Abstract
Photodynamic therapy (PDT), a highly targeted therapy with acceptable side effects, has emerged as a promising therapeutic option in oncologic pathology. One of the issues that needs to be addressed is related to the complex network of cellular responses developed by tumor cells in response to PDT. In this context, this study aims to characterize in vitro the stressors and the corresponding cellular responses triggered by PDT in the human colon carcinoma HT29 cell line, using a new asymmetric porphyrin derivative (P2.2) as a photosensitizer. Besides investigating the ability of P2.2-PDT to reduce the number of viable tumor cells at various P2.2 concentrations and fluences of the activating light, we assessed, using qRT-PCR, the expression levels of 84 genes critically involved in the stress response of PDT-treated cells. Results showed a fluence-dependent decrease of viable tumor cells at 24 h post-PDT, with few cells that seem to escape from PDT. We highlighted following P2.2-PDT the concomitant activation of particular cellular responses to oxidative stress, hypoxia, DNA damage and unfolded protein responses and inflammation. A web of inter-connected stressors was induced by P2.2-PDT, which underlies cell death but also elicits protective mechanisms that may delay tumor cell death or even defend these cells against the deleterious effects of PDT.
Highlights
Photodynamic therapy (PDT) has lately emerged as a promising targeted therapy for solid tumors
In vitro PDT was performed on the human colon carcinoma cell line HT29 using the new porphyrinic photosensitizer P2.2 (Figure 1) and activating laser light of 635 nm
PDT effect waseffect wa calculated as in samples subjected to divided by the mean value of in control calculated as optical density (OD) in samples subjected to PDT divided by the mean value of OD in control samples. sample
Summary
Photodynamic therapy (PDT) has lately emerged as a promising targeted therapy for solid tumors. As reviewed by Agostinis et al [1], PDT consists of the administration of a biocompatible photosensitizer (PS) that is inactive in “dark” conditions and is more or less selectively accumulated by tumor cells. PSs should not exhibit “dark” cytotoxicity, and the activating light is highly targeted to the diseased tissue, PDT has minimal effects on healthy tissues. Major technical issues raised by PDT, recently summarized [3], are related to PS properties which, besides having to be non-cytotoxic in “dark” conditions, should have convenient amphiphilic properties to load cells and minimal aggregation in physiologic fluids and be activated with light of sufficiently high wavelength to penetrate tissues
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