MTT assays allow quick and reliable measurement of the response of human tumour cells to photodynamic therapy

MCF-7 and HT-29 cell lines were selected as a reliable model to examine the possible parameters affecting the sensitivity of tumour cells to photodynamic therapy (PDT) using a dye-laser at 630 nm. The chemical composition of haematoporphyrin derivative (HPD) was determined by high-performance liquid chromatography (HPLC) analysis and was in agreement with reported values. MTT assays were performed to assess the time-dependency of PDT and the influence of the output power and light fluence. The results showed a maximal cytotoxicity 48 h after photoirradiation. The output power (1 or 2 W) did not significantly affect the cytoxicity when the fluence was constant (20 J/cm 2). However, an increase in fluence (10–40 J/cm 2) led to a significant enhancement of cytotoxicity until maximal values were reached (30–40 J/cm 2). A further increase in fluence (50 J/cm 2) proved to induce a fall-off in cytotoxicity related to the intense photobleaching of HPD.