title: Assessment of early changes in 3H-fluorothymidine uptake after treatment with gefitinib in human tumor xenograft in comparison with Ki-67 and phospho-EGFR expression.
abstract: BACKGROUND
  The purpose of this study was to evaluate whether early changes in 3'-deoxy-3'-3H-fluorothymidine (3H-FLT) uptake can reflect the antiproliferative effect of gefitinib in a human tumor xenograft, in comparison with the histopathological markers, Ki-67 and phosphorylated EGFR (phospho-EGFR).
  
  
  METHODS
  An EGFR-dependent human tumor xenograft model (A431) was established in female BALB/c athymic mice, which were divided into three groups: one control group and two treatment groups. Mice in the treatment groups were orally administered a partial regression dose (100 mg/kg/day) or the maximum tolerated dose of gefitinib (200 mg/kg/day), once daily for 2 days. Mice in the control group were administered the vehicle (0.1% Tween 80). Tumor size was measured before and 3 days after the start of treatment. Biodistribution of 3H-FLT and 18F-FDG (%ID/g/kg) was examined 3 days after the start of the treatment. Tumor cell proliferative activity with Ki-67 was determined. Immunohistochemical staining of EGFR and measurement of phospho-EGFR were also performed.
  
  
  RESULTS
  High expression levels of EGFR and Ki-67 were observed in the A431 tumor. After the treatment with 100 and 200 mg/kg gefitinib, the uptake levels of 3H-FLT in the tumor were significantly reduced to 67% and 61% of the control value, respectively (0.39 ± 0.09, 0.36 ± 0.06, 0.59 ± 0.11%ID/g/kg for 100 mg/kg, 200 mg/kg, and control groups, respectively; p<0.01 vs. control), but those of 18F-FDG were not. After the treatment with 100 and 200 mg/kg gefitinib, the expression levels of Ki-67 in the tumor were markedly decreased (4.6 ± 2.4%, 6.2 ± 1.8%, and 10.4 ± 5.7% for 100 mg/kg, 200 mg/kg, and control groups, respectively, p<0.01 vs. control). The expression levels of the phospho-EGFR protein also significantly decreased (29% and 21% of the control value for 100, and 200 mg/kg, respectively p<0.01 vs. control). There was no statistically significant difference in tumor size between pre- and post-treatments in each group.
  
  
  CONCLUSIONS
  In our animal model, 3H-FLT uptake levels significantly decreased after the treatment with two different doses of gefitinib before a significant change in tumor size was observed. These results were confirmed by the immunohistochemical staining of Ki-67 and phospho-EGFR protein immunoassay. Thus, it was indicated that early changes in 3H-FLT uptake may reflect the antiproliferative effect of gefitinib in a mouse model of a human epidermoid cancer.
authors.forename: Songji
authors.initials: S
authors.lastname: Zhao
authors.affiliation: Central Institute of Isotope Science, Hokkaido University, Sapporo, Japan. kuge@ric.hokudai.ac.jp.
authors.forename: Yuji
authors.initials: Y
authors.lastname: Kuge
authors.forename: Yan
authors.initials: Y
authors.lastname: Zhao
authors.forename: Satoshi
authors.initials: S
authors.lastname: Takeuchi
authors.forename: Kenji
authors.initials: K
authors.lastname: Hirata
authors.forename: Toshiki
authors.initials: T
authors.lastname: Takei
authors.forename: Tohru
authors.initials: T
authors.lastname: Shiga
authors.forename: Hirotoshi
authors.initials: H
authors.lastname: Dosaka-Akita
authors.forename: Nagara
authors.initials: N
authors.lastname: Tamaki
mesh_terms: D000818:Animals; D000970:Antineoplastic Agents / Q000008:administration & dosage / Q000494:pharmacology*; D045744:Cell Line, Tumor; D004195:Disease Models, Animal; D066246:ErbB Receptors / Q000037:antagonists & inhibitors / Q000378:metabolism*; D005260:Female; D019788:Fluorodeoxyglucose F18 / Q000378:metabolism; D000077156:Gefitinib; D006801:Humans; D019394:Ki-67 Antigen / Q000378:metabolism*; D051379:Mice; D009369:Neoplasms / Q000175:diagnosis / Q000188:drug therapy / Q000378:metabolism* / Q000473:pathology*; D010766:Phosphorylation; D011799:Quinazolines / Q000008:administration & dosage / Q000494:pharmacology*; D019275:Radiopharmaceuticals / Q000378:metabolism*; D047368:Tumor Burden / Q000187:drug effects; D023041:Xenograft Model Antitumor Assays
chemical_list: D000970:Antineoplastic Agents; D019394:Ki-67 Antigen; D011799:Quinazolines; D019275:Radiopharmaceuticals; D019788:Fluorodeoxyglucose F18; D066246:ErbB Receptors; D000077156:Gefitinib