PHILADELPHIA—A partnership sponsored by Rubenstein Partners has acquired the Penn Mutual Towers office complex  here and has retained Newmark Grubb Knight Frank as the exclusive leasing agent for the historic property.

No financial details on the transaction were reported. An announcement by Newmark Grubb Knight Frank states that the Rubenstein partnership acquired the three-building, 850,000-square-foot office property at 510-530 Walnut St. recently. The deal marks Rubenstein's return to the Center City marketplace. During parts of the 1990s, Rubenstein Partners was the largest owner of multi-tenant Class A office space in Philadelphia's central business district.

"We believe that this is the premier building in a dynamic submarket with limited opportunities for tenants looking for high quality office space," says David Rubenstein, founder and senior managing principal of Rubenstein Partners, representing the new ownership of the building. "We are excited about the potential of both the property and the Class A office market in Center City."

Rubenstein Partners says it plans a “significant investment” to modernize the building's systems and upgrade its lobbies and other common areas. "The capital investment shows how committed Rubenstein is to restoring this historic landmark office building to its previous prominence," says Jack Soloff, senior managing director at Newmark Grubb Knight Frank. "After years of transitional ownership due to capital structure issues, we now have the complete opposite situation with the financial strength and market reputation of the Rubenstein-sponsored partnership. This property is positioned to move to the next level and stand as an example of best in class in this market."

The property will have approximately 190,000 square feet available. NGKF's Soloff will work with Executive Managing Directors Jim Mullarkey and Wayne Fisher and Director Les Haggett on the leasing campaign for Penn Mutual Towers.