Mitochondrial respiration - an important therapeutic target in melanoma

The importance of mitochondria as oxygen sensors as well as producers of ATP and reactive oxygen species (ROS) has recently become a focal point of cancer research. However, in the case of melanoma, little information is available to what extent cellular bioenergetics processes contribute to the progression of the disease and related to it, whether oxidative phosphorylation (OXPHOS) has a prominent role in advanced melanoma. In this study we demonstrate that compared to melanocytes, metastatic melanoma cells have elevated levels of OXPHOS. Furthermore, treating metastatic melanoma cells with the drug, Elesclomol, which induces cancer cell apoptosis through oxidative stress, we document by way of stable isotope labeling with amino acids in cell culture (SILAC) that proteins participating in OXPHOS are downregulated. We also provide evidence that melanoma cells with high levels of glycolysis are more resistant to Elesclomol. We further show that Elesclomol upregulates hypoxia inducible factor 1-α (HIF-1α), and that prolonged exposure of melanoma cells to this drug leads to selection of melanoma cells with high levels of glycolysis. Taken together, our findings suggest that molecular targeting of OXPHOS may have efficacy for advanced melanoma. © 2012 Barbi de Moura et al

HO-1, TACO-1, and HIF-1α expression in Elesclomol-treated melanoma cells.

<p>(<b>A</b>) Whole-cell (WC), (<b>B</b>) mitochondrial and WC, and (<b>C</b>) nuclear (Nu) and cytoplasmic (Cy) lysates, prepared from WM1158 metastatic melanoma cells following treatment with increasing doses of Elesclomol (ELM). Controls were WM1158 melanoma cells that received the drug vehicle DMSO, or no treatment (no tx). The blots were probed with antibody to HO-1, TACO-1, HIF-1α, or α-tubulin, which served as loading control. LDH5 was used as a cytoplasmic protein control.</p

Basal OCR in relation to the ECAR in short-term cultures of human melanocytes, and primary and metastatic melanoma cell lines.

<p>Depicted are HEMs (red symbol), primary (green symbol) and metastatic melanoma cell lines (blue symbol), and two Vemurafenib-resistant melanoma cell lines (dark blue symbol). The two melanoma cell lines derived from tumors of a same patient are depicted by open circles.</p

Phase-contrast analysis of Elesclomol-treated melanoma cells.

<p>Phase-contrast images of a pigmented (WM852) and an amelanotic (C32) melanoma cell line treated for 12 hr with drug vehicle (DMSO), or a low (20 nM), or high dose (500 nM) of Elesclomol (ELM). (Images were captured at 20× magnification).</p

Selection of Elesclomol-resistant cells.

<p>(<b>A</b>) Following 60 days of every second day treatment of WM983-B cells with Elesclomol, a bioenergetics analysis was performed to measure the effects of continuous Elesclomol treatment upon OXPHOS and glycolysis. The arrow points to increased baseline ECAR in response to Elesclomol treatment for 60 days. (<b>B</b>) Measurement of steady-state ATP levels in WM983-B cells treated for 60 days with Elesclomol or only PBS.</p

Proteins from each of the Top 3 most significantly dysregulated pathways identified by SILAC and subsequent IPA-Tox analysis of WM1158 cells treated with Elesclomol (E) or the drug vehicle DMSO (V).

<p>u - proteins identified by unique peptides; c - proteins identified by common peptides.</p

Analysis of ρ0 melanoma cells.

<p>(<b>A</b>) Equal amounts of DNA isolated from each cell line (parental; ρ0) were analyzed by qPCR for a small (0.22 kb) mitochondrial sequence (primer set 14,620/14,841), a large (8.9 kb) mitochondrial sequence (primer set 5,999/14,841), and a 12.2 kb DNA polymerase β primer set serving as a positive control for nuclear gene expression <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0040690#pone.0040690-Qian1" target="_blank">[25]</a>. qPCR samples not containing DNA or primer sets served as negative controls. (<b>B</b>) Pharmacologic profile of OCR and ECAR of parental (solid circles) and ρ0 (open circles) WM1158 melanoma cell lines as determined by the Seahorse X24 analyzer. (<b>C</b>) Three<b>-</b>day MTT proliferation analysis of WM1158, WM983-B, and WM852 ρ0 and parental cells (no ethidium bromide, EtBr).</p

Bioenergetics analysis of melanoma cells.

<p>(<b>A</b>) Seahorse XF24 Flux analysis of Lu1205 and WM983-B metastatic melanoma cells treated for 2 hr with increasing doses of Elesclomol salt (ELM) (20, 60, 100, or 200 nM). After baseline OCR and ECAR determination, the cells were treated with oligomycin (O), FCCP (F), rotenone (R), or 2-deoxyglycose (2DG). Melanoma cells sensitive to Elesclomol, which had low reserve capacity and could not upregulate oxygen consumption in response to FCCP, are indicated by arrows. (<b>B</b>) Seahorse XF24 analysis of WM1158 cells and Vemurafenib-resistant melanoma cell lines (TPF10-741; TPF11-43) treated for 2 hr with 200 nM of Elesclomol salt (ELM) or only PBS. (C) Analysis of mitochondrial membrane potential in WM983-A and WM983-B using TMRM fluorescence following increasing doses of Elesclomol salt (20, 60, 100, 200, 500 nM) in the presence or absence of copper (5 µM).</p

Top 5 most significantly dysregulated pathways identified by SILAC and subsequent IPA-Tox analysis.

<p>WM1158 cells treated for 4 hr with Elesclomol (500 nM) or only DMSO.</p