Radioimmunoassay of a cancer-related glycoprotein. Circulating levels

Purification and partial characterization of a malignancy-associated glycoprotein

The isolation from cancer patient serum of a glycoprotein (Cc) associated with the presence of a variety of malignancies was previously reported. Although preliminary chemical and physical data indicated that Cc was different from identified circulating glycoproteins, subsequent immunological studies suggested that it was closely related to alpha 1-acid glycoprotein. Further analysis revealed the presence of two components in some Cc preparations and prompted a re-examination of the isolation and characterization data. In the present study, Cc was purified by a modified protocol which involved the use of pleural fluid obtained from individuals with cancer, and an alpha 1-acid glycoprotein antibody column to remove contaminating alpha 1-acid glycoprotein. Typically, the material not retained by the antibody column gave a single band with Mr 53,000 when subjected to sodium dodecyl sulfate-polyacrylamide electrophoresis. Amino terminal analysis revealed that the protein contained a blocked amino terminus, and carbohydrate analysis indicated that complex, asparagine-linked saccharide units were present. The product could be distinguished from alpha 1-acid glycoprotein and other previously described circulating glycoproteins by several criteria, including molecular weight, isoelectric point, and amino acid and carbohydrate composition. One of three preparations isolated had an apparent Mr of 59,000. Carbohydrate analysis as well as deglycosylation studies showed that the change in molecular weight was due to increased glycosylation.

Metastatic uveal melanoma: an ocular melanoma associated antigen in the serum of patients with metastatic disease

Two monoclonal antibodies, MAb8-1H and ME491, which bind to different determinants of the same highly glycosylated melanoma-associated antigen, were used to determine melanoma-associated antigen levels in serum samples from patients treated for primary choroidal or ciliary body melanoma and who subsequently developed systemic metastasis. An immunoassay was developed in which ME491 was absorbed to polystyrene beads in order to bind the melanoma-associated antigen present in serum. 125I-MAb8-1H was used to detect the bound antigen. This double-determinant immunoassay is both sensitive and reproducible. Supernatant fluids of tissue cultured melanoma cell lines served as positive standards for the calculation of melanoma-associated antigen units. The mean serum levels of melanoma-associated antigen were 7.7 units for patients with benign ocular conditions, 9.51 units for patients with choroidal melanoma without documented metastatic disease, and 48.3 units for patients with choroidal melanoma and documented systemic metastasis. The clinical implications of using this test as a screening method for the detection of metastatic disease is discussed.