N,N'-Bis(2-chloroethyl)-N-nitrosourea (BCNU)-induced Apoptosis of Neural Progenitor Cells in the Developing Fetal Rat Brain

Altered functional connectivity and network excitability in a model of cortical dysplasia

Focal cortical dysplasias (FCDs) are malformations of cortical development that often result in medically refractory epilepsy, with a greater incidence in the pediatric population. The relationship between the disturbed cortical morphology and epileptogenic activity of FCDs remains unclear. We used the BCNU (carmustine 1-3-bis-chloroethyl-nitrosourea) animal model of cortical dysplasia to evaluate neuronal and laminar alterations and how these result in altered activity of intracortical networks in early life. We corroborated the previously reported morphological anomalies characteristic of the BCNU model, comprising slightly larger and rounder neurons and abnormal cortical lamination. Next, the neuronal activity of live cortical slices was evaluated through large field-of-view calcium imaging as well as the neuronal response to a stimulus that leads to cortical hyperexcitability (pilocarpine). Examination of the joint activity of neuronal calcium time series allowed us to identify intracortical communication patterns and their response to pilocarpine. The baseline power density distribution of neurons in the cortex of BCNU-treated animals was different from that of control animals, with the former showing no modulation after stimulus. Moreover, the intracortical communication pattern differed between the two groups, with cortexes from BCNU-treated animals displaying decreased inter-layer connectivity as compared to control animals. Our results indicate that the altered anatomical organization of the cortex of BCNU-treated rats translates into altered functional networks that respond abnormally to a hyperexcitable stimulus and highlight the role of network dysfunction in the pathophysiology of cortical dysplasia.

Cell Models for Birth Defects Caused by Chloroethyl Nitrosourea-Induced DNA Lesions

ABSTRACT

Birth defects have been linked to administration of alkylating agents during pregnancy. The anti-tumor efficacy of alkylating agents correlate with their ability to induce DNA lesions, especially interstrand crosslinks (ICLs). Yet the role of DNA damages in birth defects remains to be clarified, owing, in part, to a lack of cell models. Here we generate DNA lesions in NIH/3T3 cells to mimic defects in fetus triggered by 3-Bis(2-chloroethyl)-1-nitrosourea (BCNU, carmustine). CCK-8 assay suggests that BCNU-induced cell death was dose-dependent. Alkaline comet tests and γ-H2AX staining confirm DNA ICLs and other forms of DNA damages caused by BCNUs. The cell cycle analysis shows cells arrest in G2/M phase until crosslinks repair is complete. Taken together, all these experiments demonstrate we have successfully established normal cell models for birth defects caused by BCNU-mediated DNA damages. The model can not only guide the development of effective and low-toxicity anticancer drugs, but also be of great significance for the study of neonatal malformation triggered by BCNUs.

Quantification of meCCNU-induced dG-dC crosslinks in oligonucleotide duplexes by liquid chromatography/electrospray ionization tandem mass spectrometry

Chloroethynitrosoureas (CENUs) are important alkylating agents widely used in the treatment of cancers. Decomposition of CENUs generates active electrophilic ions that damage DNA, including the formation of dG-dC crosslinks which represents the most important cytotoxic mechanism of CENUs. In this work, a high-performance liquid chromatography/electrospray ionization tandem mass spectrometry (HPLC/ESI-MS/MS) method was employed to analyze the dG-dC crosslinks induced by 1-(2-chloroethyl)-3-(4-methylcyclohexyl)-1-nitrosourea (meCCNU, Semustine). The direct quantitation of dG-dC crosslinks in oligonucleotide duplexes was achieved by the selected reaction monitoring (SRM) mode using synthesized (15) N(3) -labeled dG-dC as an internal standard. Methods of enzymatic digestion and HPLC separation were developed for obtaining separation and reproducibility of the dG-dC peak in chromatograms. The limit-of-detection (LOD) was determined to be 0.08 nM and the limit-of-quantification (LOQ) was determined to be 0.16 nM. The linearity of the calibration curve was 0.9997 over the range of 0.08 to 32 nM. The precision and accuracy of the method ranged from 1.1 to 6.6% and 96 to 109%, respectively. The recovery of the dG-dC crosslink in the enzymatic hydrolysates from the oligonucleotide duplex was determined to be from 91 to 106%. The results of the validation study indicate that the method is suitable for quantifying dG-dC crosslinks in DNA. Consequently, this method was used to determine meCCNU-induced dG-dC crosslinks in four duplexes with different GC contents. The results showed that the crosslinking fraction (CF) increased as the GC content in the duplex increased, and a relatively low CF was observed in the early period of the reaction.