Chemical genetics and orphan genetic diseases

Challenges in the Diagnosis and Treatment of Patients with Rare and Orphan Diseases

Orphan diseases are diverse group of disorders that have not gained much of public attention as they are rarely reported worldwide. The term orphan and rare diseases are often used interchangeably when describing diseases that fall into an orphan or rare category. Around 80% of orphan diseases are chronic, serious, or life threatening, are of genetic origin, and are more prevalent in children and in adults above 40 years of age. Due to rarity, lack of financial support and specific drug to treat these diseases, diagnosis, and treatment becomes challenging. Diagnosis is usually delayed, and patient continues to suffer by seeking multiple specialist opinion. Nonavailability of specific drug and lack of financial funding or waivers to conduct to conduct clinical trial for invention of new orphan drug are the obstacles for targeted treatment. Hence, there is need for comprehensive integrative approach to manage orphan disease patients and pharmaceutical companies should be encouraged for invention of drugs at a reasonable cost for orphan diseases. In addition, community education through genetic-based learning modules is essential to increase awareness of population about risk factors and early diagnosis of orphan diseases, and to take opinion of specific specialist for thorough clinical evaluation. This review discusses challenges faced by the specialists toward diagnosis and treatment of orphan disease for well-being of an individual living with the disorder.

Small-Molecule Screening for Genetic Diseases

The genetic determinants of many diseases, including monogenic diseases and cancers, have been identified; nevertheless, targeted therapy remains elusive for most. High-throughput screening (HTS) of small molecules, including high-content analysis (HCA), has been an important technology for the discovery of molecular tools and new therapeutics. HTS can be based on modulation of a known disease target (called reverse chemical genetics) or modulation of a disease-associated mechanism or phenotype (forward chemical genetics). Prominent target-based successes include modulators of transthyretin, used to treat transthyretin amyloidoses, and the BCR-ABL kinase inhibitor Gleevec, used to treat chronic myelogenous leukemia. Phenotypic screening successes include modulators of cystic fibrosis transmembrane conductance regulator, splicing correctors for spinal muscular atrophy, and histone deacetylase inhibitors for cancer. Synthetic lethal screening, in which chemotherapeutics are screened for efficacy against specific genetic backgrounds, is a promising approach that merges phenotype and target. In this article, we introduce HTS technology and highlight its contributions to the discovery of drugs and probes for monogenic diseases and cancer.

1,2,3-Dithiazoles – new reversible melanin synthesis inhibitors: a chemical genomics study

1,2,3-Dithiazolimines show potent and reversible inhibition of melanin synthesis in Xenopus laevis embryos.

Validating therapeutic targets through human genetics

More than 90% of the compounds that enter clinical trials fail to demonstrate sufficient safety and efficacy to gain regulatory approval. Most of this failure is due to the limited predictive value of preclinical models of disease, and our continued ignorance regarding the consequences of perturbing specific targets over long periods of time in humans. 'Experiments of nature' - naturally occurring mutations in humans that affect the activity of a particular protein target or targets - can be used to estimate the probable efficacy and toxicity of a drug targeting such proteins, as well as to establish causal rather than reactive relationships between targets and outcomes. Here, we describe the concept of dose-response curves derived from experiments of nature, with an emphasis on human genetics as a valuable tool to prioritize molecular targets in drug development. We discuss empirical examples of drug-gene pairs that support the role of human genetics in testing therapeutic hypotheses at the stage of target validation, provide objective criteria to prioritize genetic findings for future drug discovery efforts and highlight the limitations of a target validation approach that is anchored in human genetics.

Discovery, synthesis, and biological evaluation of novel SMN protein modulators

Spinal muscular atrophy (SMA) is an autosomal recessive disorder affecting the expression or function of survival motor neuron protein (SMN) due to the homozygous deletion or rare point mutations in the survival motor neuron gene 1 (SMN1). The human genome includes a second nearly identical gene called SMN2 that is retained in SMA. SMN2 transcripts undergo alternative splicing with reduced levels of SMN. Up-regulation of SMN2 expression, modification of its splicing, or inhibition of proteolysis of the truncated protein derived from SMN2 have been discussed as potential therapeutic strategies for SMA. In this manuscript, we detail the discovery of a series of arylpiperidines as novel modulators of SMN protein. Systematic hit-to-lead efforts significantly improved potency and efficacy of the series in the primary and orthogonal assays. Structure-property relationships including microsomal stability, cell permeability, and in vivo pharmacokinetics (PK) studies were also investigated. We anticipate that a lead candidate chosen from this series may serve as a useful probe for exploring the therapeutic benefits of SMN protein up-regulation in SMA animal models and a starting point for clinical development.

Spinal muscular atrophy: advances in research and consensus on care of patients

Spinal muscular atrophy (SMA) is an autosomal recessive disease characterized by degeneration of spinal cord motor neurons and muscular atrophy. Advances in recent research have led to understanding of the molecular genetics of SMA. Therapeutic strategies have been developed according to the unique genomic structure of the SMN genes. Three groups of compounds have been identified as therapeutic candidates. One group was identified before the molecular genetics of SMA was understood, chosen on the basis of their effectiveness in similar neurologic disorders. The second group was identified based on their ability to modify SMN2 gene expression. Several of these agents are currently in clinical trials. A third group, identified by large-scale drug screening, is still under preclinical investigation. In addition, other advances in medical technology have led to the publication of a consensus statement regarding the care of SMA patients.

A chemical genomic approach identifies matrix metalloproteinases as playing an essential and specific role in Xenopus melanophore migration

To dissect the function of matrix metalloproteinases (MMPs) involved in cellular migration in vivo, we undertook both a forward chemical genomic screen and a functional approach to discover modulators of melanophore (pigment cell) migration in Xenopus laevis. We identified the 8-quinolinol derivative NSC 84093 as affecting melanophore migration in the developing embryo and have shown it to act as a MMP inhibitor. Potential targets of NSC 84093 investigated include MMP-14 and MMP-2. MMP-14 is expressed in migrating neural crest cells from which melanophores are derived. MMP-2 is expressed at the relevant time of development and in a pattern that suggests it contributes to melanophore migration. Morpholino-mediated knockdown of both MMPs demonstrates they play a key role in melanophore migration and partially phenocopy the effect of NSC 84093.

Neurofibromatosis 1 associated with spinal muscular atrophy

Neurofibromatosis type 1, or von Recklinghausen disease, is a progressive, autosomal dominant, monogenic disease. Spinal muscular atrophy is a progressive, autosomal recessive, monogenic disease. Specific anti-polysaccharide antibody deficiency is an immune disorder suspected in any child older than 2 years who suffers from recurrent respiratory tract infections or in patients with unusually severe complications from infections under appropriate treatment. Reported here is the coinheritance of two monogenic syndromes in the same patient, a novel association with specific anti-polysaccharide antibody deficiency.

Spinal muscular atrophy and a model for survival of motor neuron protein function in axonal ribonucleoprotein complexes

Spinal muscular atrophy (SMA) is a neurodegenerative disease that results from loss of function of the SMN1 gene, encoding the ubiquitously expressed survival of motor neuron (SMN) protein, a protein best known for its housekeeping role in the SMN-Gemin multiprotein complex involved in spliceosomal small nuclear ribonucleoprotein (snRNP) assembly. However, numerous studies reveal that SMN has many interaction partners, including mRNA binding proteins and actin regulators, suggesting its diverse role as a molecular chaperone involved in mRNA metabolism. This review focuses on studies suggesting an important role of SMN in regulating the assembly, localization, or stability of axonal messenger ribonucleoprotein (mRNP) complexes. Various animal models for SMA are discussed, and phenotypes described that indicate a predominant function for SMN in neuronal development and synapse formation. These models have begun to be used to test different therapeutic strategies that have the potential to restore SMN function. Further work to elucidate SMN mechanisms within motor neurons and other cell types involved in neuromuscular circuitry hold promise for the potential treatment of SMA.

Spinal muscular atrophy

Spinal muscular atrophy is an autosomal recessive neurodegenerative disease characterised by degeneration of spinal cord motor neurons, atrophy of skeletal muscles, and generalised weakness. It is caused by homozygous disruption of the survival motor neuron 1 (SMN1) gene by deletion, conversion, or mutation. Although no medical treatment is available, investigations have elucidated possible mechanisms underlying the molecular pathogenesis of the disease. Treatment strategies have been developed to use the unique genomic structure of the SMN1 gene region. Several candidate treatment agents have been identified and are in various stages of development. These and other advances in medical technology have changed the standard of care for patients with spinal muscular atrophy. In this Seminar, we provide a comprehensive review that integrates clinical manifestations, molecular pathogenesis, diagnostic strategy, therapeutic development, and evidence from clinical trials.

Exploring emerging technologies using metaphors--a study of orphan drugs and pharmacogenomics

Due to uncertainties of several aspects of emerging health technologies, there is a need to anticipate these developments early. A first step would be to gather information and develop future visions about the technology. This paper introduces metaphor analysis as a novel way to do this. Specifically, we study the future of pharmacogenomics by comparing this technology with orphan drugs, which are more established and often act as a model with comparable (economic, research organisation, etc.) characteristics. The analysis consists of describing the dominant metaphors used and structurally exploring (dis)similarities between pharmacogenomics and orphan drugs developments. This comparison leads to lessons that can be learnt for the emerging pharmacogenomics future. We carried out a comprehensive literature review, extracting metaphors in a structured way from different areas of the drug research and development pipeline. The paper argues that (1) there are many similarities between orphan drugs and pharmacogenomics, especially in terms of registration, and social and economic impacts; (2) pharmacogenomics developments are regarded both as a future 'poison' and a 'chance', whereas orphan drugs are seen as a 'gift', and at the same time as a large 'problem'; and (3) metaphor analysis proves to be a tool for creating prospective images of pharmacogenomics and other emerging technologies.

Tagged small molecule library approach for facilitated chemical genetics

Chemical genetics is a powerful method which utilizes small molecule regulators to reveal the molecular basis of diverse biological processes. However, the current chemical genetic approach sometimes meets a serious bottleneck during the process of target identification. One faces difficulty in conjugating the active compound to an affinity matrix without losing or reducing its activity that leads to laborious structure-activity relationship (SAR) studies. To facilitate this process, we have developed a tagged triazine library containing a built-in linker that provides a straightforward transition from phenotypic screening to target identification. A strategy for constructing a tagged library and applications with a streamlined target identification and subsequent mechanistic study are discussed in this Account.

Inverse drug screens: a rapid and inexpensive method for implicating molecular targets

Identification of gene products that function in some specific process of interest is a common goal in developmental biology. Although use of drug compounds to probe biological systems has a very long history in teratology and toxicology, systematic hierarchical drug screening has not been capitalized upon by the developmental biology community. This "chemical genetics" approach can greatly benefit the study of embryonic and regenerative systems, and we have formalized a strategy for using known pharmacological compounds to implicate specific molecular candidates in any chosen biological phenomenon. Taking advantage of a hierarchical structure that can be imposed on drug reagents in a number of fields such as ion transport, neurotransmitter function, metabolism, and cytoskeleton, any assay can be carried out as a binary search algorithm. This inverse drug screen methodology is much more efficient than exhaustive testing of large numbers of drugs, and reveals the identity of a manageable number of specific molecular candidates that can then be validated and targeted using more expensive and specific molecular reagents. Here, we describe the process of this loss-of-function screen and illustrate its use in uncovering novel bioelectrical and serotonergic mechanisms in embryonic patterning. This technique is an inexpensive and rapid complement to existing molecular screening strategies. Moreover, it is applicable to maternal proteins, and model species in which traditional genetic screens are not feasible, significantly extending the opportunities to identify key endogenous players in biological processes.

Spinal muscular atrophy: the RNP connection

Degenerated motor neurons in the spinal cord are the pathological hallmark of spinal muscular atrophy (SMA). SMA is caused by mutations in the ubiquitously expressed survival motor neuron 1 (SMN1) gene, which lead to reduced levels of functional SMN protein. Many different functions have been assigned to SMN, including assembly of ribonucleoproteins (RNPs), splicing, transcription and axonal mRNA transport. Recently, tissue from SMA patients and animal models has been used to determine which function of SMN is affected in SMA patients. A surprising picture has emerged: the impaired assembly of RNP subunits of the spliceosome seems to be responsible for SMA pathogenesis. Here, we present a model of how this defect might cause motor-neuron degeneration and consider potential therapies.