前言：文獻報導腫瘤組織有高濃度的biotin，以及streptavidin、avidin對biotin的高親和性，因此以放射性標幟的strepta-vidin或avidin做為腫瘤造影的可能性大增。本研究評估放射性標幟streptavidin、avidin定位腫瘤的能力，並與目前臨床使用的核醫藥物比較。
方法：已長出MCF-7或BT-20人類乳癌細胞的裸鼠分別靜脈注射(a)銦-111-strepttavidin；(2)銦-111-avidin；(c)銦-111-Octrcotidc；(d)鎝-99m－MDP；(c)鎝-99m-sestamibi；(f)氟-18-FDG；(g)銦-111-AE-3抗乳癌單株抗體。在預定臨床造影的時間將動物犧牲，取出各器官，並量測其放射活度。
結果：對位於橫膈膜以上的組織，銦-111-streptavidin及銦-111-avidin均展現優異的腫瘤對正常組織比值。為維持MCF-7腫瘤組織的成長以及周圍的低度發炎反應，皮下植入贍固醇片不會增加放射性標幟streptavidin的聚集。
結論：在裸鼠身上異體移植的人類孔癌細胞組織，不論是否為動情激素依存者，銦-111-streptavidin及銦-111-avidin均會顯現優異的定位能力。比較其它日前使用中的腫瘤定位核醫藥物之腫瘤對正常組織比值確認進一步評估這兩種新腫瘤造影劑的必要性。由於人體內avidin抗體會降低放射性標幟avidin聚集腫瘤的能力。銦-111-streptavidin似為更適合發展的乳房腫瘤造影劑。

Backgrounds: The reported high concentration of biotin in tumors coupled with the high affinity of streptavidin and avidin for biotin raises the possibility that radi01abeted streptavidin or avidin could be used for tumor imaging. This study examines the tumor localizing potential of radiolabeled streptavidin and avidin and compares it to that achieved following the administration of radiopharmaceuticals currently in use.
Methods: Nude mice bearing either the MCF-7 or the BT-20 human breast tumor were injected intravenously with (a) 111In-streptavidin, (b) 111In-avidin, (c) 111In-Octreoscan, (d)99mTc-MDP, (e)99mTc-sestamibi, (f) 18F- FDO and (g) 111In-AE-3 anti-breast cancer monoclonal antibody. Animals were sacrificed at various time periods corresponding with accepted clinical protocols and tissues were obtained for determination of radioactivity.
Results: Both 111In-streptavidin and 111In-avidin demonstrated superior tumor to normal organ rations in tissues located above the diaphragm. The cholesterol pellet implanted subcutaneously to sustain MCF-7 tumor growth and the low-grade inflammatory reaction surrounding the pellet did not demonstrate increased uptake of radiolabeled streptavidin.
Conclusion: 111In-streptavidin and 111In-avidin administered as single agents demonstrate significant localization in both estrogen dependent and estrogen independent human breast tumors xenografted in mice. The overall superior tumor to normal organ ratios obtained with 111In-streptavidin and 111In-avidin compared to radiopharmaceuticals currently in use warrants further evaluation of these agents for breast tumor imaging. Since the natural human antibodies to avidin will result in fast clearance of the avidin from the circulation and limited access of the tumor to avidin, 111In-streptavidin appears to be more suitable agent to pursue.