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Drug Repurposing Hypothesis Generation Using the "RE:fine Drugs" System
Published on: December 11, 2016
Drug Development
Maxine R Nelson1, Marina Kovaliov1, Priyanka Singh1
1Switch Therapeutics, South San Francisco, CA, USA.
Background:
The greatest genetic risk factor for late-onset Alzheimer's disease (AD) is Apolipoprotein E (APOE)*ε4. Preclinical studies have demonstrated that genetic ablation or reduction of APOE4 mRNA in amyloid and tauopathy mouse models have protective effects and/or reduce pathology. Targeting central APOE, while sparing systemic APOE and cholesterol metabolism, is the holy grail for a precision medicine approach in APOE*ε4 carriers with MCI/AD. Here, we present data for the first time, demonstrating our novel, highly potent, conditionally activating siRNA (CASi) targeting APOE mRNA in the brain while sparing peripheral APOE.
Method:
A library of CASi and parental siRNA molecules targeting APOE was designed and tested in iPSC astrocytes. The in vivo activity of the most potent compounds was evaluated in human APOE4 transgenic (hE4) mice over a dose concentration range. Activity was evaluated in both brain regions and the liver for lead selection. The lead molecule was further evaluated in nonhuman primate (NHP) studies, administered intrathecally at 112mg, 168mg, or 224mg doses. Knockdown of CSF, brain and liver tissue APOE was assessed at multiple time points.
Result:
The potency of the lead CASi molecule was <20pM in iPSC astrocytes. A 10nmol dose yielded 60-85% reduction of APOE mRNA in hippocampal tissue at 2ng/mg CASi exposure. The molecule was well-tolerated in mice. No knockdown was observed in the liver, despite CASi exposure, and peripheral cholesterol levels were unchanged. The dose-response study demonstrated a tight PK/PD relationship with a significant (P<0.0001) negative correlation between CASi and APOE mRNA levels in hE4 mice. NHP studies demonstrated 50-75% APOE protein knockdown in the CSF 15 days post dosing, which was sustained until day 70. At 30 days post-dose, the entorhinal cortex and hippocampus showed a 50-75% knockdown. There was no reduction of APOE protein levels in liver or plasma across the study.
Conclusion:
We identified a potent CASi against APOE with no unwanted effects on liver APOE levels or peripheral cholesterol. The molecule holds promise as a future therapeutic for ε4 carriers suffering from MCI/AD, many of whom are contraindicated for the currently approved immunotherapies.
Insights
A novel conditionally activating siRNA (CASi) effectively reduces brain Apolipoprotein E (APOE) mRNA in Alzheimer's disease (AD) models. This targeted approach spares peripheral APOE and cholesterol, offering a promising therapy for APOE*ε4 carriers.
Area of Science:
- Neuroscience
- Genetics
- Pharmacology
Background:
- The Apolipoprotein E (APOE)*ε4 allele is the primary genetic risk factor for late-onset Alzheimer's disease (AD).
- Preclinical studies indicate that reducing APOE4 mRNA levels can mitigate AD pathology.
- Developing targeted therapies for APOE*ε4 carriers with mild cognitive impairment (MCI) or AD is crucial, necessitating brain-specific APOE reduction while preserving systemic functions.
Purpose of the Study:
- To develop and evaluate a novel, potent, conditionally activating siRNA (CASi) designed to specifically target and reduce APOE mRNA within the brain.
- To assess the safety and efficacy of the CASi in preclinical models, focusing on brain APOE reduction without impacting peripheral APOE levels or cholesterol metabolism.
Main Methods:
- A library of CASi molecules targeting APOE was designed and tested in induced pluripotent stem cell (iPSC)-derived astrocytes.
- In vivo efficacy was evaluated in human APOE4 transgenic (hE4) mice across a dose range, assessing APOE mRNA and protein levels in brain regions and the liver.
- The lead CASi candidate was further tested in nonhuman primates (NHPs) via intrathecal administration, with APOE levels measured in cerebrospinal fluid (CSF), brain tissue, and plasma.
Main Results:
- The lead CASi molecule demonstrated high potency (<20pM) in iPSC astrocytes and achieved 60-85% APOE mRNA reduction in the hippocampus of hE4 mice at a 10nmol dose.
- The CASi was well-tolerated in mice, with no observed APOE knockdown in the liver and no changes in peripheral cholesterol levels.
- NHP studies showed sustained 50-75% APOE protein knockdown in CSF and significant reduction in the entorhinal cortex and hippocampus, without affecting liver or plasma APOE.
Conclusions:
- A potent CASi targeting brain APOE was identified, demonstrating significant efficacy and a favorable safety profile with no adverse effects on liver APOE or peripheral cholesterol.
- This CASi represents a promising therapeutic candidate for APOE*ε4 carriers with MCI/AD, particularly those who cannot tolerate current immunotherapies.
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