Solstice rises with $225M to develop next-gen CTLA-4 drug from China

News Business Solstice rises with $225M to develop next-gen CTLA-4 drug from China September 9, 2026 | 2 min read | Annalee Armstrong Twitter LinkedIn Facebook Email Print Solstice Oncology, founded in February, is emerging from stealth having already secured an investigational new drug application from the FDA for a Phase 2 trial of a CTLA-4 antibody purchased from China’s Harbour BioMed. A new cancer biotech has dawned as Solstice Oncology launches with a massive $225 million Series A fundraising that will be used to advance a CTLA-4 antibody from China’s Harbour BioMed.Solstice CEO Caroline Loew said the mission will be to address cancer sooner, in the pre-surgical neoadjuvant setting when the tumor is present but the immune system is still working to keep it at bay and the patient has not yet been exposed to other treatments.At the center of the new biotech is porustobart, which has the FDA’s greenlight to be tested in a Phase 2 trial for neoadjuvant advanced colon cancer plus another undisclosed indication, according to a Wednesday release. Enrollment for the study, which will pair porustobart with Merck’s Keytruda, will begin in the fourth quarter, Solstice said.

Data are expected to arrive in the second half of 2027.“Treating patients early with an immuno-oncology combination therapy like the one we are evaluating in our Phase 2 trial could allow the immune response to act systemically, reaching micrometastatic disease well beyond the primary tumor, which is where we see the greatest opportunity to improve cure rates and long-term survival,” Loew said in a statement. IPO Biotech IPOs approach ‘escape velocity’ barring yellow flags that could threaten rebound Twenty-five biotechs have used the IPO route to go public this year—with five of those debuts occurring this month alone. It’s the most IPOs since 2021, when the industry recorded 78 during the height of the COVID-19 pandemic.

August 25, 2026 · 3 min read · Gabrielle Masson Read more Solstice was founded in February and moved quickly to prep porustobart for clinical trials. The therapy is intended to be used in combination with a checkpoint inhibitor such as Keytruda to awaken the body’s immune system and then target the cancer.Colon cancer has not typically responded to this approach, but the next-generation CTLA-4 antibodies may have better performance, according to Solstice. The biotech noted that porustobart has a short half-life, which could allow more flexible dosing and a better safety profile than previous CTLA-4 therapies.The drug was licensed by Solstice’s investors from China’s Harbour for about $105 million at signing, including a $50 million upfront payment, $5 million near-term cash and a $50 million equity stake in the biotech, according to a February press release from the Chinese company.

Harbour could also potentially receive up to $1.1 billion in commercial milestones down the road based on ex-China sales.Harbour has already tested porustobart in Phase 1b trials of patients with late-line colon cancer paired with BeOne Medicine’s checkpoint inhibitor Tevimbra. The early results showed a 30% objective response rate, or 7 out of 23 patients, with a median duration of response of 8.4 months.Solstice’s Series A financing was led be RA Capital Management, known for biotechs such as Blueprint Medicines, Global Blood Therapeutics and KalVista Pharmaceuticals—all of which were ultimately acquired. Canaan Partners, Forbion and other investors also joined the round.

Twitter LinkedIn Facebook Email Print Venture capital Startups Funding Annalee Armstrong Annalee Armstrong is an award-winning biopharma journalist covering the business of drug development. She has been a journalist for more than 18 years, covering the pharmaceutical and biotech industry for the last eight. She is senior editor at BioSpace and curates the Biopharm Executive newsletter every Wednesday.

You can reach her at annalee.armstrong@biospace.com. Follow her on LinkedIn.