[Individual sensitivity to the mutagenic agents in patients with larynx cancer]. / Ocena wrazliwosci pacjentów z rakiem krtani na czynniki mutagenne.

Patients with different cancers, induced mostly by numerous mutagenic factors, present increased genetic susceptibility to mutagenic agents known as "hidden chromosomal instability". This type of genetic instability can be detected in vitro after treating chromosomes with clastogenic substances, for example by using "bleomycine test". The purpouse of our study was to evaluate a hidden chromosome instability in patients with squamous cell carcinoma of larynx (SCCL) and to establish correlations between genetic results and both histological grade of the tumor and clinical progression of disease. Cytogenetic analysis of 126 of patients diagnosed with SCCL and 98 of controls was performed in vitro on peripheral blood lymphocytes. The analysis of sensitivity to bleomycine of larynx cancer patients in relation to histological grade of the tumor proved, that increased numbers of chromosome breaks as well as and percentage of aberrant metaphases are correlated with the tumor grading. Mean number of chromosome breaks per cell (b/c) in patients with larynx cancer was 1,01 (+/- 0.43), while in the control group was 0.74 (+/- 0.29) per cell (chi2 p < 0.001). Percentage of aberrant metaphases (% am) in patients with SCCL was 42.18 (+/- 11.61) and 36.05 (+/- 10.22) in the control (chi2 p < 0.001). The group of hypersensitive patients (b/c > 1) consisted of 51.5% percent of larynx cancer patients, while in the control, hypersensitivity occurred only in 20.4% of subjects (chi2 p < 0.001). Possible chromosome instability (0.8 < b/c < 1) was found 11.9% patients with SCCL and in 20.4% of controls (not statistically significant). Increased sensitivity to bleomycine in patients with SCCL in comparison to the control group was found. Most sensitive to bleomycine was the group of patients diagnosed with SCCL graded G2 (Scheffe's test p < 0.05)

Correlation among loss of heterozygosity, promoter methylation and protein expression of MLH1 in larynx cancer.

Extensive molecular studies in development of the squamous cell carcinoma of larynx (SCCL) indicated the involvement of a variety of genes including the MLH1. To search for possible mechanism leading to MLH1 silencing in SCCL we studied LOH and promoter methylation in a homogeneous set of 62 larynx cancers. Then we evaluated immunohistochemically the MLH1 expression for 51 tumor specimens. Further, the results were correlated with microsatellite instability and subsequently with the clinical course of the disease. LOH at the MLH1 locus and aberrant methylation of its promoter were found in 47.9 and in 22.6% of tumors, respectively. A decreased expression was observed in 27.5% of the cases. MSI analysis of tumor DNA showed a microsatellite stable phenotype in 59 cases (95.2%). From our study it can be concluded that: i) molecular alterations of MLH1 play an important role in SSCL development, ii) both LOH and aberrant methylation contribute to the MLH1 inactivation in SCCL and are associated with a less advanced stage of differentiation of larynx tumors, iii) MLH1 inactivation does not lead to MSI in larynx cancer and MSI may not contribute to the development of SCCL.

Analysis of adaptive response to bleomycin and mitomycin C.

Genetic instability resulting from the disturbances in various mechanisms of DNA-repair is the characteristic feature of cancer cells. One of the possibilities to evaluate the effectiveness of DNA-repair system is the adaptive response (AR) analysis. The AR is a phenomenon by which cells exposed to low, non-genotoxic doses of a mutagen become significantly resistant to a subsequent higher dose of the same or another genotoxic agent. Generally, it is postulated that AR is related to a reduction of damage by the induction of free radical detoxification and/or DNA-repair systems. The existence of various DNA-repair mechanisms poses the question whether there are differences in AR induced by chemicals causing DNA-damage that requires different pathways for its repair. In this paper we present the study on the AR induced by two chemical mutagens, bleomycin (BLM) and mitomycin C (MMC), which differ in their action on DNA. BLM is a radiomimetic agent causing mainly single-strand breaks (SSB) and double-strand breaks (DSB) and, thus, inducing chromosomal aberrations (CA). MMC is a potent bifunctional mutagen acting as an alkylating agent, causing DNA cross-links and inducing sister chromatid exchanges (SCEs). The protective effect induced by low doses of tested chemicals was analysed in whole blood human lymphocytes using cytogenetic endpoints (CA for BLM and SCE for MMC, respectively) as a measure of chromosomal instability. There was a significant difference between the protective effects induced by BLM and MMC in the lymphocytes of the same group of donors. The pre-treatment with a low dose of BLM-induced almost 50% decrease in the frequency of CA induced by challenging dose (CD), while the protective effect of MMC was below 20%. The higher AR induced by BLM may be related to the repair processing of BLM-induced DNA-damages. There was also a variability in ARs among individuals, which may reflect the differences in individual DNA-repair capacity.