Molecular Targeting of Epidermal Growth Factor Receptor (EGFR) and Vascular Endothelial Growth Factor Receptor (VEGFR).

Epidermal growth factor receptor (EGFR) and vascular endothelial growth factor receptor (VEGFR) are two extensively studied membrane-bound receptor tyrosine kinase proteins that are frequently overexpressed in many cancers. As a result, these receptor families constitute attractive targets for imaging and therapeutic applications in the detection and treatment of cancer. This review explores the dynamic structure and structure-function relationships of these two growth factor receptors and their significance as it relates to theranostics of cancer, followed by some of the common inhibition modalities frequently employed to target EGFR and VEGFR, such as tyrosine kinase inhibitors (TKIs), antibodies, nanobodies, and peptides. A summary of the recent advances in molecular imaging techniques, including positron emission tomography (PET), single-photon emission computerized tomography (SPECT), computed tomography (CT), magnetic resonance imaging (MRI), and optical imaging (OI), and in particular, near-IR fluorescence imaging using tetrapyrrolic-based fluorophores, concludes this review.

Click Conjugation of Boron Dipyrromethene (BODIPY) Fluorophores to EGFR-Targeting Linear and Cyclic Peptides.

Through a simple 1,3-cycloaddition reaction, three BODIPY-peptide conjugates that target the extracellular domain of the epidermal growth factor receptor (EGFR) were prepared and their ability for binding to EGFR was investigated. The peptide ligands K(N3)LARLLT and its cyclic analog cyclo(K(N3)larllt, previously shown to have high affinity for binding to the extracellular domain of EGFR, were conjugated to alkynyl-functionalized BODIPY dyes 1 and 2 via a copper-catalyzed click reaction. This reaction produced conjugates 3, 4, and 5 in high yields (70-82%). In vitro studies using human carcinoma HEp2 cells that overexpress EGFR demonstrated high cellular uptake, particularly for the cyclic peptide conjugate 5, and low cytotoxicity in light (~1 J·cm-2) and darkness. Surface plasmon resonance (SPR) results show binding affinity of the three BODIPY-peptide conjugates for EGFR, particularly for 5 bearing the cyclic peptide. Competitive binding studies using three cell lines with different expressions of EGFR show that 5 binds specifically to EGFR-overexpressing colon cancer cells. Among the three conjugates, 5 bearing the cyclic peptide exhibited the highest affinity for binding to the EGFR protein.

Synthesis, Characterization, and Evaluation of Near-IR Boron Dipyrromethene Bioconjugates for Labeling of Adenocarcinomas by Selectively Targeting the Epidermal Growth Factor Receptor.

A series of five boron dipyrromethene (BODIPY) bioconjugates containing an epidermal growth factor receptor (EGFR)-targeted pegylated LARLLT peptide and/or a glucose or biotin ethylene diamine group were synthesized, and the binding capability of the new conjugates to the extracellular domain of EGFR was investigated using molecular modeling, surface plasmon resonance, fluorescence microscopy, competitive binding assays, and animal studies. The BODIPY conjugates with a LARLLT peptide were found to bind specifically to EGFR, whereas those lacking the peptide bound weakly and nonspecifically. All BODIPY conjugates showed low cytotoxicity (IC50 > 94 µM) in HT-29 cells, both in the dark and upon light activation (1.5 J/cm2). Studies of nude mice bearing subcutaneous human HT-29 xenografts revealed that only BODIPY conjugates bearing the LARLLT peptide showed tumor localization 24 h after intravenous administration. The results of our studies demonstrate that BODIPY bioconjugates bearing the EGFR-targeting peptide 3PEG-LARLLT show promise as near-IR fluorescent imaging agents for colon cancers overexpressing EGFR.

Synthesis, photodynamic activities, and cytotoxicity of new water-soluble cationic gallium(III) and zinc(II) phthalocyanines.

The cationic Ga(III) and Zn(II) phthalocyanines carrying N-methyl-pyridinium groups at eight peripheral ß-positionshave been synthesized. These complexes are highly soluble in dimethyl sulfoxide (DMSO) and moderately soluble in water and phosphate buffered saline (PBS); both Ga(III)Cl and Zn(II) complexes have shown no aggregation in water up to 1.2 × 10-4 and 1.5 × 10-5 M, respectively. A higher water-solubility of Ga(III)Cl complex as compared to Zn(II) complex is ascribed to the presence of an axially coordinated chloride. The spectroscopic properties, photogeneration of singlet oxygen (1O2), and cytotoxicity of these complexes have been investigated. The absolute quantum yields (ΦΔabsolute) for the photogeneration of singlet oxygen using Ga(III)Cl and Zn(II) complexes have been determined to be 4.4 and 5.3%, respectively, in DMSO solution. The cytotoxicity and intracellular sites of localization of Ga(III)Cl and Zn(II) complexes have been evaluated in human HEp2 cells. Both complexes, localized intracellularly in multiple organelles, have shown no cytotoxicity in the dark. Upon exposure to a low light dose (1.5 J/cm2), however, Zn(II) complex has exhibited a high photocytotoxicity. The result suggests that Zn(II) complex can be considered as a potential photosensitizer for Photodynamic therapy (PDT).

Structure Based Modulation of Electron Dynamics in meso-(4-Pyridyl)-BODIPYs: A Computational and Synthetic Approach.

The effects of structural modification on the electronic structure and electron dynamics of cationic meso-(4-pyridyl)-BODIPYs were investigated. A library of 2,6-difunctionalized meso-(4-pyridyl)-BODIPYs bearing various electron-withdrawing substituents was designed, and DFT calculations were used to model the redox properties, while TDDFT was used to determine the effects of functionalization on the excited states. Structural modification was able to restructure the low-lying molecular orbitals to effectively inhibit d-PeT. A new meso-(4-pyridyl)-BODIPY bearing 2,6-dichloro groups was synthesized and shown to exhibit enhanced charge recombination fluorescence. The fluorescence enhancement was determined to be the result of functionalization modulating the kinetics of the excited state dynamics.

Synthesis and in vitro PDT evaluation of new porphyrins containing meso-epoxymethylaryl cationic groups.

OBJECTIVES: Photodynamic therapy (PDT) is an effective cancer treatment that uses photosensitizers, light, and oxygen to destroy malignant cells. Porphyrins, and in particular the cationic derivatives, are the most investigated photosensitizers for PDT. In this context, it is important to study new methodologies to develop efficient cationic photosensitizers for use in PDT. MATERIALS AND METHODS: New porphyrins bearing cationic epoxymethylaryl groups were synthesized and characterized. Their cellular uptake, intracellular localization, and phototoxicity were evaluated in human HEp2 cells, and compared with their methylated analogs. RESULTS: All cationic porphyrins were efficient generators of singlet oxygen, with quantum yields in the range 0.35-0.61. The two methylated derivatives (3 and 4) accumulated the most within cells at all times investigated, up to 24 hours. Of these two porphyrins, 4 was the most phototoxic to the cells (LD50 = 2.4 µM at 1.5 J/cm2 ); however, porphyrin 3 also showed high phototoxicity (LD50 = 7.4 µM at 1.5 J/cm2 ). The epoxymethyl-containing porphyrins were found to be less phototoxic than the methylated derivatives, with LD50 > 38 µM. The neutral porphyrins showed no phototoxicity up to the 100 µM concentrations investigated, and had the lowest singlet oxygen quantum yields. All cationic porphyrins localized mainly in the cell ER, Golgi apparatus, and lysosomes. CONCLUSION: Our results suggest that cationic methylated porphyrin derivatives are promising PDT photosensitizing agents. The epoxymethyl-containing derivatives showed increased efficacy relative to the neutral analogs, and are good candidates for further investigation. Lasers Surg. Med. 50:566-575, 2018. © 2018 Wiley Periodicals, Inc.