Troubled Seattle biotech company Dendreon has put back on the market most of the office space at its headquarters in downtown’s Russell Investments Center.

Four floors — about 90,000 square feet — were listed for sublease Friday, according to commercial real-estate database Officespace.com.

Dendreon, then flying high, in March 2011 leased eight upper floors, 32 through 39, in the 42-story Russell Center for 5½ years. Since then, sales of the company’s pioneering immune-system treatment for prostate cancer have been disappointing, and Dendreon has been cutting costs and laying off employees.

Real-estate website Zillow leased the 32nd floor in June. Now the 33rd through 36th floors are on the market.

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A Dendreon representative did not respond to requests for comment.

In September, the company said it would eliminate 600 jobs, 145 of them in Seattle.

The company in March 2011 also leased 97,000 square feet on Eastlake Avenue East for its research labs.

The Russell Center, built as Washington Mutual’s headquarters in 2006, emptied in 2009 after the thrift’s collapse. But high-profile tenants leased most of it over the next three years.

The tower, at Second Avenue and Union Street, was sold in April for $480 million.

Eric Pryne: epryne@seattletimes.com or 206-464-2231