Drug Development

Alzheimer's Disease (AD) is defined by deposition of amyloid beta (A𝛣), phosphorylated tau (p-Tau), and neurodegeneration. Several A𝛣-targeting antibodies have been approved for AD in recent years, but cause swelling/hemorrhaging of the brain and fail to reduce p-Tau, which drives disease progression. Oligonucleotide therapeutic approaches have recently shown promise and have been well tolerated in early-stage clinical trials, with an amyloid precursor protein (APP) siRNA reducing amyloid beta and a microtubule-associated protein tau (MAPT) ASO reducing p-Tau. We have developed a novel class of multi-targeting siRNAs called chemically optimized stringed modifiable oligonucleotides (COSMOs) which are capable of simultaneously targeting APP and MAPT to reduce both A𝛣 and p-Tau.

Unique siRNAs targeting APP or MAPT were designed, synthesized, and screened to select top hits for COSMO synthesis. Human SK-N-AS cells were transfected with COSMOs as well as individual siRNAs for 2-5 days prior to quantifying mRNA levels of APP and MAPT with qPCR as well as protein levels of APP, Tau, A𝛣42, and p-Tau181 with ELISA. Cellular viability following transfection was determined with CellTiter Glo. COSMOs were incubated with cellular lysates from SK-N-AS cells for 72 hours at 37C prior to running gel electrophoresis to determine COSMO cleavability.

We first found that our top APP- and MAPT-targeting siRNAs are active at picomolar concentrations in vitro. We then confirmed that co-transfection of our top siRNAs simultaneously reduces both A𝛣 and p-Tau. Following synthesis and transfection of APP- and MAPT-targeting COSMOs, we observed simultaneous reductions of APP, Tau, A𝛣, and p-Tau protein at picomolar concentrations. We also show that APP- and MAPT-targeting COSMOs are less toxic than individual siRNAs in vitro. Lastly, COSMOs can be engineered to be either cleavable or non-cleavable for optimal pharmacokinetics and pharmacodynamics.

To date, there are no approved therapeutics for AD capable of reducing both A𝛣 and p-Tau. Oligonucleotide therapeutics for AD have shown early clinical success in reducing either A𝛣 or p-Tau, but not both. COSMOs are a promising new class of therapeutics capable of reducing both A𝛣 and p-Tau for AD.