Maximizing the Efficacy of CRISPR/Cas Homology-Directed Repair Gene Targeting

Clustered regularly interspaced short palindromic repeats/CRISPR-associated system (CRISPR/Cas) is a powerful gene editing tool that can introduce double-strand breaks (DSBs) at precise target sites in genomic DNA. In mammalian cells, the CRISPR/Cas-generated DSBs can be repaired by either template-free error-prone end joining (e.g., non-homologous end joining/microhomology-mediated end joining [NHEJ]/[MMEJ]) or templated error-free homology-directed repair (HDR) pathways. CRISPR/Cas with NHEJ/MMEJ DNA repair results in various length insertions/deletion mutations (indels), which can cause frameshift mutations leading to a stop codon and subsequent gene-specific knockout (i.e., loss of function). In contrast, CRISPR/Cas with HDR DNA repair, utilizing an exogenous repair template harboring specific nucleotide (nt) changes, can be employed to intentionally edit out or introduce mutations or insertions at specific genomic sites (i.e., targeted gene knock-in). This review provides an overview of HDR-based gene-targeting strategies to facilitate the knock-in process, including improving gRNA cleavage efficiency, optimizing HDR efficacy, decreasing off-target effects, suppressing NHEJ/MMEJ activity, and thus expediting the screening of CRISPR/Cas-edited clonal cells

Induction of Human Breast Cancer Cell Apoptosis from G2/M Preceded by Stimulation into the Cell Cycle by Z-1,1-dichloro-2,3-diphenylcyclopropane

We have shown previously that Z-1,1-dichloro-2,3-diphenylcyclopropane (a.k.a. Analog II, AII) inhibits human breast cancer cell proliferation regardless of estrogen receptor status or estrogen sensitivity, and that its cellular targets include microtubules. In the present study, we investigated the apoptosis-inducing effects of AII. MCF-7, MCF-7/LY2, and MDA-MB-231 cells all showed nuclear fragmentation in response to 100 μM AII when stained with Hoechst 33342 and examined by fluorescence microscopy. Pulsed field gel electrophoretic analysis showed that each of the cell lines also developed specific high molecular weight DNA fragments: a low level of 1–2 Mb fragments appeared after 6 hr, while 30–50 kb fragments accumulated subsequently. At 24 hr of drug exposure, the majority of cells became nonadherent, and the 30–50 kb fragments were restricted to detached MCF-7 and MDA-MB-231 cells. Both adherent and detached MCF-7/LY2 cells exhibited these fragments. A previous study by single-color (propidium) flow cytometry demonstrated that AII blocks MDA-MB-231 cells in G2/M of the cell cycle. More refined analyses in the present study showed this same result for MDA-MB-231 cells, but MCF-7 and MCF-7/LY2 cells did not reveal apparent drug-induced cell cycle block. AII demonstrated growth inhibitory, cell cycle-perturbing, and hypodiploidy-inducing activity against other human breast carcinoma lines, i.e. BT-20, CAMA-1, and SKBR-3, but no such actions in the non-tumorigenic, “normal” human breast epithelial line MCF-10A. Bromodeoxyuridine labeling and two-color flow cytometric analysis, however, suggested that AII caused stimulation into S phase, and that G2/M was the phase of the cell cycle from which cells apoptosed. AII caused cell rounding, detachment from the growth matrix, and nuclear shrinkage and fragmentation in parallel with biochemical changes. Cycloheximide inhibited AII-induced cell death, indicating that its toxicity requires de novo protein synthesis

Design, synthesis and biological evaluation of a novel series of anthrapyrazoles linked with netropsin-like oligopyrrole carboxamides as anticancer agents

Photograph of the restored Guard House at Fort Supply