Plus Therapeutics, Inc. announced it has successfully completed key validation testing and implementation of its tumor cell enumeration assay, known as CSF-01, to be used initially as an exploratory endpoint in its ReSPECT-LM clinical trials. Plus? CSF-01 cancer cell enumeration test is an exploratory endpoint in the ReSPECT-LM Phase 1 trial that has shown promise in the trial?s early cohorts.

In Phase 1/Part A of the ReSPECT-LM trial presented at the 2023 SNO/ASCO Meeting in San Francisco, Plus showed an average 53% reduction in CSF tumor cells 28 days after a single intrathecal administration of rhenium (186Re) obisbemeda in patients with LM. On December 12, 2023, Plus announced its partnership with K2bio (Houston, Texas) to implement Plus? CSF-01 diagnostic for LM cancers in the ReSPECT-LM trials.

While validated for use in Plus? clinical development programs, full Clinical Laboratory Improvement Amendments (CLIA) certification is not anticipated until 2025. The ReSPECT-LM trial, including support for CSF-01 testing, is currently receiving grant funding from the Cancer Prevention and Research Institute of Texas (CPRIT).

The FORSEE trial was performed by the original developer and licensor of CSF-01 and is a multi-center, prospective clinical trial enrolling patients with breast or non-small cell lung cancer (NSCLC) who have suspicious or confirmed LM. If the FORSEE data is positive, the company intend to work toward increasing commercial reimbursement for the CLIA-certified test and explore partnerships to maximize diagnostic utilization for the broader CNS cancer space. About Leptomeningeal Metastases (LM): LM is a rare complication of cancer in which the primary cancer spreads to the cerebrospinal fluid (CSF) and leptomeninges surrounding the brain and spinal cord.

All malignancies originating from solid tumors, primary brain tumors, or hematological malignancies have this LM complication potential with breast cancer as the most common cancer linked to LM, with 3-5% of breast cancer patients developing LM. Additionally, lung cancer, GI cancers, and melanoma can also spread to the CSF and result in LM. LM occurs in approximately 5% of people with cancer and is usually terminal, with a 1-year and 2-year survival of just 7% and 3%, respectively.

The incidence of LM is on the rise, partly because cancer patients are living longer and partly because many standard chemotherapies cannot reach sufficient concentrations in the spinal fluid to kill the tumor cells. Yet, there are no FDA-approved therapies specifically for LM patients, who often succumb to this complication within weeks to several months if untreated. About Rhenium (186Re) obisbemeda: Rhenium (186Re) obisbemeda is a novel injectable radiotherapy specifically formulated to deliver directly targeted high-dose radiation in CNS tumors in a safe, effective, and convenient manner to optimize patient outcomes.

Rhenium (186Re) obisbemeda 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. Rhenium (186Re) obisbemeda is being evaluated for the treatment of recurrent glioblastoma and leptomeningeal metastases in the ReSPECT-GBM and ReSPECT-LM 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).