Intracranial Infection Model

Central nervous system infection is among the most serious consequences of microbial disease. The blood-brain barrier that protects the CNS from most systemic pathogens is the same barrier that limits the number of drugs able to reach it in therapeutic concentrations. When an organism crosses that barrier – establishing meningitis, meningoencephalitis, or encephalitis – the treatment challenge is twofold: the drug has to clear infection in the brain at the same time it has to get there.

TransPharm Preclinical Solutions’s intracranial model addresses both problems directly. Animals are challenged by injection into the subarachnoid space via the cisterna magna – placing the organism in the same cerebrospinal fluid compartment where clinical CNS disease plays out – and the model supports both systemic and direct intracranial test article delivery, which allows CNS penetration and local efficacy to be assessed in the same study.

Research Applications

This model is appropriate when the question concerns CNS infection specifically, rather than systemic infection with secondary CNS involvement.

The cisterna magna challenge route is the model’s defining feature. Depositing the challenge organism directly into the subarachnoid space bypasses the blood-brain barrier as a source of inoculum variability and establishes CNS infection at the site of disease. This is the most direct way to assess whether a candidate controls established infection in the CNS compartment — the claim that matters most for a meningitis program and the hardest to make from systemic infection data alone.

Equally distinctive is the intracranial treatment route. Where systemically dosed agents must cross the blood-brain barrier to reach the infection site, test article can be delivered directly into the CNS, which is relevant for programs developing CNS-penetrant formulations, intrathecal delivery approaches, or agents whose systemic exposure is limited by design. The ability to compare direct and systemic delivery in the same model supports a head-to-head within a single study.

Typical uses include:

• CNS efficacy screening of novel antifungal candidates against cryptococcal meningoencephalitis
• Assessment of blood-brain barrier penetration, where systemic dosing is used and brain drug concentrations are measured alongside CNS burden
• Comparison of direct CNS delivery against systemic dosing for the same candidate
• Evaluation against the established first-line regimen of amphotericin B plus flucytosine, which is the standard comparator for cryptococcal meningitis programs

Scientific Scope

TransPharm Preclinical Solutions has validated the intracranial model with Cryptococcus neoformans:

• Cryptococcus neoformans – ATCC 24067

1. neoformans is the leading cause of fungal meningitis and the top-ranked pathogen on the WHO 2022 Fungal Priority Pathogens List. Its signature virulence factor — a thick polysaccharide capsule — blunts the host immune response and allows it to establish and persist in the CNS. It causes approximately 180,000 deaths per year, predominantly among people with HIV/AIDS in sub-Saharan Africa.

ATCC 24067 is a serotype D (var. neoformans) strain, originally recovered from the cerebrospinal fluid of a patient with cryptococcal meningitis, making its provenance directly relevant to the disease model. Serotype selection is worth considering against the clinical background: serotype A (var. grubii) accounts for the majority of clinical disease globally, while serotype D is more prevalent in Europe and is the serotype of the reference isolate. Where a program needs the dominant clinical variant, alternative isolates including serotype A strains can be sourced and validated to program specifications.

Additional validations are available on request. The intracranial model can accommodate other CNS pathogens, and client-supplied isolates can be characterized and validated before a study begins.

The intracranial model carries the same add-on measurements available across all in vivo work at TransPharm Preclinical Solutions: pharmacokinetic profiling and PK/PD analysis, blood chemistry, additional tissue harvests, and histopathology, each available on request. All studies run in an AAALAC-accredited preclinical efficacy testing laboratory.

Study Design

Procedure

Animals are challenged by injection through the cisterna magna into the subarachnoid space. Studies are run in mice. Every study parameter is configurable to the scientific question: challenge organism and strain, host strain, immune status, comparator agents, and dosing schedule.

Routes of Administration

Test article may be administered by oral gavage (PO), intracranial (IC) injection, or by subcutaneous (SC), intravenous (IV), or intraperitoneal (IP) injection. The intracranial route allows direct delivery to the CNS and is the only treatment route of this kind available across all models at TransPharm Preclinical Solutions.

Endpoints

The primary readouts are survival (mortality tracking) and fungal burden in the brain and other harvested organs and/or blood. Brain burden is the principal efficacy endpoint for a CNS infection model, giving a direct, quantitative measure of treatment effect at the disease site. Blood and peripheral organ burden confirm whether systemic clearance accompanies CNS control. Pharmacokinetic profiling — including brain tissue drug concentrations — blood chemistry, additional tissue harvests, and histopathology can be added to any study on request.