In vitro characterization of next generation photosensitiser Photosoft™ for photodynamic therapy in ovarian cancer

Chen Y1,2 and Stephens AN1,2,3

  1. Hudson Institute of Medical Research, Australia.
  2. Molecular and Translational Biosciences, Monash University, Australia.
  3. Invion Ltd, Australia.

Ovarian cancers have >70% 5-year mortality, and patients almost universally develop recurrent, chemo-resistant disease; new therapies are urgently needed. Photodynamic therapy (PDT), combining a photo-sensitising compound and light to generate destructive reactive oxygen species (ROS), is an alternative, FDA-approved clinical strategy for direct tumour ablation. We have commenced in vitro characterisation of PhotosoftTM, a photosensitiser with improved safety profile and enhanced cytotoxic capacity, for development as an ovarian cancer therapy. The spectral characteristics and generation of reactive oxygen species (ROS) by Photosoft were examined in vitro. Cellular uptake and clearance were monitored using fluorescence (ex405, em650) in multiple ovarian cancer cell lines (2D and 3D culture), with sub-cellular localization determined using specific organelle staining (ER, Golgi, lysosomes, mitochondria). Cell death and IC90 were determined following exposure to red light (652nm). The mechanism of induced cell death was determined using antibody arrays. Photosoft excitation/emission spectra were characteristic of chlorin-based photosensitisers, and light-induced activation at 652nm efficiently produced ROS. Uptake into ovarian cancer cells was time and concentration dependent, with discrete localization to lysosomes and the ER. In the absence of activation, Photosoft remained non-toxic even at high concentrations (up to 100mg/ml); following activation, rapid cell death occurred dependent on time, concentration and light energy. Both caspase-dependent and –independent cell death were observed, dependent on total light energy delivered. Moreover, Photosoft penetrated effectively into 3D spheroids to induce cell death, suggesting its suitability for ablation of established, solid tumours. Our data demonstrate that Photosoft efficiently produces ROS to destroy tumour cells in vitro, and that modulation of light energy can be used to control the mechanism of induced cell death. Further work will focus on preclinical trials of Photosoft as an indication for chemoresistant, solid ovarian tumours.