Design of the New Closo-Dodecarborate-Containing Gemcitabine Analogue for the Albumin-Based Theranostics Composition.

Combination therapy is becoming an increasingly important treatment strategy because multi-drugs can maximize therapeutic effect and overcome potential mechanisms of drug resistance. A new albumin-based theranostic containing gemcitabine closo-dodecaborate analogue has been developed for combining boron neutron capture therapy (BNCT) and chemotheraphy. An exo-heterocyclic amino group of gemcitabine was used to introduce closo-dodecaborate, and a 5'-hydroxy group was used to tether maleimide moiety through an acid-labile phosphamide linker. The N-trifluoroacylated homocysteine thiolactone was used to attach the gemcitabine analogue to human serum albumin (HSA) bearing Cy5 or Cy7 fluorescent dyes. The half-maximal inhibitory concentration (IC50) of the designed theranostic relative to T98G cells was 0.47 mM with the correlation coefficient R = 0.82. BNCT experiments resulted in a decrease in the viability of T98G cells, and the survival fraction was ≈ 0.4.

Homocystamide Conjugates of Human Serum Albumin as a Platform to Prepare Bimodal Multidrug Delivery Systems for Boron Neutron Capture Therapy.

Boron neutron capture therapy is a unique form of adjuvant cancer therapy for various malignancies including malignant gliomas. The conjugation of boron compounds and human serum albumin (HSA)-a carrier protein with a long plasma half-life-is expected to extend systemic circulation of the boron compounds and increase their accumulation in human glioma cells. We report on the synthesis of fluorophore-labeled homocystamide conjugates of human serum albumin and their use in thiol-'click' chemistry to prepare novel multimodal boronated albumin-based theranostic agents, which could be accumulated in tumor cells. The novelty of this work involves the development of the synthesis methodology of albumin conjugates for the imaging-guided boron neutron capture therapy combination. Herein, we suggest using thenoyltrifluoroacetone as a part of an anticancer theranostic construct: approximately 5.4 molecules of thenoyltrifluoroacetone were bound to each albumin. Along with its beneficial properties as a chemotherapeutic agent, thenoyltrifluoroacetone is a promising magnetic resonance imaging agent. The conjugation of bimodal HSA with undecahydro-closo-dodecaborate only slightly reduced human glioma cell line viability in the absence of irradiation (~30 µM of boronated albumin) but allowed for neutron capture and decreased tumor cell survival under epithermal neutron flux. The simultaneous presence of undecahydro-closo-dodecaborate and labeled amino acid residues (fluorophore dye and fluorine atoms) in the obtained HSA conjugate makes it a promising candidate for the combination imaging-guided boron neutron capture therapy.

Human Serum Albumin Labelling with a New BODIPY Dye Having a Large Stokes Shift.

BODIPY dyes are photostable neutral derivatives of 4,4-difluoro-4-bora-3a,4a-diaza-s-indacene. These are widely used as chemosensors, laser materials, and molecular probes. At the same time, BODIPY dyes have small or moderate Stokes shifts like most other fluorophores. Large Stokes shifts are preferred for fluorophores because of higher sensitivity of such probes and sensors. The new boron containing BODIPY dye was designed and synthesized. We succeeded to perform an annulation of pyrrole ring with coumarin heterocyclic system and achieved a remarkable difference in absorption and emission maximum of obtained fluorophore up to 100 nm. This BODIPY dye was equipped with linker arm and was functionalized with a maleimide residue specifically reactive towards thiol groups of proteins. BODIPY residue equipped with a suitable targeting protein core can be used as a suitable imaging probe and agent for Boron Neutron Capture Therapy (BNCT). As the most abundant protein with a variety of physiological functions, human serum albumin (HSA) has been used extensively for the delivery and improvement of therapeutic molecules. Thiolactone chemistry provides a powerful tool to prepare albumin-based multimodal constructions. The released sulfhydryl groups of the homocysteine functional handle in thiolactone modified HSA were labeled with BODIPY dye to prepare a labeled albumin-BODIPY dye conjugate confirmed by MALDI-TOF-MS, UV-vis, and fluorescent emission spectra. Cytotoxicity of the resulting conjugate was investigated. This study is the basis for a novel BODIPY dye-albumin theranostic for BNCT. The results provide further impetus to develop derivatives of HSA for delivery of boron to cancer cells.