Plus Therapeutics Shares Data on REYOBIQ's Efficacy and Safety in Leptomeningeal Metastases Trial

An abstract showcasing the potential of Plus Therapeutics, Inc.'s lead compound, REYOBIQ™ (rhenium Re186 obisbemeda), has been published ahead of the upcoming Nuclear Medicine and Neurooncology Conference. This abstract, set for presentation in Vienna, Austria, on May 9-10, 2025, provides promising data about the compound's efficacy in treating Leptomeningeal Metastases (LM). The development of REYOBIQ™ is part of Plus Therapeutics' broader initiative to improve outcomes for patients with central nervous system (CNS) cancers.

The abstract, titled "Rhenium Obisbemeda (REYOBIQ) in Leptomeningeal Metastases," reveals findings from the company's completed Phase 1 ReSPECT-LM dose escalation trial. This trial demonstrates a noticeable dose-dependent increase in the average absorbed radiation dose to the cranial and spinal subarachnoid space, with the highest recorded dose reaching 253Gy in Cohort 5. Neuroimaging response data was analyzed for 16 patients, with 31% showing a partial response. Notably, seven additional patients exhibited stable disease according to neuroimaging through day 112, resulting in a Clinical Benefit Rate—comprising complete response, partial response, and stable disease—of 75%.

In terms of clinical response, physician evaluations identified a decrease in disease symptoms in two of 14 evaluable patients (14%), while 10 patients showed stable findings through day 112, leading to an 86% Clinical Benefit Rate. Importantly, no dose-limiting toxicity (DLT) was noted in the initial four cohorts, though grade 4 DLT (thrombocytopenia) was observed in one patient each from Cohorts 5 and 6.

Furthermore, RNA sequencing of LM cells indicated early initiation of apoptosis, followed by an innate immune response and an increase in T cells, culminating in an adaptive immune response by Day 28. These findings suggest a potent therapeutic action of REYOBIQ™ in combating LM.

Dr. Marc H. Hedrick, President and CEO of Plus Therapeutics, expressed confidence in the potential utility of REYOBIQ™ for patients battling the severe and often terminal diagnosis of Leptomeningeal Metastases. He highlighted the compound's ability to deliver high radiation doses directly to cancer cells, showing encouraging response data across various parameters while maintaining tolerance in normal organs and tissues.

Leptomeningeal Metastases is a rare but severe cancer complication where the primary cancer spreads to the cerebrospinal fluid and the leptomeninges surrounding the brain and spinal cord. While all malignancies originating from solid tumors, primary brain tumors, or hematological cancers have the potential to develop LM, breast cancer is most commonly associated with this condition, affecting 3-5% of breast cancer patients. LM occurs in approximately 5% of cancer patients and is typically terminal, with severely limited survival rates of 7% at one year and 3% at two years.

The increasing incidence of LM is partly due to prolonged patient survival and the ineffectiveness of many standard chemotherapy treatments in reaching therapeutic concentrations in the spinal fluid. Currently, there are no FDA-approved therapies specifically for LM, leaving these patients with few options and often resulting in death within weeks to months if untreated.

REYOBIQ™ is designed as a novel injectable radiotherapy to deliver targeted high-dose radiation in CNS tumors safely and effectively. This compound aims to reduce off-target risks and improve outcomes for CNS cancer patients through a more focused and potent radiation dose. Rhenium-186, the radioisotope used in REYOBIQ™, has ideal properties for CNS applications, including a short half-life and energies suitable for both destroying cancerous tissue and real-time imaging. The compound is under evaluation in clinical trials for recurrent glioblastoma and leptomeningeal metastases, supported by significant funding from the National Cancer Institute and the Cancer Prevention & Research Institute of Texas.

Plus Therapeutics, based in Houston, Texas, is at the forefront of developing targeted radiotherapeutics for challenging CNS cancers. The company is focused on advancing a pipeline of product candidates, with leading programs targeting leptomeningeal metastases and recurrent glioblastoma. By utilizing image-guided local beta radiation and targeted drug delivery approaches, Plus Therapeutics aims to enhance clinical outcomes for patients suffering from these challenging conditions.