PO-010 Dual chemotherapy and photodynamic therapy: a synergistic strategy to improve cancer treatment

IntroductionPhotodynamic therapy (PDT) is a clinical-approved option in several diseases characterised by uncontrolled cell proliferation, as cancer. PDT is recognised as a minimally invasive and toxic treatment. It is based on the administration of light activatable molecule known as photosensitizer (PS). After irradiation, a photochemical reaction between the PS and molecular oxygen leads to the generation of reactive oxygen species (ROS), which results in tumour regression.Nowadays different strategies are being introduced in order to enhance PDT effectiveness, such as combination of PDT with chemotherapy or improvement of PS features.Material and methodsA new combined PDT-chemotherapy comprising two drugs widespread in clinical research -the hydrophobic Zinc(II)-phthalocyanine (ZnPc) as PS and the common chemotherapeutic agent doxorubicin (DOX)- was tested in tumour cell lines and primary cells from patients affected by metastatic breast cancer. ZnPc was incorporated into nanoliposomes to increase its solubility and uptake into tumoral cells. This dual-therapy was also assayed in vivo (intravenously administrated) in a breast cancer xenograft model following tumour growth by luciferase activity.Results and discussionsMTT cytotoxicity assay showed that combination of both therapies remarkably increases the effectiveness of the treatment by inducing a synergistic cell death effect when compared to DOX or ZnPc monotherapy. In addition, annexin-V detection by flow cytometry, analysis of active caspase-3 and cytochrome c by immunofluorescence and time-lapse videomicroscopy corroborated a fine-tunable effect depending on light dose, leading to apoptotic or necrotic mechanism of cell death.Subcellular location visualised by fluorescence microscopy confirmed internalisation of both drugs. Using DCFH-DA probe, we demonstrate that a significant higher ROS generation into cells was the main cause of the synergistic effect of this combined treatment. Further, mammosphere formation efficiency assay (MFE) showed a reduced breast cancer stem cell activity in established cell line and primary cells obtained from patients, even using DOX at much lower concentration than clinical level. Finally, studies in human breast cancer xenografts indicated a high efficiency also in vivo.ConclusionAll these results provide novel and valuable information that contribute to consider chemophototherapy as a promising tool in current antitumoral treatments, potentially overcoming resis