B7-H3 is expressed in roughly 90% of prostate cancer specimens, yet no approved radiopharmaceutical targets it — and that gap is precisely what makes Aktis Oncology‘s Phase 1b initiation of AKY-2519 in metastatic castration-resistant prostate cancer more than a routine first-in-human milestone. The trial’s structure is the real story: two distinct cohorts, one PLUVICTO-naïve and one PLUVICTO-experienced, enrolled simultaneously at multiple U.S. radioligand therapy centers across three dose levels each. That design generates sequentially useful data rather than forcing a post-hoc subgroup analysis later — a deliberate choice that reflects how genuinely different the treatment history of lutetium-PSMA patients is from those who never received it.
The scientific premise deserves scrutiny. PSMA-targeted therapy fails a meaningful fraction of mCRPC patients either because PSMA expression is too low for adequate tumor uptake or because disease progresses despite initial response. B7-H3 is not correlated with PSMA expression, which means AKY-2519 does not simply compete for the same population — it addresses a biologically distinct patient segment. Aktis’ miniprotein scaffold is designed for rapid renal clearance and strong tumor internalization, two properties that matter enormously for the therapeutic index of a radioconjugate. Whether that pharmacokinetic profile holds in heavily pretreated mCRPC tissue, which is often fibrotic and heterogeneous, is the central unanswered question this Phase 1b must address.
The two-trial strategy — the mCRPC-dedicated study now open plus a basket trial in lung, colorectal, and other B7-H3-high solid tumors expected to launch in the second half of 2026 — is an efficient use of a single scaffold’s indication-agnostic biology. Running them in parallel rather than sequentially accelerates the company’s ability to identify where the signal is strongest before committing to Phase 2 dose selection. AKY-2519 is also Aktis’ second miniprotein program to enter the clinic within 12 months, following the Nectin-4-targeting AKY-1189, which itself targets a set of tumor types with substantial overlap with the basket trial population.
Preliminary mCRPC data are expected in 2027, and the single number to watch is tumor uptake on pre-therapeutic imaging in the PLUVICTO-experienced cohort. If B7-H3 targeting delivers adequate lesion-level dosimetry in patients whose disease already progressed through lutetium-PSMA, that finding reframes the entire post-PSMA treatment sequence in mCRPC.
Jon Napitupulu is Director of Media Relations at The Clinical Trial Vanguard. Jon, a computer data scientist, focuses on the latest clinical trial industry news and trends.
