Dental caries is one of the most common childhood diseases, and people continue to be susceptible to it throughout their lives. Although dental caries can be arrested and potentially even reversed in its early stages, it is often not self-limiting and progresses without proper care until the tooth is destroyed. Early childhood caries (ECC) is often complicated by inappropriate feeding practices and heavy infection with mutans streptococci. Such children should be targeted with a professional preventive program that includes oral hygiene instructions for mothers or caregivers, along with fluoride and diet counseling. However, these strategies alone are not sufficient to prevent dental caries in high-risk children; prevention of ECC also requires addressing the socioeconomic factors that face many families in which ECC is endemic. The aim of this paper is to systematically review information about ECC and to describe why many children are suffering from dental caries.

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To improve the efficacy and selectivity of gene therapy for hepatocellular carcinoma (HCC), we designed a strategy for suicide gene therapy in conjunction with radiation therapy using an HVJ-liposome vector system. The radio-inducible suicide gene was constructed by insertion of the early growth response gene 1 (Egr-1) promoter upstream of the HSV-tk gene (EGF-tk). First, to test the tumor specificity of Egr-1, RT-PCR and immunohistochemistry were performed. The Egr-1 gene was highly expressed in HCC compared with normal liver, where expression was barely detectable. Next, radiation-inducible activity of the Egr-1 promoter was examined in primary cultured normal hepatocytes and human hepatoma cell lines Huh7, HepG2, and PLC/PRF/5 by luciferase assay as a reporter gene system. Egr-1 promoter activity was markedly increased in hepatoma cell lines in a radiation dose-dependent manner, with maximum activation (15- to 28-fold) 12 hr after irradiation. In contrast, only a twofold increase in activation was noted in normal hepatocytes. An in vitro gene therapy experiment showed that EGR-tk-transduced hepatoma cells became highly sensitive to ganciclovir (GCV) after irradiation, but not without irradiation. GCV with or without irradiation did not show any cytotoxic effects against control gene-transfected cells. In addition, a "radiosensitization effect" was also demonstrated by combination therapy with the HSV-tk/GCV system and irradiation. To examine the efficacy of this EGR-tk/GCV gene therapy in vivo, xenografted liver tumors in nude mice were targeted using the HVJ-liposome vector system. EGR-tk-transfected tumors regressed significantly after a combination therapy of irradiation and GCV in all mice (n = 8), and almost disappeared in 3 weeks without any side effects. In comparison, tumors continued to grow in all mice (n = 8 in each group) treated by transfer of EGR-tk followed by either irradiation without GCV or GCV without irradiation. Our data indicate that HSV-tk gene therapy under the control of a radioinducible promoter is effective, and might be selective for hepatoma cells because of its inducible and radiosensitive capacity after radiation exposure as well as its tumor-specific activation.

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