Comparison between two labeled agents in mice using a coinjection-ratio approach in contrast to a conventional group approach

作者：Dou Shuping; Wang Yuzhen; Barton Bruce; Chen Ling; Rusckowski Mary; Shultz Leonard D; Greiner Dale L; Liu Guozheng^*

来源：Nuclear Medicine and Biology, 2014, 41(1): 127-131.

DOI：10.1016/j.nucmedbio.2013.10.001

• Statistical analysis
• In vivo evaluation
• Biodistribution
• Translational study
• Tumor pretargeting

Introduction: The differences between two agents often need to be accurately defined in vivo. Usually they are injected respectively into two groups of subjects. However, if the two agents do not interact with each other in vivo, a coinjection would serve the same purpose. We believe some individual differences in biodistribution may be circumvented through this approach by calculating organ level ratios.
Methods: A model system of MORF/cMORF pretargeting (MORF/cMORF is a complementary pair of DNA analogues) was employed in connection with an on-going tumor therapeutic project. Human LS174T cells were implanted into the flank of severely immuno-compromised NOD-scid IL2rg(null) mice. The tumor was confirmed to express TAG-72 antigens. At 16 days post tumor inoculation, mice received IV 60 mu g of MORF-conjugated CC49 (an antiTAG-72 antibody), followed 2 days later by a low-mass-dose IV coinjection containing 2.5 mu g of Y-99-cMORF and 2.5 n of Tc-99m-cMORF. At 3 h post radioactivity injection, the distribution of Tc-99m was imaged on a SPECT/CT camera and then organs were excised and counted for Y-99 and Tc-99m. Because the two labeled cMORFs do not react or interact with each other in vivo, the two groups of NV and Tc-99m data enabled a conventional group comparison. In a new effort, Y-99/Tc-99m ratios were calculated. Student's t-test and retrospective power analysis were performed for both approaches. In the new approach, the ratios were set at 1 as the null hypothesis.
Results: The Student's t-test in the conventional group approach indicated that the two labeled cMORFs distributed similarly, but significant differences were observed in salivary gland and large intestines. The coinjection-ratio approach certainly did not subvert the results of the conventional approach but revealed subtler differences. The P values were reduced, the powers were increased in most organs, and more significant differences were observed. The increased sensitivity was due td the reduced CV%s (SD/ average*100%) of the Y-99/Tc-99m ratios. Therefore, some individual differences were circumvented and notably the ratio approach differentiated individual differences into ratio-correctable and ratio-uncorrectable.
Conclusions: Although the conventional approach is reliable, the coinjection-ratio approach using organ level ratios is more sensitive and therefore is recommended whenever possible. In addition, it differentiates individual differences into "coinjection correctable" and "coinjection uncorrectable".

• 出版日期2014-1