RAV12 is a chimeric IgG1 monoclonal antibody directed against a glycotope expressed by >90 % of gastric, colon and pancreatic adenocarcinomas, and smaller proportions of prostate, ovarian, breast and renal cell carcinomas. RAV12 was constructed based on its murine precursor, KID3, which was generated by immunization of mice with a Raven proprietary human kidney progenitor cell line and selected for development because of its cytotoxic activity in vitro. Like KID3, RAV12 exhibited cytotoxic activity in vitro (ED50 =15 ug/mL) against the COLO 205 human colon tumor-derived cell line, which expresses high levels of the RAV12 epitope, RAAG12. The mechanism of action of RAV12-induced cytotoxicity in vitro is consistent with oncotic cell death, in that within hours after RAV12 treatment, cells increase in volume, followed by bursting of the plasma membrane and release of LDH. This cytotoxicity is attenuated by reduced extracellular sodium conditions. Cytotoxic activity was correlated with high and uniform antigen expression levels, antigen cross-linking, and internalization of RAV12. Biochemical studies demonstrated that RAV12 recognizes a primate-specific N-linked glycotope expressed on multiple proteins present on the cell surface of tumor-derived cell lines. RAV12 exhibited potent anti-tumor activity in murine tumor xenograft models. RAV12/KID3 reduced the average size of four different human gastrointestinal tumor cell xenografts grown beneath the renal capsule of mice by more than 90% at the end of the 2-week dose period. At doses of 50 mg/kg and above, RAV12 eliminated detectable subrenal capsule tumor xenografts, with no tumor re-growth seen 2 weeks following the cessation of dosing. In subcutaneous tumor xenografts, the minimal efficacious dose of RAV12 dosed twice weekly via the iv route was 3 mg/kg in the SNU-16 gastric tumor xenograft model, conferring 70-82% tumor growth inhibition. Corresponding serum trough levels of RAV12 at this dose and regimen averaged 55 ug/mL. In pharmacokinetic studies in cynomolgus monkeys, serum trough levels above 55 ug/mL were achieved by dosing once weekly between 10 and 30 mg/kg/dose. The human equivalent dose range by allometric scaling is approximately 3-10 mg/kg, which is within the dose escalation scheme of a planned RAV12 phase I clinical study. In addition to its prevalent expression by many tumor types, RAAG12 is also expressed by normal non-keratinizing epithelia, including some ductal epithelia, stratified squamous epithelia, and gastrointestinal epithelia. Although RAAG12 is expressed by normal epithelia, RAV12 was well tolerated in a repeat dose toxicology study in cynomolgus monkeys, in which a NOAEL was established supporting the proposed starting dose for the planned phase I study. An IND application was filed in November 2004.

[Proc Amer Assoc Cancer Res, Volume 46, 2005]