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This review, one in a series on myotonic dystrophy (DM), is focused on the development and potential use of small molecules as therapeutics for DM. The complex mechanisms and pathogenesis of DM are covered in the associated reviews. Here, we examine the various small molecule approaches taken to target the DNA, RNA, and proteins that contribute to disease onset and progression in myotonic dystrophy type 1 (DM1) and 2 (DM2).

In 2011, an intronic (G4C2)•(G2C4) expansion was shown to cause the most common forms of amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD). This discovery linked ALS with a clinically distinct form of dementia and a larger group of microsatellite repeat diseases, and catalyzed basic and translational research.

International audience; Myotonic dystrophy, caused by DM1 CTG/CAG repeat expansions, shows varying instability levels between tissues and across ages within patients. We determined DNA replication profiles at the DM1 locus in patient fibroblasts and tissues from DM1 transgenic mice of various ages showing different instability. In patient cells, the repeat is flanked by two replication origins demarcated by CTCF sites, with replication diminished at the expansion. In mice, the expansion replicated from only the downstream origin (CAG as lagging template). In testes from mice of three different ages, replication toward the repeat paused at the earliest age and was relieved at later ages-coinciding with increased instability. Brain, pancreas and thymus replication varied with CpG methylation at DM1 CTCF sites. CTCF sites between progressing forks and repeats reduced replication depending on chromatin. Thus, varying replication progression may affect tissue- and age-specific repeat instability.

At least 25 inherited disorders in humans result from microsatellite repeat expansion. Dramatic variation in repeat instability occurs at different disease loci and between different tissues; however, cis-elements and trans-factors regulating the instability process remain undefined. Genomic fragments from the human spinocerebellar ataxia type 7 (SCA7) locus, containing a highly unstable CAG tract, were previously introduced into mice to localize cis-acting “instability elements,” and revealed that genomic context is required for repeat instability. The critical instability-inducing region contained binding sites for CTCF—a regulatory factor implicated in genomic imprinting, chromatin remodeling, and DNA conformation change. To evaluate the role of CTCF in repeat instability, we derived transgenic mice carrying SCA7 genomic fragments with CTCF binding-site mutations. We found that CTCF binding-site mutation promotes triplet repeat instability both in the germ line and in somatic tissues, and that CpG methylation of CTCF binding sites can further destabilize triplet repeat expansions. As CTCF binding sites are associated with a number of highly unstable repeat loci, our findings suggest a novel basis for demarcation and regulation of mutational hot spots and implicate CTCF in the modulation of genetic repeat instability., Author Summary The human genome contains many repetitive sequences. In 1991, we discovered that excessive lengthening of a three-nucleotide (trinucleotide) repeat sequence could cause a human genetic disease. We now know that this unique type of genetic mutation, known as a “repeat expansion,” occurs in at least 25 different diseases, including inherited neurological disorders such as the fragile X syndrome of mental retardation, myotonic muscular dystrophy, and Huntington's disease. An interesting feature of repeat expansion mutations is that they are genetically unstable, meaning that the repeat expansion changes in length when transmitted from parent to offspring. Thus, expanded repeats violate one major tenet of genetics—i.e., that any given sequence has a low likelihood for mutation. For expanded repeats, the likelihood of further mutation approaches 100%. Understanding why expanded repeats are so mutable has been a challenging problem for genetics research. In this study, we implicate the CTCF protein in the repeat expansion process by showing that mutation of a CTCF binding site, next to an expanded repeat sequence, increases genetic instability in mice. CTCF is an important regulatory factor that controls the expression of genes. As binding sites for CTCF are associated with many repeat sequences, CTCF may play a role in regulating genetic instability in various repeat diseases—not just the one we studied.

Fever and chills occur frequently with amphotericin B (AB) administration, but the mechanism that causes these reactions has not been definitively established. A variety of proinflammatory cytokines, including interleukin-1 (IL-1) and tumor necrosis factor, have been shown to be important mediators of fever. In order to clarify the cellular and biochemical responses associated with AB-induced fever, the experiments described sought to (i) establish whether human mononuclear cells exposed to AB in vitro expressed IL-1 beta, (ii) evaluate whether clinically used premedications for fever prophylaxis in AB-treated patients were effective in down-regulating IL-1 beta expression in vitro, (iii) evaluate whether methylxanthine agents with immunomodulatory actions effected in vitro IL-1 beta expression, and (iv) define the dose and time dependency of the modulating effects. Peripheral blood mononuclear cells were isolated by density centrifugation and resuspended to 10(6) cells per ml in culture wells of Linbro plates. When cocultured for 2 h with human mononuclear cells, both Escherichia coli lipopolysaccharide and AB stimulated IL-1 beta expression in a dose-related fashion. AB-induced IL-1 beta expression was suppressed by hydrocortisone (HC), pentoxifylline, and an investigational theobromine, A81-3138, in a linear, dose-related manner. In contrast, indomethacin, meperidine, and diphenhydramine had no effect on IL-1 beta expression. Our in vitro data indicate that serum HC concentrations of greater than 1 to 2 micrograms/ml may be sufficient to modulate IL-1 beta expression. Pentoxifylline and A81-3138 may also be effective in modulating IL-1 beta expression by mononuclear cells at concentrations achievable in serum. These new agents may prove to be effective alternatives to HC or may be added with HC to suppress febrile reactions secondary to AB administration. Clinical studies with pentoxifylline as a premedication for AB seem warranted.