title: Pretargeting of necrotic tumors with biotinylated hypericin using 123I-labeled avidin: evaluation of a two-step strategy.
abstract: As an alternative to directly targeting of necrotic tissue using hypericin, we synthesized a conjugate of hypericin to biotin for use in a pretargeting approach. With this conjugate, we explored the possibility of a two-step pretargeting strategy using (123)I-labeled avidin as effector molecule directed against necrotic RIF-1 tumors. Hypericin was conjugated to biotin-ethylenediamine in a straightforward coupling method using n-hydroxysuccinimide and dicyclohexylcarbodiimide. The necrosis avidity of the conjugate was first confirmed in necrotic liver tissue by means of fluorescence microscopy. Using autoradiography imaging and whole body-biodistribution, the accumulation of (123)I-avidin in necrotic tumor tissue was evaluated 24 h after administration and 48 h after pretargeting with hypericin-biotin. Analysis of autoradiography images show a higher accumulation of (123)I-avidin in pretargeted compared to nontargeted tissue. However, absolute accumulation of (123)I-avidin in necrotic tumors was low as shown by biodistribution experiments. Direct injection of hypericin-biotin or biotin-fluorescein did not substantially improve (123)I-avidin accumulation after pretargeting, pointing towards a poor penetration of avidin in necrotic tissue. Our results show the feasibility of a pretargeting technique using a small molecule as targeting agent. However, for a more efficient accumulation of the effector molecule in necrotic tissue, other pretargeting strategies need to be investigated.
authors.affiliation: Laboratorium voor Farmaceutische Biologie, Faculteit Farmaceutische Wetenschappen, KU Leuven, Herestraat 49-bus 824, B-3000, Leuven, Belgium.
authors.forename: Thierry
authors.initials: T
authors.lastname: Marysael
authors.forename: Matthias
authors.initials: M
authors.lastname: Bauwens
authors.forename: Yicheng
authors.initials: Y
authors.lastname: Ni
authors.forename: Guy
authors.initials: G
authors.lastname: Bormans
authors.forename: Jef
authors.initials: J
authors.lastname: Rozenski
authors.forename: Peter
authors.initials: P
authors.lastname: de Witte
mesh_terms: D000818:Animals; D000873:Anthracenes; D000970:Antineoplastic Agents / Q000008:administration & dosage* / Q000737:chemistry; D001360:Avidin / Q000008:administration & dosage* / Q000493:pharmacokinetics; D001710:Biotin / Q000008:administration & dosage* / Q000737:chemistry; D019921:Biotinylation; D045744:Cell Line, Tumor; D003287:Contrast Media / Q000008:administration & dosage / Q000493:pharmacokinetics; D000431:Ethanol; D005260:Female; D007457:Iodine Radioisotopes; D051379:Mice; D008809:Mice, Inbred C3H; D009336:Necrosis / Q000139:chemically induced / Q000378:metabolism* / Q000473:pathology; D009369:Neoplasms / Q000378:metabolism* / Q000473:pathology; D010569:Perylene / Q000008:administration & dosage / Q000031:analogs & derivatives* / Q000737:chemistry; D014018:Tissue Distribution
chemical_list: D000873:Anthracenes; D000970:Antineoplastic Agents; D003287:Contrast Media; D007457:Iodine Radioisotopes; D001360:Avidin; D000431:Ethanol; D010569:Perylene; D001710:Biotin; C004965:hypericin