Plus Therapeutics Highlights Leptomeningeal Metastases Acquisition and FORESEE Trial Data

Plus Therapeutics, Inc., a clinical-stage pharmaceutical company focused on developing targeted radiotherapeutics for central nervous system (CNS) cancers, recently provided insights from its investor call. The discussion revolved around the rationale behind acquiring the leptomeningeal metastases (LM) diagnostic platform, CNSide™, and highlighted topline data from the FORESEE clinical trial.

Leptomeningeal metastases (LM) represents a significant clinical challenge due to underdiagnosis, as current diagnostic tools like MRI and cytology exhibit limited sensitivity. Dr. Priya U. Kumthekar, Associate Professor of Neurology and Medicine at Northwestern University, emphasized the importance of the CNSide assay, noting its high sensitivity and potential to revolutionize the clinical management of LM.

Key points from the investor call included Plus Therapeutics' strategy to develop the CNSide diagnostic platform alongside its primary radiotherapeutic candidate, rhenium (Re186) obisbemeda. The company aims to explore potential partnerships for CNSide. Topline data from the FORESEE trial was also presented, indicating that the CNSide test met its primary endpoint of clinical utility in 40 patients with LM caused by breast or non-small cell lung cancer. A comprehensive presentation of these findings is scheduled for the SNO/ASCO Meeting in August 2024.

Dr. Marc H. Hedrick, President and CEO of Plus Therapeutics, highlighted the critical need for better LM diagnostics to improve patient outcomes and expand the market for their lead radiotherapeutic candidate, rhenium (Re186) obisbemeda. He expressed optimism about the potential financial returns and long-term market impact of this transaction.

LM is a rare but severe complication where primary cancers spread to the cerebrospinal fluid (CSF) and the brain and spinal cord's leptomeninges. Cancers originating from solid tumors, primary brain tumors, or hematological malignancies can lead to LM, with breast cancer being the most common. The incidence of LM is rising, partly due to longer patient survival times and the inability of standard chemotherapies to reach effective concentrations in the spinal fluid. LM is usually terminal, with dismal 1-year and 2-year survival rates of 7% and 3%, respectively. There are currently no FDA-approved therapies specifically for LM patients, who often face a grim prognosis without treatment.

Rhenium (186Re) obisbemeda is an innovative injectable radiotherapy designed to deliver high-dose targeted radiation to CNS tumors safely and effectively. This approach aims to minimize off-target risks and improve patient outcomes compared to existing therapies. Rhenium-186 is particularly suited for CNS applications due to its short half-life and its beta and gamma energy properties, which are advantageous for both destroying cancerous tissue and enabling real-time imaging. This radiotherapeutic is being evaluated in clinical trials for recurrent glioblastoma (GBM) and LM under the ReSPECT-GBM and ReSPECT-LM studies, respectively.

CNSide is a laboratory-developed test (LDT) based on a proprietary method for capturing and detecting tumor cells, coupled with assays to identify actionable molecular treatment targets. As metastatic cancer spreads to the CNS, genetic changes occur, making the evaluation of CSF through CNSide a unique opportunity to identify biomarkers and guide therapy selection. The test also allows for serial monitoring of tumor cell counts, providing a more effective way to gauge treatment response compared to current methods.

The FORESEE Study is a multi-center, prospective clinical trial involving patients with breast or non-small cell lung cancer who have suspicious or confirmed LM. Traditional diagnostic methods for LM, including clinical evaluation, MRI, and cytology, lack sufficient sensitivity and specificity, complicating treatment decisions. The FORESEE Study aims to evaluate CNSide's performance in monitoring LM response to treatment and its impact on clinical decisions.

Plus Therapeutics, Inc. is committed to advancing targeted radiotherapeutics for challenging CNS cancers, leveraging a robust pipeline and strategic partnerships to develop, manufacture, and potentially commercialize its products. The company operates in key cancer clinical development hubs in Austin and San Antonio, Texas.