Modern Times Bookstore Collective, a 45-year-old Mission District worker-owned store renowned for its radical politics, will close its doors Nov. 15.

“Despite the small staff’s best efforts, the store could not sustain itself following its move to 24th Street in the face of an untenable rent increase in 2011 at its beloved Valencia Street location,” Modern Times said Tuesday.

Most recently located at 2919 24th St., Modern Times was founded as a collective by a group of friends opposed to the Vietnam War. The original shop was in a 750-square-foot space at 17th and Sanchez streets. The initial investment was all of $5,000.

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“The store has not been breaking even for a very long time,” Modern Times book buyer Ashton Di Vito said by phone. “It’s quite a blow,” he said about the store’s closure. “I’ve worked here for a few years, and it’s kind of like my home.”

Modern Times has long had a varied inventory of new and used books, including feminist and LGBT sections — the first in the city, the store says — as well as Spanish-language titles and books on Latino history and culture. Roughly a quarter of the store’s best-selling titles are published by small presses. The 2,800-square-foot store holds roughly 40,000 titles, Di Vito said.

While Modern Times did not provide revenue figures, the American Booksellers Association reported average annual sales per square foot of $334 in its 2010 survey of independent bookstores. Some bookstores do considerably more business than that, according to Paz & Associates, ranging from $500 to $1,000 per square foot. Meanwhile, annual retail rents have risen sharply in San Francisco from $35 per square foot to $45 in just the past three years, according to LoopNet, a commercial real estate database. Wages, too, have gone up, along with other costs.

Over the years, Modern Times has held numerous events promoting progressive conversations. There have been series on globalization, post-9/11 U.S. foreign policy in the Middle East, and discussions on gentrification in San Francisco.

“The Mission community is very saddened to hear the news that Modern Times is closing its doors,” Erick Arguello, co-founder and president of the Calle 24 Latino Cultural District said in a statement. “Modern Times has been a tremendous asset to the city as a whole, from its early days responding to the Vietnam War through the gay liberation movement and through today’s fight with gentrification.”

Among the authors the store has hosted are Sherman Alexie, Adam Hochschild, Alice Walker and Slavoj Žižek.

Steve Silberman, the author of “NeuroTribes: The Legacy of Autism and the Future of Neurodiversity,” bemoaned the loss of the store, tweeting “Another irreplaceable part of SF goes under: gloriously radical Modern Times Books, where I read as a young poet.”

Modern Times promoted a membership program, which provided shoppers with store discounts and free admission to events, but it wasn’t enough to make the business profitable. Other stores that have benefited from innovative sponsorship programs include Adobe Books and Arts Cooperative and Borderlands Books, both in San Francisco.

The store has scheduled a closing party at 1 p.m. Oct. 22. The event also will serve as a retirement party for longtime bookseller Ruth Mahaney.

John McMurtrie is The San Francisco Chronicle’s book editor. Email: jmcmurtrie@sfchronicle.com Twitter: @McMurtrieSF