e-Poster Presentation Clinical Oncology Society of Australia Annual Scientific Meeting 2021

5-FU Induces acute neurodegeneration followed by persistent neuroinflammation: A new mechanistic hypothesis for the neurological complications of cancer therapy (#206)

Courtney B Subramaniam 1 , Hannah Rose R Wardill 1 2 , Marc A Gladman 1 , Joanne M Bowen 1
  1. The University of Adelaide, Adelaide, SA, Australia
  2. South Australian Health and Medical Research Institute (SAHMRI), Adelaide, SA, Australia

Aims
Neurological complications of cancer therapy, including changes in cognition and mood, remain a significant supportive care challenge with limited understanding of pathobiology. This study therefore aimed to:

  • Develop a mouse model of chemotherapy-induced neuroinflammation and,
  • Characterise the acute and chronic changes to astrocyte function and neuronal proliferation following chemotherapy, which may underlie the development of neurological complications.

Methods
Female C57Bl/6 mice were treated with 5-fluorouracil (5-FU) and killed at acute (1 & 2 days after 5-FU) subacute (4 & 8 days after 5-FU) and chronic (16 & 32 days after 5-FU) timepoints (n=24). Changes to neuronal proliferation and neuroinflammatory profiles were characterised using immunohistochemical analysis of doublecortin (DXC) and the immunologic marker of astrocyte activation, glial acidic fibrillary protein (GFAP) in the hippocampus, prefrontal cortex, hypothalamus and midbrain. The expression of pro-inflammatory markers, such as interleukin-6 receptor (IL-6R), were quantified using rtPCR and blood brain barrier (BBB) integrity was assessed by immunohistochemical analysis of albumin extravasation.

Results
A profound decrease in DXC expression was seen in the acute, subacute (p=0.0095) and chronic setting following 5-FU treatment, highlighting a decrease in neuronal proliferation indicative of neurodegeneration. Elevated positive GFAP staining, indicative of astrocytic reactivity, was observed in the CA1 region (p=0.0126) and dentate gyrus (p=0.0051) of the hippocampus, as well as the prefrontal cortex (p=0.0001), hypothalamus (p=0.0013) and midbrain (p=0.0358), with staining intensity increasing from acute to chronic timepoints. This was seen alongside an increase in IL-6R expression (p=0.0333) and evidence of albumin extravasation, suggestive of BBB damage.

Conclusions
These data strongly position direct neuronal cell death as the initiating factor for downstream neuroinflammation which together drive neurological complications of chemotherapy. Importantly these data refute the long-standing assumption that chemotherapeutic drugs do not cross the BBB, and therefore warrant future investigation of how this barrier can be strengthened.