Polyamine biosynthesis in relation to K-ras and p-53 mutations in colorectal carcinoma

Polyamines are important polycations found in high concentrations in gastrointestinal neoplasms, and ornithine decarboxylase is the key enzyme in their biosynthesis. Also genes with oncogenic potential (e.g. K-ras and p53) contribute to neoplastic transformation by modifying normal cellular proliferation and differentiation. Our aim was to evaluate the ornithine decarboxylase activity and polyamine levels in samples of colorectal carcinoma and uninvolved surrounding mucosa from 86 patients (52 men and 34 women) showing different patterns of K-ras/p53 mutations.

Polyamines were evaluated by high performance liquid chromatography. Ornithine decarboxylase activity was determined using the radiometric method. K-ras and p53 mutations were investigated by PCR followed by restriction fragment length polymorphism (PCR-RFLP) and single strand conformational polymorphism (PCR-SSCP), respectively. Multiple linear regression analysis was used to analyse relationships among polyamine biosynthesis, clinical-pathological variables and K-ras/p53 mutations.

ODC activity and polyamine levels were significantly higher in neoplastic samples than in normal surrounding mucosa. K-ras codon 12 mutation was found in 25/86 patients (29.1%) and p53 gene mutation in 41/86 (47.7%). Polyamine biosynthesis was significantly higher in cancers showing K-ras mutation, either with or without p53 mutation [K-ras(+)/p53(-) and K-ras(+)/p53(+)], compared to samples with K-ras wild type [K-ras(-)/p53(-) and K-ras(-)/p53(+)]. Multiple linear regression analysis confirmed this finding.

The present study provides evidence of a close relationship between K-ras mutation and polyamine biosynthesis in human colorectal carcinoma in a way that is largely p53 independent. In addition, our data support the hypothesis of different pathways in colorectal tumorigenesis reflecting different combinations of biochemical parameters and genetic alterations.