Shoji Tachikawa

Development of High Boron Content Liposomes and Their Promising Antitumor Effect for Neutron Capture Therapy of Cancers

Mercaptoundecahydrododecaborate (BSH)-encapsulating 10% distearoyl boron lipid (DSBL) liposomes were developed as a boron delivery vehicle for neutron capture therapy. The current approach is unique because the liposome shell itself possesses cytocidal potential in addition to its encapsulated agents. BSH-encapsulating 10% DSBL liposomes have high boron content (B/P ratio: 2.6) that enables us to prepare liposome solution with 5000 ppm boron concentration. BSH-encapsulating 10% DSBL liposomes displayed excellent boron delivery efficacy to tumor: boron concentrations reached 174, 93, and 32 ppm at doses of 50, 30, and 15 mg B/kg, respectively. Magnescope was also encapsulated in the 10% DSBL liposomes and the real-time biodistribution of the Magnescope-encapsulating DSBL liposomes was measured in a living body using MRI. Significant antitumor effect was observed in mice injected with BSH-encapsulating 10% DSBL liposomes even at the dose of 15 mg B/kg; the tumor completely disappeared three weeks after thermal neutron irradiation ((1.5-1.8) × 10(12) neutrons/cm(2)). The current results enabled us to reduce the total dose of liposomes to less than one-fifth compared with that of the BSH-encapsulating liposomes without reducing the efficacy of boron neutron capture therapy (BNCT).

Towards new boron carriers for boron neutron capture therapy: metallacarboranes bearing cobalt, iron and chromium and their cholesterol conjugates.

A method for the synthesis of cholesterol-metallacarborane conjugates bearing cobalt, iron and chromium was developed. Effective incorporation of the cholesterol conjugate bearing cobalt into liposome membrane was revealed. Using the metallacarborane-encrusted liposomes as boron delivery system in vivo biodistribution experiments in tumor-bearing mice, high accumulation and selective delivery of boron into tumor tissues was observed. The results demonstrate that the cholesterol-metallacarborane conjugates can be considered as a potential candidate for boron delivery vehicle in BNCT.

Synthesis of protoporphyrin–lipids and biological evaluation of micelles and liposomes

Protoporphyrin IX (PPIX) lipids were synthesized by introducing a long alkyl chain, such as C13, C15, and C17, at each vinyl group on PPIX via hydrobromination. The PPIX lipids exhibited a water-soluble property by forming their micelles in water and the PPIX-lipid micelles showed relatively low cytotoxicity toward HeLa cells (IC50=151.7-379.9μM) without light irradiation. PL-C17 liposomes (post-inserted liposomes) were readily prepared by adding PL-C17 micelle solution to the liposome solution. The IC50 values of PPIX, PL-C17 micelles, and PL-C17 liposomes toward HeLa cells were 0.53, 5.65, and 12.9μM, respectively, after irradiation with a xenon lamp in the 400-800nm range for 2min. PL-C17 liposomes were selectively accumulated in the Golgi apparatus in cells.

A novel photodynamic therapy for drug-resistant prostate cancer cells using porphyrus envelope as a novel photosensitizer

BACKGROUND In the clinic, it is often very difficult to treat drug-resistant advanced prostate cancer by conventional treatments. Photodynamic therapy (PDT) is a minimally invasive treatment that takes advantage of photochemical reactions between a photosensitizer and light. On the basis of several of its key characteristics, PDT is considered to be a promising novel method for treating drug-resistant prostate cancer. OBJECTIVES For effective treatment of drug-resistant prostate cancer, we developed a novel agent termed porphyrus envelope, which was produced from PpIX lipid and hemagglutinating virus of Japan envelope (HVJ-E). MATERIALS AND METHODS We inserted PpIX lipid into HVJ-E by centrifugation, and used the resultant porphyrus envelope in PDT of two drug-resistant prostate cancer cell lines, PC-3 and PC-3-DR. RESULTS Porphyrus envelope enhanced uptake of PpIX, and cytotoxicity of PDT, relative to free PpIX lipid or PpIX induced by 5-ALA. CONCLUSION PDT using porphyrus envelope has potential as a method for treating drug-resistant prostate cancer.

Localization-dependent cell-killing effects of protoporphyrin (PPIX)-lipid micelles and liposomes in photodynamic therapy.

The protoporphyron (PPIX)-lipid (PL-C17) liposomes were successfully prepared from the corresponding micelles by post-inserted method. Both the PL-C17 micelles and liposomes were distributed in plasma membrane and cytoplasm after incubation of the cells with PL-C17 liposomes for 1h. They translocated from plasma membrane into a certain organelle in the cells after incubation in the photosensitizer-free medium. Higher photo-cytotoxicity was observed in the PL-C17 micelles and liposomes localized in plasma membrane in comparison with those localized in the cytoplasm under light irradiation. The LDH assay revealed that cytopathic damages of the plasma membrane were observed in the PL-C17 micelles and liposomes highly localized in plasma membrane. The fluorescent intensity of the calcein-encapsulating DOPC liposomes post-inserted with PL-C17 increased after light irradiation, suggesting that the membrane disruption is possibly caused by oxidation of membrane lipids with ROS generated from photosensitizers and affects the photo-cytotoxicity in PDT.

Synthesis of oligo-closo-dodecaborates by Hüisgen click reaction as encapsulated agents for the preparation of high-boron-content liposomes for neutron capture therapy

High-boron-content compounds, 8, 10, and 13, were designed and synthesized as boron agents encapsulated in liposomes by the Huisgen click cycloaddition of closo-dodecaborate-containing azides and alkynes. These compounds have relatively low cytotoxicities and their GI50 values for B16, CT26, and HeLa cells are higher than 0.14 mM, indicating toxicities similar to that of BSH. High-boron-content liposomes were prepared using 13, which has the largest number of boron atoms in a molecule among the synthesized compounds. The final boron concentration in 13-encapsulating liposomes reached 11.0 × 103 ppm with a B/P ratio of 5.1. A significantly high tumor boron accumulation (72.2 ppm) was observed in tumor-bearing mice 36 h after the injection of 13-encapsulating liposomes at a dose of 15 mgB kg−1 body weight with the tumor/blood (T/B) ratio of approximately 14.

Hemagglutinating virus of Japan envelope (HVJ-E) allows targeted and efficient delivery of photosensitizer for photodynamic therapy against advanced prostate cancer

Selective and efficient photosensitizer delivery was accomplished by utilizing inactivated Sendai virus particle. Drug delivering mechanism was addressed via transmission electron microscope and photocytotoxic activity was investigated thorough performing photodynamic therapy on cultured cells.

Effective photodynamic therapy in drug-resistant prostate cancer cells utilizing a non-viral antitumor vector (a secondary publication).

BACKGROUND AND AIMS There is an urgent need to develop an efficient strategy for the treatment of drug-resistant prostate cancer. Photodynamic therapy (PDT), in which low incident levels of laser energy are used to activate a photosensitizer taken up by tumor cells, is expected as a novel therapy for the treatment of prostate cancer because of the minimal invasive nature of PDT. The present study was designed to assess the efficacy of a novel vector approach combined with a conventional porphyrin-based photosensitizer. MATERIALS AND METHODS Our group focused on a non-viral vector (hemagglutinating virus of Japan envelope; HVJ-E) combined with protoporphyrin IX (PpIX) lipid, termed the porphyrus envelope (PE). It has been previously confirmed that HVJ-E has drug-delivering properties and can induce cancer-specific cell death. The PE (HVJ-E contained in PpIX lipid) was developed as a novel photosensitizer. In this study, the antitumor and PDT efficacy of the PE against hormone-antagonistic human prostate cancer cells (PC-3) were evaluated. RESULTS AND CONCLUSIONS Our results demonstrated that, under specific circumstances, PDT using the PE was very effective against PC-3 cells. A novel therapy for drug-resistant prostate cancer based on this vector approach is eagerly anticipated.

Photodynamic therapy using hemagglutinating virus of Japan envelope (HVJ-E): a novel therapeutic approach for the treatment of hormone antagonistic prostate cancer

Traditional treatment options for prostate cancer are insufficient to cure advanced drug-resistant prostate cancer. Thus, as an alternative form of cancer therapy, photodynamic therapy (PDT) has become the main subject of intense investigation as a possible treatment modality. In this study, ultraviolet-inactivated viral vector, called hemagglutinating virus of Japan envelope (HVJ-E) was utilized to establish an effective delivery system for photosensitizer. Lipidated protoporphyrin IX (PpIX lipid) was inserted in HVJ-E by centrifugation to create a new drug delivering system that allows selective accumulation of photosensitizers in cancer cells. To study in vitro drug release mechanism of porphyrus envelope, the ultra-high voltage electron microscope tomography was applied. Next, to evaluate the photodynamic efficiency of porphyrus envelope for hormone antagonistic prostate cancer cells (PC-3), uptake of porphyrus envelope derived PpIX lipid and PpIX induced from exogenously administered precursor of 5-aminolevulinic acid hydrochloride (5-ALA) were compared by measuring fluorescence intensity of PpIX. Finally, to evaluate the efficacy of porphyrus envelope-PDT, laser light at a wavelength of 405 nm was irradiated to PC-3 cells. As a result, incorporation of porphyrus envelope-derived PpIX lipid occurred via membrane fusion, giving the highest fluorescence intensity when compared to 5-ALA-induced PpIX. Also, results from PDT experiment revealed the 28.6 × 103-fold and 206-fold increase in therapeutic efficacy when compared to those of PDT using 5-ALA induced PpIX and PpIX lipid, respectively. Our findings suggest how porphyrus envelope can induce efficient accumulation of PpIX lipid, which can enhance the therapeutic efficacy of PDT against hormone antagonistic prostate cancer.