Monitoring tumor response with radiolabeled nucleoside analogs in a hepatoma-bearing mouse model early after doxisome(®) treatment

Monitoring Tumor Response after Liposomal Doxorubicin in Combination with Liposomal Vinorelbine Treatment Using 3'-Deoxy-3'-[18F]Fluorothymidine PET

PURPOSE

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.

PROCEDURES

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 × 10⁵ of CT-26 cells in the right hind flank. When tumor size reached 200 ± 50 mm³, 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.

RESULTS

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 D₁V₁) than those injected with lipoDox plus VNB (1 mg/kg each, namely D₁fV₁). No severe side effects were detected in each group. The tumor-to-muscle ratio (T/M) derived from 3'-dexoy-3'-[¹⁸F]fluorothymidine ([¹⁸F]FLT) micro positron emission tomography (PET) images of D₁V₁- and D₁fV₁-treated mice and the controls on day 7 was 6.88 ± 0.54, 7.50 ± 0.84, and 9.87 ± 0.73, respectively, suggesting that D₁V₁ 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 [¹⁸F]FLT microPET imaging.

CONCLUSION

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 [¹⁸F]FLT-PET is a promising approach in monitoring the treatment outcome at early stage.

Determining efficacy of breast cancer therapy by PET imaging of HER2 mRNA

INTRODUCTION

Monitoring the effectiveness of therapy early and accurately continues to be challenging. We hypothesize that determination of Human Epidermal Growth Factor Receptor 2 (HER2) mRNA in malignant breast cancer (BC) cells by positron emission tomography (PET) imaging, before and after treatment, would reflect therapeutic efficacy.

METHOD

WT4340, a peptide nucleic acid (PNA) 12-mer complementary to HER2 mRNA was synthesized together with -CSKC, a cyclic peptide, which facilitated internalization of the PNA via IGFR expressed on BC cells, and DOTA that chelated Cu-64. Mice (n = 8) with BT474 ER+/HER2+ human BC received doxorubicin (DOX, 1.5mg/kg) i.p. once a week for six weeks. Mice (n = 8) without DOX served as controls. All mice were PET imaged with F-18-FDG and 48 h later with Cu-64-WT4340. PET imaging were performed before and 72 h after each treatment. Standardized uptake values (SUVs) were determined and percent change calculated. Animal body weight (BW) and tumor volume (TV) were measured.

RESULTS

SUVs for Cu-64-WT4340 after DOX treatment declined by 54% ± 17% after the second dose, 41% ± 15% after the fourth dose, and 29% ± 7% after the sixth dose, compared with 42% ± 22%, 31% ± 18%, and 13% ± 9% (p<0.05) for F-18-FDG. In untreated mice, the corresponding percent SUVs for Cu-64-WT4340 were 145% ± 82%, 165% ± 39%, and 212% ± 105% of pretreatment SUV, compared with 108% ± 28%, 151% ± 8%, and 152% ± 35.5%, (p<0.08) for F-18-FDG. TV in mice after second dose was 114.15% ± 61.83%, compared with 144.7% ± 64.4% for control mice. BW of DOX-treated mice was 103.4% ± 7.6% of pretreatment, vs. 100.1% ± 4.3% for control mice.

CONCLUSION

Therapeutic efficacy was apparent sooner by molecular PET imaging than by determination of reduction in TV.