The HPLC was equipped with both an in-line radioactivity detector and a Waters 2487 dual wavelength absorbance detector (Milford, MA). == MN14-MORF Conjugation, evaluation and radiolabeling == For the preparation of MN14(SANH)-MORF, typically the MN14 antibody was incubated with a five to ten fold molar excess of NHS-SANH in 100 mM PBS (pH=8.0) for 1 h at room heat. tumored nude mice and the results compared to that obtained historically with MN14-MORF prepared by carbodiimide (EDC) coupling. == Results == Both new methods of conjugation provided between 1 and 2 gpm compared to 0.2 achieved previously by EDC. Furthermore, by repeat SE HPLC with and without CEA, both showed unimpaired immunoreactive fraction. MN14 (SANH)-MORF Epiberberine tolerated long-term storage best. More importantly, when labeled by hybridization with99mTc-labeled complementary MORF (99mTc-cMORF), the Epiberberine biodistribution of MN14 (SANH)-MORF was more favorable than that of MN14(SFB)-MORF in normal mice with lower liver (5.7 vs 9.4 %ID/g at 18 h) and spleen (3.5 vs. 8.4 %ID/g) accumulations and higher blood levels (4.8 vs. 3.4 %ID/g). Accordingly, only MN14 (SANH)-MORF was used in a pretargeting study in tumored mice. When targeted with99mTc -cMORF and at 2 days post injection of antibody-MORF, the results obtained with 6 g of antibody prepared in this way were essentially identical to that obtained previously with 30 g of antibody prepared via EDC. == Conclusions == Hydralink was used successfully to conjugate MORF to MN14 at higher gpm than that achieved earlier and without obvious compromise of properties. Using MN14 (SANH)-MORF, the influence of the higher gpm on pretargeting permitted lowering the dosages of MN14 administered and may permit administering higher levels of radioactivity in connection with therapy. Keywords:Pretargeting, conjugates, morpholino, monoclonal antibody, affinity enhancement == Introduction == Pretargeting has become an important approach to improve tumor targeting. In pretargeting, the long-circulating anti-tumor antibody conjugate is Epiberberine usually first administered and allowed time for specific localization in tumor and clearance from blood and other normal tissues before the injection of a short-circulating small radiolabeled effector. This technique has been shown to provide tumor targeting comparable to that of conventional targeting with directly labeled antibody but much earlier at 13 h post-administration of radiolabeled effector and, moreover, to dramatically improve the target/non-target ratio. The three Epiberberine approaches to pretargeting that have been reported thus far use biotin-(strep)avidin, bi-specific antibodies or oligonucleotides. Regardless of the approach, the high affinity and binding specificity of a tumor associated antibody is employed as the first injectate (15). The effector molecule is usually monovalent but bivalent effectors can show greatly enhanced residence time in tumor (6) by what has been called affinity enhancement (3,78). This laboratory has recently begun exploring DNA and other oligomers, in particular phosphorodiamidate morpholios (MORFs), for amplification pretargeting (910), conventional pretargeting (45) and, most recently, affinity enhancement pretargeting (11). Our preliminary in vitro studies of affinity enhancement using surface plasmon Rabbit polyclonal to CCNA2 resonance has shown that the target density is an important determinant of affinity enhancement pretargeting (12). One method of achieving the required higher density in MORF pretargeting is usually to increase the number of MORFs attached to each antibody. It therefore has become important to develop methods of conjugating anti-tumor antibodies with several MORFs per molecule and without compromise of antibody immunoreactivity or adversely influencing antibody pharmacokinetics. We reported herein on the use of commercially available reagents (Hydralink) for the conjugation of the anti-tumor antibody MN14 with Epiberberine MORF (Scheme 1). == Scheme 1. == Hydralink approach to conjugation of MN14 with MORF. == Materials and Methods == == Reagents == All MORFs were purchased from Gene Tools (Philomath, OR) with an amine group around the 3 comparative terminal for conjugation with either SANH/SFB or S-Acetyl mercaptoacetyltriglycine (MAG3). Each MORF was analyzed by the manufacturer.