Abstract B38: Photochemical internalisation for the local delivery of chemotherapy in prostate cancer
Authors: MARTINEZ DE PINILLOS ALEJANDRA , DONDI RUGGERO , WANG L. , YAGHINI ELNAZ , WOODHAMS JOSEPHINE H. , MOORE CAROLINE M. , EGGLESTON IAN M. , MACROBERT ALEXANDER J. 
Published: May 2016

• Introduction

Prostate cancer is fifth leading cause of death from cancer in men. Although chemotherapy is the gold standard treatment for a wide range of cancers including the prostate, there are several limitations (systemic toxicity, multidrug resistance or inadequate cellular delivery) and there is growing interest in developing focal therapies when appropriate.

Photochemical Internalisation (PCI) is a focal light-triggered drug delivery system, which combines low dose Photodynamic Therapy (PDT) with chemotherapy agents to enhance delivery of the agents to their specific subcellular target. PCI is particularly suitable for agents prone to endolysosomal sequestration, thererefore the photosensitisers (PS) used for PCI localise in endolysosomal membranes which upon visible light exposure leads to the production of reactive oxygen species (ROS), causing photooxidative disruption of membranes and subsequent cytosolic release of the entrapped agents. These will then reach their intended targets more efficiently, improving efficacy and potentially reducing the therapeutic dose.

The present project focuses on the use of PCI to deliver Saporin, a ribosome inactivating (RIP) type 1 protein. RIPs are able to cause permanent damage to eukaryotic ribosomes; however, despite its intrinsic high toxicity, endolysosomal sequestration impairs its ability to inhibit protein synthesis.

• Aim

To assess the potential of PCI for enhanced delivery of Saporin in human and rat prostate cancer cells. In addition, a CXCR4-targeted peptide-PS conjugate was tested.

• Materials & Methods

Porphyrin and chlorin-based PS were co-administered with Saporin. Cells were incubated for 24hrs with different drug combinations then exposed to light, and cell viability was measured at different time points post illumination using the MTT assay. Subcellular location of Saporin and PS were observed using confocal microscopy.

• Results

PCI resulted in a synergistic effect between sub-lethal PDT and Saporin. Despite minimal cell kill when the toxin or PS were administered alone, PCI delivery enhanced Saporin cytotoxicity using only 20pM in the rat Mat-LyLu and 2nM in PC3 human cell lines. PCI elicits up to 1.5-fold higher efficacy in cell kill vs. PDT 48hrs after light treatment and 3.5-fold higher 96hrs after light treatment in rat and human prostate cancer cells accordingly (p&lt;0.05). In addition, PS doses were reduced by 20 times when targeted against CXCR4 receptor (overexpressed in prostate cancer among others). This resulted in 75% reduction of cell viability compared to 79% using the 20-fold higher dose of untargeted PS. Moreover, a 3-fold higher efficacy in cell kill of PCI vs. PDT 96hrs after light treatment in human cells was observed.

Intracellular redistribution following endolysosomal release of fluorescently labelled Saporin and PS following illumination was confirmed with confocal microscopy.

• Conclusions

These results demonstrate the potential of PCI for prostate cancer treatment in vitro and in vivo tumour experiments are in progress.

Citation Format: ALEJANDRA MARTINEZ DE PINILLOS, RUGGERO DONDI, L. WANG, ELNAZ YAGHINI, JOSEPHINE H. WOODHAMS, CAROLINE M. MOORE, IAN M. EGGLESTON, ALEXANDER J. MACROBERT. Photochemical internalisation for the local delivery of chemotherapy in prostate cancer. [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2015 Nov 5-9; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2015;14(12 Suppl 2):Abstract nr B38.