Awash in Funding, Sutro Biopharma Files for $75 Million IPO

Initial public offering letters on an electronic stock board

Only a month after raising $85.4 million in a Series E financing, Sutro Biopharma filed for an initial public offering (IPO). The company plans to raise $75 million with the IPO.

The company had a wholly-owned pipeline of cancer therapeutics, which includes two internally-developed antibody drug conjugates (ADCs). They are STRO-001, which is in Phase I clinical testing for lymphoma and multiple myeloma, and STRO-002, which is expected to enter the clinic in early 2019 for ovarian and endometrial cancer. The drugs were developed with the company’s proprietary cell-free protein synthesis and site-specific conjugation platforms. These platforms allow for precise design and rapid optimization of protein conjugates.

Sutro’s chief scientific officer, Trevor Hallam, at the time of the Series E financing, stated, “With XpressCF+, we incorporate non-natural amino acids into specific positions on the generated antibody for site-specific conjugation of cytotoxins with a linker and warhead to enable consistent, stable, pinpoint placement of STRO-001’s toxic payload. This leads to highly efficient delivery of the cytotoxin to tumor cells. By contrast, earlier generations of ADCs can have unpredictable pharmacologic properties, resulting in the potential for sub-optimal stability, compromised efficacy and poor tolerability for patients.”

The Series E was led by Samsara BioCapital and Surveyor Capital (a Citadel company). It was supported by current investors, Alta Partners, Amgen Ventures, Celgene Corporation, Lilly Ventures, Skyline Ventures and SV Health Investors. It also included first-time investors Eventide, Nexthera Capital, Vida Ventures and funds managed by Tekla Capital Management. And if the heavy-hitters of Amgen, Celgene, and Eli Lily weren’t enough, Merck also invested and committed to a future investment.

With the Series E round, the company has raised more than $175 million since it was founded in 2003.

Sutro filed with the U.S. Securities and Exchange Commission (SEC) on June 1, 2018. It plans to list on the Nasdaq under the symbol STRO. Cowen and Piper Jaffray are the joint bookrunners. No mention of IPO list price has been released.

On July 24, Sutro inked a collaboration and license deal with Merck to discover and develop novel immune-modulating therapies for cancer and autoimmune disorders. It will utilize Sutro’s the platforms. Sutro will be responsible for preclinical research and Merck will pick up exclusive worldwide rights to candidates that come from the collaboration. Merck paid Sutro $60 million upfront with potential milestone “bio-bucks” payments of up to $1.6 billion.

“Sutro has an impressive suite of technologies that make possible the discovery, characterization and manufacture of novel therapeutic proteins in a timely manner,” said Joe Miletich, senior vice president, Discovery, Preclinical and Early Development, Merck Research Laboratories, in a statement. “We look forward to collaborating with Sutro to further expand our pipeline of promising candidates targeting oncology and autoimmune diseases.”

And on August 13, Sutro partnered with The Leukemia & Lymphoma Society to develop STRO-001. The LLS is contributing undisclosed funds to Sutro through its Therapy Acceleration Program. Sutro plans to use the funds for a Phase I trial that began in April 2018 and is enrolling at City of Hope Comprehensive Cancer Center in Duarte, California, Medical College of Wisconsin in Milwaukee, Texas Oncology in Austin, Rocky Mountain Cancer Centers in Aurora, Colorado, and Virginia Cancer Specialists in Fairfax. It appears to be almost a loan arrangement because Sutro is required to make payments to LLS on pre-specified late-stage clinical development, regulatory and commercialization milestones.

“LLS is committed to advancing therapies to address critical unmet need,” said Lee Greenberger, LLS’s chief scientific officer, in a statement. “New options for therapies are vital for patients with non-Hodgkin’s lymphoma and myeloma who do not respond to available treatments. Sutro’s approach offers a promising option for these patients.”

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