Africa.
authors.forename: Fa Nsole
authors.initials: FN
authors.lastname: Biteghe
authors.affiliation: Redox Laboratory, Level 6, Anatomy Building, Department of Human Biology, Faculty of Health Sciences, UCT Medical School, Observatory, 7925 Cape Town, South Africa. Electronic address: Lester.Davids@uct.ac.za.
authors.forename: L M
authors.initials: LM
authors.lastname: Davids
mesh_terms: D000873:Anthracenes; D000970:Antineoplastic Agents / Q000494:pharmacology / Q000627:therapeutic use*; D045744:Cell Line, Tumor; D003606:Dacarbazine / Q000627:therapeutic use; D006801:Humans; D008545:Melanoma / Q000188:drug therapy* / Q000473:pathology; D009362:Neoplasm Metastasis; D010569:Perylene / Q000031:analogs & derivatives / Q000627:therapeutic use; D010778:Photochemotherapy; D012878:Skin Neoplasms / Q000188:drug therapy* / Q000473:pathology
chemical_list: D000873:Anthracenes; D000970:Antineoplastic Agents; D010569:Perylene; D003606:Dacarbazine; C004965:hypericin
keywords: ABC transporters; Cutaneous melanoma; Dacarbazine; Photodynamic therapy