DNA Damage, Genome Stability, and Adaptation: A Question of Chance or Necessity?

DNA damage causes the mutations that are the principal source of genetic variation. DNA damage detection and repair mechanisms therefore play a determining role in generating the genetic diversity on which natural selection acts. Speciation, it is commonly assumed, occurs at a rate set by the level of standing allelic diversity in a population. The process of speciation is driven by a combination of two evolutionary forces: genetic drift and ecological selection. Genetic drift takes place under the conditions of relaxed selection, and results in a balance between the rates of mutation and the rates of genetic substitution. These two processes, drift and selection, are necessarily mediated by a variety of mechanisms guaranteeing genome stability in any given species. One of the outstanding questions in evolutionary biology concerns the origin of the widely varying phylogenetic distribution of biodiversity across the Tree of Life and how the forces of drift and selection contribute to shaping that distribution. The following examines some of the molecular mechanisms underlying genome stability and the adaptive radiations that are associated with biodiversity and the widely varying species richness and evenness in the different eukaryotic lineages.

Temozolomide Resistance: A Multifarious Review on Mechanisms Beyond O-6-Methylguanine-DNA Methyltransferase

BACKGROUND

Chemotherapy with the oral alkylating agent temozolomide still prevails as a linchpin in the therapeutic regimen of glioblastoma alongside radiotherapy. Because of the impoverished prognosis and sparse chemotherapeutic medicaments associated with glioblastoma, the burgeoning resistance to temozolomide has made the whole condition almost irremediable.

OBJECTIVE

The present review highlights the possible mechanisms of drug resistance following chemotherapy with temozolomide.

METHODS

The review summarizes the recent developments, as published in articles from Scopus, PubMed, and Web of Science search engines.

DESCRIPTION

One of the prime resistance mediators, O-6-methylguanine-DNA methyltransferase, upon activation, removes temozolomide-induced methyl adducts bound to DNA and reinstates genomic integrity. In the bargain, neoteric advances in the conception of temozolomide resistance have opened the door to explore several potential mediators like indirect DNA repair systems, efflux mechanisms, epigenetic modulation, microenvironmental influences, and autophagy-apoptosis processes that constantly lead to the failure of chemotherapy.

CONCLUSION

This review sheds light on recent discoveries, proposed theories, and clinical developments in the field of temozolomide resistance to summarize the complex and intriguing involvement of oncobiological pathways.