Altered methylation of the human MDR1 promoter is associated with acquired multidrug resistance

One of the most important forms of drug resistance in acute myeloid leukemia is the multidrug resistance (MDR) phenotype, which is characterized by the expression of the MDR1 gene product, P-glycoprotein. Although a number of factors affect MDR1 gene expression, the genetic events that "switch on" the human MDR1 gene in tumor cells that were previously P-glycoprotein negative have remained elusive. Here, we report evidence that the methylation status of the human MDR1 promoter may serve as a basis for this "switch." Based on Southern analysis using methylation-sensitive and methylation-insensitive restriction enzymes, a tight correlation was found between MDR phenotype and demethylation of the 5' region of the MDR1 gene in a human T cell leukemia cell line. Similar results were obtained from the analysis of P-glycoprotein-positive and P-glycoprotein-negative samples of chronic lymphocytic leukemia. Treatment of the cell lines with the demethylating agent 5'-azadeoxycytidine altered the methylation pattern of the MDR1 promoter in P-glycoprotein-negative cells to resemble that of P-glycoprotein-positive cells and activated the promoter such that MDR1 mRNA was now detectable. Treatment also resulted in an increased resistance to epirubicin and decreased daunomycin accumulation, both of which were reversible by verapamil, a characteristic of the classical MDR phenotype in cells expressing P-glycoprotein. These results suggest that the MDR phenotype may be acquired as a result of changes in methylation of the MDR1 promoter.

Epiglottic enlargement secondary to laryngeal sarcoidosis

A case of laryngeal sarcoidosis manifesting as epiglottic enlargement in a 15-year-old boy is presented. Sarcoidosis of the larynx is unusual in children but should be included in the differential diagnosis of epiglottic enlargement.

Intracranial Serratia infection in preterm newborn infants

Four cases of cerebral Serratia infection in preterm infants were diagnosed with the aid of real-time sector sonography. Three cases had brain abscesses and one case had ventriculitis. In two cases brain abscesses had ruptured into the ventricles. Serratia brain abscess was common in our series of brain abscesses. Sonographic patterns of cerebritis, abscess formation, and ventriculitis correlated well with computed tomographic scans. Bedside cerebral sonography proved to be useful for the diagnosis, location, and follow-up of intracranial Serratia infection.