Lars Brichta

In vitro and ex vivo evaluation of second-generation histone deacetylase inhibitors for the treatment of spinal muscular atrophy

Among a panel of histone deacetylase (HDAC) inhibitors investigated, suberoylanilide hydroxamic acid (SAHA) evolved as a potent and non‐toxic candidate drug for the treatment of spinal muscular atrophy (SMA), an α‐motoneurone disorder caused by insufficient survival motor neuron (SMN) protein levels. SAHA increased SMN levels at low micromolar concentrations in several neuroectodermal tissues, including rat hippocampal brain slices and motoneurone‐rich cell fractions, and its therapeutic capacity was confirmed using a novel human brain slice culture assay. SAHA activated survival motor neuron gene 2 (SMN2), the target gene for SMA therapy, and inhibited HDACs at submicromolar doses, providing evidence that SAHA is more efficient than the HDAC inhibitor valproic acid, which is under clinical investigation for SMA treatment. In contrast to SAHA, the compounds m‐Carboxycinnamic acid bis‐Hydroxamide, suberoyl bishydroxamic acid and M344 displayed unfavourable toxicity profiles, whereas MS‐275 failed to increase SMN levels. Clinical trials have revealed that SAHA, which is under investigation for cancer treatment, has a good oral bioavailability and is well tolerated, allowing in vivo concentrations shown to increase SMN levels to be achieved. Because SAHA crosses the blood–brain barrier, oral administration may allow deceleration of progressive α‐motoneurone degeneration by epigenetic SMN2 gene activation.

In vivo activation of SMN in spinal muscular atrophy carriers and patients treated with valproate.

Spinal muscular atrophy results from loss of the survival motor neuron 1 (SMN1) gene and malfunction of the remaining SMN2. We investigated whether valproic acid can elevate human SMN expression in vivo.

Valproic acid induces antioxidant effects in X-linked Adrenoleukodystrophy

X-linked adrenoleukodystrophy (X-ALD) is a fatal, axonal demyelinating, neurometabolic disease. It results from the functional loss of a member of the peroxisomal ATP-binding cassette transporter subfamily D (ABCD1), which is involved in the metabolism of very long-chain fatty acids (VLCFA). Oxidative damage of proteins caused by excess of the hexacosanoic acid, the most prevalent VLCFA accumulating in X-ALD, is an early event in the neurodegenerative cascade. We demonstrate here that valproic acid (VPA), a widely used anti-epileptic drug with histone deacetylase inhibitor properties, induced the expression of the functionally overlapping ABCD2 peroxisomal transporter. VPA corrected the oxidative damage and decreased the levels of monounsaturated VLCFA (C26:1 n-9), but not saturated VLCFA. Overexpression of ABCD2 alone prevented oxidative lesions to proteins in a mouse model of X-ALD. A 6-month pilot trial of VPA in X-ALD patients resulted in reversion of the oxidative damage of proteins in peripheral blood mononuclear cells. Thus, we propose VPA as a promising novel therapeutic approach that warrants further clinical investigation in X-ALD.

Spinal muscular atrophy and therapeutic prospects.

The molecular genetic basis of spinal muscular atrophy (SMA), an autosomal recessive neuromuscular disorder, is the loss of function of the survival motor neuron gene (SMN1). The SMN2 gene, a nearly identical copy of SMN1, has been detected as a promising target for SMA therapy. Both genes are ubiquitously expressed and encode identical proteins, but markedly differ in their splicing patterns: While SMN1 produces full-length (FL)-SMN transcripts only, the majority of SMN2 transcripts lacks exon 7. Transcriptional SMN2 activation or modulation of its splicing pattern to increase FL-SMN levels is believed to be clinically beneficial and therefore a crucial challenge in SMA research. Drugs such as valproic acid, phenylbutyrate, sodium butyrate, M344 and SAHA that mainly act as histone deacetylase inhibitors can mediate both: they stimulate the SMN2 gene transcription and/or restore the splicing pattern, thereby elevating the levels of FL-SMN2 protein. Preliminary phase II clinical trials and individual experimental curative approaches SMA patients show promising results. However, phase III double-blind placebo controlled clinical trials have to finally prove the efficacy of these drugs.