Monitoring Tumor Response after Liposomal Doxorubicin in Combination with Liposomal Vinorelbine Treatment Using 3'-Deoxy-3'-[ super(18)F]Fluorothy midine PET

Surgical resection is the standard treatment for localized colorectal cancer, which is the most common type of gastrointestinal cancer. However, over 40 % cases are diagnosed metastasized and apparently inoperable. Systemic chemotherapy provides an alternative to these patients. This study aims to evaluate the therapeutic potential of liposomal doxorubicin (lipoDox) in combination with liposomal vinorelbine (lipoVNB) in a CT-26 colon carcinoma-bearing mouse model. The in vitro cytotoxicity of Dox and VNB on CT-26 cancer cells was determined by MTT and colony formation assays. Mice were subcutaneously inoculated with 2 10 super(5) of CT-26 cells in the right hind flank. When tumor size reached 200 plus or minus 50 mm super(3) , mice were assigned to receive different treatment protocols. The pharmacokinetics, micro single-photon emission computed tomography/x-ray computed tomography imaging, biodistribution, and immunohistochemical staining studies were performed to survey the therapeutic efficacy of each regimen. Based on the results of pharmacokinetic study, co-administration of lipoDox and lipoVNB did not affect their individual systemic distribution, while lipoDox retained longer in blood than lipoVNB did. Superior tumor growth retardation was observed in the group received lipoDox plus lipoVNB administration (1 mg/kg each, namely D sub(1)V sub(1)) than those injected with lipoDox plus VNB (1 mg/kg each, namely D sub(1)fV sub(1)). No severe side effects were detected in each group. The tumor-to-muscle ratio (T/M) derived from 3'-dexoy-3'-[ super(18)F]fluorothy midine ([ super(18)F]FLT) micro positron emission tomography (PET) images of D sub(1)V sub(1)- and D sub(1)fV sub(1)-treated mice and the controls on day 7 was 6.88 plus or minus 0.54, 7.50 plus or minus 0.84, and 9.87 plus or minus 0.73, respectively, suggesting that D sub(1)V sub(1) is a more efficacious regimen against CT-26 xenografts. The results of proliferating cell nuclear antigen (PCNA) immunohistochemical staining were consistent with those findings obtained from [ super(18)F]FLT microPET imaging. This study demonstrated that lipoDox in combination with lipoVNB was more efficacious than clinically used regimen, lipoDox plus VNB, in the treatment of colon carcinoma and [ super(18)F]FLT-PET is a promising approach in monitoring the treatment outcome at early stage.