Synthesis of sialyl Lewis super(a) (sLe super(a), CA19-9) and construction of an immunogenic sLe super(a) vaccine

• Published in: Cancer Immunology, Immunotherapy Immunotherapy, 2009-09, Vol.58 (9), p.1397-1405
• Main Authors: Ragupathi, Govind, Damani, Payal, Srivastava, Geeta, Srivastava, Om, Sucheck, Steven J, Ichikawa, Yoshi, Livingston, Philip O
• Format: Article
• Language: English
• ISSN: 0340-7004; 1432-0851
• DOI: 10.1007/s00262-008-0654-7

Sialyl Lewis super(a) (sLe super(a)), also termed CA19-9 antigen, is recognized by murine mAb19-9 and is expressed on the cancer cell surface as a glycolipid and as an O-linked glycoprotein. It is highly expressed in a variety of gastrointestinal epithelial malignancies including colon cancer and pancreatic cancer, and in breast cancer and small cell lung cancer, but has a limited expression on normal tissues. sLe super(a) is known to be the ligand for endothelial cell selectins suggesting a role for sLe super(a) in cancer metastases and adhesion. For these reasons, sLe super(a) may be a good target for antibody mediated immunotherapy including monoclonal antibodies and tumor vaccines. However, sLe super(a) is structurally similar to sLe super(x) and other blood group related carbohydrates which are widely expressed on polymorphonucleocytes and other circulating cells, raising concern that immunization against sLe super(a) will induce antibodies reactive with these more widely expressed autoantigens. We have shown previously both in mice and in patients that conjugation of a variety of carbohydrate cancer antigen to keyhole limpet hemocyanin (KLH) and administration of this conjugate mixed with saponin adjuvants QS-21 or GPI-0100 are the most effective methods for induction of antibodies against these cancer antigens. We describe here for the first time the total synthesis of pentenyl glycoside of sLe super(a) hexasaccharide and its conjugation to KLH to construct a sLe super(a)-KLH conjugate. Groups of five mice were vaccinated subcutaneously four times over 6weeks. Sera were tested against sLe super(a)-HSA by ELISA and against sLe super(a) positive human cell lines adenocarcinoma SW626 and small cell lung cancer (SCLC) DMS79 by FACS. As expected, mice immunized with unconjugated sLe super(a) plus GPI-0100 or unconjugated sLe super(a) mixed with KLH plus GPI-0100 failed to produce antibodies against sLe super(a). However, mice immunized with sLe super(a)-KLH conjugate without GPI-0100 produced low levels of antibodies and mice immunized with sLe super(a)-KLH plus GPI-0100 produced significantly higher titer IgG and IgM antibodies against sLe super(a) by ELISA. These antibodies were highly reactive by FACS and mediated potent complement mediated cytotoxicity against sLe super(a) positive SW626 and DMS79 cells. They showed no detectable cross reactivity against a series of other blood group-related antigens, including Le super(y), Le super(x), and sLe super