Apoptosis induced by hematoporphyrin monomethyl ether combined with He–Ne laser irradiation in vitro on canine breast cancer cells

Hematoporphyrin monomethyl ether (HMME) is a novel and promising porphyrin-related photosensitizer for photodynamic therapy (PDT). The aim of this study was to investigate HMME-induced apoptosis in CHMm cells, a canine breast cancer cell line. CHMm cells were treated with HMME and a He–Ne laser at a wavelength of 632.8 nm. Cell viability was determined using the trypan blue exclusion assay. Apoptosis was analyzed using Hoechst 33258, AO/EB, Annexin V/PI staining and single-cell gel electrophoresis (comet assay). Apoptotic morphology was further confirmed by Giemsa staining and transmission electron microscopy. Rates of apoptosis increased following PDT–HMME treatment in a time-dependent manner. Taken together, these results demonstrated that apoptosis plays a major role in PDT–HMME-induced reduction in the viability of CHMm cells.