Synergistic Effect of a Combination of Proteasome and Ribonucleotide Reductase Inhibitors in a Biochemical Model of the Yeast Saccharomyces cerevisiae and a Glioblastoma Cell Line

Proteasome inhibitors are used in the therapy of several cancers, and clinical trials are underway for their use in the treatment of glioblastoma (GBM). However, GBM becomes resistant to chemotherapy relatively rapidly. Recently, the overexpression of ribonucleotide reductase (RNR) genes was found to mediate therapy resistance in GBM. The use of combinations of chemotherapeutic agents is considered a promising direction in cancer therapy. The present work aimed to evaluate the efficacy of the combination of proteasome and RNR inhibitors in yeast and GBM cell models. We have shown that impaired proteasome function results in increased levels of RNR subunits and increased enzyme activity in yeast. Co-administration of the proteasome inhibitor bortezomib and the RNR inhibitor hydroxyurea was found to significantly reduce the growth rate of S. cerevisiae yeast. Accordingly, the combination of bortezomib and another RNR inhibitor gemcitabine reduced the survival of DBTRG-05MG compared to the HEK293 cell line. Thus, yeast can be used as a simple model to evaluate the efficacy of combinations of proteasome and RNR inhibitors.

Complete and Prolonged Inhibition of Herpes Simplex Virus Type 1 Infection In Vitro by CRISPR/Cas9 and CRISPR/CasX Systems

Almost all people become infected with herpes viruses, including herpes simplex virus type 1 (HSV-1), during their lifetime. Typically, these viruses persist in a latent form that is resistant to all available antiviral medications. Under certain conditions, such as immunosuppression, the latent forms reactivate and cause disease. Moreover, strains of herpesviruses that are drug-resistant have rapidly emerged. Therefore, it is important to develop alternative methods capable of eradicating herpesvirus infections. One promising direction is the development of CRISPR/Cas systems for the therapy of herpesvirus infections. We aimed to design a CRISPR/Cas system for relatively effective long-term and safe control of HSV-1 infection. Here, we show that plasmids encoding the CRISPR/Cas9 system from Streptococcus pyogenes with a single sgRNA targeting the UL30 gene can completely suppress HSV-1 infection of the Vero cell line within 6 days and provide substantial protection within 9 days. For the first time, we show that CRISPR/CasX from Deltaproteobacteria with a single guide RNA against UL30 almost completely suppresses HSV-1 infection of the Vero cell line for 3 days and provides substantial protection for 6 days. We also found that the Cas9 protein without sgRNAs attenuates HSV-1 infection. Our results show that the developed CRISPR/Cas systems are promising therapeutic approaches to control HSV-1 infections.

[A Test System for Assessment of the Activity of Mutant Cas9 Variants in Saccharomyces cerevisiae]

The key component of the revolutionary Streptococcus pyogenes CRISPR/Cas genome editing technology is the multidomain protein Cas9. However, the specificity of wild type Cas9 is not sufficiently high for editing large genomes of higher eukaryotes, which limits the realization of the potential of genomic editing both in fundamental investigations and in the therapy of genetic diseases. The main way to obtain more specific variants of Cas9 is through mutagenesis followed by characterization of mutant proteins in in vitro or in vivo test systems. The in vitro and some in vivo test systems described in the literature are often labor-intensive and have scaling limitations, which makes it challenging to screen SpCas9 mutant variant libraries. In order to develop a simple method for high-throughput screening of Cas9 mutants in vivo, we characterized three test systems using CRISPR/Cas9-mediated inactivation of the reporter genes, tsPurple, ADE2, and URA3, in the Saccharomyces cerevisiae yeast as a model subject. We measured the activities of high-precision forms of Cas9, evoCas9, and HiFiCas9, and compared them with the wild-type form. ADE2 gene inactivation was found to be the most valid method for the evaluation of Cas9 activity. In the test-system developed, the sensitivity to chromatin structure was demonstrated for the high-fidelity variant of Cas9, HiFiCas9. The proposed test-system can be used for the development of new generation genome editors.