Macrocyclic MnII and GdIII MRI Contrast Agents for Biotoxicity Reduction
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Solution Overview
Problem
Current MRI contrast agents based on MnII and GdIII ions suffer from biotoxicity issues, with MnII causing neurotoxic effects and GdIII associated with nephrogenic systemic fibrosis, necessitating the development of safer alternatives with improved imaging capabilities.
Innovation Solution
Development of MnII and GdIII-based Schiff-base macrocyclic complexes with high relaxivity values and low biotoxicity, incorporating a synthetic pathway for azido-functionalized pyridine head-units to create bi-functional contrast agents for enhanced imaging potential.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If MnII-based contrast agents are used to achieve imaging functionality, then imaging capability is provided, but neurotoxic effects occur due to rapid dissociation from the ligand
Solution Approach 1:
A macrocyclic ligand acts as an intermediary between the MnII ion and the biological system. The ligand tightly binds the MnII ion within a macrocyclic cage structure, preventing its dissociation and subsequent neurotoxic effects while still allowing the complex to function as an MRI contrast agent. The macrocyclic structure serves as a protective intermediary that maintains imaging functionality while eliminating toxicity.
Solution Approach 2:
The contrast agent is designed as a composite system combining the paramagnetic MnII ion with a specifically designed macrocyclic ligand framework. This composite structure integrates the imaging capability of the metal ion with the stability and biocompatibility of the macrocyclic ligand, creating a material that exhibits both high relaxivity and low toxicity.
2Reliability
If GdIII-based contrast agents are used to enhance MRI contrast, then imaging effectiveness is improved, but nephrogenic systemic fibrosis occurs in patients with suppressed renal function
Solution Approach 1:
The macrocyclic ligand serves as a protective intermediary that sequesters the GdIII ion within its cavity structure. This tight binding prevents the release of free GdIII ions that would otherwise accumulate in patients with renal impairment and cause nephrogenic systemic fibrosis. The ligand mediates between the imaging functionality of GdIII and the safety requirements of clinical use.
Solution Approach 2:
The patent changes the chemical parameters of the contrast agent by transitioning from linear or acyclic ligands to macrocyclic ligands. This structural parameter change fundamentally alters the stability constants and kinetic inertness of the metal-ligand complex, resulting in dramatically improved in vivo stability and reduced toxicity while maintaining imaging effectiveness.
3Reliability
If relaxivity is increased by maximizing molecular tumbling rate and water exchange rate, then imaging sensitivity is improved, but complex molecular design is required to control these parameters
Solution Approach 1:
The patent systematically adjusts key molecular parameters including the coordination geometry of the metal ion within the macrocyclic cage, the number of coordinated water molecules (q value), and the rotational correlation time (τR) through ligand structure modification. By optimizing these parameters within the macrocyclic framework, high relaxivity is achieved through a unified design approach rather than separate optimization of multiple independent factors.
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 complexes demonstrate high relaxivity and stability, exhibiting low biotoxicity and good imaging potential, offering a safer alternative for MRI contrast agents with improved tissue targeting and imaging capabilities.
Implementation Method 1
compounds containing paramagnetic metal ions which enhance the contrast, for example, between healthy and diseased tissue. Contrast agents operate by altering the local magnetic field strength of a tissue and changing the relaxation times (T1 and T2, in s) of the surrounding water protons.
Implementation Method 2
relaxivity increases as the rate of molecular tumbling (τR) decreases, and as the rate of water exchange increases. Relaxivity also increases with the number of coordinated water molecules, q.
Data Source
AI summary
The present application relates to methods and compounds for enhancing contrast in magnetic resonance imaging. The methods comprise administering compounds of Formula I(a) or I(b) to a subject and obtaining a magnetic resonance image of the subject. The present application also relates to methods of preparing compounds of the Formula I(a) as well as intermediate compounds used in such a method of preparation.