Materials and Methods: KB and Hep2 cells ( oral and laryngeal squamous cell carcinoma cell lines) were used as PDT ‘targets’. m-THPC was added to exponentially growing cell cultures at concentrations between 0.5 and 4 µg/ml for 3 and 18 h. The cells were then subjected to 652 nm laser light to deliver between 1 and 4 J/cm2. After 24 h the proportion of cells remaining viable was determined using the MTT assay. Control cultures received either m-THPC or light treatment, but not both.
Result: A survival rate of 50% was found for KB cells incubated with 0.5 µg/ml m-THPC for 3 h, and given 2 J/cm2 light. Similar toxicity was obtained with the Hep2 cells, but only at a higher m-THPC concentration (1 µg/ml). However, it was possible to achieve only 10% survival with a higher dose of drug (1 µg/ml) for 18 h and with 1 J/cm2, although HEp2 cells were again notably less sensitive to PDT (ie, higher survival rate) compared with the KB cell line. Control experiments showed that both drug and light were required for any significant cytotoxicity to either cell line.
Conclusion: The extent of cell killing was found to be stringently dependent on the drug dose and exposure time and on the light applied, all of which could be modulated to produce very extensive toxicity in vitro and possibly improve the clinical efficacy of PDT for oral cancer in vivo.