Amelioration of thrombocytopenia with concomitant ornithine in sarcoma-bearing rats receiving high dose difluoromethylornithine

Herbacetin Is a Novel Allosteric Inhibitor of Ornithine Decarboxylase with Antitumor Activity

Ornithine decarboxylase (ODC) is a rate-limiting enzyme in the first step of polyamine biosynthesis that is associated with cell growth and tumor formation. Existing catalytic inhibitors of ODC have lacked efficacy in clinical testing or displayed unacceptable toxicity. In this study, we report the identification of an effective and nontoxic allosteric inhibitor of ODC. Using computer docking simulation and an in vitro ODC enzyme assay, we identified herbacetin, a natural compound found in flax and other plants, as a novel ODC inhibitor. Mechanistic investigations defined aspartate 44 in ODC as critical for binding. Herbacetin exhibited potent anticancer activity in colon cancer cell lines expressing high levels of ODC. Intraperitoneal or oral administration of herbacetin effectively suppressed HCT116 xenograft tumor growth and also reduced the number and size of polyps in a mouse model of APC-driven colon cancer (ApcMin/+). Unlike the well-established ODC inhibitor DFMO, herbacetin treatment was not associated with hearing loss. Taken together, our findings defined the natural product herbacetin as an allosteric inhibitor of ODC with chemopreventive and antitumor activity in preclinical models of colon cancer, prompting its further investigation in clinical trials.

Effect of ornithine in parenteral nutrition regimens on difluoromethylornithine-induced platelet suppression and changes in tumor polyamine content

We have demonstrated that DFMO-induced thrombocytopenia can be ameliorated with concomitant ornithine (Orn) in chow-fed rats; a reversal in DFMO-associated tumor polyamine reduction and antitumor activity, however, was also evident. To determine the effect of Orn in total parenteral nutrition (TPN) regimens on DFMO-induced thrombocytopenia and changes in tumor polyamine concentrations, Ward-colon-tumor-bearing (WCT) rats were given TPN with arginine (ENA) or with ornithine substituted for arginine (ENO) alone or with DFMO (1.5 g/day) added directly to the infusate. After 4 days, the peripheral blood platelet counts for ENA (917 +/- 151 x 10(3)/mm3) or ENO (908 +/- 67 x 10(3)/mm3) were equivalent to those of chow fed rats (901 +/- 42 x 10(3)/mm3). ENA/DFMO rats had significant thrombocytopenia (607 +/- 185 x 10(3)/mm3), which was completely ameliorated for ENO/DFMO rats (939 +/- 111 x 10(3)/mm3). Peripheral white blood count, hematocrit, and other hematological parameters were not affected. Tumor putrescine content for ENA rats (46.9 +/- 8.7 nmol/g) was equal to that for chow-fed rats (44.8 +/- 6.2 nmol/g) and ENO rats (53.6 +/- 8.3 nmol/g). The reduction in tumor putrescine content for ENO/DFMO rats (19.6 +/- 6.9 nmol/g) was equivalent to that of ENA/DFMO rats (14.7 +/- 3.0 nmol/g). Tumor spermidine was reduced only for the ENA/DFMO rats while spermine was slightly elevated. Tumor spermine content for ENO/DFMO rats (57.2 +/- 12.0 nmol/g) was equal to that for ENO rats (65.6 +/- 8.7 nmol/g) but was significantly (p = 0.004) reduced when compared with rats receiving ENA/DFMO (89.4 +/- 20.4 nmol/g). The results of this study show that TPN with Orn substituted for arginine can be used with a chemotherapeutic dose of DFMO to ameliorate the thrombocytopenia. The DFMO-induced reduction in tumor putrescine content, however, was not affected when Orn was substituted for arginine in a parenteral nutrition regimen. These results suggest that the antitumor activity of DFMO would not be adversely affected by coadministering DFMO with a TPN regimen with Orn substituted for arginine.