Onc genes and other new targets for cancer chemotherapy

Tyrosine kinase receptors as attractive targets of cancer therapy

Receptor tyrosine kinases (RTKs) are the main mediators of the signaling network that transmit extracellular signals into the cell, and control cellular differentiation and proliferation. Recent and rapid advances in our understanding of cellular signaling by receptor tyrosine kinases, in normal and malignant cells, have brought to light the potential of RTKs as selective anti-cancer targets. Their activity is normally tightly controlled and regulated. Overexpression of RTK proteins or functional alterations caused by mutations in the corresponding genes or abnormal stimulation by autocrine growth factor loops contribute to constitutive RTK signaling, resulting in dysregulated cell growth and cancer. The mechanisms of uncontrolled RTK signaling that leads to cancer has provided the rationale for anti-RTK drug development. Herceptin, Gleevec, and Iressa are the first examples of drugs which have successfully translated basic research on oncogenes into cancer therapeutics. RTKs can be viewed as multifunctional targets, and strategies towards the prevention and inhibition of RTK signaling include antibodies, antagonist ligands, small molecule inhibitors of protein kinase activity, and inhibitors of protein-protein interactions. Progresses in the field of rational drug design and computational chemistry will vastly benefit from the availability of increasing structural knowledge of both the kinase domains and the ligand-binding sites of these receptors.

DNA sequences of human papillomavirus types 11, 16 or 18 in invasive cervical carcinoma of Western Australian women

The presence of human papillomavirus (HPV) types 11, 16 and 18 in 77 biopsies of cervical intraepithelial neoplasia (dysplasia) and carcinoma of the uterine cervix of a sample of women from Western Australia was examined using "Southern" blot hybridisation. HPV-DNA was found in 17 of the 23 dysplasias and 43 of the 54 invasive carcinomas examined but not in the 5 biopsies obtained from areas assessed as normal by colposcopy and histology. Five of 11 biopsies of mild to moderate dysplasias contained HPV type 11 (HPV-11), 2 HPV-16 and 1 HPV-18. Of 12 severe dysplasias/carcinoma in situ, 2 contained HPV-11, 4 HPV-16 and 2 HPV-18. One biopsy contained both HPV-11 and HPV-16. Of 45 squamous cell carcinomas examined for HPV-DNA, 24 contained HPV-16, 5 HPV-11 and 1 HPV-18. Both HPV-11 and HPV-16 were found in 6 of the squamous cell carcinomas and 2 contained both HPV-16 and HPV-18. Of 6 adenosquamous carcinomas examined, 3 contained HPV-DNA, 2 with HPV-16 and 1 with HPV-11. HPV types 16 or 18 were also found in 2 of 3 adenocarcinomas. This study shows a strong association between the papillomavirus and uterine cervical cancer in a sample of women from Western Australia. HPV-16 was more frequently associated with severe dysplasia and cancer than with mild or moderate dysplasia supporting the view that this HPV genotype may have a greater oncogenic potential than HPV-11.

Actinomycin D inhibition of monoclonal antibody binding to nucleolar phosphoprotein 37/5.2 (B23)

Actinomycin D was found to block binding of a monoclonal antibody to nucleolar phosphoprotein 37/5.2 (B23) when incubated either simultaneously with or prior to addition of the antibody. Daunorubicin had no significant blocking activity of this antigen-antibody reaction. In comparative studies with a monoclonal antibody to nucleolar phosphoprotein 110/5.2 (C23), actinomycin D exhibited little blocking activity. When a 42-mer peptide containing the epitope of protein 37/5.2 (B23) was tested as the antigen, similar inhibition by actinomycin D of binding of the monoclonal antibody was found. These results provide evidence for binding of actinomycin D to a specific epitope of protein 37/5.2 (B23).