However, at the present, different levels of protein expression and distinct modulation of the enzymatic activity between ALAS2 and variants cannot be ruled out as possibilities. Treatment with 100 mM ALA, a positive control for PPIX accumulation, caused a similar cell death after light exposure to expression of the ZsGreen1 protein alone. In summary, the highest cell death was seen in light-treated HeLa cells expressing ZsGreen1 and either WT, HPVT, or R433K, in culture medium supplemented with 100 mM glycine. The total cell death was observed to be as high as 90% in the cells expressing both ZsGreen1 and R433K. This represents a substantial improvement upon the 26% cell death reported previously, and indicates that this approach, if carefully developed, may eventually find some clinical utility. Because ALAS2, especially highly stable and active variants of ALAS2, would be useful in the development of multiplex cancer treatments involving PDT, we experimented with combination PDT and drug treatments of HeLa cells. Paclitaxel is currently approved in the United States for the treatment of AIDS-related Kaposi sarcoma, breast cancer, non-small lung cell lung cancer, and ovarian cancer. Paclitaxel induces apoptosis in cancer cells by binding to tubulin and inhibiting the disassembly of microtubules, thereby resulting in the inhibition of cell division. As expected, paclitaxel did not affect PPIX accumulation, as CCG 50014 indicated by the similar mean PPIX fluorescence values between untreated and paclitaxel-treated cells. However, paclitaxel had an additive effect to PDT and increased cell death in all samples by 10�C25%. HeLa cells expressing R433K treated with paclitaxel exhibited the highest percentage of cell death. Ever since PDT was first shown to be able to elicit an immune response, many recent advances in PDT are aiming toward creating PDT-generated cancer vaccines. Using highly active and stable ALAS2 variants as part of a vaccine strategy for photosensitization may be useful for this vaccine approach. Further experiments, both in cell culture and live animals, are necessary to test for potential immune Bismuth Subsalicylate response stimulated by ALAS2-PDT.