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Further development of boron neutron capture therapy (BNCT) requires new neutronsensitizers with improved ability to deliver 10B isotopes in cancer cells. Conjugation of boron nanoparticles with porphyrin derivatives is an attractive and recognized strategy to solve this task. We report on breakthroughs in the structural optimization of conjugates of chlorin e6 derivative with cobalt-bis(dicarbollide) nanoparticles resulting in the creation of dimethyl ester 13-carbomoylchlorin e6 [N-hexylamine-N′-ethoxyethoxy]-cobalt-bis(dicarbollide) (conjugate 1). Conjugate 1 is able to accumulate quickly and efficiently (distribution factor of 80) in cancer cells, thus delivering more than 109 boron atoms per cell when its extracellular concentration is more than 1 μmol L−1. Also 1 is an active photosensitizer and is phototoxic towards human lung adenocarcinoma A549 cells at 80 nmol L−1 (50% cell death). Photoinduced cytotoxicity of 1 is associated with lipid peroxidation, lysosome rupture and protease activity enhancement. Conjugate 1 fluoresces in the red region (670 nm), which is useful to monitor its accumulation and distribution in vivo. It is not toxic to cells without activation by neutrons or photons. Structural features that improve the functional properties of 1 are discussed. The properties of 1 warrant its preclinical evaluation as a multifunctional agent for BNCT, photodynamic therapy and fluorescent tumor diagnosis. [ABSTRACT FROM AUTHOR]

Conjugation of boron nanoparticles with porphyrins is an attractive way to create dual agents for anticancer boron neutron capture therapy (BNCT) and photodynamic therapy (PDT). Properties of chlorin e6 conjugated with two cobalt bis(dicarbollide) nanoparticles (1) or with a closo-dodecaborate nanoparticle (2) are reported. Fluorescent dianionic conjugates 1 and 2 penetrate in A549 human lung adenocarcinoma cells, stain cytoplasm diffusely and accumulate highly in lysosomes but are not toxic themselves for cells. Average cytoplasmic concentration of boron atoms (B) achieves 270 μM (ca. 2 × 108 B/cell) and 27 μM (ca. 2 × 107 B/cell) at the 1.5 μM extracellular concentration of 1 and 2, respectively, that makes conjugate 1 especially suitable for BNCT. Conjugate 2 causes photoinduced cell death at micromolar concentrations and can be considered also as a photosensitizer for PDT. Conjugates 1 and 2 have high quantum yields of singlet oxygen generation (0.55 and 0.85 in solution, respectively), identical intracellular localization and similar lipid-like microenvironment but conjugate 1 possesses no photoinduced cytotoxicity. A presence of cobalt complexes in conjugate 1 is supposed to be a reason of the observed antioxidative effect in cellular environment, but an exact mechanism of this intriguing phenomenon is unclear. Due to increased intracellular accumulation and absence of photoinduced cytotoxicity conjugate 1 is promising for fluorescence diagnostics of cancer. [ABSTRACT FROM AUTHOR]