Investigation of TNBC metastatic potential following synergistic photodynamic therapy and chemotherapy

Triple-negative breast cancer (TNBC) is the most aggressive subtype of breast cancer due to a lack of targetable receptors and a high rate of metastasis. The current standard of care for TNBC involves neoadjuvant chemotherapy, such as doxorubicin (DOX), a systemic intervention that affects both cancerous and healthy growing cells throughout the body. In contrast, photodynamic therapy (PDT) offers a minimally invasive alternative, utilizing photosensitizers like benzoporphyrin derivative (BPD) activated by a specific wavelength of light to induce localized cell death. While PDT, both as a standalone treatment and in combination with chemotherapy, has been shown to enhance treatment efficacy in TNBC, its effects on metastatic potential remain poorly understood. To address this knowledge gap, we utilize in vitro assays characterizing cell morphology and invasion as predictors of in vivo metastasis of human TNBC cell lines (BT-20, MDA-MB-231, LM2) following treatments with BPD-PDT alone and in combination with DOX. In this study, we observed that both treatments administered individually demonstrated high sensitivity in BT-20 cells, moderate sensitivity in LM2 cells, and the lowest sensitivity in MDA-MB-231 cells. Comparatively, we found that the combination treatment is most synergistic in LM2 cells and least in BT-20 cells. To assess metastatic potential, we characterized changes in in vitro cell morphology after administering BPD-PDT alone. We discovered that sublethal doses of BPD-PDT alone reduce 3D single-cell and spheroid invasion in LM2 and BT-20 cells, suggesting a decrease in metastatic potential. In contrast, the combination treatment reduced spheroid invasion and led to a more significant increase in pro-apoptotic factors in LM2 and MDA-MB-231 cells compared to BT-20 cells. Overall, our findings highlight the distinct impacts of BPD-PDT alone and the synergistic effects of combination treatment on metastatic potential in TNBC.