Generation and characterization of LPA-KIV9, a murine monoclonal antibody binding a single site on apolipoprotein(a).

Lipoprotein(a) [Lp(a)] is a risk factor for cardiovascular disease and a target of therapy, but Lp(a) measurements are not globally standardized. Commercially-available assays generally use polyclonal antibodies that detect multiple sites within the kringle (K) IV2 repeat region of Lp(a) and may lead to inaccurate assessments of plasma levels. With increasing awareness of Lp(a) as a cardiovascular risk factor and the active clinical development of new potential therapeutic approaches, the broad availability of reagents capable of providing isoform-independence of Lp(a) measurements is paramount. To address this issue, we generated a murine monoclonal antibody that binds to only one site on apolipoprotein(a). A BALB/C mouse was immunized with a truncated version of apolipoprotein(a) that contained eight total KIV repeats, including only one copy of KIV2. We generated hybridomas, screened them and successfully produced a KIV2-independent monoclonal antibody, named LPA-KIV9. Using a variety of truncated apolipoprotein(a) constructs to map its binding site, we found that LPA-KIV9 binds to KIV9, without binding to plasminogen. Fine peptide mapping revealed that LPA-KIV9 bound to the sequence 4076LETPTVV4082 on KIV9. In conclusion, the generation of monoclonal antibody LPA-KIV9 may be a useful reagent in basic research studies and in the clinical application of Lp(a) measurements.