Abstract
Photosensitizers (PSs) inevitably release a large amount of energy in the form of fluorescence during photodynamic therapy (PDT). However, under the premise of satisfying fluorescence imaging, a large amount of energy is lost, which limits the efficiency of tumor therapy. Accordingly, in this study, we developed a new strategy (BDP-CR) using the single-molecule Förster resonance energy transfer (smFRET) mechanism to transfer part of the fluorescent energy into heat for combined PDT and photothermal therapy (PTT) featuring the “1 + 1 > 2” amplification effect. Under the 671 nm light irradiation, BDP-CR can produce singlet oxygen (1O2) for PDT based on the BDP moiety and also generate hyperthermia to achieve the PTT effect by exciting CR based on the smFRET effect, which effectively kills cancer cells both in vitro and in vivo. This strategy exhibits a broad absorption peak with strong light-harvesting ability, which improves photon utilization for treatment while realizing fluorescence imaging. Of note, owing to the smFRET effect, we achieve a combination treatment outcome at relatively low concentrations and light doses. Thus, we believe that this design concept will provide a new strategy for single-molecule FRET photosensitizers in combination therapy of cancer with potential clinical application prospects.
Highlights
Phototherapy, involving photodynamic therapy (PDT) and photothermal therapy (PTT), has been acknowledged as one of the most representative therapeutic strategies for the treatment of cancer owing to its precision and noninvasiveness.[1−4] For PDT, triplet photosensitizers (PSs) sensitize oxygen to generate high levels of reactive oxygen species (ROS) to kill cancer cells, which achieves tumor suppression through the apoptotic pathway.[5−8] PDT is an oxygendependent process which limits its function owing to the hypoxic environment of the tumor.[9,10]
We reported that the improvement of photon utilization could be achieved by hypoxia-induced treatment conversion from PDT to PTT.[20]
After the cells were incubated with BDP-CR under normoxia with 671 nm light irradiation (100 mW/cm2) for 5 min, cell viability decreased to 30%, which was significantly lower than that of cells incubated with BDP, CR, or BDP + CR, which suggested a considerable improvement in the killing effect of cancer cells (Figure 3b)
Summary
Phototherapy, involving photodynamic therapy (PDT) and photothermal therapy (PTT), has been acknowledged as one of the most representative therapeutic strategies for the treatment of cancer owing to its precision and noninvasiveness.[1−4] For PDT, triplet photosensitizers (PSs) sensitize oxygen to generate high levels of reactive oxygen species (ROS) to kill cancer cells, which achieves tumor suppression through the apoptotic pathway.[5−8] PDT is an oxygendependent process which limits its function owing to the hypoxic environment of the tumor.[9,10] PTT is a typical light− heat energy conversion therapeutic strategy.[11−13] PSs in the excited state return to the ground state through nonradiative transition with a release of heat, which induces local heat shock to kill tumor cells by the apoptosis and/or necrosis pathway without oxygen consumption.[14,15] On the other hand, the low concentration and light dose of PS ensure its good biological safety in PDT.[16−18] Comparatively, current PTT PSs exhibit strong absorption in the near-infrared (NIR) region, while the concentrations and light doses are relatively high.[13]. After the cells were incubated with BDP-CR under normoxia with 671 nm light irradiation (100 mW/cm2) for 5 min, cell viability decreased to 30%, which was significantly lower than that of cells incubated with BDP, CR, or BDP + CR, which suggested a considerable improvement in the killing effect of cancer cells (Figure 3b).
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