Genistein combined polysaccharide (GCP) is highly active in both human and canine lymphoma models

Abstract

14126 Background: The soy isoflavones genistein and daidzein have demonstrated anticancer activity in vitro in multiple tumor types including leukemia/lymphoma, with evidence for a role in chemoprevention. GCP (Amino Up Chemical Co.) is a fermentation product of soy extract and the mycelium of Basidiomycetes, a process which converts soy isoflavones to their aglycone form, greatly increasing intestinal absorption. In humans, GCP has negligible toxicity at potentially active concentrations. We hypothesized that GCP would have significant anticancer activity in hematologic malignancies. Methods: Three human lymphoma cell lines (Jurkat, Raji, and Ramos), a leukemia line (HL60), and four canine lymphoid cell lines (GL-1, CLGL-90, CL1, and CLL-1390) were treated with GCP at doses ranging from 25 to 200 μg/ml. Growth effects were assessed by trypan blue exclusion 5–7 days following a single treatment. Flow cytometry and Westerns were used to measure changes in cell cycling, protein expression and apoptosis. We are conducting a single-agent dose escalation clinical trial in chemo-naïve canines with lymphoma. Results: GCP had striking cytotoxic effects in both canine and human lymphoma cell lines. In all human lines, the 50% inhibitory concentrations (IC50s) were less than 25μg/ml. At 100μg/ml, a concentration achievable in patient plasma, virtually no viable cells remained. Three of four canine lines were sensitive with IC50s in the range of 15–50μg/ml. Substantial G2 cell cycle accumulation was observed, apparent within two hours and maintained for at least 48h. GCP treatment induced apoptosis, as shown by an increase in sub-G1 DNA content and cleavage of PARP and caspase 3. At higher doses, elevated Bcl-2 levels were observed, suggesting a potential mechanism of resistance. These results provided the rationale for a clinical trial in canine patients at UC Davis. One patient with aggressive diffuse large B-cell lymphoma treated at 93 mg/kg/day (dose level 2) had a confirmed partial response. Conclusions: GCP has potent anticancer activity in vitro against lymphoid cell lines, with almost complete cell kill at doses achievable in patient plasma with minimal toxicity. A phase I clinical trial in canine lymphoma will determine whether testing in human lymphoma patients is warranted. No significant financial relationships to disclose.