Multispectral autofluorescence imaging for detection of cervical lesions: A preclinical study

AIM: The aim of this study was to develop a novel optical imaging system for detecting protoporphyrin IX (PpIX) autofluorescence, to prove that PpIX autofluorescence is as useful as 5-aminolevulinic acid (5-ALA)-induced fluorescence for detecting and localizing cervical cancer, and to monitor the change in PpIX autofluorescence or induced PpIX fluorescence before, during, and after photodynamic therapy (PDT). METHODS: TC-1 cells - highly tumorigenic cells immortalized using human papillomavirus type 16 proteins E6 and E7 - were subcutaneously grafted into the thighs of nude mice. The suspected tumor tissues were visualized using autofluorescence imaging and induced fluorescence imaging under 5-ALA administration. When the 5-ALA-induced PpIX was sufficiently accumulated in tumor tissues, PDT was performed using a 635-nm laser. We observed the change in fluorescence intensity during PDT. For 3 weeks after PDT, we monitored tumor remission by using white-light imaging and fluorescence imaging. RESULTS: The transplanted cells were visualized by PpIX autofluorescence, which was induced by heme synthesis. After 5-ALA administration, PpIX could be targeted by using PDT, which decreased PpIX autofluorescence. Photobleaching is useful for monitoring PDT dosimetry and for determining the photodynamic response to therapy. CONCLUSION: PpIX autofluorescence clearly differentiated the tumor from adjacent normal tissues. The results of PpIX autofluorescence imaging and 5-ALA-induced fluorescence imaging were identical. PpIX autofluorescence imaging is a simple and cost-effective cervical cancer screening method that could be performed during or after PDT to ensure effective treatment or remission as a change in fluorescence intensity can be observed in real time without a blinding effect.