BUZZ-Gladstone Commercial Corp: Slumps on common-stock offering

** U.S. real estate investment trust's shares down 6.3 pct at $20.35 premarket

** Company on Wednesday announced common stock offering

** Plans to use proceeds from offering to fund pending and future property acquisitions, prepay existing debt

* Up to Wednesday's close, stock had risen 8.1 pct this year, significantly underperforming the 18.6 rise in Nasdaq Composite index