Nobuya Kobashi1, Hiroki Matsumoto2, Songji Zhao3, Shunsuke Meike1, Yuki Okumura1, Tsutomu Abe1, Hiromichi Akizawa4, Kazue Ohkura5, Ken-Ichi Nishijima3, Nagara Tamaki3, Yuji Kuge6. 1. Research Center, Nihon Medi-Physics Co., Ltd., Sodegaura, Japan. 2. Research Center, Nihon Medi-Physics Co., Ltd., Sodegaura, Japan hiroki_matsumoto@nmp.co.jp. 3. Graduate School of Medicine, Hokkaido University, Sapporo, Japan. 4. Showa Pharmaceutical University, Machida, Japan. 5. Faculty of Pharmaceutical Sciences, Health Sciences University of Hokkaido, Ishikari-Tobetsu, Japan; and. 6. Graduate School of Medicine, Hokkaido University, Sapporo, Japan Central Institute of Isotope Science, Hokkaido University, Sapporo, Japan.
Abstract
UNLABELLED: Recently, companion diagnostics with nuclear medicine techniques have been anticipated as more suitable means than biopsy for predicting treatment efficacy. The anticancer effect of capecitabine, an orally administered chemotherapeutic agent activated by thymidine phosphorylase (TP), is positively associated with tumor TP expression levels. This study aimed to assess whether TP imaging using a radiolabeled uracil derivative, (123)I-5-iodo-6-[(2-iminoimidazolidinyl)methyl]uracil ((123)I-IIMU), could predict the efficacy of capecitabine treatment. METHODS: Sensitivity to doxifluridine, a metabolite of capecitabine and direct substrate for TP, was assessed by water-soluble tetrazolium salt assays in vitro for 3 human colon cancer cell lines with different TP expression profiles. The intracellular uptake and retention of (123)I-IIMU were evaluated. Mice inoculated with each cell line were treated with capecitabine for 2 wk, and tumor growth was compared. In vivo distribution studies and SPECT/CT imaging of (123)I-IIMU were performed in inoculated mice. RESULTS: In vitro experiments showed a positive relation between TP expression levels and doxifluridine sensitivity. In vitro studies revealed that intracellular uptake and retention of (123)I-IIMU were dependent on TP expression levels. In vivo experiments in inoculated mice showed that (123)I-IIMU accumulation in tumor tissue was in line with TP expression levels and susceptibility to capecitabine treatment. Moreover, SPECT/CT imaging of (123)I-IIMU in tumor-inoculated mice showed that (123)I-IIMU reflects TP expression levels in tumor tissues. CONCLUSION: (123)I-IIMU could be used as an in vivo companion diagnostic for predicting the efficacy of capecitabine treatment.
UNLABELLED: Recently, companion diagnostics with nuclear medicine techniques have been anticipated as more suitable means than biopsy for predicting treatment efficacy. The anticancer effect of capecitabine, an orally administered chemotherapeutic agent activated by thymidine phosphorylase (TP), is positively associated with tumor TP expression levels. This study aimed to assess whether TP imaging using a radiolabeled uracil derivative, (123)I-5-iodo-6-[(2-iminoimidazolidinyl)methyl]uracil ((123)I-IIMU), could predict the efficacy of capecitabine treatment. METHODS: Sensitivity to doxifluridine, a metabolite of capecitabine and direct substrate for TP, was assessed by water-soluble tetrazolium salt assays in vitro for 3 humancolon cancer cell lines with different TP expression profiles. The intracellular uptake and retention of (123)I-IIMU were evaluated. Mice inoculated with each cell line were treated with capecitabine for 2 wk, and tumor growth was compared. In vivo distribution studies and SPECT/CT imaging of (123)I-IIMU were performed in inoculated mice. RESULTS: In vitro experiments showed a positive relation between TP expression levels and doxifluridine sensitivity. In vitro studies revealed that intracellular uptake and retention of (123)I-IIMU were dependent on TP expression levels. In vivo experiments in inoculated mice showed that (123)I-IIMU accumulation in tumor tissue was in line with TP expression levels and susceptibility to capecitabine treatment. Moreover, SPECT/CT imaging of (123)I-IIMU in tumor-inoculated mice showed that (123)I-IIMU reflects TP expression levels in tumor tissues. CONCLUSION: (123)I-IIMU could be used as an in vivo companion diagnostic for predicting the efficacy of capecitabine treatment.