FPGS and colorectal cancer: Secondly, preclinical studies suggested that folyl-polyglutamate synthase (FPGS) expression, the enzyme required for polyglutamation of RTX but not BGC9331, may be lower in human ovarian tumour cell lines compared with human colorectal cancer cell lines and BGC9331 overcomes the associated resistance to RTX in these cells (Jackman et al, 2002).