Allosteric Modifier Of Hemoglobin Research Articles

The effect of RSR13, a synthetic allosteric modifier of hemoglobin, on brain tissue pO2 (measured by EPR oximetry) following severe hemorrhagic shock in rats.

RSR13 is a synthetic allosteric modifier of hemoglobin that decreases the oxygen binding affinity of hemoglobin, potentially increasing oxygen availability to hypoxic tissues. Using in vivo EPR to directly measure cortical pO2, we examined whether RSR13 would improve brain tissue pO2 following severe hemorrhagic shock in rats. Hemorrhagic shock was induced by withdrawing blood (2.7-2.8 mL/100 g/15 min). Following a 30 min shock period, resuscitation was performed by infusion with Ringer lactate plus RSR13 (150 mg/kg) or saline (control). Following hemorrhage, brain pO2 decreased by about 14 mm Hg in both groups. Following crystalloid resuscitation brain pO2 remained depressed in the control group but returned to the pre-hemorrhage values in the rats that received RSR13. RSR13 immediately increased and maintained the paO2 while controls had a very gradual increase towards pre-hemorrhage values. There was no difference in the blood pressure or heart rate between groups. RSR13 may have useful applications to decrease the effects of acute hemorrhagic hypoxemia by increasing brain oxygenation.

The dose-dependent effect of RSR13, a synthetic allosteric modifier of hemoglobin, on physiological parameters and brain tissue oxygenation in rats.

RSR13 is a synthetic allosteric modifier of hemoglobin that decreases the oxygen-binding affinity of hemoglobin, increasing the P50. As a result, tissue oxygen tension is expected to increase. Using the capabilities of in vivo EPR, we directly examined the effect of RSR13 on brain pO2 in rats and the relationship between any change in brain oxygenation and changes in physiological parameters, including blood gases. The brain pO2 and arterial blood paO2 were increased significantly (p < 0.005) following RSR13 administration. The peak increase of brain tissue pO2 was 8.8 +/- 1.2 mm Hg in the animals receiving 150 mg/kg RSR13 and 13 +/- 3 mm Hg in the animals receiving 300 mg/kg RSR13. There was no difference among groups in MBP, heart rate, paCO2, pH, or HCO3. These data indicate that in anesthetized rats, RSR13 dose-dependently increases brain pO2 without affecting other physiologic parameters. This capability is likely to be very useful in circumstances where the pO2 of the brain is compromised.

Pharmacological correction of hypothermic P(50) shift does not alter outcome from focal cerebral ischemia in rats.

Hypothermia decreases the arterial PO(2) at which hemoglobin is 50% saturated (P(50)), increasing hemoglobin O(2)-binding affinity. We used RSR13, a synthetic allosteric modifier of hemoglobin that increases P(50), to study the role of altered hemoglobin O(2)-binding affinity in mild hypothermic neuroprotection. RSR13 (150 mg/kg iv) restored P(50) to normothermic values. Rats underwent 70 min of middle cerebral artery occlusion (MCAO) at 30.0, 34.0, or 37.5 degrees C with hemoglobin saturation held at 98-100%. The 34.0 degrees C group received RSR13 or vehicle before ischemia. After 7 days of recovery, infarct volumes were reduced in all hypothermic groups, without evidence of a detrimental effect on infarct size or neurological score as a result of P(50) correction. To examine for a beneficial effect of P(50) correction, ischemia duration was increased to 120 min in rats maintained at 34.0 degrees C. Correction of P(50) by RSR13 did not alter cerebral infarct sizes or neurological scores. The decrease in P(50), caused by mild hypothermia, could not be associated with infarct size or neurological deficit resulting from ischemic brain hypoxia in rats.

Synthesis and X-ray studies of chiral allosteric modifiers of hemoglobin.

This study was designed to investigate the effect of chirality on the allosteric activity of a series of Hb allosteric modifiers. The chiral analogues were based on the lead compound (4), JP7, [1-[4-(((3,5-dimethylanilino)carbonyl)methyl)phenoxy]cyclopentanecarboxylic acid] with different D- and L-amino acids conjugated to the JP7 acid moiety. The D-isomers were the most potent in vitro effectors in Hb solutions as well as with whole blood. In general, this study demonstrated that the chirality of extended amino acid side chains in JP7 conjugates plays an important role in observed degree of allosteric activity. The binding site interactions for four analogues were determined by single crystallographic diffraction studies. Conclusions show that the chiral configuration of some of the D-isomers enable the effectors to bind with a greater number of interactions with the protein residues. D- and L-isomers with equivalent or near equivalent allosteric activity did not show any significant differences or interactions between their amino acid side chains and the protein. The most potent effectors, in vitro, were compounds 15 and 19, D-isomers of leucine and phenylalanine, respectively. Compounds 21, 22, 30, and32 were more potent in vitro in Hb solutions than JP7.

RSR13 e modificação alostérica da afinidade hemoglobina-oxigênio: abuso entre atletas

O ácido metilpropiônico (RSR13) é um modificador alostérico da hemoglobina, com a qual se liga de forma não-covalente, diminuindo sua afinidade pelo oxigênio de modo dose-dependente e, conseqüentemente, aumentando a oxigenação periférica. O objetivo deste artigo é apresentar brevemente as evidências científicas acerca das características farmacológicas e funcionais, indicações médicas e efeitos adversos do uso do RSR13 por atletas, a mais recente alternativa de aumento artificial do desempenho. Estudos experimentais preliminares verificaram algum efeito positivo do RSR13 sobre a recuperação do miocárdio isquêmico e sobre a extensão da isquemia cerebral, mas as principais indicações estudadas atualmente são a cirurgia com hipotermia e cardioplegia durante circulação extracorpórea e o uso como agente coadjuvante potenciador da radioterapia para certos tumores sólidos. Somente um estudo em modelo canino mostrou aumento do consumo máximo de oxigênio em músculo isolado, não existindo evidências de que o RSR13 possa efetivamente melhorar o desempenho em humanos. Em realidade, já foram descritos efeitos adversos, como diminuição da perfusão sanguínea, elevação da pressão arterial e diminuição da função renal. Antecipando o potencial aumento da utilização do RSR13 por atletas, métodos já foram desenvolvidos para sua detecção em amostras de urina humana.

RSR13, a potential athletic performance enhancement agent: detection in urine by gas chromatography/mass spectrometry

RSR13 (2-[4-[[(3,5-dimethylanilino)carbonyl]methyl]phenoxyl]-2-methylpropionic acid) is a synthetic allosteric modifier of hemoglobin that is currently in a phase III clinical trial as a radio-enhancing agent. RSR13 has been shown to increase maximum oxygen uptake (VO(2max)) in a canine skeletal model, which makes it a potential performance-enhancing agent for endurance athletes, since VO(2max) is an index of aerobic capacity. In this study we present a method for the detection of RSR13-bis-TMS in human urine by gas chromatography/electron impact ionization mass spectrometry (GC/EI-MS) suitable for doping control laboratories. The presence of RSR13 is detected by monitoring the ions m/z 485 ([M](+.)) and 470 ([M - CH3](+)). The limit of detection (LOD) is less than 2 ng/mL in urine. Urine samples collected from clinical trial subjects immediately prior to receiving an infusion of RSR13 showed no evidence of RSR13, whereas post-infusion urine samples contained up to 1181 microg/mL. A urine sample collected 36 h after administration of a small dose (10 mg/kg) and diluted 100-fold showed a signal 80 times higher than the LOD. Urine samples obtained from 100 randomly selected athletes in our routine testing program did not show any traces of RSR13. Sport authorities may wish to add RSR13 to the list of prohibited substances.

Enhancement of tumor oxygenation and radiation response by the allosteric effector of hemoglobin, RSR13.

Prior studies using pO(2) microelectrodes have shown that RSR13, an allosteric modifier of hemoglobin, increases tissue oxygenation in vivo. Recently, measurements of tissue oxygenation have been performed by many investigators using blood oxygen level-dependent magnetic resonance imaging (BOLD MRI). In this study, we tested the hypothesis that the BOLD MRI signal ratio in tumors will change after administration of RSR13. NCI-H460 human lung carcinoma cells were used as a xenograft in athymic nude mice. Mice with 1-cm(3) tumors in the flank were anesthetized and mounted on the MRI apparatus, and various doses of RSR13 were administered intraperitoneally (i.p.). MR images were then acquired at 10-min intervals for up to 60 min after injection. The effect of RSR13 on tumor response was studied using the same mouse xenograft model with tumor growth delay measurements. RSR13 increased the MRI signal ratio [Intensity(t)/Intensity(t = 0)] in a dose-dependent manner, with maximum increases occurring 30 min after RSR13 was administered. An RSR13 dose of 200 mg/kg proved to be optimum. Since the MRI signal ratio has been shown previously to be linearly related to tissue oxygenation, the changes in the MRI signal ratio can be attributed to changes in tumor oxygen levels. Using a 200-mg/kg dose of RSR13, with a 10-Gy dose of radiation administered to tumors 30 min later, enhancement of radiation-induced tumor growth delay by RSR13 was observed (enhancement factor = 2.8). Thus our MRI results support and verify the previously reported RSR13-induced increase in tumor oxygenation obtained using pO(2) microelectrodes. Based upon these results and other previous studies, the mechanism of enhancement of the effect of radiation by RSR13 probably involves an increase in tumor oxygenation.

Allosteric Modification of Oxygen Delivery by Hemoglobin

Hemoglobin affinity for oxygen is altered by pH, temperature, and high altitude, making oxygen more readily available to the tissues. RSR13 (Allos Therapeutics, Denver, CO), an analog of the drugs clofibrate and bezofibrate, causes a dose-dependent, rightward shift of the oxygen dissociation curve in animals and humans. We tested the safety, pharmacodynamic, and pharmacokinetics of RSR13, an allosteric modifier of hemoglobin, in patients having general surgery in a prospective, randomized, double-blinded, placebo-controlled, dose-escalation clinical trial. After the induction of general anesthesia with endotracheal intubation, 26 patients who consented were randomly assigned to receive an infusion of RSR13 or placebo (2:1) in an ascending dose scheme. Doses studied were 10, 20, 30, 40, 50, 60, 75, and 100 mg/kg infused for 30–60 minutes. Samples were taken for determination of RSR13 concentration in plasma, red blood cells, and urine, as well as for determination of the p50 in blood by using three-point tonometry at frequent intervals after the infusion of the study drug. The RSR13 administration resulted in a dose-dependent rightward shift of the oxygen dissociation curve, with the target p50 shift of 10 mm Hg achieved at the 75- and 100-mg/kg doses. No differences were seen between RSR13 and placebo groups in laboratory or hemodynamic findings, with the exception of a transient, limited increase in serum creatinine in 3 patients who received RSR13. These increases peaked at 48 h (2.2, 3.5, and 4.5 mg/dL respectively), were not associated with oliguria, did not require treatment, and did not prolong hospitalization in any patient. The reasons for the unexplained increases in serum creatinine were not evident, but potentially included surgery itself (nephrectomy), patient condition, or the concomitant administration of renally cleared medications or drugs that affect renal blood flow.

Post-ischemic RSR13 amplifies the effect of dizocilpine on outcome from transient focal cerebral ischemia in the rat

In a recent study of focal cerebral ischemia in rats, pre-ischemic administration of the synthetic allosteric hemoglobin modifier RSR13 (2-[4-[[3,5-dimethylanilino) carbonyl] methyl] phenoxy]-2-methylproprionic acid) reduced cerebral infarct size when combined with the NMDA receptor antagonist dizocilpine (MK-801) but not when given alone. We hypothesized that post-ischemic RSR13 administration would enhance neuroprotection afforded by NMDA receptor antagonism in a rat model of transient middle cerebral artery occlusion (MCAO). Fasted normothermic Wistar rats underwent 75 min of temporary MCAO. At onset of reperfusion, rats randomly received: (1) 0.9% NaCl (vehicle) i.v. alone ( n=16); (2) 0.9% NaCl+dizocilpine (0.25 mg/kg) i.v. ( n=16); or (3) RSR13 (150 mg/kg)+dizocilpine (0.25 mg/kg) i.v. ( n=17). Seven days later, neurologic deficit and cerebral infarct size were determined. Dizocilpine alone compared to vehicle reduced mean±S.D. subcortical (52±24 mm 3 vs. 122±64 mm 3, P=0.003) and cortical (35±35 mm 3 vs. 125±72 mm 3, P=0.00074) infarct volumes. When compared to dizocilpine alone, the combination of RSR13+dizocilpine further reduced subcortical (37±14 mm 3 vs. 52±24 mm 3, P=0.034) and cortical (8±19 mm 3 vs. 35±35 mm 3, P=0.018) infarct size. RSR13+dizocilpine improved neurologic scores vs. either dizocilpine alone ( P=0.0014) or vehicle ( P=10 −7). The combination of NMDA receptor antagonism and a RSR13 mediated rightward shift of the oxy-hemoglobin dissociation curve improved outcome from MCAO. Because this occurred after reperfusion, our results suggest that the post-ischemic brain continues to suffer from hypoperfusion defects, which are amenable to therapy by enhanced O 2 delivery. The results also support the concept that neuroprotective strategies, which combine drugs with different mechanisms of action, may yield cumulative benefits.

RSR13, a Synthetic Allosteric Modifier of Hemoglobin, Improves Myocardial Recovery Following Hypothermic Cardiopulmonary Bypass

Background —During hypothermic blood cardioplegia, oxygen delivery to myocytes is minimal with ineffective anaerobic metabolism predominating. RSR13, 2-[4-[[(3,5-dimethylanilino) carbonyl]methyl]phenoxy]-2-methylpropionic acid, a synthetic allosteric modifier of hemoglobin (Hb), increases release of oxygen from Hb, increasing oxygen availability to hypoxic tissues, and reverses the hypothermia-dependent increase in Hb oxygen affinity. We studied recovery of myocardial mechanical and metabolic function and examined myocardial morphology after cardioplegia, comparing RSR13 (1.75 mmol/L)-supplemented blood (RSR13-BC) to standard blood cardioplegia (BC). Methods and Results —Twelve dogs underwent 15 minutes of 37°C global ischemia on cardiopulmonary bypass, followed by 75 minutes of hypothermic cardioplegia (13°C) with either BC (n=6) or RSR13-BC (n=6). There were no differences in baseline function between groups. Cardiac function was assessed after 30 minutes of 37°C reperfusion (BC versus RSR13-BC, respectively) by measuring: % return to normal sinus rhythm (0/100%), % of baseline+dP/dt (33.7±1.7/76.3±1.9), % of baseline−dP/dt (26.6±2.0/81.1±1.6), stroke volume (3.5±0.5/7.1±0.9 mL), cardiac output (340±20/880±40.3 mL/min), and LVEDP (11.3±2.2/0.3±2.9 mm Hg). Postischemic oxidative and metabolic parameters including myocardial lactate, pyruvate, ATP content, and percent water content also were determined. Histological analysis demonstrated preservation of endothelial and myocyte morphology in hearts receiving RSR13-BC compared with BC. Conclusions —These results indicate that in the setting of hypothermic cardiopulmonary bypass, RSR13 improves recovery of myocardial mechanical and metabolic function compared with standard hypothermic BC. Findings from this study suggest that RSR13-BC, by decreasing hemoglobin oxygen affinity, improves oxidative metabolism and preserves cellular morphology, resulting in significantly improved contractile recovery on reperfusion.

RSR13, a synthetic allosteric modifier of hemoglobin, improves myocardial recovery following hypothermic cardiopulmonary bypass.

During hypothermic blood cardioplegia, oxygen delivery to myocytes is minimal with ineffective anaerobic metabolism predominating. RSR13, 2-[4-[[(3,5-dimethylanilino) carbonyl]methyl]phenoxy]-2-methylpropionic acid, a synthetic allosteric modifier of hemoglobin (Hb), increases release of oxygen from Hb, increasing oxygen availability to hypoxic tissues, and reverses the hypothermia-dependent increase in Hb oxygen affinity. We studied recovery of myocardial mechanical and metabolic function and examined myocardial morphology after cardioplegia, comparing RSR13 (1.75 mmol/L)-supplemented blood (RSR13-BC) to standard blood cardioplegia (BC). Twelve dogs underwent 15 minutes of 37 degrees C global ischemia on cardiopulmonary bypass, followed by 75 minutes of hypothermic cardioplegia (13 degrees C) with either BC (n=6) or RSR13-BC (n=6). There were no differences in baseline function between groups. Cardiac function was assessed after 30 minutes of 37 degrees C reperfusion (BC versus RSR13-BC, respectively) by measuring: % return to normal sinus rhythm (0/100%), % of baseline+dP/dt (33.7+/-1.7/76.3+/-1.9), % of baseline-dP/dt (26.6+/-2.0/81.1+/-1.6), stroke volume (3.5+/-0.5/7.1+/-0.9 mL), cardiac output (340+/-20/880+/-40.3 mL/min), and LVEDP (11.3+/-2.2/0. 3+/-2.9 mm Hg). Postischemic oxidative and metabolic parameters including myocardial lactate, pyruvate, ATP content, and percent water content also were determined. Histological analysis demonstrated preservation of endothelial and myocyte morphology in hearts receiving RSR13-BC compared with BC. These results indicate that in the setting of hypothermic cardiopulmonary bypass, RSR13 improves recovery of myocardial mechanical and metabolic function compared with standard hypothermic BC. Findings from this study suggest that RSR13-BC, by decreasing hemoglobin oxygen affinity, improves oxidative metabolism and preserves cellular morphology, resulting in significantly improved contractile recovery on reperfusion.

Effects of RSR13, a synthetic allosteric modifier of hemoglobin, alone and in combination with dizocilpine, on outcome from transient focal cerebral ischemia in the rat

This study examined the effect of a pharmacologically induced rightward shift in the partial pressure of oxygen at which 50% of hemoglobin is saturated ( P 50) on outcome from transient focal cerebral ischemia in the rat. Halothane anesthetized rats ( n=20 per group) were given saline or a single 15-min infusion of 150 mg/kg RSR13 (2-[4-[[3,5-dimethylanilino) carbonyl]methyl]phenoxy]-2-methylproprionic acid) intravenously before or 30 min after onset of 75 min of middle cerebral artery filament occlusion (MCAO). Seven days later, severity of hemiparesis and cerebral infarct size were examined. RSR13 alone did not significantly improve outcome. Conscious normothermic rats ( n=12 per group) were also given RSR13 (150 mg/kg) or 0.9% NaCl intravenously and subjected to 75 min of MCAO with 7 days of recovery. Again, RSR13 alone did not significantly reduce infarct size or improve neurologic score. A dose–response curve for dizocilpine (MK-801) was then constructed in conscious normothermic rats subjected to 75 min of MCAO. Dizocilpine (0.5 mg/kg i.v.) caused a 90% reduction in mean infarct size while 0.25 mg/kg reduced infarct size by 48%. Other rats were then subjected to 75 min of MCAO after being given dizocilpine (0.25 mg/kg i.v.; n=18) or RSR13 (150 mg/kg i.v.)+dizocilpine (0.25 mg/kg i.v.; n=15). RSR13+dizocilpine resulted in smaller cortical infarct volume (8±14 mm 3 vs. 34±37 mm 3, p<0.02) and total cerebral infarct volume (46±28 mm 3 vs. 81±60 mm 3, p<0.05) compared to dizocilpine alone, respectively. We conclude that a pre-ischemic peak increase in P 50 of ∼25 mmHg alone is insufficient to reduce focal ischemic injury, but may be advantageous when used in conjunction with other neuroprotective agents.

Reducing hemoglobin oxygen affinity does not increase hydroxyl radicals after acute subdural hematoma in the rat.

Extensive evidence is available to show the importance of ischemia after severe human head injury. We have previously shown that pharmacologically increasing the release of oxygen in brain tissue where the local oxygen pressure is low reduces infarct size in animal models. To study the possible negative effects of this strategy, we tested the effect of an allosteric modifier of hemoglobin (RSR13) on free radical production in the rat acute subdural hematoma (ASDH) model, both under normoxic as well as under hyperoxic, normobaric conditions. When compared to baseline, induction of ASDH resulted in a significant increase (p < 0.05) in 2,3-DHBA (2,3 dihydroxybenzoic acid, produced from salicylate after attack by hydroxyl radicals) at 30 and 60 min postinduction, both for the control group (39% and 91%) as well as the RSR13-treated group (41% and 62%). The 2,5-DHBA also increased significantly (p < 0.05) in the drug-treated animals at the 30- and 60-min time points when compared to baseline (49% and 77%). At all time points, except the 30-min, the increase in 2,3-DHBA was less marked in the RSR13 animals than in the control group. Similarly, the 2,5-DHBA increase after ASDH was lower at all time points except for the 30-min time point in the RSR13-treated group. These results indicate that enhanced tissue oxygen release by the allosteric modifier of hemoglobin RSR13 does not increase hydroxyl radical production after ASDH. Clinical trials are needed to test this compound in humans after severe head injury.

Increased VO2 max with right-shifted Hb-O2 dissociation curve at a constant O2 delivery in dog muscle in situ.

If the diffusive component of O2 transport in muscle is important in determining exercise capacity, an increased capillary-to-tissue PO2 difference should enhance gas exchange from blood to skeletal muscle during exercise. Thus a rightward shift in the O2 dissociation curve should theoretically increase O2 extraction and improve maximal O2 uptake (VO2 max). To test this hypothesis, we used the canine gastrocnemius muscle to study maximal exercise in eight dogs at a normal P50 (33.1 +/- 0.4 Torr) and with the O2 dissociation curve shifted to the right by an allosteric modifier of hemoglobin (Hb) (methylpropionic acid, RSR-13; P50 = 53.2 +/- 5.0 Torr). Four control dogs were also studied before and after infusion of vehicle. O2 (100%) was inspired during exercise to maintain arterial saturation in both conditions. The muscle was surgically isolated and electrically stimulated (tetanic train: 0.2-ms stimuli for 200-ms duration at 50 Hz, once per s). To maintain O2 delivery (pre-RSR-13 = 19.1 +/- 2.9; RSR-13 = 19.6 +/- 2.5 ml . 100 g-1 . min-1), the muscle was pump perfused. At a constant O2 delivery, RSR-13 significantly increased percent O2 extraction (pre-RSR-13 = 61 +/- 4.0; RSR-13 = 75.5 +/- 4.7) and muscle VO2 max (pre-RSR-13 = 11.8 +/- 2.1; RSR-13 = 14.2 +/- 1.5 ml . 100 g-1 . min-1). This improvement in VO2 max with increased P50 demonstrates its O2 supply dependence when P50 is normal and the importance of O2 diffusive transport to muscle at maximal exercise.

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Right-shifting the oxyhemoglobin dissociation curve with RSR13: effects on high-energy phosphates and myocardial recovery after low-flow ischemia.

RSR13[2-(4[[(3,5-Dimethylanilino)carbonyl] methyl] phenoxy)-2-methyl propionic acid], a synthetic allosteric modifier of hemoglobin, increases O2 release from hemoglobin at low oxygen tension. The isolated blood-perfused rat heart was examined during potassium-arrest to determine the effects of RSR13 on the concentration of phosphocreatine (PCr) and adenosine triphosphate (ATP) by using 31P nuclear magnetic resonance (NMR) spectroscopy throughout an episode of low-flow ischemia. All hearts were perfused at constant flow during control (2.0 ml/min) and low-flow (0.2 ml/min) conditions. In normoxic hearts, RSR13 had no effect on either the 31P NMR spectrum or the rate-pressure product. In hearts subjected to 30 min of reduced flow, treatment with RSR13 improved mechanical function on reperfusion (p = 0.026 after 20 min; p = 0.032 after 25 min; and p = 0.045 after 30 min) at 2.0 ml/min with normokalemic blood perfusate. In potassium-arrested hearts, the rate of decrease of [ATP] was reduced in hearts exposed to RSR13 (p < or = 0.05 between 10 and 35.8 min of ischemia except at 28.4 min) during low flow. These results indicate a protective effect of RSR13 on high-energy phosphates during low-flow ischemia and mechanical recovery after reperfusion.

RSR13, a synthetic allosteric modifier of hemoglobin, as an adjunct to radiotherapy: preliminary studies with EMT6 cells and tumors and normal tissues in mice.

RSR13, 2[4-[[(3,5dimethylanilino)carbonyl]methyl]phenoxy]-2-methylpropion ic acid, a synthetic allosteric modifier of hemoglobin, reduces the affinity of hemoglobin for oxygen. The experiments reported here examined the effect of treatment with RSR13, combined with oxygen breathing, on the radiation response of EMT6 mammary tumors in BALB/c mice and of two normal tissues. RSR13 plus oxygen breathing increased the response of EMT6 tumors to irradiation. RSR13 had no discernible effects on tumors rendered maximally hypoxic by nitrogen asphyxiation, no discernible cytotoxic effects in EMT6 tumors, and no effect on the viability or radiation response of EMT6 cells in vitro under either aerobic or hypoxic conditions. The effects of RSR13 therefore reflect changes in tumor oxygenation, rather than a direct cytotoxic or radiosensitizing effect of the drug. RSR13 plus oxygen reduced the hypoxic fraction to 9% from the value of 24% found in both air-breathing and oxygen-breathing mice. Treatment with RSR13 plus oxygen did not alter the radiation response of the bone marrow progenitor cells (CFU-S) or acute radiation reactions in the skin. The improvement in tumor radiation response produced by treatment with RSR13 plus oxygen, combined with the absence of enhanced radiation reactions in the normal tissues, support further testing of RSR13 as an adjunct to radiotherapy.

Effect of RSR13 on temperature-dependent changes in hemoglobin oxygen affinity of human whole blood.

RSR13, 2-[4-[[(3,5-Dimethylanilino)carbonyl]methyl]phenoxy]-2-methylpropionic acid sodium salt (MW 363), is a synthetic allosteric modifier of hemoglobin (Figure 1). RSR13 is a small molecule that noncovalently binds in the central water cavity of the hemoglobin tetramer, reduces hemoglobin-oxygen (Hb-O2) affinity1 and enhances the diffusion of oxygen from the blood to the tissues.2,3,4 RSR13 emulates the function of natural allosteric modifiers such as hydrogen ions, carbon dioxide, and 2,3-diphosphoglycerate. This therapeutic strategy of “turbocharging” oxygen unloading from hemoglobin to tissue emulates and amplifies physiological tissue oxygenation. This approach has potential application in clinical conditions characterized by tissue hypoxia due to: 1) inadequate blood flow (regional or global), 2) insufficient oxygen carrying capacity (e.g., hemorrhage or dilutional anemia), 3) increased tissue oxygen demand unmatched by supply, and/or 4) insufficient oxygen loading/unloading capacity of hemoglobin (e.g., hypothermia).

RSR13, a synthetic allosteric modifier of hemoglobin, enhances recovery of stunned myocardium in dogs.

RSR132-[4-[[(3,5-dimethylanilino)carbonyl]methyl]phenoxyl]-2-methylproprionic acid sodium salt; (Figure 1) is a compound that mimics the natural physiological effects of 2,3-diphosphoglycerate by allosterically modifying hemoglobin (Hb) saturation. RSR13 binds to and stabilizes deoxyHb in vitro (1). These actions cause a rightward shift of the oxygen (O2)-Hb dissociation curve and increase tissue O2 delivery in vivo (2). RSR13 maintains pH and preserves high-energy phosphates during myocardial ischemia by improving O2 delivery (3). Thus, allosteric modification of Hb affinity for O2 with drugs that stabilize the deoxyHb may be an important new approach to the treatment of myocardial hypoxemia due to ischemic heart disease. We tested the hypothesis that RSR13 enhances the recovery of contractile function of postischemic, reperfused myocardium generated by repetitive, brief episodes of ischemia and reperfusion in barbiturate-anesthetized, acutely instrumented dogs.KeywordsLeft Anterior DescendMyocardial Blood FlowAllosteric ModifierStun MyocardiumRightward ShiftThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

RSR13, a synthetic allosteric modifier of hemoglobin, as an adjunct to radiotherapy: Preliminary studies with EMT6 cells and tumors and normal tissues in mice

RSR13, 2[4-[[(3,5Dimethylanilino)carbonyl]methyl]phenoxy]-2-methylpropionic acid, a synthetic allosteric modifier of hemoglobin, reduces the affinity of hemoglobin for oxygen. The experiments reported here examined the effect of treatment with RSR13, combined with oxygen breathing, on the radiation response of EMT6 mammary tumors in BALB/c mice and of two normal tissues. RSR13 plus oxygen breathing increased the response of EMT6 tumors to irradiation. RSR13 had no discernible effects on tumors rendered maximally hypoxic by nitrogen asphyxiation, no discernible cytotoxic effects in EMT6 tumors, and no effect on the viability or radiation response of EMT6 cells in vitro under either aerobic or hypoxic conditions. The effects of RSR13 therefore reflect changes in tumor oxygenation, rather than a direct cytotoxic or radiosensitizing effect of the drug. RSR13 plus oxygen reduced the hypoxic fraction to 9% from the value of 24% found in both air-breathing and oxygen-breathing mice. Treatment with RSR13 plus oxygen did not alter the radiation response of the bone marrow progenitor cells (CFU-S) or acute radiation reactions in the skin. The improvement in tumor radiation response produced by treatment with RSR13 plus oxygen, combined with the absence of enhanced radiation reactions in the normal tissues, support further testing of RSR13 as an adjunct to radiotherapy. Radiat. Oncol. Invest. 6:199–208, 1998. © 1998 Wiley-Liss, Inc.