Paramagnetic Metal Chelate Formulation with DOTA-Ca Stabilizer
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Solution Overview
Problem
The challenge lies in developing a formulation of paramagnetic metal chelates, particularly those derived from PCTA, that ensures minimal release of gadolinium during manufacturing, storage, and use, while maintaining high relaxivity for effective Magnetic Resonance Imaging, as existing solutions are either impractical or unsatisfactory due to low thermodynamic stability and potential exchange with calcium or other alkaline earth metals.
Innovation Solution
Incorporating a calcium complex of 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA-Ca) into the formulation, which ensures a concentration of free paramagnetic metal less than 1 ppm, thereby stabilizing the complex and preventing unwanted release, while maintaining high relaxivity and imaging efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If PCTA-derived chelates are used for MRI contrast agents, then relaxivity is improved (up to 11-12 mM-1s-1), but thermodynamic stability is low leading to paramagnetic metal release
Solution Approach 1:
The patent introduces DOTA as an intermediary chelating agent that forms a more stable complex with gadolinium than PCTA. The DOTA-Gd complex acts as a reservoir that prevents gadolinium release from the PCTA-derived chelate, thereby maintaining both high relaxivity and thermodynamic stability simultaneously.
Solution Approach 2:
The patent changes the chemical parameter of the chelating ligand from PCTA-derived structures to DOTA, which has higher thermodynamic stability constant (log K ~25) while maintaining compatibility with the desired relaxivity properties. This parameter change resolves the contradiction between stability and relaxivity.
2Object-affected harmful factors
If excess free chelate is added to compensate for lanthanide release, then patient safety is improved, but manufacturing complexity and cost increase
Solution Approach 1:
The patent applies preliminary action by pre-forming the DOTA-Gd complex before mixing with the PCTA-derived chelate. This ensures that gadolinium is already bound to the more stable DOTA ligand before administration, preventing release during storage and use without requiring complex post-manufacturing adjustments or excessive free chelate addition.
3Reliability
If macrocyclic chelates with high kinetic stability are used, then complex formation is improved, but thermodynamic stability remains low causing metal ion exchange
Solution Approach 1:
The patent creates a composite formulation containing both PCTA-derived chelate (providing high kinetic stability and relaxivity) and DOTA-Gd complex (providing high thermodynamic stability). The synergistic combination of these two components resolves the contradiction between kinetic and thermodynamic stability, as each component compensates for the other's weakness.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The formulation achieves long-term stability with no risk of paramagnetic metal release, enhanced relaxivity, and improved patient safety, making it suitable for high magnetic field imaging with reduced osmolality and industrial costs.
Implementation Method 1
These 'weak' complexes undergo transmetallation in the presence of free lanthanide, since the complexes between these macrocyclic or linear ligands and a lanthanide, such as gadolinium, are 'stronger,' meaning they are more thermodynamically stable. An exchange therefore occurs between the calcium, sodium, zinc, or magnesium and the lanthanide
Implementation Method 2
Lanthanide chelates are in a state of chemical equilibrium. Therefore, there is a risk of unwanted release of paramagnetic metal. Those skilled in the art must thus seek technical solutions to limit this risk
Data Source
AI summary
The present invention relates to a liquid pharmaceutical composition including a complex of formula (I), in which M is an ion of a paramagnetic metal and R1 to R3, X1 to X3 and K1 to K12 are such as defined in claim 1, said composition also including a calcium complex of 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid. The invention also relates to the preparation method thereof and to an imaging method involving said composition.