Liposome and co-spray-dried PVP / o-carborane formulations for BNCT treatment of cancer

Purpose: Boron neutron capturetherapy (BNCT) is a method for selectively destroying malignant (normally glioma) cells whilst sparing normal tissue. Irradiation of 10B (large neutron capturecross-section) with thermal neutrons effects the nuclear fissionreaction: 10B + 1n → → 7Li+ + α + γ; where the penetration of α-particles and 7Li+ is only 8 and 5 µm, respectively, i.e., within a single cell thickness. Poor selectivity is the main reason why BNCT has not become a mainstream cancer therapy. Carboranes. a third generation of high 10B -containing, low-toxicity, BNCT compounds, are currently being investigated. Towards the aim of producing new BNCT formulations, monodispersed dipalmitoylphosphatidylcholineand 1,2-distearoyl-sn-glycero-3- phosphocholinesmall unilammellar vesicle (SUV) liposomes and spray-dried powders both containing the model boron agent o- carboranewere produced. The particle sizes were designed to pass through the blood brain barrier (< 100 nm) and target bronchioles in the lungs (1 – 2 µm), respectively, for the effective BNCT treatment of gliomas and lung cancer. Malignant cell preferential targeting was also investigated using carboranesderivatised with delocalised lipophilic cations (DLCs), specifically the dequaliniumbis nido carborane(DC) salt. Method: SUV liposomes were successfully produced by thin film rehydration method. Atomic force microscopy (AFM) was used to investigated morphology and stability. Liposome integrity, in serum, was ascertained using as %latency and %retention experiments using a fluorescent hydrophilic marker ( calcein). The Nile Redfluorescence method and IC-MS were used to measure o- carboraneentrapment. Uptake of DC by IN699 (glioma, WHO grade IV) and SC1800 (non-neoplastic astrocyte) cells was investigated using live cell (fluorescence) imaging. Polyvinylpyrrolidone (PVP) / o- carboraneco-spray-dried microparticles were produced using spray drying (Buchi B-290). Results: Liposomes were monodispersed (PDI < 0.5) and had particle diameters of ca. 80 – 100 nm. AFM studies showed the loaded liposomes were stable (63 days, 4°C, if re-probing was employed). The liposome membrane integrity in serum was found to be high for both types of liposomes prepared using cholesterol. Carboranewas successfully entrapped in the liposomes. Specific targeting glioma cells, rather than non-neoplastic astrocyte cells, with DC was demonstrated using live cell (fluorescence) imaging. 1H NMR studies revealed the high temperatures (180 °C) of the spray drying process did not degrade PVP. Mean particle diameters (x90) were in the 2 – 10 µm range, with finer fractions being present (x10 ≅ 1 – 2 µm). SEM imaging showed the particles to be spherical, with dimplesand cavities caused by the spray drier nozzle characteristics. Conclusion: Liposomes containing o- carboranehad sizes suitable for transit across the BBB. The cationic moiety of DC allowed selective targeting of glioma mitochondria, thought to be due to differences in mitochondrial membrane potentials between malignant and non-neoplastic cells. PVP / o- carboraneco-spray-dried particles had diameters suitable for delivery to the lungs.