Investigation of novel photosensitisers for photodynamic cancer therapy

THESIS 10291Photodynamic therapy (PDT) has developed over last century and is now becoming a more widely used medical tool having gained regulatory approval for the treatment of various diseases such as cancer and macular degeneration. It is based on photochemical reactions between light and tumour tissue with exogenous photosensitising agents (PS), most often porphyrins. Photochemical reactions lead to the conversion of molecular oxygen (3O2) into singlet oxygen (1O2) which is a key cytotoxic agent that damages cells

Transferrin conjugation does not increase the efficiency of liposomal Foscan during in vitro photodynamic therapy of oesophageal cancer

Photodynamic therapy (PDT) is based on the delivery of photocytotoxic agents to a target tissue, followed by irradiation. In order to increase the efficiency of PDT in oesophageal cancer therapy, polyethylene glycol (PEG)-grafted, transferrin (Tf)-conjugated liposome formulations of 5,10,15,20-tetra(m-hydroxyphenyl)chlorin (Foscan), a second-generation photosensitiser, were prepared. Expression of transferrin receptors (CD71) in the oesophageal cancer cell line, OE21, was confirmed by immunoblot and confocal laser scanning microscopy. The anti-proliferative effect of Foscan liposomes was evaluated and compared with plain formulations (i.e., without Tf) as well as with free drug. In addition, the intracellular accumulation was studied using high content analysis. Surprisingly, delivering Foscan by transferrin-conjugated PEG-liposomes to oesophageal cancer cells did not improve the photocytotoxicity or the intracellular accumulation of Foscan when compared to unmodified liposomes or indeed free photosensitiser. Tf-targeted drugs and drug delivery systems have shown improvedthe therapy of many cancers. Our study, however, did not corroborate these findings. If this is due to the tumour type, the choice of in vitro model or the delivery systems remains to be confirmed

High content screening as high quality assay for biological evaluation of photosensitizers in vitro.

A novel single step assay approach to screen a library of photdynamic therapy (PDT) compounds was developed. Utilizing high content analysis (HCA) technologies several robust cellular parameters were identified, which can be used to determine the phototoxic effects of porphyrin compounds which have been developed as potential anticancer agents directed against esophageal carcinoma. To demonstrate the proof of principle of this approach a small detailed study on five porphyrin based compounds was performed utilizing two relevant esophageal cancer cell lines (OE21 and SKGT-4). The measurable outputs from these early studies were then evaluated by performing a pilot screen using a set of 22 compounds. These data were evaluated and validated by performing comparative studies using a traditional colorimetric assay (MTT). The studies demonstrated that the HCS assay offers significant advantages over and above the currently used methods (directly related to the intracellular presence of the compounds by analysis of their integrated intensity and area within the cells). A high correlation was found between the high content screening (HCS) and MTT data. However, the HCS approach provides additional information that allows a better understanding of the behavior of these compounds when interacting at the cellular level. This is the first step towards an automated high-throughput screening of photosensitizer drug candidates and the beginnings of an integrated and comprehensive quantitative structure action relationship (QSAR) study for photosensitizer librarie

Graphical representation of the results obtained from the 24 hour MTS assay performed in the previously identified hits (compounds 2, 4, 8, 16, 22, 24 and 27) as well as three non-toxic compounds (3, 14 and 16) tested in OE21 cells (A and B) OE33 cells (C and D) and SKGT-4 cells (E and F).

<p>Data are representative of three independent experiments and values are expressed in mean ± SEM.</p

Examples of images collected with the InCell imaging system for the different treatments used with OE21 cells treated with 3µM Temoporfin for 24 hours before illumination and fixed at 4 four hours post illumination in 4% paraformaldehyde.

<p>Cells were labeled with Hoechst–nucleus (blue at 345 excitation, 435 emission), phalloidin–F-actin (green at 475 excitation and 535 emission), <i>m</i>THPC (red) was aquired at 560 excitation and 700 emission. Images were acquired by an InCell Analyzer automated microscope using a 10x objective (image size 0.897 mm×0.671 mm).</p

OE21 cells treated with increasing concentrations of <i>m</i>THPC and with equivalent concentrations of vehicle alone (illuminated and non-illuminated) were assessed for toxicity using a traditional cell proliferation assay (MTT).

<p>Data are representative of independent experiments and values are expressed in mean ± SEM.</p

IC50 values determined for the various compounds screened and cells lines tested when illuminated.

<p>These were generated by fitting a non-linear regression (log(inhibitor) <i>versus</i> response with variable slope in Graphpad prism. Results are representative of three independent experiments and values were rounded to units.</p

Graphical representation of the results obtained from InCell analysis for OE21 cultures treated with 2 µM <i>m</i> THPC and followed for up to 24 hours.

<p>Cell number was compared to cell area over time (A) and to nuclear area over time (B). Data are representative of three independent experiments and values are expressed in mean ± SEM.</p

Graphical representation of the results obtained from InCell analysis for photosensitizer parameters.

<p>Intracellular integrated intensity (A) and area (B) in OE21 cells. Data are representative of three independent experiments and values are expressed in mean ± SEM.</p

Graphical representation of the data for porphyrin 2, using MTT (A) and the InCell image analysis (B and C) in OE21 cells.

<p>Representation of the nuclear area with increasing concentrations of <i>m</i>THPC and porphyrin 2 (B) and the equivalent for cellular area (C) in illuminated and dark cells (A and B). Data for illuminated cells were compared to establish the degree of correlation with both HCA parameters tested (D and E). Data are representative of three independent experiments and values are expressed in mean ± SEM and linear regressions were fitted (A, B and C).</p