Suppression of hypoxia-induced HIF-1α and of angiogenesis in endothelial cells by myo -inositol trispyrophosphate-treated erythrocytes

doi:10.1073/pnas.0607109103

Suppression of hypoxia-induced HIF-1α and of angiogenesis in endothelial cells by myo-inositol trispyrophosphate-treated erythrocytes

*Centre de Biophysique Moléculaire, Centre National de la Recherche Scientifique, Unité Propre de Recherche 4301, 45045 Orléans, France;
^†Oxyplus, Inc., 200 Boston Avenue, Medford, MA 02155; and
^‡Institut de Science et d'Ingénierie Supramoléculaires, Université Louis Pasteur, 8 Allée Gaspard Monge, BP 70028, 67083 Strasbourg Cedex, France

Contributed by Jean-Marie Lehn, August 18, 2006

Abstract

Allosteric regulation of oxygen delivery by RBCs may have significant effects on tumor growth. Indeed, angiogenesis, the formation of new blood vessels, is induced in growing tumors by low oxygen partial pressure. Hypoxia-inducible genes are switched on, among which are the VEGF gene and its receptors. Most important, under hypoxia, hypoxia-inducible factor 1α has a significantly prolonged half-life and up-regulates a number of hypoxia genes. Human microvascular endothelial cells (MECs), when subjected in vitro to hypoxia, align to form vessel-like structures as in the angiogenic process. We report here that, when cultured in hypoxic conditions in the presence of human RBCs loaded with a new membrane-permeant allosteric effector of Hb, myo-inositol trispyrophosphate (ITPP), endothelial cells (ECs) do not align, i.e., do not form “vessel”-like structures, because the “loaded” RBCs are capable of releasing under hypoxia more oxygen than their “normal” counterparts. Levels of VEGF and of hypoxia-inducible factor 1α, elevated in the human MECs under hypoxia, were dramatically reduced or even suppressed in the presence of the ITPP-loaded RBCs. Treatment of these ECs directly with free ITPP at different concentrations had no effect on their ability to undertake angiogenesis. Incubation with ITPP enhances the capacity of Hb to release bound oxygen, leading to higher oxygen tension in the hypoxic environment, thus inhibiting hypoxia-induced angiogenesis. These observations are suggestive of a potential in vivo role of ITPP-loaded, “low-O₂-affinity” RBCs in cancer therapy.

Footnotes

^¶To whom correspondence may be addressed. E-mail: lehn{at}isis.u-strasbg.fr or cnicolau{at}oxyplusinc.com
Author contributions: C.K., J.-M.L., and C.N. designed research; and R.G., C.C.D.S., and K.C.F. performed research.
↵ ^§Present address: Molecular Biology and Genetics Department, Democritus University of Thrace, Dimitras 19, 68100 Alexandroupolis, Greece.
Conflict of interest statement: R.G., J.-M.L., and C.N. own stock in Oxyplus, Inc., which holds the patents on the applications of inositol trisphosphate; they are listed as coinventors together with K.C.F. on these patents. In addition, R.G. and C.N. are employed by Oxyplus, Inc.
↵ ‖ To be etymologically correct, this compound should be named myo-inositol trispyrophosphate, rather than trispyrophosphate (28).
This paper was submitted directly (Track II) to the PNAS office.
Abbreviations:

EC,

endothelial cell;

MEC,

microvascular EC;

HBrMEC,

human brain-derived MEC;

HLMEC,

human lung-derived MEC;

HSkMEC,

human skin-derived MEC;

ITPP,

myo-inositol trispyrophosphate;

IP6,

myo-inositol hexakisphosphate;

PO2,

oxygen partial pressure;

HIF,

hypoxia-inducible factor