Abstract
Cancer resistance is a primary concern in cancer treatment, and developing an effective
modality or strategy to improve therapeutic outcomes is imperative. Photodynamic therapy (PDT) is
a treatment modality that targets the tumor with a photoactive molecule and light for the specific
destruction of cancer cells. Photobiomodulation (PBM) is a light exposure of cells to energize their
biomolecules to respond to therapy. In the present study, we used PBM to mediate and improve
the anti-tumor efficacy of zinc phthalocyanine tetrasulfonic acid (ZnPcS4)-PDT on resistant MCF-
7 breast cancer cells and explore molecular changes associated with cell death. Different laser
irradiation models were used for PBM and PDT combination. The combined treatment demonstrated
an additive effect on the viability and Annexin-V/PI-staining cell death assessed through MTT
assay and mitochondrial release of cytochrome c. Rhodamine (Rh123) showed increased affinity to
mitochondrial disruption of the strategic treatment with PBM and PDT. Results from the autophagy
assay indicate an interplay between the mitochondrial and autophagic proteins. These findings were
indicative that PBM might improve the anti-tumor of PDT by inducing autophagy in resistant MCF-7
breast cancer cells that evade apoptosis.