Plus Therapeutics Achieves Phase 1 Survival Signal for REYOBIQ in Leptomeningeal Metastases at AANS 2026

Plus Therapeutics' intrathecally delivered radiopharmaceutical REYOBIQ (rhenium Re186 obisbemeda) is generating clinical signals that will force manufacturing and regulatory teams to confront the compounding complexity of CNS-targeted, short-half-life radioisotope production at scale. Phase 1 data from the ReSPECT-LM single-dose escalation study, presented in a plenary session at the 2026 American Association of Neurological Surgeons Annual Scientific Meeting on May 2, were the first public airing of translational evidence alongside survival outcomes.

At the recommended Phase 2 dose, median overall survival reached approximately 9 months against a historical benchmark of 2–6 months in leptomeningeal metastases, a CNS indication with no FDA-approved therapy. The dataset also showed circulating tumor cell reduction across evaluable patients and a target-to-off-target absorbed dose ratio exceeding 100:1, a dosimetric precision figure that carries direct implications for sterility assurance and fill-finish specifications when working with rhenium-186's 3.7-day half-life.

Translational analyses presented alongside the survival data indicate REYOBIQ may activate CD8+ T cells and remodel the tumor microenvironment, opening a pathway toward combination regimens with checkpoint inhibitors. For development teams, that possibility adds a formulation complexity layer: any future co-administration protocol will require compatibility assessments and potentially revised 21 CFR Part 211 process validation packages to account for immunotherapy co-formulation or sequencing.

The nanoliposome carrier underpinning REYOBIQ demands sterile fill-finish capabilities that most standard CDMOs are not configured to support. Rhenium-186 production requires cyclotron or reactor access, and the short half-life compresses the release-testing window to hours rather than days, placing acute pressure on in-process controls and batch disposition workflows aligned with ICH Q10 pharmaceutical quality system expectations. The ongoing ReSPECT-LM multiple-dose trial, enrolling at UT Health San Antonio, will generate the repeat-dosing safety and tolerability data that any future BLA package will need to address these manufacturing variables at defined dose intervals.

The ReSPECT-LM program is funded by a three-year, $17.6 million grant from the Cancer Prevention and Research Institute of Texas, providing a defined financial runway against which manufacturing scale-up timelines can be benchmarked as the multiple-dose cohort matures.

Source: Plus Therapeutics via GlobeNewswire, May 8, 2026.