Abstracts

Haploinsufficiency of SYNGAP1 resulting from truncating or loss of function mutations causes SYNGAP1-related disorders (SRD), a collection of devastating neurodevelopmental and neurological conditions including intellectual disability, severe behavioral problems, seizures, motor abnormalities, and impaired communication. Mutations result in loss of expression of the affected allele, resulting in haploinsufficiency. Insufficient levels of SYNGAP1 lead to increased incorporation of AMPA receptor at the post-synaptic membrane and increased neuronal activity. Hyperexcitability throughout development and life causes the aforementioned constellation of severe neurological phenotypes.

Restoring SYNGAP1 levels has the potential to address the root cause of SRD. To this end, CAMP4 is targeting regulatory RNAs (regRNAs), which are short-lived, noncoding RNAs expressed from enhancers and promoters that act locally to regulate gene expression. Through binding to transcription factors (TFs), regRNAs create a local concentration of TFs proximal to the promoter and enhancers that modulate gene transcription. Targeting regRNAs with antisense oligonucleotides (ASOs) disrupts regRNA structure and may displace negative acting factors, resulting in an overall increase in transcription. Our RAP Platformä enables the identification of regRNAs and ASOs targeting these regRNAs to increase target gene expression. Here, we describe CMP-SYNGAP-01, an ASO that upregulates SYNGAP1 transcription with the potential to restore healthy protein levels in patients with mutations that cause SYNGAP1 haploinsufficiency.

CMP-SYNGAP-01 targets a SYNGAP1 regRNA to increase SYNGAP1 transcription and protein levels in multiple cell types, including patient-derived neurons. Upon administration by intracerebroventricular injection to a humanized SYNGAP1^hu knock-in/knock-out mouse, the ASO increased SYNGAP1 protein levels by up to ~2-fold. We demonstrated that the haploinsufficient humanized SYNGAP1 mice exhibit multiple disease-relevant deficits in cognition, motor function and hyperactivity. Critically, these phenotypes were reversed following CMP-SYNGAP-01 administration, demonstrating that increasing protein through targeting the regRNA can directly impact SYNGAP1 function and mitigate phenotypes caused by haploinsufficiency.  Finally, intrathecal administration of CMP-SYNGAP-01 to cynomolgus monkeys resulted in a dose-linear exposure across disease-relevant brain regions where it significantly increased SYNGAP1 protein levels.

These data demonstrate that targeting a SYNGAP1 regRNA with an ASO increases SYNGAP1 transcription in vitro and in vivo. Importantly, administration of CMP-SYNGAP-01 reversed disease-relevant behaviors in a humanized mouse model of SYNGAP1 haploinsufficiency and increased SYNGAP1 protein when administered by a clinical route of administration. These data support the continued advancement of this drug candidate for the potential treatment for patients with SYNGAP1 haploinsufficiency.