Intravital evaluation of time-course efficacy of anticancer drugs on colorectal liver metastases in the same living mice using two-photon laser scanning microscopy.

Abstract

10621 Background: There is a significant site-specific variation in response to chemotherapy for human solid tumors. Whether subcutaneous non-metastatic xenograft models are representative of clinically metastatic disease remains an unanswered question. Metastatic xenograft models may be ideal and practical for preclinical anti-cancer drug evaluation. We evaluated intravitally the time-course efficacy of anti-cancer drugs at the metastatic site in the same living mice using two-photon laser scanning microscopy (TPLSM). Methods: Red fluorescent protein expressing human colorectal cancer cell line (HT29) was inoculated to the spleen of green fluorescent protein expressing mice for experimental liver metastasis models. 5-fluorouracil (50 mg/kg) or irinotecan (20 mg/kg) was administered intraperitoneally three times a week for three weeks after the confirmation of macroscopic liver metastases. TPLSM was used for intravital visualization of treatment efficacy at a magnification of over 600×. Intravital TPLSM was performed by exteriorizing and fixing the liver lobe of living mice. This procedure was repeated several times for the time-course imaging of treatment efficacy on liver metastases in the same mice. Results: Approximately eight weeks later, HT29 cells formed macroscopic liver metastases. Under the first TPLSM, micrometastatic nodules consisting of viable cancer cells (red) and surrounding stroma with tumor vessels (green) were visualized in the living liver of living mice. After anti-cancer drug treatment, morphologic change of micrometastatic nodules was observed in the same mouse under the second TPLSM. The fragmentation of cancer cells surrounding residual metastatic colonies was visualized three-dimentionally. There was no apparant morphological difference in tumor responsiveness on liver metastases between 5-fluorouracil and irinotecan. Conclusions: Intravital time-course visualization of treatment efficacy in the same mouse using metastatic xenograft model under TLPSM could be ideal and practical for screening and evaluating new anti-cancer drugs with less interindividual variability.