42P Developing a photodynamic therapy strategy targeted to endometrial cancer stem cells

Cancer stem cells (CSC) motivate the investigation of novel anticancer-targeted therapies. In endometrial cancer (EC), overexpression of aldehyde dehydrogenase (ALDH) was associated with endometrial CSC, highlighting its therapeutic target potential. Photodynamic therapy (PDT), a minimally invasive anticancer approach, emerges as a promising targeted therapy for endometrial CSC, through a structural modulation of optimized photosensitisers with aldehyde moieties. Thus, the aim is to investigate PDT based on the 4,5,6,7-tetrahydropyrazolo[1,5-a]pyridine-fused chlorins (PX), modulated to target endometrial CSC by incorporation of aldehyde substituents. A solution of a mono-esther/mono-alcohol derivative chlorin was added to Dess-Martin periodinane in dichloromethane solution and stirred to synthesise a mono-aldehyde derivative of 4,5,6,7-tetrahydropyrazolo[1,5-a]pyridine-fused chlorin (A-PX). The presence of the aldehyde group was confirmed by proton nuclear magnetic resonance (1H-NMR). The ALDH1A1-promoted oxidation of A-PX was followed through reverse-phase high-performance liquid chromatography (HPLC). This was done by reacting 50nM ALDH1A1 with 1mM A-PX in a 2% DMSO, Tris pH 7.5, KCl, DTT and β-NAD solution at 37 °C. The reaction was stopped every 30’ with acetonitrile. To evaluate A-PX-based PDT (7.5mW/cm2, 10J) the resazurin assay was performed on endometrial CSC. The A-PX 1H-NMR revealed a peak at 10.28ppm corresponding to the aldehyde. The kinetics of the enzymatic reaction, followed by HPLC, showed the decreasing relative area of the aldehyde peak (retention = 2’13’’) in parallel with the increase of the carboxylic acid (retention = 3’04’’) formed by ALDH1A1-promoted oxidation, reaching complete conversion at 120'. Preliminary results of the A-PX-PDT cytotoxicity on the endometrial CSC pointed to decreased proliferation, while A-PX per se did not show toxicity. It was possible to develop chlorins able to interact with ALDH1A1, allowing the in situ modification of the hydrophilicity of the photosensitizer. A-PX seem to be effective PDT agents against endometrial CSC. The promising results encourage further studies to confirm this rationale for endometrial CSC-targeted PDT.