Publications

BACKGROUND

It has recently been recognized that atrial fibrillation can originate from focal sources in the pulmonary veins (PVs). However, the mechanisms of focal atrial fibrillation have not been well characterized. We assessed the electrophysiological characteristics of the PVs using high-resolution optical mapping.

METHODS AND RESULTS

Coronary-perfused, isolated whole-atrial preparations from 33 normal dogs were studied. Programmed electrical stimulation was performed, and a 4-cm2 area of the PV underwent optical mapping of transmembrane voltage to obtain 256 simultaneous action potentials. Marked conduction slowing was seen at the proximal PV, compared with the rest of the vein, on both the epicardial (31.3+/-4.47 versus 90.2+/-20.7 cm/s, P=0.001) and endocardial (45.8+/-6.90 versus 67.6+/-10.4 cm/s, P=0.012) aspects. Pronounced repolarization heterogeneity was also noted, with action potential duration at 80% repolarization being longest at the PV endocardium. Nonsustained reentrant beats were induced with single extrastimuli, and the complete reentrant loop was visualized (cycle length, 155+/-30.3 ms); reentrant activity could be sustained with isoproterenol. Sustained focal discharge (cycle length, 330 to 1100 ms) was seen from the endocardial surface in the presence of isoproterenol; each focus was localized near the venous ostium.

CONCLUSIONS

The normal PV seems to have the necessary substrate to support reentry as well as focal activity. Although reentry occurred more distally in the vein, focal activity seemed to occur more proximally.

PURPOSE

To select a daily dose of arzoxifene (LY353381), a selective estrogen receptor modulator, for use in future studies in women with locally advanced or metastatic breast cancer who are either potentially tamoxifen sensitive (TS) or tamoxifen refractory (TR).

PATIENTS AND METHODS

This trial was a randomized, double-blind, phase II study of arzoxifene 20 mg (n = 55) and 50 mg (n = 57) in women with advanced or metastatic breast cancer. Patients were randomly assigned to balance for number of metastatic disease sites, prior tamoxifen therapy, and estrogen receptor status. The primary end point was tumor response rate (RR). Secondary end points included clinical benefit rate (CBR), time to progression (TTP), and toxicity.

RESULTS

Forty-nine patients were TS and 63 were TR. According to independent review, among TS patients, RR was higher in the 20-mg arm than the 50-mg arm (26.1% v 8.0%), with a longer TTP (8.3 v 3.2 months; P >.05). Among the TR patients, response rate was the same in the 20-mg and 50-mg arms (10.3%) with similar TTP (2.7 and 2.8 months, respectively; P >.05). CBR was higher in the 20-mg arm than in the 50-mg arm among TS patients (39.1% v 20.0%) and TR patients (13.8% v 10.3%). Arzoxifene was well tolerated. Dose-dependent toxicity was not demonstrated. There were no deaths during study.

CONCLUSION

Arzoxifene is effective in the treatment of TS and TR patients with advanced or metastatic breast cancer at the 20-mg and 50-mg dose levels. Toxicities are minimal, and the therapy is tolerated. The 20-mg dose seems to be at least as effective as the 50-mg dose. Accordingly, arzoxifene 20 mg/d was selected for further study in patients with breast cancer.

Integrins are heterodimeric cell-surface proteins that regulate cell growth, migration and survival. We have shown previously that the epithelial-restricted integrin alpha(v)beta6 has another critical function; that is, it binds and activates latent transforming growth factor-beta (TGF-beta). Through a global analysis of pulmonary gene expression in the lungs of mice lacking this integrin (Itgb6 null mice) we have identified a marked induction of macrophage metalloelastase (Mmp12)--a metalloproteinase that preferentially degrades elastin and has been implicated in the chronic lung disease emphysema. Here we report that Itgb6-null mice develop age-related emphysema that is completely abrogated either by transgenic expression of versions of the beta6 integrin subunit that support TGF-beta activation, or by the loss of Mmp12. Furthermore, we show that the effects of Itgb6 deletion are overcome by simultaneous transgenic expression of active TGF-beta1. We have uncovered a pathway in which the loss of integrin-mediated activation of latent TGF-beta causes age-dependent pulmonary emphysema through alterations of macrophage Mmp12 expression. Furthermore, we show that a functional alteration in the TGF-beta activation pathway affects susceptibility to this disease.