Role of loss of o⁶-methylguanine dna methyltransferase (MGMT) expression in non-small cell lung carcinomas (NSCLCs): with reference to the relationship with p53 overexpression

Relationship Between the Expression of O6-Methylguanine-DNA Methyltransferase (MGMT) and p53, and the Clinical Response in Metastatic Pancreatic Adenocarcinoma Treated with FOLFIRINOX

BACKGROUND

To date, no predictive biomarker for the efficacy of FOLFIRINOX in metastatic pancreatic adenocarcinoma has been demonstrated. Deficiency in O6-methylguanine-DNA methyltransferase (MGMT) has been associated with a therapeutic response in endocrine tumors of the pancreas and the lack of expression of protein 53 (p53) could interfere with the action of MGMT.

OBJECTIVE

The aim of our study was to assess the prevalence of MGMT and p53 in patients with metastatic pancreatic adenocarcinoma treated with FOLFIRINOX as a first-line treatment and to investigate their association with therapeutic response and survival.

PATIENTS AND METHODS

The immunohistochemical expression of MGMT was recorded as present or absent and the expression of p53 was semi-quantitatively scored in 30 patients with metastatic pancreatic adenocarcinoma, at Angers Hospital in France between September 2011 and June 2015. Clinical and radiologic data were collected retrospectively.

RESULTS

The presence or absence of MGMT expression entailed no significant differences in response rate. Median values of progression-free survival (PFS) and overall survival (OS) were lower in patients with MGMT expression, but sample size is too small to conclude that there is a statistically significant difference. No significant relationship for response rate and PFS was observed in relation with p53 expression. By contrast, patients with a strong tumor expression of p53 had a significantly lower OS compared to patients with no or weak expression of the protein (p = 0.027). There was a positive correlation between the expression of p53 and MGMT (p = 0.08).

CONCLUSIONS

These preliminary findings suggest that for patients treated with FOLFIRINOX as a first-line treatment for metastatic pancreatic adenocarcinoma, the immunohistochemical evaluation of MGMT could not predict the clinical outcome; however, the survival was not significant probably because of the under-powered study (due to small sample size). A strong tumor expression of p53 is associated with a poor prognosis of OS.

Expression profiling of O(6) methylguanine-DNA-methyl transferase in prolactinomas: a correlative study of promoter methylation and pathological features in 136 cases

BACKGROUND

Low-level expression of O(6) methylguanine-DNA-methyl transferase (MGMT) prolactinomas has been noted previously in case reports, although what modulates MGMT expression remains unclear. This study therefore aimed to delineate the factors regulating MGMT expression in prolactinomas.

METHODS

We retrospectively reviewed 136 prolactinoma patients who were treated in our center between January 2000 and September 2013. Expression of MGMT, Ki-67, and p53 protein were examined by immunohistochemical staining, and MGMT promoter methylation evaluated with methylation-specific PCR.

RESULTS

MGMT immunopositivity was <25 % in 106/136 tumor specimens (77.94 %). MGMT immunoexpression was positively correlated with age (r = 0.251, p = 0.003), but inversely correlated with p53 staining (r = -0.153, p = 0.021). Moreover, reduced MGMT expression was more frequent in atypical prolactinomas (p = 0.044). Methylated MGMT promoter was confirmed in 10/46 specimens (21.7 %), all of which had low level or absent MGMT staining. Both p53 protein (r = -0.33, p = 0.025) and promoter methylation (r = -0.331, p = 0.025) were negatively associated with MGMT expression. Multivariate logistic analysis indicated that age (odds ratio [OR] = 1.127. 95 % confidence interval [CI] 1.027-1.236, p = 0.012) and p53 (OR = 0.116. 95 % CI 0.018-0.761, p = 0.025) staining were independent determents of MGMT expression.

CONCLUSIONS

The majority of prolactinomas, especially atypical prolactinomas, showed low-level or no MGMT immunoexpression, providing a rationale for the utility of temozolomide as an alternative to managing prolactinomas. In summary, epigenetic and transcriptional regulation are involved in silencing MGMT expression.

Immunohistochemical Assessment of O(6)-Methylguanine-DNA Methyltransferase (MGMT) and Its Relationship with p53 Expression in Endometrial Cancers

O⁶-Methylguanine-DNA methyltransferase (MGMT) is a DNA repair protein, the loss of MGMT expression was commonly known due to hypermethylation of CpG islands in its promoter region. Overexpression of p53 protein may be associated with downregulated MGMT expression in brain tumors. The aims of this study were to investigate the role of MGMT expression loss and its correlation with p53 overexpression in endometrial cancers. MGMT and p53 expression was examined in formalin-fixed, paraffin-embedded tissues from 36 endometrial cancer cases using immnunohistochemical staining. The loss of MGMT expression was detected in 11 (30.6%) out of the 36 endometrial cancers and p53 immunoreactivity was detected in 23 (63.9%) out of the 36 endometrial cancers. Ten (90.9%) of the 11 cases with negative MGMT immunoreactivity showed positive p53 expression, so the loss of MGMT expression was significantly associated with the p53 overexpression (P=0.03). These findings suggest that the loss of MGMT expression may be one of factors capable of p53 overexpression in endometrial cancer. Further studies are needed to define the relation between MGMT and p53 for examining the mechanisms of tissue-specific MGMT expression.

Bayesian inference supports a location and neighbour-dependent model of DNA methylation propagation at the MGMT gene promoter in lung tumours

We exploit model-based Bayesian inference methodologies to analyse lung tumour-derived methylation data from a CpG island in the O6-methylguanine-DNA methyltransferase (MGMT) promoter. Interest is in modelling the changes in methylation patterns in a CpG island in the first exon of the promoter during lung tumour development. We propose four competils of methylation state propagation based on two mechanisms. The first is the location-dependence mechanism in which the probability of a gain or loss of methylation at a CpG within the promoter depends upon its location in the CpG sequence. The second mechanism is that of neighbour-dependence in which gain or loss of methylation at a CpG depends upon the methylation status of the immediately preceding CpG. Our data comprises the methylation status at 12 CpGs near the 5' end of the CpG island in two lung tumour samples for both alleles of a nearby polymorphism. We use approximate Bayesian computation, a computationally intensive rejection-sampling algorithm to infer model parameters and compare models without the need to evaluate the likelihood function. We compare the four proposed models using two criteria: the approximate Bayes factors and the distribution of the Euclidean distance between the summary statistics of the observed and simulated datasets. Our model-based analysis demonstrates compelling evidence for both location and neighbour dependence in the process of aberrant DNA methylation of this MGMT promoter CpG island in lung tumours. We find equivocal evidence to support the hypothesis that the methylation patterns of the two alleles evolve independently.