Comparative analyses of the two proliferating cell nuclear antigens from the hyperthermophilic archaeon,Thermococcus kodakarensis

The DNA sliding clamp is a multifunctional protein involved in cellular DNA transactions. In Archaea and Eukaryota, proliferating cell nuclear antigen (PCNA) is the sliding clamp. The ring‐shaped PCNA encircles double‐stranded DNA within its central hole and tethers other proteins on DNA. The majority of Crenarchaeota, a subdomain of Archaea, have multiple PCNA homologues, and they are capable of forming heterotrimeric rings for their functions. In contrast, most organisms in Euryarchaeota, the other major subdomain, have a single PCNA forming a homotrimeric ring structure. Among the Euryarchaeota whose genome is sequenced, Thermococcus kodakarensis is the only species with two genes encoding PCNA homologues on its genome. We cloned the two genes from the T. kodakarensis genome, and the gene products, PCNA1 and PCNA2, were characterized. PCNA1 stimulated the DNA synthesis reactions of the two DNA polymerases, PolB and PolD, from T. kodakarensis in vitro. PCNA2, however, only had an effect on PolB. We were able to disrupt the gene for PCNA2, whereas gene disruption for PCNA1 was not possible, suggesting that PCNA1 is essential for DNA replication. The sensitivities of the Δpcna2 mutant strain to ultraviolet irradiation (UV), methyl methanesulfonate (MMS) and mitomycin C (MMC) were indistinguishable from those of the wild‐type strain.     

Predicting the intrauterine fetal death of fetuses with cystic hygroma in early pregnancy

We investigated whether it was possible to predict the prognosis of fetuses with cystic hygroma in early pregnancy based on the degree of neck thickening. We retrospectively analyzed 57 singleton pregnancies with fetuses with cystic hygroma who were examined before the 22nd week of pregnancy. The fetuses were categorized according to the outcome, structural abnormalities at birth, and chromosomal abnormalities. Here, we proposed a new sonographic predictor with which we assessed neck thickening by dividing the width of the neck thickening by the biparietal diameter, which is expressed as the cystic hygroma width/biparietal diameter ratio. The median cystic hygroma width/biparietal diameter ratio in the intrauterine fetal death group (0.51) was significantly higher than that in the live birth group (0.27). No significant difference in the median cystic hygroma width/biparietal diameter ratio was found between the structural abnormalities group at birth and the no structural abnormalities group, and no significant difference in the median cystic hygroma width/biparietal diameter ratio was found between the chromosomal abnormality group and the no chromosomal abnormality group. We used receiver operating characteristic analysis to evaluate the cystic hygroma width/biparietal diameter ratio to predict intrauterine fetal death. When the cystic hygroma width/biparietal diameter ratio cut‐off value was 0.5, intrauterine fetal death could be predicted with a sensitivity of 52.9% and a specificity of 100%. It is possible to predict intrauterine fetal death in fetuses with cystic hygroma in early pregnancy if cystic hygroma width/biparietal diameter ratio is measured. However, even if cystic hygroma width/biparietal diameter ratio is measured, predicting the presence or absence of a structural abnormality at birth or a chromosomal abnormality is difficult.     

Potent and specific antitumor effect of CEA‐targeted photoimmunotherapy

Conventional photodynamic therapy (PDT) for cancer is limited by the insufficient efficacy and specificity of photosensitizers. We herein describe a highly effective and selective tumor‐targeted PDT using a near‐infrared (NIR) photosensitizer, IRDye700DX, conjugated to a human monoclonal antibody (Ab) specific for carcinoembryonic antigen (CEA). The antitumor effects of this Ab‐assisted PDT, called photoimmunotherapy (PIT), were investigated in vitro and in vivo. The Ab‐IRDye conjugate induced potent cytotoxicity against CEA‐positive tumor cells after NIR‐irradiation, whereas CEA‐negative cells were not affected at all, even in the presence of excess photoimmunoconjugate. We found an equivalent phototoxicity and a predominant plasma membrane localization of Ab‐IRDye after both one and six hours of incubation. Either no or little caspase activation and membrane peroxidation were observed in PIT‐treated cells and a panel of scavengers for reactive oxygen species showed only partial inhibition of the phototoxic effect. Strikingly, Ab‐IRDye retained significant phototoxicity even under hypoxia. We established a xenograft model, which allowed us to sensitively investigate the therapeutic efficacy of PIT by non‐invasive bioluminescence imaging. Luciferase‐expressing MKN‐45‐luc human gastric carcinoma cells were subcutaneously implanted into both flanks of nude mice. NIR‐irradiation was performed for only the tumor on one side. In vivo imaging and measurement of the tumor size revealed that a single PIT treatment, with intraperitoneal administration of Ab‐IRDye and subsequent NIR‐irradiation, caused rapid cell death and significant inhibition of tumor growth, but only on the irradiated side. Together, these data suggest that Ab‐IRDye‐mediated PIT has great potential as an anticancer therapeutics targeting CEA‐positive tumors.