The effect of photochemical internalization of bleomycin in the treatment of urothelial carcinoma of the bladder: an in vitro study

Abstract

Objectives: In this in vitro study, we determined whether meso-tetraphenyl chlorin disulphonate (TPCS2a)-based photochemical delivery of bleomycin was able to potentiate the cytotoxicity of bleomycin on bladder cancer cells.

Materials and methods: The human RT4, RT112, 253J, T24, and rat AY-27 urothelial carcinoma cell lines were used. Cells were seeded in 96-well plates. TPCS2a was added to the growth medium and the plates were incubated overnight. Cells were then resuspended in TPCS2a-free culture medium and incubated for 3 hours. Subsequently, cells were treated for 60 minutes with increasing doses of epirubicin, gemcitabine, mitomycin C, or bleomycin followed by illumination for different periods. Cell viability was measured with a colorimetric assay after 72 hours.

Results: For the single treatments, in all 5 cell lines a dose-dependent inhibition of cell proliferation was observed. This was seen both after treatment with TPCS2a-based photodynamic therapy (PDT), as well as after treatment with either bleomycin or one of the control chemotherapeutic agents. After treatment with PDT (240-s illumination), bleomycin 9.0 µM, and the combination of these treatments, relative survival percentages were 89.2 ± 13.0, 70.2 ± 8.9, and 30.5 ± 6.1, respectively, in the T24 cell line. After treatment with PDT (120-s illumination), bleomycin 27 µM and the combination of these treatments, relative survival percentages were 93.6 ± 15.7, 74.7 ± 9.6, and 30.0 ± 11.1, respectively, in the AY-27 cell line. In both cell lines, PDT combined with bleomycin showed significantly (P<0.001) higher cell kill than the sum of the single treatments, suggesting a photochemical internalization effect.

Conclusions: TPCS2a-based photochemical internalization of bleomycin showed a significant, at least, additive antiproliferative activity against human and rat urothelial carcinoma cells in vitro. Thus, photochemical internalization may have therapeutic potential as an intravesical strategy against bladder cancer. As the effect is heterogeneous, biomarker studies are warranted to be able to predict the effects of a photochemical internalization-based treatment.

Keywords: Cytotoxicity; Photochemical internalization; Photodynamic therapy; Urinary bladder neoplasms; Urothelial carcinoma.