Plus Therapeutics, Inc. recently announced the completion of a Type B meeting with the US FDA on next steps on REYOBIQ pivotal trial strategy for leptomeningeal metastases (LM).  The meeting resulted in constructive discussion with the FDA regarding key elements of the potential pivotal study design for REYOBIQ in LM. Plus intends to incorporate the FDA’s feedback in the current dose optimization trial and seek alignment with the FDA on a revised protocol, likely later this year. The company’s goal is to be ready for a potential pivotal trial following completion of the current dose optimization trial and, ultimately, work towards the potential approval of REYOBIQ for patients affected by LM.

Highlights of FDA responses to the Company’s key enquiries:

Accelerated approval – FDA indicated that accelerated approval may be appropriate for the LM indication, but there are insufficient data to support the use of circulating tumor cells (CTCs) as an intermediate clinical endpoint. FDA and Plus discussed that additional steps would be necessary to validate CTCs as a surrogate endpoint to potentially support other future applications.

Primary and key endpoints – FDA recommended that the study evaluate an endpoint with established clinical benefit, such as overall survival, while encouraging further study of patient reported outcomes and neurologic function as endpoints that could potentially support a marketing application.  FDA and Plus aligned that CTCs could be considered for use as a secondary endpoint.

Trial design and comparator group – FDA and Plus discussed a randomized controlled trial design approach and that the study may include an intrathecal chemotherapeutic as a comparator, as well as approaches to standardize the comparator and any additional interventions available under the trial protocol.

Treated populations – FDA conveyed it may be reasonable to incorporate multiple histologies (i.e., multiple underlying disease etiologies) 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 REYOBIQ for patients with LM,” said Dr. Marc H. Hedrick, President & Chief Executive of Plus Therapeutics. “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 REYOBIQ commercial manufacturing and scale-up activities to meet an expedited timeline.”

About LM

Leptomeningeal metastases (LM) are a rare but severe complication of advanced cancer, affecting the fluid-lined structures of the central nervous system. LM occurs in approximately 5% of patients with metastatic cancer, with breast cancer, lung cancer, and melanoma being the most common sources. Median survival is typically 2-6 months, and effective treatment options are limited, highlighting the urgent need for novel therapies.

About REYOBIQ (rhenium Re186 obisbemeda)

REYOBIQ (rhenium Re186 obisbemeda) is a novel injectable radiotherapy specifically formulated to deliver direct targeted high dose radiation in CNS tumors in a safe, effective, and convenient manner to optimize patient outcomes. REYOBIQ has the potential to reduce off target risks and improve outcomes for CNS cancer patients, versus currently approved therapies, with a more targeted and potent radiation dose. Rhenium-186 is an ideal radioisotope for CNS therapeutic applications due to its short half-life, beta energy for destroying cancerous tissue, and gamma energy for real-time imaging. REYOBIQ is being evaluated for the treatment of recurrent glioblastoma, leptomeningeal metastases, and pediatric brain cancer in the ReSPECT-GBM, ReSPECT-LM, and ReSPECT-PBC clinical trials. ReSPECT-GBM is supported by an award from the National Cancer Institute (NCI), part of the U.S. National Institutes of Health (NIH), and ReSPECT-LM is funded by a three-year $17.6M grant by the Cancer Prevention & Research Institute of Texas (CPRIT). The Company’s ReSPECT-PBC clinical trial for pediatric brain cancer is supported by a $3 million grant from the U.S. Department of Defense’s Peer Reviewed Cancer Research Program.

About CNSide Diagnostics, LLC 

CNSide Diagnostics, LLC is a wholly owned subsidiary of Plus Therapeutics, Inc. that develops and commercializes proprietary laboratory-developed tests, such as CNSide®, designed to identify tumor cells that have metastasized to the central nervous system in patients with carcinomas and melanomas. The CNSide® CSF Assay Platform enables quantitative analysis of the cerebrospinal fluid that informs and improves the management of patients with leptomeningeal metastases.  For more information, visit https://www.cnside-dx.com/.

About Plus Therapeutics

Headquartered in Houston, Texas, Plus Therapeutics, Inc. is a clinical-stage pharmaceutical company developing targeted radiotherapeutics for difficult-to-treat cancers of the central nervous system with the potential to enhance clinical outcomes. Combining image-guided local beta radiation and targeted drug delivery approaches, the Company is advancing a pipeline of product candidates with lead programs in leptomeningeal metastases (LM) and recurrent glioblastoma (GBM). The Company has built a supply chain through strategic partnerships that enable the development, manufacturing, and future potential commercialization of its products. For more information, visit https://www.plustherapeutics.com.