Publisher Summary As normal cells progress to tumorigenicity, they must develop two distinct new characteristics not possessed by the normal cells from which they arise: they must become able to multiply without restraint and they must be able to create in vivo an environment where this newly acquired growth potential can be realized. Normal cells are antiangiogenic, because they secrete only low levels of inducers of angiogenesis and high levels of molecules that inhibit neovascularization. These cells develop into successful tumors that are potently angiogenic and secrete high levels of a cocktail of molecules that induce neovascularization. It is possible to halt the production and/or release of angiogenic activity by tumor cells themselves using retinoic acid and similar compounds. Endothelial cells that form the vessels that support tumor growth can be disabled in two distinct ways. Antiangiogenic agents have distinct advantages over conventional cytotoxic cancer therapies. Although the importance of angiogenesis to the growth of tumors is now well established, the mechanism by which tumor cells develop this crucial ability to attract new blood vessels is just beginning to be explored. Available data suggest that the angiogenic phenotype develops gradually as a result of many of the same genetic changes in oncogenes and tumor suppressor genes that are also responsible for the deregulation of cell growth. The inhibitors of angiogenesis offer a new and promising avenue for tumor therapy.

How tumors become angiogenic

Mutations in the p53 gene are most frequent in cancer. Many p53 mutants possess transforming activity in vitro. In cells transformed by such mutants, the mutant protein is oligomerized with endogenous cell p53. To determine the relevance of oligomerization for transformation, miniproteins containing C-terminal portions of p53 were generated. These miniproteins, although carrying no point mutation, transformed at least as efficiently as full-length mutant p53. Transforming activity was coupled with the ability to oligomerize with wild-type p53, as well as with the ability to abrogate sequence-specific DNA binding by coexpressed wild-type p53. These findings suggest that p53-mediated transformation may operate through a dominant negative mechanism, involving the generation of DNA binding-incompetent oligomers.

/pdf/identification-of-a-minimal-transforming-domain-of-p53-tmt66cmflu.pdf

Identification of a minimal transforming domain of p53: negative dominance through abrogation of sequence-specific DNA binding.

Immunohistochemical staining for the p53 protein was performed in 107 snap frozen primary endometrial adenocarcinomas and 15 benign uterine tissues using monoclonal antibody PAb1801. No staining was seen in benign samples, whereas intense nuclear staining of cancer cells consistent with overexpression of the p53 protein was observed in 22 of 107 cancers (21%). p53 overexpression was more frequent in advanced (Stage III/IV) cancers (41%) than in early (Stage I/II) cancers (9%) (P

https://cancerres.aacrjournals.org/content/canres/52/6/1622.full.pdf

Overexpression and mutation of p53 in endometrial carcinoma.

Preinvasive lesions of squamous cell carcinoma are well defined morphologically and provide a model for multistage carcinogenesis. Since alterations in the p53 tumor suppressor gene occur frequently in invasive esophageal squamous cell carcinoma, we examined a set of preinvasive lesions to investigate the timing of p53 mutation. Surgically resected tissues from nine patients with esophageal squamous cell carcinoma contained precursor lesions which had not yet invaded normal tissues. Immunohistochemistry showed high levels of p53 protein in both pre-invasive lesions and invasive carcinomas in six cases; sequence analysis of all invasive tumors identified p53 missense mutations in two cases. Preinvasive lesions from both tumors with mutations plus one wild-type tumor were microdissected and sequenced. In one patient there were different mutations in the invasive carcinoma (codon 282, CGGara > TGGtrp) and a preinvasive lesion (codon 272, GTGval > T/GTGleu/val). In a second case, an invasive carcinoma had a mutation in codon 175 (CGCarR > CAChis), and adjacent preinvasive lesions contained a wild-type sequence. A carcinoma and preinvasive lesion from the third case contained high levels of protein and a wild-type DNA sequence. Therefore, p53 mutation may precede invasion in esophageal carcinogenesis, and multifocal esophageal neoplasms may arise from independent clones of transformed cells. The timing of p53 protein accumulation is favorable for an intermediate biomarker in multistage esophageal carcinogenesis.

/pdf/p53-mutation-and-protein-accumulation-during-multistage-4rt6jxg8mf.pdf

p53 mutation and protein accumulation during multistage human esophageal carcinogenesis.

Overexpression of cyclin D1 is frequently found in various types of human tumours and results from clonal rearrangement and/or amplification involving chromosomal region 11q13. In order to evaluate the pathological relevance of cyclin D1 overexpression in human breast cancer, we generated a polyclonal antiserum against the carboxy-terminal part of the cyclin D1 protein. After affinity purification, the antiserum specifically detected overexpression of cyclin D1 in formalin-fixed, paraffin-embedded tumour material also. The intensity of the nuclear stainings was, in general, proportional to the degree of cyclin D1 amplification. We did not encounter significant variability of staining within individual tumours with overexpression of cyclin D1. Overexpression of cyclin D1 appeared to be associated with oestrogen receptor-positive breast tumours, but not with any other clinicopathological parameter tested. Overexpression of cyclin D1 was not prognostic value for recurrence of survival in a consecutive series of 248 operable breast cancer patients (stage I and II). Overexpression of p53 was also not of prognostic significance in this series, but was associated with undifferentiated histology and oestrogen receptor-negative breast tumours, as has been reported previously by others. A high proportion of breast tumours with a low grade of malignancy in this series of operable breast cancer patients may explain discrepancies concerning the prognostic value of amplification and of overexpression of cyclin D1.

A clinicopathological study on overexpression of cyclin D1 and of p53 in a series of 248 patients with operable breast cancer.

Overexpression of the nuclear phosphoprotein p53 is one of the most common abnormalities in primary human cancer and appears to be due to point mutation within a highly conserved region of the p53 gene which then encodes for a mutant, more stable protein. In this study different stages of breast cancer progression were examined, from in situ to metastatic disease, to determine at what stage mutational activation occurs and whether it is maintained during tumor progression. Two (13%) of 15 pure intraductal tumors expressed high levels of p53 in all malignant epithelial cells. Sequencing of p53 mRNA from one of these tumors demonstrated a nucleotide substitution altering the amino acid composition of the protein. Six (17%) of 35 specimens which contained both in situ and invasive disease expressed high levels of p53. All malignant epithelial cells in these 6 cases stained positively and in no specimen did one component express different levels of the protein than the other growth phase. Sequence analysis of a tissue with significant amounts of both in situ and invasive disease revealed only a single point mutation, without evidence of wild-type nucleotide at the site of substitution, suggesting that p53 mRNA from each component of the tumor contained the same nucleotide substitution. Eleven (50%) of 22 pairs of primary tumors and their lymph node metastases expressed elevated levels of p53, and in each case, expression levels were identical in the primary and secondary sties. Identical mutations were found in the p53 mRNA from two paired primary and metastatic sites. Therefore, mutation within a highly conserved region of the p53 gene leading to overexpression of the protein product can occur in the earliest recognized phase of breast cancer and this alteration is maintained during progression from intraductal to infiltrating carcinoma. Mutations are also conserved during the process of metastatic spread.

https://cancerres.aacrjournals.org/content/canres/51/10/2605.full.pdf

Maintenance of p53 alterations throughout breast cancer progression.

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Maintenance of p53 alterations throughout breast cancer progression.