Masahiko Hirata

Anti-tumor activity of new orally bioavailable 2-amino-5-(thiophen-2-yl)benzamide-series histone deacetylase inhibitors, possessing an aqueous soluble functional group as a surface recognition domain

New orally bioavailable 5-(thiophen-2-yl)-substituted 2-aminobenzamide-series histone deacetylase inhibitors were synthesized. These compounds possess a morpholine or piperadine-derived moiety as an aqueous soluble functional group. Among them, 8b, having a 4-ethyl-2,3-dioxopiperazine-1-carboxamide group as a surface recognition domain, showed promising inhibitory activities against HCT116 cell growth and HDAC1/2. Notably, unlike MS-275, this compound did not induce apoptosis in the cell cycle tests. We therefore conducted antitumor tests of 8b and MS-275 against HCT116 cell xenografts in nude mice. Compound 8b reduced the volume of tumor mass to T/C: 60% and 47% at 45 and 80mg/kg over 16days, respectively. These values were comparable to the rate (T/C: 51% at 45mg/kg) for MS-275. Furthermore, 8b, at neither 45 nor 80mg/kg, induced the weight loss which was observed in the mice given MS-275 at 45mg/kg.

Bio-imaging of hydroxyl radicals in plant cells using the fluorescent molecular probe rhodamine B hydrazide, without any pretreatment.

Rhodamine B hydrazide can be used to detect hydroxyl radicals in plant cells. RBH was easily inserted into plant cells without any pretreatment, and specifically reacted with intracellular hydroxyl radicals produced by antimycin A. RBH will be a powerful tool for detecting hydroxyl radicals in plant cells.

Development of novel PET probes targeting phosphatidylinositol 3-kinase (PI3K) in tumors

Phosphatidylinositol 3-kinase (PI3K) activity and protein expression levels are often increased in tumor regions. Since PI3K plays a crucial role in regulating cell growth and proliferation, inhibiting PI3K-dependent pathways could be a promising approach for cancer treatment. In clinical practice, however, evaluation of PI3K expression levels is limited to immunohistochemistry of patient samples, which requires invasive biopsies. Here we report the synthesis of three candidate compounds, FMTA-1, 2 and 3, and evaluate their capacity to detect PI3K expression levels with positron emission tomography (PET). Among the three candidates, FMTA-2 showed a lower IC50 value for PI3K. (18)F Radiolabeling of FMTA-2 to produce [(18)F]FMTA-2 was accomplished and its capacity for detecting PI3K expression levels was evaluated in vitro and in vivo. Cell uptake of [(18)F]FMTA-2 correlated well with cellular PI3K expression levels, and was suppressed by the ATP-competitive PI3K inhibitor ZSTK474. In an in vivo experiment using tumor-transplanted model mice, a higher signal-to-noise ratio (S/N) was seen with [(18)F]FMTA-2 in animals transplanted with DMS114 cells (expressing high PI3K levels) relative to DU145 cells (expressing low PI3K levels). However, in vivo pharmacokinetics of [(18)F]FMTA-2 was undesirable and the absolute amount of this compound that accumulated at the tumor region was low. To the best of our knowledge, this study represents the first trial of a PET tracer for detecting PI3K. Although further improvement of the probe is required prior to clinical application, these results should encourage future work.

PET probe detecting non-small cell lung cancer susceptible to epidermal growth factor receptor tyrosine kinase inhibitor therapy

Tyrosine kinase inhibitors for epidermal growth factor receptor (EGFR-TKIs) are used as molecular targeted therapy for non-small cell lung cancer (NSCLC) patients. The therapy is applied to the patients having EGFR-primary L858R mutation, but drug tolerance caused by EGFR-secondary mutation is occurred within one and half years. For the non-invasive detection of the EGFR-TKIs treatment positive patients by positron emission tomograpy (PET) imagaing, fluorine-18 labeled thienopyrimidine derivative, [18F]FTP2 was newly synthesized. EGFR inhibition assay, cell uptake study, and blocking study indicated [18F]FTP2 binds with high and selective affinity for EGFR with L858R mutation, and not with L858R/T790M dual mutations. On animal PET study using tumor bearing mice, H3255 cells expressing L858R mutated EGFR was more clearly visualized than H1975 cells expressing L858R/T790M dual mutated EGFR. [18F]FTP2 has potential for detecting NSCLC which is susceptible to EGFR-TKI treatment.