Affiliations: [a] Ordu University, Faculty of Medicine, Department of Physiology, Ordu, Turkey | [b] Koc University School of Medicine, Sariyer, Istanbul, Turkey | [c] EpicentRx Inc, 4445 Eastgate Mall, Suite 200, San Diego, CA, USA | [d] Department of Bioengineering, University of California San Diego (UCSD), La Jolla, CA, USA
Correspondence:
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Corresponding author: Dr. Ozlem Yalcin, Koc University School of Medicine, Sariyer, Istanbul, Turkey. Tel.: +90 212 338 1136; Fax: +90 212 338 1168; E-mail: [email protected]
Abstract: 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.
