Background:
Mutations in the Valosin-containing protein (VCP) gene cause inclusion body myopathy with early-onset Paget disease and frontotemporal dementia (IBMPFD) or multisystem Proteinopathy due to gain of function VCP mutations. Many types of cancer in humans are associated with elevated expression of VCP. CB-5083 is a novel VCP inhibitor that binds to VCP reversibly and competitively. Trials in patients with myeloid leukemia and solid tumors indicated an adverse effect of the drug in patients’ vision, potentially due to CB-5083 off-targeting PDE6, a photoreceptor protein complex essential for visual signal transmission. Here, we hypothesize that treating IBMPFD patient myoblasts and the VCPR155H knock-in mouse models of IBMPFD with CB-5083 can ameliorate disease phenotypes by correcting the gain of function and low doses would avoid the off target effects.
Objectives: Aim 1: Treatment of VCP disease patient myoblasts with CB-5083 VCP inhibitor. Aim 2: In vivo treatment of VCPR155H disease mouse model to correct muscle and spinal cord pathology.
Methods: Patient-derived myoblasts were treated with variable dosage of CB-5083. Immunoblotting, immunohistochemistry and MTT analysis were performed to measure cellular pathology and survival.
Wildtype control, homozygous and heterozygous VCP R155H mice were gavaged daily with 15mg/kg CB-5083 or vehicle for five months. To evaluate the effect of CB-5083 on mouse motor function, weight, rotarod testing and grip strength were monitored monthly. To assess the toxicity of CB-5083 on visual function, electroretinogram (ERG) and optical coherence tomography (OCT) analyzing the retinal electrophysiology and structure to assess the CB-5083 toxicity. Furthermore, to assess the effect of CB-5083 on cellular pathology, immunoblotting and immunohistochemistry analysis were performed in muscle tissue to evaluate TDP43 and mitochondria pathology.
Results: CB-5083 treatment in VCP R155H knock-in mice resulted in functional improvements in Rotarod behavioral test. Muscle biopsy pathology showed reduction of pathological biomarkers, suggesting that CB-5083 may lead to improvement of disease pathology. Importantly, no significant visual abnormalities were observed after 5-month chronic treatment of CB-5083. Furthermore, treatment of patient-specific IBMPFD myoblasts showed that myoblasts tolerated up to 300nM CB-5083 dosage. Improvement in the typical disease pathology, such as TDP43 accumulation was also observed.
Conclusions VCP inclusion body myopathy with early-onset Paget disease, frontotemporal dementia (IBMPFD) +/- ALS is caused by a gain of function mutation of the VCP gene. Our studies showed that there was improvement of cellular pathology in patient-derived myoblasts with CB-5083 treatment. The IBMPFD mouse model tolerated the CB-5083 treatment with improvement of motor behavior and cellular pathology. Our results suggest that CB-5083 is a potential safe and effective therapy in patients with VCP inclusion body myopathy.