Abstract
Neuronal ceroid lipofuscinoses (NCLs; Batten disease) are a group of thirteen genetically heterogenous lysosomal storage diseases that, collectively, are the most common cause of fatal neurodegeneration in children. CLN6 Batten disease (CLN6 BD), also known as LakeCavanagh disease, is a late infantile onset variant of the NCLs caused by loss-of-function mutations in the CLN6 gene. Mutations in both alleles of the gene result in classic NCL symptoms – blindness, epilepsy and progressive cognitive and motor decline – as well as characteristic pathophysiological features such as premature and accelerated neuronal cell death, chronic neuroinflammation and the intracellular accumulation of autofluorescent storage material in lysosomes. As a monogenic, inherited and fatal disorder, CLN6 BD is an excellent candidate for experimental gene therapy.
Several preclinical and clinical trials of gene therapy have been conducted for a range of genetic disorders, including several NCL variants, and these have shown promising results. Subsequently, a clinical phase I/II CLN6 BD trial was initiated by the Gray Foundation and Amicus Therapeutics in 2016. This trial, which is ongoing at the time of writing, has produced optimistic safety and tolerance interim data. But, past experience with clinical gene therapy trials for several other genetic and metabolic disorders suggests that any improvements will not be curative. For this reason, the Gray Foundation began to investigate complementary treatments that might augment the therapeutic efficacy of gene therapy in CLN6 BD. This project used a naturally occurring murine model of CLN6 BD (the Cln6nclf mouse) to investigate the efficacy of two small molecule (drug) therapies – gemfibrozil and cannabidiol (CBD) – alone and in combination with adenovirus associated virus (AAV2/9)-
mediated gene therapy, as protection against the CLN6 behavioural phenotype. Specifically, Cln6nclf and C57Bl/6 (control) mice received a unilateral intracerebroventricular (i.c.v) injection iv of gene therapy (an AAV2/9 vector expressing hCLN6 under the control of a chicken β-actin
gene promoter) or saline (1x PBS) on post-natal days 0-2. Post-weaning, mice were dosed orally (every second day) with either gemfibrozil, CBD, a combination of the two drug therapies or a vehicle solution. Behavioural testing (ataxia phenotyping and rotarod performance) was conducted at 6, 9 and 12 months of age.
Testing of over 500 animals determined that the oral administration of gemfibrozil, CBD, or a combination of the two drugs did not make any consistently significant improvements to untreated or gene-therapy treated Cln6nclf mouse behaviour. The study was successful, however, in reaffirming the apparent efficacy of i.c.v gene therapy in protecting against CLN6 BD behaviour in Cln6nclf mice (of both sexes), with no significant reduction in behavioural scores, when compared to healthy controls.
This study represents the first long-term, large-scale preclinical study of this particular combination of therapies for CLN6 BD. It provides a solid foundation for further work searching for a comprehensive and curative treatment regimen for CLN6 BD.