RESUMO
Small-molecule compounds that target mismatched base pairs in DNA offer a novel prospective for cancer diagnosis and therapy. The potent anticancer antibiotic echinomycin functions by intercalating into DNA at CpG sites. Surprisingly, we found that the drug strongly prefers to bind to consecutive CpG steps separated by a single T:T mismatch. The preference appears to result from enhanced cooperativity associated with the binding of the second echinomycin molecule. Crystallographic studies reveal that this preference originates from the staggered quinoxaline rings of the two neighboring antibiotic molecules that surround the T:T mismatch forming continuous stacking interactions within the duplex. These and other associated changes in DNA conformation allow the formation of a minor groove pocket for tight binding of the second echinomycin molecule. We also show that echinomycin displays enhanced cytotoxicity against mismatch repair-deficient cell lines, raising the possibility of repurposing the drug for detection and treatment of mismatch repair-deficient cancers.
Assuntos
Pareamento Incorreto de Bases/efeitos dos fármacos , DNA/química , Equinomicina/farmacologia , Conformação de Ácido Nucleico/efeitos dos fármacos , Antibióticos Antineoplásicos/química , Antibióticos Antineoplásicos/metabolismo , Antibióticos Antineoplásicos/farmacologia , Pareamento Incorreto de Bases/genética , Sobrevivência Celular/efeitos dos fármacos , Cristalografia por Raios X , DNA/genética , DNA/metabolismo , Equinomicina/química , Equinomicina/metabolismo , Células HCT116 , Humanos , Substâncias Intercalantes/química , Substâncias Intercalantes/metabolismo , Substâncias Intercalantes/farmacologia , Estrutura Molecular , Neoplasias/tratamento farmacológico , Neoplasias/genética , Neoplasias/metabolismoRESUMO
Repetitive DNA sequences are ubiquitous in life, and changes in the number of repeats often have various physiological and pathological implications. DNA repeats are capable of interchanging between different noncanonical and canonical conformations in a dynamic fashion, causing configurational slippage that often leads to repeat expansion associated with neurological diseases. In this report, we used single-molecule spectroscopy together with biophysical analyses to demonstrate the parity-dependent hairpin structural polymorphism of TGGAA repeat DNA. We found that the DNA adopted two configurations depending on the repeat number parity (even or odd). Transitions between these two configurations were also observed for longer repeats. In addition, the ability to modulate this transition was found to be enhanced by divalent ions. Based on the atomic structure, we propose a local seeding model where the kinked GGA motifs in the stem region of TGGAA repeat DNA act as hot spots to facilitate the transition between the two configurations, which may give rise to disease-associated repeat expansion.
