Development of antibodies against the fluoroquinolone sarafloxacin and molecular modeling studies of cross-reactive compounds

Polyclonal antibodies were prepared against the fluoroquinolone sarafloxacin. Sarafloxacin was conjugated directly to cationized bovine serum albumin (BSA) and ovalbumin. Balb/c mice were immunized with the sarafloxacin-BSA conjugate (cBSA-saraflox) and sarafloxacin-reactive sera (1-5) were obtained from these mice. Serum from mouse 1 (Ab1) exhibited the lowest IC50 for free sarafloxacin using an indirect competitive inhibition ELISA (ci-ELISA). Other structurally related quinolones, including difloxacin, enrofloxacin, norfloxacin, trovafloxacin and nalidixic acid, demonstrated cross-reactivity with the sarafloxacin antibodies as determined by ci-ELISA. ln an effort to correlate antibody binding with three-dimensional properties of the cross-reactive compounds, all of the fluoroquinolones as well as nalidixic acid were modeled, and global energy minima were determined using molecular mechanical and quantum mechanical methods. The results demonstrate that the three-dimensional models can yield information that explains observed cross-reactivity data. These models are particularly helpful when the chemical structure of an analog varies greatly from the immunogen yet the IC50 value for the compound is not vastly different. Furthermore, conformational and electronic data from this study can be used to predict whether other fluoroquinolones will exhibit good cross-reactivity in this ELISA.