Multifunctional gold nanoparticles (AuNPs) may serve as a scaffold to integrate diagnostic and therapeutic functions into one theranostic system, thereby simultaneously facilitating diagnosis and therapy and monitoring therapeutic responses. Herein, albumin-AuNP theranostic agents have been obtained by conjugation of an anticancer nucleotide trifluorothymidine (TFT) or a boron-neutron capture therapy drug undecahydro-closo-dodecaborate (B₁₂H₁₂) to bimodal human serum albumin (HSA) followed by reacting of the albumin conjugates with AuNPs. In vitro studies have revealed a stronger cytotoxicity by the AuNPs decorated with the TFT-tagged bimodal HSA than by the boronated albumin conjugates. Despite long circulation time, lack of the significant accumulation in the tumor was observed for the AuNP theranostic conjugates. Our unique labelling strategy allows for monitoring of spatial distribution of the AuNPs theranostic in vivo in real time with high sensitivity, thus reducing the number of animals required for testing and optimizing new nanosystems as chemotherapeutic agents and boron-neutron capture therapy drug candidates.

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.

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.

Objective: A combination of boron neutron capture therapy and chemotherapy can ensure good efficacy in cancer treatment. The development of therapeutic constructs that combine these two functions, specifically the possibility of in vitro and in vivo visualization and a convenient platform for selective delivery to the tumor, is of great relevance today. Methods: In this study, we focused on human serum albumin, a well-known drug delivery platform, and developed, based on albumin functionalized with boron clusters, therapeutic constructs, which as analogs of the chemotherapeutic molecule gemcitabine and signaling molecules. To create such constructs, we developed new analogs of homocysteine thiolactone containing closo-dodecaborate or cobalt bis(dicarbollide) and a gemcitabine analog containing closo-dodecaborate attached to the C⁵ carbon atom of the nitrogenous base. Results and Discussion: It was demonstrated that the the conjugates modified with the gemcitabine analogs exhibit increased cytotoxicity against human glioblastoma cell lines. Among the obtained conjugates, the highest cytotoxicity is demonstrated by that containing cobalt bis(dicarbollide). The resulting structures accumulate well in the cytoplasm of cancer cells. The albumin conjugate containing cobalt bis(dicarbollide) and the boron-containing gemcitabine analog is capable of accumulating in the nuclei of T98G cell lines. Conclusions: The resulting albumin constructs showed sufficient in vitro activity against human glioma cells. It is expected that the obtained therapeutic conjugates will significantly enhance the anticancer efficacy of irradiation with epithermal neutrons. Combining a chemotherapeutic residue and a boron-containing group in a single construct provides potential for more effective glioma therapy.

Combining boron neutron capture therapy with chemotherapy can provide good therapy efficacy and is of great relevance today. In this study, we focused on serum albumin, a well-known drug delivery system, and developed homocysteine-functionalized boron albumin conjugate with chemotherapeutic molecules (monomethyl auristatin E, MMAE and auristatin F, MMAF). The new N-acylated homocysteine thiolactone bearing a cobalt bis(dicarbollide) derivative was used to create the fluorophore-albumin based construct. We report on the synthesis of a fluorophore-labeled boron-homocystamide conjugates of human serum albumin and their use in thiol-‘click’ chemistry to prepare a novel multifunctional constructs with the antitubulin agents MMAE or MMAF. We demonstrate that boron-equipped albumin conjugate with MMAE was more potent than MMAF conjugate, in the killing tumor cells. The half-maximal inhibitory concentration (IC₅₀) of the designed theranostics was not less than 0.034 µM relative to T98G glioma cells with the correlation coefficient not less than R = 0.88, and not less than 0.97 µM relative U 87 glioma cells with the correlation coefficient not less than R = 0.71.