Clinical-stage pharmaceutical company Plus Therapeutics Inc (Nasdaq:PSTV) announced on Friday an expansion of its supply agreement with Biocept, securing an option for exclusive licensing of Biocept's CNSide, a cerebrospinal fluid (CSF)-based tumour cell capture and enumeration platform.

CNSide is a diagnostic assay for patients suspected of having central nervous system (CNS) cancers.

Under this agreement, Biocept grants Plus Therapeutics a non-exclusive licence for its CNSide cell enumeration assay for Plus' investigational therapy for leptomeningeal metastases (LM), rhenium (186Re) obisbemeda, and an option for an exclusive license to the assay. In consideration, Plus will issue USD150,000 worth of its common stock to Biocept.

Plus Therapeutics retains the option for exclusivity in the field of radiotherapy, exercisable at its discretion, by making a payment of USD1.0m before 1 January 2025.

CNSide is a proprietary assay that combines quantitative tumour cell capture, advanced digital imaging and molecular markers to detect, characterise and quantify tumour cells in the CSF of patients with various solid organ carcinomas and suspected LM, particularly breast and lung cancer and melanoma which are leading causes of LM. CNSide offers a sensitive and specific method to assess tumour status and treatment response, surpassing traditional CSF cytology or imaging monitoring.

In March 2023, Biocept initiated the FORESEE trial using CNSide, aiming to enrol up to 40 patients with breast or non-small cell lung cancer and suspicious or confirmed LM. The study assesses the performance of CNSide in monitoring LM response to treatment and its impact on treatment decisions. The feasibility phase is expected to conclude in the first half of 2024, followed by a validation phase with an estimated 40 to 100 subjects.

Leptomeningeal metastases (LM) is a rare complication of cancer where the primary cancer spreads to the cerebrospinal fluid and leptomeninges around the brain and spinal cord. This complication can occur in malignancies originating from solid tumours, primary brain tumours or haematological malignancies. Breast cancer is the most common cancer linked to LM, affecting 3-5% of breast cancer patients. LM, which is usually terminal, occurs in approximately 5% of cancer cases, with a one-year survival rate of 7% and a two-year survival rate of 3% without treatment. Currently, there are no FDA-approved therapies specifically for LM patients.