FDA Type B Meeting Offers Direction for Rhenium Re 186 Obisbemeda in LM

A Type B meeting between the FDA and Plus Therapeutics offered clarity and direction for the next steps in development of rhenium Re 186 obisbemeda (Reyobiq), a novel injectable radiotherapy, for patients with leptomeningeal metastases (LM), advancing toward a future pivotal trial.¹

The agent’s ongoing development in LM is currently driven by the phase 1 ReSPECT-LM trial (NCT05034497), which is expected to conclude by mid-year 2026.² For next steps in development, the FDA provided guidance for a future pivotal trial which would ultimately help support submission for approval. The FDA indicated that accelerated approval may appropriate, but there is currently insufficient data. To remedy this, the FDA and Plus Therapeutics discussed additional steps to validate circulating tumor cells as a surrogate end point to potentially support future applications.

Further, the FDA recommended that the study evaluate overall survival as an end point, in addition to studying patient reported outcomes and neurologic function. The FDA and Plus Therapeutics also discussed a randomized controlled design approach and including an intrathecal chemotherapeutic as a comparator.

Lastly, the FDA suggested that it may be reasonable to incorporate multiple histologies in a single trial.

“Our recent FDA end of phase meeting was constructive, and we hope will help us speed up our clinical development timelines and facilitate faster submission of an application for the approval of [rhenium Re 186 obisbemeda] for patients with LM,” said Marc H. Hedrick, MD, president and CEO of Plus Therapeutics, in a news release. “As there are no approved drugs for LM, this discussion with the FDA early in clinical development will allow us to make relevant amendments to our current trial protocol and to begin meaningful planning for an anticipated pivotal trial. Furthermore, based in part on this meeting, we will plan to accelerate [rhenium Re 186 obisbemeda] commercial manufacturing and scale-up activities to meet an expedited timeline.”

Trial Design and Methodology

The ReSPECT-LM trial is an open-label, phase 1 study that is evaluating a single 5cc dose of rhenium Re 186 obisbemeda administered through an intraventricular catheter in patients with LM.²

The study will include the evaluation at separate dose levels with 3 to 6 patients treated at each dose. The maximum number of patients to be enrolled is 27. Patients will be followed for up to 12 months after rhenium Re 186 obisbemeda is administered. This study has 6 locations across the US.

Future Directions

The ReSPECT-LM data suggest that rhenium Re 186 obisbemeda may offer a more potent and targeted alternative to external beam radiation.

Plus Therapeutics intends to incorporate the FDA’s feedback in the current dose optimization trial and revise protocol with insight from the FDA later this year.

REFERENCES

1.Plus Therapeutics announces read out of type B meeting with the FDA with goal of accelerating approval of REYOBIQ for leptomeningeal metastases. Plus Therapeutics. News release. January 8, 2026. Accessed January 8, 2026. https://tinyurl.com/yeezx66e

2.Intraventricular administration of rhenium-186 nanoliposome for leptomeningeal metastases (ReSPECT-LM). ClinicalTrials.gov. Updated March 26, 2025. Accessed January 8, 2026. https://clinicaltrials.gov/study/NCT05034497