Chemotherapeutic deletion of CTG repeats in lymphoblast cells from DM1 patients

Abstract

Myotonic dystrophy type 1 (DM1) is caused by the expansion of a (CTG).(CAG) repeat in the DMPK gene on chromosome 19q13.3. At least 17 neurological diseases have similar genetic mutations, the expansion of DNA repeats. In most of these disorders, the disease severity is related to the length of the repeat expansion, and in DM1 the expanded repeat undergoes further elongation in somatic and germline tissues. At present, in this class of diseases, no therapeutic approach exists to prevent or slow the repeat expansion and thereby reduce disease severity or delay disease onset. We present initial results testing the hypothesis that repeat deletion may be mediated by various chemotherapeutic agents. Three lymphoblast cell lines derived from two DM1 patients treated with either ethylmethanesulfonate (EMS), mitomycin C, mitoxantrone or doxorubicin, at therapeutic concentrations, accumulated deletions following treatment. Treatment with EMS frequently prevented the repeat expansion observed during growth in culture. A significant reduction of CTG repeat length by 100-350 (CTG).(CAG) repeats often occurred in the cell population following treatment with these drugs. Potential mechanisms of drug-induced deletion are presented.

New Classification and Treatment for Myotonic Disorders

“…Experimental therapy was performed by using lymphoblast cells of DM1 patients and CTG repeat expansion can be reduced by chemotherapeutic agents; ethylmethanesulfonate, mitomycin C, mitoxantrone, doxorubicin (31). This may be eventually applicable to 17 neurological intractable diseases including spinocerebellar degeneration in addition to DM1.…”

Oxidative DNA Damage Modulates Trinucleotide Repeat Instability Via DNA Base Excision Repair

“…Chemotherapeutic drugs that are used to treat cancer can also attack DNA and result in DNA damage including bulky DNA adducts and interstrand cross-link (ICL) (26,32). Some DNA lesions are highly mutagenic and cause mutations in the genome, thereby altering genetic information that is passed from parent cells to daughter cells.…”

“…Trinucleotide repeat deletions can be induced in human lymphoblasts (32), bacterial cells (26) and mouse sperm (175), by DNA-damaging agents including ethyl methanesulfonate, mitomycin C, ethylnitrosourea, ultraviolet radiation, cisplatin and ionizing radiation (32,175,176). Because the DNA-damaging agents can induce alkylating DNA damage, DNA strand breaks, DNA cross-links that are usually subjected to BER and nucleotide excision repair, it suggests that BER and NER are actively involved in mediating TNR deletion.…”

“…Twenty nanograms of the repaired DNA was used for subsequent DNA fragment analysis. All substrates were 32 Pradiolabeled at the 5'-end of the strand that contained a deoxyuridine or a THF residue.…”

“…Substrates were 32 P-labeled at the 3'-or 5'-end of the strand with an 8-oxoG or a THF residue, the upstream primer and downstream primer.…”