The presence of prostate-specific antigen-related genes in primates and the expression of recombinant human prostate-specific antigen in a transfected murine cell line.

Human prostate-specific antigen (PSA) has been shown as an aid in the early detection of prostate cancer (W. J. Catalona et al., J. Am. Med. Assoc., 270: 948-954, 1993) and was approved in 1994 by the Food and Drug Administration for early detection of prostate cancer. Immunotherapies directed against PSA have been suggested in patients with metastatic prostate cancer. One of the essential questions is to define which nonhuman species express PSA for experimental studies. Using Southern blot analyses, genes related to human PSA have been detected in several nonhuman primate species, including chimpanzee, orangutan, gorilla, macaque, and rhesus monkey, but not in other mammalian species, including rabbit, cow, pig, dog, rat, or mouse. Immunohistochemical staining with anti-human PSA antisera detected strong staining in both human and monkey prostatic epithelial cells with no reactivity to rat prostate cells. Because the PSA gene is not present in the murine genome, a matched set of murine cell lines has been developed that may be useful to study the biochemical functions of PSA and as an experimental target for PSA-directed immunotherapy. To establish such cell lines, a C57BL/6 murine colon adenocarcinoma cell line, MC-38, was transfected with a retroviral vector containing cDNA encoding the human PSA gene. Genetic analysis of a PSA-secreting clone, PSA/MC-38, demonstrated that the PSA gene had been stably integrated into the MC-38 genome. The PSA/MC-38 cell line was found to secrete PSA into tissue culture medium, producing a protein of approximately M(r) 30,000. In vivo, PSA/MC-38 grew as a s.c. tumor in male and female mice. PSA/MC-38 tumors grew more rapidly in athymic mice than in syngeneic C57BL/6 mice, and in both mouse strains, the PSA/MC-38 tumors grew more slowly than control vector-transduced tumors. PSA was detected in the serum and tumors of PSA/MC-38 tumor-bearing mice. It is proposed that PSA/MC-38 cells may be used as a murine tumor model to test potential therapeutic vaccines and other experimental therapies directed against PSA.