Selective Cytotoxicity and Combined Effects of Camptothecin or Paclitaxel with Sodium-R-Alpha Lipoate on A549 Human Non-Small Cell Lung Cancer Cells

Nonsmall cell lung cancer (NSCLC) is the most common type of lung cancer and remains the deadliest form of cancer in the United States and worldwide. New therapies are highly sought after to improve outcome. The effect of sodium-R-alpha lipoate on camptothecin- and paclitaxel-induced cytotoxicity was evaluated on A549 NSCLC and BEAS-2B “normal” lung epithelial cells. Combination indices (CI) and dose reduction indices (DRI) were investigated by studying the cytotoxicity of sodium-R-alpha lipoate (0–16 mM), camptothecin (0–25 nM) and paclitaxel (0–0.06 nM) alone and in combination. 3-(4,5-dimethylthiazol-2-Yl)-2,5-diphenyltetrazolium-bromide (MTT) was used to assess cytotoxicity. The combinational cytotoxic effects of sodium-R-alpha lipoate with camptothecin or paclitaxel were analyzed using a simulation of dose effects (CompuSyn® 3.01). The effects of sodium-R-alpha lipoate on camptothecin- and paclitaxel-induced cytotoxicity varied based on concentrations and treatment times. It was found that sodium-R-alpha lipoate wasn't cytotoxic toward BEAS-2B cells at any of the concentrations tested. For A549 cells, CIs (additive (CI = 1); synergistic (CI < 1); antagonistic (CI < 1)] were lower and DRIs were higher for the camptothecin/sodium-R-alpha-lipoate combination (CI = ～0.17–1.5; DRI = ～2.2–22.6) than the paclitaxel/sodium-R-alpha-lipoate combination (CI = ～0.8–9.9; DRI = ～0.10–5.8) suggesting that the camptothecin regimen was synergistic and that the addition of sodium-R-alpha lipoate was important for reducing the camptothecin dose and potential for adverse effects.