Unveiling Theranostics: Nanocomplex-Assisted Photodynamic Eradication of Aggressive Cancer Cells and Modulation of Tumor-Associated Macrophages.

BACKGROUND

Photodynamic therapy (PDT) is a promising tool that utilizes photosensitizers (PS) for two functions: cancer imaging by fluorescence (diagnostics), and treatment by the generation of reactive oxygen species (therapy). Despite its theranostic approach, the efficacy of PDT is often hampered by limited penetration of light into tissues, tumor heterogeneity, and the immunosuppressive tumor microenvironment (TME). Moreover, diagnostics and treatment are activated simultaneously, without the possibility of switching between two processes.

METHODS

We used photosensitizer chlorin e6 (Ce6) and luminescent quantum dots (QDs) to create a theranostic nanocomplex. Two different light sources were used (980 nm or 650 nm light) to activate either the photoluminescence of quantum dots (QDs) or the generation of singlet oxygen by Ce6. Four distinct CRC cell lines were utilized to represent tumor heterogeneity. The therapeutic efficacy of nanocomplex was assessed in CRC and tumor-associated macrophages (TAMs), a key component of the immunosuppressive TME. Immunomodulatory effects were explored by exposing resident and recruited TAM models to a conditioned medium from PDT-treated CRC cells, followed by gene expression analysis.

RESULTS

Spectral characterization of the QDs-Ce6 nanocomplex demonstrated selective switching between diagnostic and therapeutic modes. Two-photon absorption was activated in QDs by 980 nm laser, thus broadening its excitation capabilities into the infrared region. The nanocomplex accumulated efficiently and uniformly across all CRC cell lines, regardless of their aggressiveness or drug sensitivity. The effect of nanocomplex-assisted PDT was the same among CRC cell lines, contrasting with the variable sensitivity to 5-fluorouracil. Additionally, the PDT caused M2 macrophages to lose their pro-tumor characteristics while potentiating their ability to present antigens. Additionally, M0 macrophages displayed a reduction in immunosuppressive signaling.

CONCLUSION

The QDs-Ce6 nanocomplex exhibits robust photodynamic cytotoxicity and immunomodulatory potential. These findings highlight the potential of nanocomplex for targeting the aggressive type of tumor cells and the TAM.