Evaluating the global cellular pharmacological effects of photodynamic therapy using label-free surface-enhanced Raman spectroscopy.

Abstract

Photodynamic therapy (PDT) has attracted widespread attention as an emerging cancer treatment, yet real-time monitoring of tumor oxidative stress during therapy remains challenging due to unclear mechanistic insights, delayed efficacy evaluation, and inefficient drug screening. This study employed label-free dynamic surface-enhanced Raman spectroscopy (D-SERS) to evaluate the cellular pharmacological effects of PDT, enabling the mechanism-based classification of agents. Label-free D-SERS was used to monitor real-time spectral changes in human melanoma cells during PDT, characterizing the differences between apoptosis-inducing (type A) and necrosis-inducing (type B) photosensitizers. Type A exhibited concentration-dependent increases in Raman peaks at 652, 742, 828, and 1000 cm^-1, a trend absent in Type B. By analyzing DNA, lipid, and amino acid peak ratios, cells treated with these photosensitizers were clearly classified into two mechanistic groups (A and B). Furthermore, D-SERS was applied to study the Type B agent 5-ALA in combination with heme oxygenase-1 (HO-1) modulators, verifying the associated enzyme-regulatory processes. This study presents a proof-of-concept model for the spectral mechanism-based screening of photosensitizers and enzyme modulators, thus aiding the optimization of PDT efficacy and targeted drug development.