Acute myelogenous leukemia (AML) is often a fatal disease where after strong induction therapy most patients relapse and die. A-type proanthocyanidins (A-PACs) are a unique class of compounds found in cranberries (Vaccinium macrocarpon Ait.) that we have found to be effective against several leukemia cell lines and primary AML samples in vitro. Moreover, A-PACs possess a unique ether bond and have ortho-hydroxyl phenolic groups that have the potential to bind to iron, alter redox status, and other biological effects.

We found that pre-treatment with antioxidants or holo-transferrin (iron-saturated transferrin) partially protected AML cells from A-PAC induced cell death (p<0.01). A-PACs were also found to selectively ablate leukemia stem and progenitor cells, with minimal effects on normal hematopoetic stem cells. Furthermore, AML engraftment of cells treated ex vivo with 62.5 μg/ml A-PACs was decreased (90.6%, n = 3, p<0.001), whereas normal CD34+ cells retained engraftment capability in immunodeficient mice. It was also found that a fraction consisting of A-PACs that ranged from 2 to 7 degrees of polymerization were more effective than individual A-PACs. This information led us to investigate the anti-leukemia effects of A-PACs in AML patient-derived xenografts (AML-PDX) and to further investigate the mechanisms associated with these compounds.

AML-PDX mice (n = 15), were treated for 2.5 weeks via intraperitoneal injections of A-PACs (25 or 50 mg/kg dose every 3 days) or a vehicle control (PBS every 3 days). Mice were sacrificed and leukemia engraftment was evaluated using anti-human CD45 and CD33. Moreover, primary cells treated with A-PACs were assessed for effects on iron metabolism, oxidative stress, cytokine response, and survival pathways by gene expression analysis or flow cytometry.

Administration of A-PACs to AML-PDX tumors reduced tumor burden. Mice that were treated with the vehicle control had engraftment of AML primary cells equivalent to 12.51% (95% CI: 4.9, 20.11; n = 5), whereas the mice treated with the 50 mg/kg and 25 mg/kg A-PACs showed a level of engraftment of 5.2% (95% CI: 1.5, 8.9; n = 5) and 5.4% (95% CI: 2.3, 8.5; n = 5), respectively. These results indicated more than a 50% reduction in engraftment, which was better or equal to the effects we observed in mice treated with high-dose cytarabine, a standard care drug. Moreover, no toxic effects were observed in the mice. It was also found that both cells and mice treated with A-PACs lead to the production of specific subset of cytokines. Global gene expression data showed consistent upregulation of some of these cytokines, and also upregulation of NF-κB and enzymes indicative of oxidative stress.

The results indicate that A-PACs not only target primary AML cells in vitro, but are also effective in vivo by a potentially novel mechanism. Further elucidation of this mechanism may uncover new vulnerabilities of this disease.

Citation Format: Laura M. Bystrom, Luis Andres Lara-Martinez, Bernardo Gomel, Burak Isal, Hongliang Zong, Sabrina Martinez, Catherine Neto, Stefano Rivella, Monica L. Guzman. A-type proanthocyanidins selectively target acute myeloid leukemia cells in vitro and in vivo. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 1232.