In hot market for lab space, a biotech startup to replace the former CambridgeSide Sears

Prime Medicine signs lease for three floors in shuttered East Cambridge department store,

This rendering of the CambridgeSide's redevelopment envisioned a new future for the complex.

As the demand for lab space in Cambridge continues to soar, it’s no surprise that a biotech startup will soon replace a bankrupt department store chain.

Prime Medicine has agreed to lease nearly 150,000 square feet at the CambridgeSide shopping center, in a new building that’s replacing a Sears that went out of business in 2018. The redevelopment is the latest phase in the ongoing evolution of CambridgeSide, which in the years before the pandemic was among the most successful malls in Greater Boston.

Prime will take over the third, fourth, and fifth floors of the new building at 60 First St., which today is little more than iron beams from the mostly dismantled Sears. But it is set to reopen next year as a five-story office building with street-level retail. The company is focusing on developing a unique approach to gene editing and emerged from stealth mode in July with $315 million in financing.

Keith Gottesdiener, the chief executive of the company, told the Globe in July that Prime planned to reach 100 employees by the end of 2021. According to Middlesex County property records, Prime’s lease term will begin in fall 2022 and last for at least 10 years. The company declined to comment on the deal.

A recent report from brokerage firm CBRE found that East Cambridge is the most expensive place in the area for biotechs to set up shop. Asking rents averaged about $125 per square foot toward the end of 2021.

“The competition for the limited available space has never been more cutthroat,” CBRE wrote in the report.

And as demand for space in traditional indoor malls has faded amid the rise of online shopping, CambridgeSide owner New England Development has tried to leverage its location to make space for companies that want to be close to booming Kendall Square.

The Sears at the CambridgeSide shopping center closed in 2018. David L. Ryan

In 2019, the company filed plans to convert the entire top floor of the three-story shopping center into 140,000 square feet of office space. Real estate industry sources at the time said the owner had a deal in place with coworking giant WeWork to fill it. That deal never materialized before WeWork’s ill-fated public offering in 2019.

Then came the pandemic and today the space sits empty, except for twice-weekly COVID testing held there by the City of Cambridge.

But elsewhere in the huge CambridgeSide complex, New England Development has pushed ahead with plans to build a series of large buildings around the outside of the mall, including an office and lab building on the site of the old Macy’s along Land Boulevard, while adding more retail space along the street, not just the mall’s indoor center atrium. The Sears building — which is owned separately by Anchor Line Partners — is part of that vision as well. Later phases will replace the mall’s above-ground parking garages on First Street with housing, retail, and office space.

Meanwhile, inside, the roster of brand-name stores slowly dwindles, with the mall’s H&M and Olympia Sports closing in the wake of the holidays.

Real estate firms are increasingly swapping traditional shopping center tenants for those with deeper pockets and plans for rapid growth. Developers are eyeing both the Neiman Marcus store in Natick and the Watertown Mall as potential targets for lab space conversions.