Elastin-Like Polypeptide Photosensitizer Conjugates for Aggregation Control
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Solution Overview
Problem
Existing photosensitizers, particularly phthalocyanines, suffer from uncontrolled aggregation and low tumor site accumulation due to hydrophobicity, leading to inefficient biodistribution and therapeutic outcomes in photodynamic therapy.
Innovation Solution
A bioconjugate is formed by covalently coupling a photosensitizer with a recombinant elastin-like polypeptide containing sulfur-containing amino acids, which self-assembles into particles at physiological temperature and disassembles upon oxidation by reactive oxygen species generated during photodynamic therapy, allowing deeper tissue penetration and enhanced therapeutic efficacy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If photosensitizers like phthalocyanines are used for photodynamic therapy, then high singlet oxygen production and strong absorption at therapeutic wavelengths are achieved, but uncontrolled aggregation and low tumor site accumulation occur due to hydrophobicity
Solution Approach 1:
The patent uses elastin-like polypeptides (ELPs) as intermediary carriers to deliver hydrophobic photosensitizers. The ELPs contain hydrophobic regions that bind the photosensitizer and hydrophilic regions that enable solubility and controlled biodistribution. This mediator resolves the contradiction by allowing high photosensitizer potency while controlling aggregation and improving tumor accumulation through the ELP's temperature-responsive self-assembly properties.
Solution Approach 2:
The invention creates a composite material system combining photosensitizer molecules with elastin-like polypeptide carriers. This composite approach allows the photosensitizer to maintain its high singlet oxygen production capability while the ELP component provides controlled solubility, prevents uncontrolled aggregation, and enables tumor-targeted delivery through passive accumulation mechanisms.
2Area of stationary object
If photosensitizers are administered systemically, then broad coverage is achieved, but uncontrolled aggregation and rapid clearance occur leading to low tumor site accumulation
Solution Approach 1:
The patent exploits temperature as a critical parameter to control the behavior of ELP-carried photosensitizers. At physiological temperature (37°C), the ELPs undergo a phase transition that promotes self-assembly into nanoparticles, enhancing tumor accumulation through the enhanced permeability and retention (EPR) effect. This parameter change allows systemic administration with broad coverage while improving tumor site accumulation through temperature-responsive control.
Solution Approach 2:
The ELP carriers exhibit dynamic behavior in response to physiological conditions. They remain soluble at lower temperatures during circulation but self-assemble into stable nanoparticles at body temperature, dynamically adapting to the thermal environment. This dynamic property enables broad systemic distribution followed by controlled accumulation at the tumor site without uncontrolled aggregation.
3Power
If hydrophobic photosensitizers are used to maintain photophysical properties, then high extinction coefficient and singlet oxygen quantum yield are achieved, but uncontrolled aggregation occurs in physiological medium
Solution Approach 1:
The elastin-like polypeptide carrier exhibits local quality differentiation with hydrophobic segments that bind the photosensitizer and maintain its photophysical properties, and hydrophilic segments that prevent aggregation in physiological medium. This local quality variation allows the photosensitizer to maintain high extinction coefficient and singlet oxygen quantum yield while the ELP's hydrophilic exterior prevents uncontrolled aggregation.
Solution Approach 2:
The ELP acts as an intermediary between the hydrophobic photosensitizer and the aqueous physiological environment. It provides a hydrophobic binding interface that preserves the photosensitizer's photophysical properties while presenting a hydrophilic exterior to the physiological medium, thereby preventing aggregation while maintaining high extinction coefficient and singlet oxygen production capability.
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 bioconjugate achieves improved photosensitizer delivery and therapeutic benefit by allowing deeper tissue penetration and maximizing damage in diseased tissues, enhancing the effectiveness of photodynamic therapy.
Implementation Method 1
Photodynamic therapy (PDT) is an attractive non-invasive disease treatment alternative with high selectivity
Implementation Method 2
selective activation of the photosensitizer, accumulated at a tumor site, by light at an appropriate wavelength
Implementation Method 3
energy or electron is transferred from the excited triplet state of the activated photosensitizer to nearby molecular oxygen
Implementation Method 4
The generated reactive oxygen species cause multiple oxidative damages to the surrounding microenvironment
Implementation Method 5
recombinant elastin-like polypeptide containing periodic cysteine residues (cELP)
Implementation Method 6
Due to their intrinsic hydrophobicity, the phthalocyanine molecules have a strong tendency to aggregate in physiological medium
Implementation Method 7
disassembles upon oxidation by reactive oxygen species generated during photodynamic therapy
Implementation Method 8
The disassembled bioconjugate thus obtained, in its free dissociated form, is then able to diffuse more easily into dense tissues
Implementation Method 9
The disassembled bioconjugate thus obtained, in its free dissociated form, is then able to diffuse more easily into dense tissues
Data Source
AI summary
A bioconjugate including a photosensitizer unit, in particular a phthalocyanine unit, and an elastin-like polypeptide conjugated thereto, the elastin-like polypeptide containing at least one occurrence of a monomeric unit having the formula Xaa1PXaa2Xaa3G, wherein P represents a prolyl residue, G represents a glycyl residue, Xaa2 represents a glycyl residue or an alanyl residue and either Xaa1 represents a valyl residue and Xaa3 represents a sulfur-containing amino acid residue having a side chain of formula —(CH2)z—S—R′ or Xaa3 represents a valyl residue and Xaa1 represents a sulfur-containing amino acid residue having a side chain of formula —(CH2)z—S—R′. This bioconjugate proves particularly useful for the treatment of diseases by photodynamic therapy.