Mechanisms of gefitinib-induced QT prolongation.

Gefitinib, a tyrosine kinase inhibitor, was the first targeted therapy for non-small cell lung cancer (NSCLC). Gefitinib could block human Ether-à-go-go-Related Gene (hERG) channel, an important target in drug-induced long QT syndrome. However, it is unclear whether gefitinib could induce QT interval prolongation. Here, whole-cell patch-clamp technique was used for evaluating the effect of gefitinib on rapidly-activating delayed rectifier K+ current (IKr), slowly-activating delayed rectifier K+ current (IKs), transient outward potassium current (Ito), inward rectifier K+ current (IK1) and on action potentials in guinea pig ventricular myocytes. The Langendorff heart perfusion technique was used to determine drug effect on the ECG. Gefitinib depressed IKr by binding to open and closed hERG channels in a concentration-dependent way (IC50: 1.91 µM). The inhibitory effect of gefitinib on wildtype hERG channels was reduced at the hERG mutants Y652A, S636A, F656V and S631A (IC50: 8.51, 13.97, 18.86, 32.99 µM), indicating that gefitinib is a pore inhibitor of hERG channels. In addition, gefitinib accelerated hERG channel inactivation and decreased channel steady-state inactivation. Gefitinib also decreased IKs with IC50 of 23.8 µM. Moreover, gefitinib increased action potential duration (APD) in guinea pig ventricular myocytes and the corrected QT interval (QTc) in isolated perfused guinea pig hearts in a concentration-dependent way (1-30 µM). These findings indicate that gefitinib could prolong QTc interval by potently blocking hERG channel, modulating kinetic properties of hERG channel. Partial block of KCNQ1/KCNE1 could also contribute to delayed repolarization and prolonged QT interval. Thus, caution should be taken when gefitinib is used for NSCLC treatment.

[Familial Y chromosome microdeletion with pericentric inversion of chromosome 19].

OBJECTIVE: To investigate the familial cytomolecular genetics of an infertile male. METHODS: We analyzed the clinical phenotypes and karyotypes of three males from the family of an infertile man, detected the sequence-tagged sites (STS) in the AZF deletions of the Y chromosome by multiplex polymerase chain reaction (PCR), and identified the target genes by multiplex ligation-dependent probe amplification (MLPA). RESULTS: The karyotypes of the proband and his brother were 46, XY, inv (19) (p13.3q13.1) and that of his father was 46, XY. The three males were all carriers of AZFc deletion of the Y chromosome, and all found with the same reduction of the gene copy number in the AZFb and AZFc regions. CONCLUSIONS: Combined use of karyotype analysis, Y chromosome STS PCR, and MLPA revealed the genetic causes of the male infertile family.