# Build a human model of the barrier that guards the brain fluid

Source: https://onco.cc/ideas/idea-bio2-blood-csf-barrier-model/  
OnCo record `idea-bio2-blood-csf-barrier-model` (Idea). Data CC BY-NC 4.0, attribute "Data from OnCo (onco.cc)"; commercial use needs a licence.

## TL;DR

Drugs that reach brain tissue may still fail to reach the fluid where cancer spreads along the linings. A lab model of that second barrier would let us screen for drugs that cross it.

## Summary

Leptomeningeal disease is governed by the blood-cerebrospinal fluid barrier at the choroid plexus, which differs from the blood-brain barrier in transporters and tight junction composition. Stem-cell-derived choroid plexus organoids that produce cerebrospinal fluid-like secretion have been reported, giving a human in vitro system for screening cerebrospinal fluid penetration and for studying how tumour cells survive in that nutrient-poor compartment.

## Fields

- Kind: Idea
- Last checked: 2026-09-08
- Hypothesis: Choroid plexus organoid permeability ranks drugs concordantly with measured human cerebrospinal fluid-to-plasma ratios, making it a usable screening assay for leptomeningeal indications.
- Rationale: Leptomeningeal metastasis is rarely survived beyond a few months and is increasingly common as systemic control improves, yet drug selection for it is guesswork. A quantitative human assay for the correct barrier is a prerequisite for rational selection.
- Proposed test: Benchmark organoid permeability against 20 drugs with published human cerebrospinal fluid-to-plasma ratios; report rank correlation and cost per compound.
- Maturity: preclinical-evidence
- Actor: engineering

## Sources

- Bottleneck evidence (The brain: barrier and sanctuary): Stupp et al., Radiotherapy plus concomitant and adjuvant temozolomide for glioblastoma (NEJM 2005): https://doi.org/10.1056/NEJMoa043330

## Connected records

- cancers: [HER2-positive breast cancer](https://onco.cc/cancers/breast-her2-positive/), [Melanoma](https://onco.cc/cancers/melanoma/), [Non-small-cell lung cancer](https://onco.cc/cancers/nsclc/)
- technologies: [Patient-derived organoids](https://onco.cc/technologies/organoids/)
- terms: [Blood-brain barrier (BBB)](https://onco.cc/terms/blood-brain-barrier/)
- bottlenecks: [Lab models that fail to predict what happens in patients](https://onco.cc/bottlenecks/b-preclinical-models/), [The brain: barrier and sanctuary](https://onco.cc/bottlenecks/b-brain-delivery/)

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