The firm was represented by Bob Chodos and Steve Levitas of Colliers Bennett & Kahnweiler, while the Sears Tower was represented by Derek Rolison and Mike Kazmierczak, SVPs with U.S Equities Asset Management LLC, which acts as the building's management and leasing agent.

"They've told us that for clients around the globe and their team locally, the Sears Tower is a distinguished iconic landmark that's a natural fit for them," Rolison tells GlobeSt.com. "It's a great location for them with panoramic views from their space."

The building will undergo a name change in the coming months, being redubbed Willis Tower, for the insurance firm which will take occupancy of 140,000 square feet in mid-summer. Willis' deal is one of four that was closed in the first quarter, totaling around 267,000 square feet. The iconic 110-story building is now 85% leased.

Asking lease rates at the building range from $16 to $21 per square foot net, Rolison says. Built in 1973, the property is owned by 233 S. Wacker LLC, which includes American Landmark Properties, the Chetrit Group and the Moinian Group.

The property is in the West Loop submarket, where average asking lease rates range from $32 to $38 per square foot and occupancy rates are near 86%, according to Grubb & Ellis' Q1 office market report. "Class A West Loop office space is still the most sought after in the Chicago market," Rolison says. "There's been solid traction and a lot of activity which has been translating into actual signed leases."