Nitrite may serve as a combination partner and a biomarker for the anti-cancer activity of RRx-001

Biorheology. 2019;56(4):221-235. doi: 10.3233/BIR-190213.


Background: RRx-001 is an anti-cancer immunotherapeutic that increases the sensitivity of drug resistant tumors via multiple mechanisms which involve binding to hemoglobin and enhancing nitrite reductase activity of deoxyhemoglobin.

Objective: In the present study, the effect of clinically used doses of RRx-001 on erythrocyte deformability was examined.

Methods: A dose dependent effect of RRx-001 (1-1000 micro molar) on erythrocyte deformability was measured by ektacytometer under hypoxia (n = 8). Low dose RRx-001 (20 micro molar) in the presence of ODQ (1H-[1,2,4]Oxadiazolo[4,3-a]quinoxalin-1-one), L-NAME (L-NG-Nitroarginine methyl ester) or nitrite were examined both in normoxia and hypoxia. Intracellular nitric oxide (NO) levels were measured fluorometrically with DAF-FM-DA.

Results: Higher doses of RRx-001 (100, 1000 micro molar) significantly decreased erythrocyte deformability under hypoxia (p < 0.01; p < 0.05, respectively). RRx-001 (20 micro molar), alone or in combination with ODQ or L-NAME, did not change deformability. However, RRx-001 and nitrite caused an increase in deformability (p < 0.01) under hypoxia. RRx-001 induced NO production was more pronounced in the presence of nitrite (p < 0.05).

Conclusions: Co-administration of RRx-001 and nitrite under hypoxic conditions results in a significant increase in erythrocyte deformability that is related to increased NO production. We suggest that measurement of serum nitrite level in RRx-001 treated cancer patients should be routinely undertaken and supplemented if levels are low for maximal activity.

Keywords: RRx-001; deformability; erythrocyte; hypoxia; nitric oxide.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Antineoplastic Agents / pharmacology*
  • Azetidines / pharmacology*
  • Biomarkers / blood
  • Erythrocyte Deformability / drug effects
  • Erythrocytes / cytology
  • Erythrocytes / drug effects
  • Humans
  • NG-Nitroarginine Methyl Ester / pharmacology
  • Neoplasms / blood*
  • Neoplasms / drug therapy
  • Nitric Oxide / blood*
  • Nitrites / pharmacology*
  • Nitro Compounds / pharmacology*


  • Antineoplastic Agents
  • Azetidines
  • Biomarkers
  • Nitrites
  • Nitro Compounds
  • RRx-001
  • Nitric Oxide
  • NG-Nitroarginine Methyl Ester