For all of the benefit that radiopharmaceuticals offer, these treatments currently address a limited number of cancer targets. Aktis Oncology has technology that could broaden the reach of this type of therapy, potentially addressing more targets to help more patients. The clinical-stage company now has $318 million in IPO cash to support development of its pipeline.
Following a lackluster 2025 that saw limited biotech IPO activity, Aktis found sufficient investor interest to boost the size of its deal to 17.65 million shares, up from the 11.77 million shares it planned to offer in preliminary financial terms set earlier this week. Late Thursday, Aktis priced those shares at $18 each, which was the top of company’s projected price range. Shares of the Boston-based company will trade on the Nasdaq under the stock symbol “AKTS.”
A radiopharmaceutical reaches its tumor destination by leveraging the targeting ability of another molecule, such as a peptide or an antibody. But these targeting molecules have limitations. The large size of antibodies makes it hard for them to penetrate tumors. Also, their long circulating half-life means the therapy stays in the body longer, risking radiation exposure to healthy organs and tissue. Meanwhile, the small size of peptides makes it difficult for them to hit certain cancer targets.
Aktis’s approach falls somewhere in between antibodies and peptides. Its radiopharmaceuticals employ a targeting molecule it calls a miniprotein, which is comprised of chains of amino acids that make this targeting molecule smaller than an antibody but larger than a peptide. These miniproteins come from a proprietary Aktis technology platform. In the IPO filing, Aktis says its miniprotein radiopharmaceuticals offer the potential for both potent antitumor activity and better safety and tolerability.
“The small size of miniproteins allows them to rapidly penetrate tumors,” Aktis said. “Furthermore, our miniprotein radioconjugates are able to internalize into cancer cells, which we believe drives prolonged retention. We have reproducibly generated high affinity miniprotein binders to specific tumor targets. Tumor killing is achieved through delivery of absorbed radiation dose, which is enhanced by high tumor penetration, high binding affinity for tumor targets, and prolonged retention of drug in the tumor.”
Lead Aktis drug candidate AKY-1189 is in development for treating solid tumors that express a protein called Nectin-4. This target is already drugged by Padcev, an antibody drug conjugate (ADC) marketed by Pfizer and Astellas Pharma for urothelial cancer. While this product is a blockbuster seller, its uses in other cancers is likely limited by the need to develop a companion diagnostic for tissue testing when using this ADC, Aktis said in the filing.
Aktis plans to use imaging radioisotopes conjugated to AKY-1189 to select the patients most likely to benefit from the radiopharmaceutical. The company also sees the potential to expand this therapy to more tumor types, such as breast and lung cancers. AKY-1189 is currently in Phase 1b testing for urothelial cancers and other solid tumors that express Nectin-4. Preliminary data from the dose-escalation portion of the study are expected in the first quarter of 2027.
The next program in the Aktis pipeline is AKY-2519, a radiopharmaceutical designed to target B7-H3. This protein is highly expressed by a range of solid tumors, including prostate cancer cells. This program offers the potential to expand the reach of radiopharmaceuticals beyond PSMA, the target of Novatis’s Pluvicto and targeted radiation therapies in development by other companies. Aktis plans an investigational new drug application for AKY-2519 in the first half of this year, according to the filing.
Under a collaboration started with Eli Lilly in 2024, Aktis is using its technology to discover radiopharmaceuticals for multiple cancer targets selected by the pharma giant. Those targets remain undisclosed, but Aktis said they are separate from its wholly owned pipeline. Lilly will take over the developments programs from the partnership once they’ve reached the clinic. Lilly began the alliance with a $60 million up front payment and an additional equity investment in Aktis. The radiopharmaceutical developer has been paid $1 million for the achievement of a milestone, and could receive up to $1.2 billion in additional milestone payments, according to the filing.
Aktis formed in 2020, founded and incubated by MPM Capital. The startup emerged from stealth in 2021 backed by a Series A round that included participation from Novartis and Bristol Myers Squibb. Before the IPO, Aktis had raised $345.5 million since its inception, most recently a $175 million Series B round in 2024. MPM is Aktis’s largest shareholder owning 17.4% of the company followed by Vida Ventures’ 9.5% stake, according to the filing.
Aktis has the opportunity to boost its cash haul further. In its updated prospectus, Aktis said Lilly indicated interest in purchasing about $100 million worth of the company’s shares at the IPO price. As of the end of the third quarter of 2025, Aktis reported its cash position was $246.2 million. Combined with the IPO proceeds, Aktis said it plans to spend between $140 million and $150 million for the ongoing Phase 1b test of AKY-1189 for nectin-4 expressing tumors. Another $70 million to $80 million will go toward advancing Ac-AKY-2519 to a Phase 1b clinical trial for B7-H3 expressing tumors. Aktis estimates its capital will last into the first half of 2028.
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