Tumor immunolocalization using monoclonal antibodies which bind placental alkaline phosphatase

Increased levels of PLAP in the serum of patients with certain types of cancer, particularly ovarian cancer and seminoma, indicate that PLAP may be a useful marker for detection of those tumors. Our goal was to further examine the usefulness of PLAP as a tumor marker by investigating the possibility that monoclonal antibodies binding PLAP may be useful for detection of the growth and metastasis of tumors which express the enzyme. Thus, we developed an experimental system where both a PLAP- positive and PLAP- negative tumor were grown in nude mice. The mice were then injected with radioactively-labeled F(ab)'2 fragments of a monoclonal antibody. The results are in accord with those of others and indicate that the monoclonal antibody localized in the PLAP-positive tumor 10 times or more often than it localized in the PLAP-negative tumor or in normal mouse tissues. Therefore, PLAP would appear to be a useful marker for the immunodetection of certain tumors in humans by external scintigraphy. PLAP may similarly be effective as a target for the delivery of toxic reagents to tumor cells in vivo using drugs conjugated to PLAP-specific monoclonal antibodies.