The ribosome inhibiting protein riproximin shows antineoplastic activity in experimental pancreatic cancer liver metastasis

Pancreatic ductal adenocarcinoma (PDAC) has one of the poorest prognoses of all malignancy types. To improve the survival of patients with PDAC, the development of novel anticancer agents is warranted. Riproximin (Rpx) is a newly identified plant lectin, which was isolated from Ximenia americana. The ribosome inactivating protein of type II exhibits potent anticancer activity as recently demonstrated. The rat PDAC cell line ASML was used for in vitro and in vivo studies. The antiproliferative effect of Rpx was assessed using an MTT assay. The modulation of proteins involved in apoptosis was evaluated using western blotting. Tumor-bearing nude rats were treated with Rpx, gemcitabine (GEM) or dinaline (DIN) as single agents, or a combination of Rpx with GEM, or DIN. Rpx was administered intraperitoneally at doses of 1.7-5.4 µg/kg, three times/week, GEM was administered intravenously (50 mg/kg/week) and DIN perorally (10 mg/kg, 5 times/week). Rpx inhibited ASML cell proliferation at IC50-values of 0.8-172 pM, caused apoptosis and reduced tumor growth significantly by 90% (P<0.05). The survival rate of rats was significantly increased (21.8 days for Rpx treated vs. 17.6 days for control rats; P=0.05). Higher doses of Rpx caused no further reduction in tumor size when compared with the low dose of Rpx or a combination of Rpx with GEM, or DIN. The standard drug GEM alone was less effective compared with Rpx. In addition, DIN was ineffective, and in combination, reduced the activity of Rpx. These results suggest that Rpx has an evident potential for use in pancreatic cancer treatment. Further experiments are required in order to elucidate its affinity for certain cancer cells and to optimize the combination therapy with other antineoplastic agents.