Improved Efficacy of Synthesizing∗MIII-Labeled DOTA Complexes in Binary Mixtures of Water and Organic Solvents. A Combined Radio- and Physicochemical Study

Marylaine Pérez-Malo, Gergely Szabó, Elisabeth Eppard, Adrienn Vagner, Ernö Brücher, Imre Tóth, Alessandro Maiocchi, Eul Hyun Suh, Zoltán Kovács, Zsolt Baranyai, Frank Rösch

Research output: Contribution to journalArticle

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Abstract

Typically, the synthesis of radiometal-based radiopharmaceuticals is performed in buffered aqueous solutions. We found that the presence of organic solvents like ethanol increased the radiolabeling yields of [68Ga]Ga-DOTA (DOTA = 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacatic acid). In the present study, the effect of organic cosolvents [ethanol (EtOH), isopropyl alcohol, and acetonitrile] on the radiolabeling yields of the macrocyclic chelator DOTA with several trivalent radiometals (gallium-68, scandium-44, and lutetium-177) was systematically investigated. Various binary water (H2O)/organic solvent mixtures allowed the radiolabeling of DOTA at a significantly lower temperature than 95 °C, which is relevant for the labeling of sensitive biological molecules. Simultaneously, much lower amounts of the chelators were required. This strategy may have a fundamental impact on the formulation of trivalent radiometal-based radiopharmaceuticals. The equilibrium properties and formation kinetics of [M(DOTA)]- (MIII= GaIII, CeIII, EuIII, YIII, and LuIII) complexes were investigated in H2O/EtOH mixtures (up to 70 vol % EtOH). The protonation constants of DOTA were determined by pH potentiometry in H2O/EtOH mixtures (0-70 vol % EtOH, 0.15 M NaCl, 25 °C). The log K1 H and log K2 H values associated with protonation of the ring N atoms decreased with an increase of the EtOH content. The formation rates of [M(DOTA)]- complexes increase with an increase of the pH and [EtOH]. Complexation occurs through rapid formation of the diprotonated [M(H2DOTA)]+ intermediates, which are in equilibrium with the kinetically active monoprotonated [M(HDOTA)] intermediates. The rate-controlling step is deprotonation (and rearrangement) of the monoprotonated intermediate, which occurs through H2O (M(HL)kH2O) and OH- (M(HL)kOH) assisted reaction pathways. The rate constants are essentially independent of the EtOH concentration, but the M(HL)kH2O values increase from CeIII to LuIII. However, the logKM(HL) H protonation constants, analogous to the log KH 2 value, decrease with increasing [EtOH], which increases the concentration of the monoprotonated M(HDOTA) intermediate and accelerates formation of the final complexes. The overall rates of complex formation calculated by the obtained rate constants at different EtOH concentrations show a trend similar to that of the complexation rates determined with the use of radioactive isotopes.

Original languageEnglish
Pages (from-to)6107-6117
Number of pages11
JournalInorganic Chemistry
Volume57
Issue number10
DOIs
Publication statusPublished - May 21 2018

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Protonation
Binary mixtures
Organic solvents
binary mixtures
Radiopharmaceuticals
Chelating Agents
Complexation
Water
Rate constants
Ethanol
Lutetium
Scandium
water
Deprotonation
Gallium
2-Propanol
Radioisotopes
Labeling
ethyl alcohol
potentiometric analysis

ASJC Scopus subject areas

  • Physical and Theoretical Chemistry
  • Inorganic Chemistry

Cite this

Improved Efficacy of Synthesizing∗MIII-Labeled DOTA Complexes in Binary Mixtures of Water and Organic Solvents. A Combined Radio- and Physicochemical Study. / Pérez-Malo, Marylaine; Szabó, Gergely; Eppard, Elisabeth; Vagner, Adrienn; Brücher, Ernö; Tóth, Imre; Maiocchi, Alessandro; Suh, Eul Hyun; Kovács, Zoltán; Baranyai, Zsolt; Rösch, Frank.

In: Inorganic Chemistry, Vol. 57, No. 10, 21.05.2018, p. 6107-6117.

Research output: Contribution to journalArticle

Pérez-Malo, M, Szabó, G, Eppard, E, Vagner, A, Brücher, E, Tóth, I, Maiocchi, A, Suh, EH, Kovács, Z, Baranyai, Z & Rösch, F 2018, 'Improved Efficacy of Synthesizing∗MIII-Labeled DOTA Complexes in Binary Mixtures of Water and Organic Solvents. A Combined Radio- and Physicochemical Study', Inorganic Chemistry, vol. 57, no. 10, pp. 6107-6117. https://doi.org/10.1021/acs.inorgchem.8b00669
Pérez-Malo, Marylaine ; Szabó, Gergely ; Eppard, Elisabeth ; Vagner, Adrienn ; Brücher, Ernö ; Tóth, Imre ; Maiocchi, Alessandro ; Suh, Eul Hyun ; Kovács, Zoltán ; Baranyai, Zsolt ; Rösch, Frank. / Improved Efficacy of Synthesizing∗MIII-Labeled DOTA Complexes in Binary Mixtures of Water and Organic Solvents. A Combined Radio- and Physicochemical Study. In: Inorganic Chemistry. 2018 ; Vol. 57, No. 10. pp. 6107-6117.
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abstract = "Typically, the synthesis of radiometal-based radiopharmaceuticals is performed in buffered aqueous solutions. We found that the presence of organic solvents like ethanol increased the radiolabeling yields of [68Ga]Ga-DOTA (DOTA = 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacatic acid). In the present study, the effect of organic cosolvents [ethanol (EtOH), isopropyl alcohol, and acetonitrile] on the radiolabeling yields of the macrocyclic chelator DOTA with several trivalent radiometals (gallium-68, scandium-44, and lutetium-177) was systematically investigated. Various binary water (H2O)/organic solvent mixtures allowed the radiolabeling of DOTA at a significantly lower temperature than 95 °C, which is relevant for the labeling of sensitive biological molecules. Simultaneously, much lower amounts of the chelators were required. This strategy may have a fundamental impact on the formulation of trivalent radiometal-based radiopharmaceuticals. The equilibrium properties and formation kinetics of [M(DOTA)]- (MIII= GaIII, CeIII, EuIII, YIII, and LuIII) complexes were investigated in H2O/EtOH mixtures (up to 70 vol {\%} EtOH). The protonation constants of DOTA were determined by pH potentiometry in H2O/EtOH mixtures (0-70 vol {\%} EtOH, 0.15 M NaCl, 25 °C). The log K1 H and log K2 H values associated with protonation of the ring N atoms decreased with an increase of the EtOH content. The formation rates of [M(DOTA)]- complexes increase with an increase of the pH and [EtOH]. Complexation occurs through rapid formation of the diprotonated [M(H2DOTA)]+ intermediates, which are in equilibrium with the kinetically active monoprotonated [M(HDOTA)] intermediates. The rate-controlling step is deprotonation (and rearrangement) of the monoprotonated intermediate, which occurs through H2O (M(HL)kH2O) and OH- (M(HL)kOH) assisted reaction pathways. The rate constants are essentially independent of the EtOH concentration, but the M(HL)kH2O values increase from CeIII to LuIII. However, the logKM(HL) H protonation constants, analogous to the log KH 2 value, decrease with increasing [EtOH], which increases the concentration of the monoprotonated M(HDOTA) intermediate and accelerates formation of the final complexes. The overall rates of complex formation calculated by the obtained rate constants at different EtOH concentrations show a trend similar to that of the complexation rates determined with the use of radioactive isotopes.",
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T1 - Improved Efficacy of Synthesizing∗MIII-Labeled DOTA Complexes in Binary Mixtures of Water and Organic Solvents. A Combined Radio- and Physicochemical Study

AU - Pérez-Malo, Marylaine

AU - Szabó, Gergely

AU - Eppard, Elisabeth

AU - Vagner, Adrienn

AU - Brücher, Ernö

AU - Tóth, Imre

AU - Maiocchi, Alessandro

AU - Suh, Eul Hyun

AU - Kovács, Zoltán

AU - Baranyai, Zsolt

AU - Rösch, Frank

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N2 - Typically, the synthesis of radiometal-based radiopharmaceuticals is performed in buffered aqueous solutions. We found that the presence of organic solvents like ethanol increased the radiolabeling yields of [68Ga]Ga-DOTA (DOTA = 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacatic acid). In the present study, the effect of organic cosolvents [ethanol (EtOH), isopropyl alcohol, and acetonitrile] on the radiolabeling yields of the macrocyclic chelator DOTA with several trivalent radiometals (gallium-68, scandium-44, and lutetium-177) was systematically investigated. Various binary water (H2O)/organic solvent mixtures allowed the radiolabeling of DOTA at a significantly lower temperature than 95 °C, which is relevant for the labeling of sensitive biological molecules. Simultaneously, much lower amounts of the chelators were required. This strategy may have a fundamental impact on the formulation of trivalent radiometal-based radiopharmaceuticals. The equilibrium properties and formation kinetics of [M(DOTA)]- (MIII= GaIII, CeIII, EuIII, YIII, and LuIII) complexes were investigated in H2O/EtOH mixtures (up to 70 vol % EtOH). The protonation constants of DOTA were determined by pH potentiometry in H2O/EtOH mixtures (0-70 vol % EtOH, 0.15 M NaCl, 25 °C). The log K1 H and log K2 H values associated with protonation of the ring N atoms decreased with an increase of the EtOH content. The formation rates of [M(DOTA)]- complexes increase with an increase of the pH and [EtOH]. Complexation occurs through rapid formation of the diprotonated [M(H2DOTA)]+ intermediates, which are in equilibrium with the kinetically active monoprotonated [M(HDOTA)] intermediates. The rate-controlling step is deprotonation (and rearrangement) of the monoprotonated intermediate, which occurs through H2O (M(HL)kH2O) and OH- (M(HL)kOH) assisted reaction pathways. The rate constants are essentially independent of the EtOH concentration, but the M(HL)kH2O values increase from CeIII to LuIII. However, the logKM(HL) H protonation constants, analogous to the log KH 2 value, decrease with increasing [EtOH], which increases the concentration of the monoprotonated M(HDOTA) intermediate and accelerates formation of the final complexes. The overall rates of complex formation calculated by the obtained rate constants at different EtOH concentrations show a trend similar to that of the complexation rates determined with the use of radioactive isotopes.

AB - Typically, the synthesis of radiometal-based radiopharmaceuticals is performed in buffered aqueous solutions. We found that the presence of organic solvents like ethanol increased the radiolabeling yields of [68Ga]Ga-DOTA (DOTA = 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacatic acid). In the present study, the effect of organic cosolvents [ethanol (EtOH), isopropyl alcohol, and acetonitrile] on the radiolabeling yields of the macrocyclic chelator DOTA with several trivalent radiometals (gallium-68, scandium-44, and lutetium-177) was systematically investigated. Various binary water (H2O)/organic solvent mixtures allowed the radiolabeling of DOTA at a significantly lower temperature than 95 °C, which is relevant for the labeling of sensitive biological molecules. Simultaneously, much lower amounts of the chelators were required. This strategy may have a fundamental impact on the formulation of trivalent radiometal-based radiopharmaceuticals. The equilibrium properties and formation kinetics of [M(DOTA)]- (MIII= GaIII, CeIII, EuIII, YIII, and LuIII) complexes were investigated in H2O/EtOH mixtures (up to 70 vol % EtOH). The protonation constants of DOTA were determined by pH potentiometry in H2O/EtOH mixtures (0-70 vol % EtOH, 0.15 M NaCl, 25 °C). The log K1 H and log K2 H values associated with protonation of the ring N atoms decreased with an increase of the EtOH content. The formation rates of [M(DOTA)]- complexes increase with an increase of the pH and [EtOH]. Complexation occurs through rapid formation of the diprotonated [M(H2DOTA)]+ intermediates, which are in equilibrium with the kinetically active monoprotonated [M(HDOTA)] intermediates. The rate-controlling step is deprotonation (and rearrangement) of the monoprotonated intermediate, which occurs through H2O (M(HL)kH2O) and OH- (M(HL)kOH) assisted reaction pathways. The rate constants are essentially independent of the EtOH concentration, but the M(HL)kH2O values increase from CeIII to LuIII. However, the logKM(HL) H protonation constants, analogous to the log KH 2 value, decrease with increasing [EtOH], which increases the concentration of the monoprotonated M(HDOTA) intermediate and accelerates formation of the final complexes. The overall rates of complex formation calculated by the obtained rate constants at different EtOH concentrations show a trend similar to that of the complexation rates determined with the use of radioactive isotopes.

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