The use of Trichomonas vaginalis purine nucleoside phosphorylase to activate fludarabine in the treatment of solid tumors

Treatment with fludarabine phosphate (9-β-D-arabinofuranosyl-2-F-adenine 5′-phosphate, F-araAMP) leads to regressions and cures of human tumor xenografts that express Escherichia coli purine nucleoside phosphorylase (EcPNP). This occurs despite the fact that fludarabine (F-araA) is a relatively poor substrate for EcPNP, and is cleaved to liberate 2-fluoroadenine at a rate only 0.3% that of the natural E. coli PNP substrate, adenosine. In this study, we investigated a panel of naturally occurring PNPs to identify more efficient enzymes that may be suitable for metabolizing F-araA as part of experimental cancer therapy. We show that Trichomonas vaginalis PNP (TvPNP) cleaves F-araA with a catalytic efficiency 25-fold greater than the prototypic E. coli enzyme. Cellular extracts from human glioma cells (D54) transduced with lentivirus stably expressing TvPNP (D54/TvPNP) were found to cleave F-araA at a rate similar to extracts from D54 cells expressing EcPNP, although much less enzyme was expressed per cell in the TvPNP transduced condition. As a test of safety and efficacy using TvPNP, human head and neck squamous cell carcinoma (FaDu) xenografts expressing TvPNP were studied in nude mice and shown to exhibit robust tumor regressions, albeit with partial weight loss that resolved post-therapy. F-araAMP was also a very effective treatment for mice bearing D54/TvPNP xenografts in which approximately 10% of tumor cells expressed the enzyme, indicating pronounced ability to kill non-transduced tumor cells (high bystander activity). Moreover, F-araAMP demonstrated activity against D54 tumors injected with an E1, E3 deleted adenoviral vector encoding TvPNP. In that setting, despite higher F-araA cleavage activity using TvPNP, tumor responses were similar to those obtained with EcPNP, indicating factors other than F-Ade production may limit regressions of the D54 murine xenograft model. Our results establish that TvPNP is a favorable enzyme for activating F-araA, and support further studies in combination with F-araAMP for difficult-to-treat human cancers.     

Involvement of TSC genes and differential expression of other members of the mTOR signaling pathway in oral squamous cell carcinoma

Background  

Despite extensive research, the five-year survival rate of oral squamous cell carcinoma (OSCC) patients has not improved. Effective treatment of OSCC requires the identification of molecular targets and signaling pathways to design appropriate therapeutic strategies. Several genes from the mTOR signaling pathway are known to be dysregulated in a wide spectrum of cancers. However, not much is known about the involvement of this pathway in tumorigenesis of OSCC. We therefore investigated the role of the tumor suppressor genes, TSC1 and TSC2, and other members of this pathway in tumorigenesis of OSCC.     

Carriage of Haemophilus influenzae and Streptococcus pneumoniae in healthy Chinese and Vietnamese children in Hong Kong

Nasopharyngeal carriage of Haemophilus influenzae and Streptococcus pneumoniae was studied in 621 healthy Chinese children and 300 healthy Vietnamese children aged from 2 months to 5 years in Hong Kong. The carriage rate of H, influenzae type b in Vietnamese children was 1.3% (CI 0.04-2.63%); it was zero in Chinese. The carriage rate of non-typable H. influenzae was 5.8% (CI 1.4-7.6%) in Chinese and 65.4% (CI 58.9-69.8%) in Vietnamese. The carriage rates of S. pneumoniae were 10.8% (CI 8.3-13.2%) and 55.7% (CI 50.1-61.3%) in Chinese and Vietnamese children, respectively. Univariate and multivariate logistic regression analyses were performed to search for factors associated with differences in carriage rates of both H. influenzae and S. pneumoniae between Chinese and Vietnamese children. Although older age, smaller living area and parental smoking were associated with higher carriage rates, these could not explain the remarkably low carriage rates of both bacteria in Chinese children.     

DNA testing for fragile X syndrome in schools for learning difficulties

Fragile X syndrome is the most common inherited cause of mental retardation. Early diagnosis is important not only for appropriate management of individuals but also to identify carriers who are unaware of their high risk of having an affected child. The disorder is associated with a cytogenetically visible fragile site (FRAXA) at Xq27.3, caused by amplification of a (CGG)n repeat sequence within the gene at this locus designated FMR1. Clinical and molecular studies have been undertaken to screen for fragile X syndrome in 154 children with moderate and severe learning difficulties of previously unknown origin. Southern blot analysis of peripheral blood showed the characteristic abnormally large (CGG)n repeat sequence associated with fragile X syndrome in four of the 154 children. The findings were confirmed by cytogenetic observation of the fragile site and by further molecular studies. The families of the affected children were offered genetic counselling and DNA tests to determine their carrier status. These findings show that there are still unrecognised cases of fragile X syndrome. Given the difficulty of making a clinical diagnosis and the implications for families when the diagnosis is missed, screening in high risk populations may be justified. The issues involved in screening all children in special schools for fragile X syndrome are discussed.     

Growth, puberty and obesity after treatment for leukaemia

Final height, body proportions, pubertal growth and body mass index were studied retrospectively in 142 survivors of acute lymphoblastic leukaemia (ALL). Treatment consisted of combination chemotherapy and cranial irradiation (18 or 24 Gy). Significant standing height loss and disproportion, with a relatively short back, was seen in both radiation dose groups. Girls were more severely affected than boys. Pubertal growth was adversely affected, with a reduction in peak height velocity in both sexes. Puberty occurred early in girls but at the normal time in boys. Nearly half the group were obese at final height, with no significant difference in incidence between the sexes. The relative roles of cranial irradiation and chemotherapy in the disturbance of growth, puberty and body composition observed in survivors of childhood ALL remain unclear. The aetiology is almost certainly multifactorial, with radiation-induced growth hormone insufficiency, early puberty, steroids and chemotherapy all having a role.