Functional benefit of CRISPR-Cas9-induced allele deletion for RYR1 dominant mutation.

More than 700 pathogenic or probably pathogenic variations have been identified in the RYR1 gene causing various myopathies collectively known as "RYR1-related myopathies." There is no treatment for these myopathies, and gene therapy stands out as one of the most promising approaches. In the context of a dominant form of central core disease due to a RYR1 mutation, we aimed at showing the functional benefit of inactivating specifically the mutated RYR1 allele by guiding CRISPR-Cas9 cleavages onto frequent single-nucleotide polymorphisms (SNPs) segregating on the same chromosome. Whole-genome sequencing was used to pinpoint SNPs localized on the mutant RYR1 allele and identified specific CRISPR-Cas9 guide RNAs. Lentiviruses encoding these guide RNAs and the SpCas9 nuclease were used to transduce immortalized patient myoblasts, inducing the specific deletion of the mutant RYR1 allele. The efficiency of the deletion was assessed at DNA and RNA levels, and at the functional level after monitoring calcium release induced by the stimulation of the RyR1-channel. This study provides in cellulo proof of concept regarding the benefits of mutant RYR1 allele deletion, in the case of a dominant RYR1 mutation, from both a molecular and functional perspective, and could apply potentially to 20% of all patients with a RYR1 mutation.

Gene therapies for RyR1-related myopathies.

Myopathies related to variations in the RYR1 gene are genetic diseases for which the therapeutic options are sparse, in part because of the very large size of the gene and protein, and of the distribution of variations all along the sequence. Taking advantage of the progress made in the gene therapy field, different approaches can be applied to the different genetic variations, either at the mRNA level or directly at the DNA level, specifically with the new gene editing tools. Some of those have already been tested in cellulo and/or in vivo, and for the development of the most innovative gene editing technology, inspiration can be sought in other genetic diseases.

Huntingtin regulates calcium fluxes in skeletal muscle.

The expression of the Huntingtin protein, well known for its involvement in the neurodegenerative Huntington's disease, has been confirmed in skeletal muscle. The impact of HTT deficiency was studied in human skeletal muscle cell lines and in a mouse model with inducible and muscle-specific HTT deletion. Characterization of calcium fluxes in the knock-out cell lines demonstrated a reduction in excitation-contraction (EC) coupling, related to an alteration in the coupling between the dihydropyridine receptor and the ryanodine receptor, and an increase in the amount of calcium stored within the sarcoplasmic reticulum, linked to the hyperactivity of store-operated calcium entry (SOCE). Immunoprecipitation experiments demonstrated an association of HTT with junctophilin 1 (JPH1) and stromal interaction molecule 1 (STIM1), both providing clues on the functional effects of HTT deletion on calcium fluxes. Characterization of muscle strength and muscle anatomy of the muscle-specific HTT-KO mice demonstrated that HTT deletion induced moderate muscle weakness and mild muscle atrophy associated with histological abnormalities, similar to the phenotype observed in tubular aggregate myopathy. Altogether, this study points toward the hypotheses of the involvement of HTT in EC coupling via its interaction with JPH1, and on SOCE via its interaction with JPH1 and/or STIM1.

Dysthyroidism during immune checkpoint inhibitors is associated with improved overall survival in adult cancers: data mining of 1385 electronic patient records.

BACKGROUND: Dysthyroidism (DT) is a common toxicity of immune checkpoint inhibitors (ICIs) and prior work suggests that dysthyroidism (DT) might be associated with ICI efficacy. PATIENTS AND METHODS: ConSoRe, a new generation data mining solution, was used in this retrospective study, to extract data from electronic patient records of adult cancer patients treated with ICI at Institut Paoli-Calmettes (Marseille, France). Every DT was verified and only ICI-induced DT was retained. Survival analyses were performed by Kaplan-Meier method (log-rank test) and Cox model. To account for immortal time bias, a conditional landmark analysis was performed (2 months and 6 months), together with a time-varying Cox model. RESULTS: Data extraction identified 1385 patients treated with ICI between 2011 and 2021. DT was associated with improved overall survival (OS) (HR 0.46, (95% CI 0.33 to 0.65), p<0.001), with a median OS of 35.3 months in DT group vs 15.4 months in non-DT group (NDT). Survival impact of DT was consistent using a 6-month landmark analysis with a median OS of 36.7 months (95% CI 29.4 to not reported) in the DT group vs 25.5 months (95% CI 22.8 to 27.8) in the NDT group. In multivariate analysis, DT was independently associated with improved OS (HR 0.49, 95% CI 0.35 to 0.69, p=0.001). After adjustment in time-varying Cox model, this association remained significant (adjusted HR 0.64, 95% CI 0.45 to 0.90, p=0.010). Moreover, patients with DT and additional immune-related adverse event had increased OS compared with patients with isolated DT, with median OS of 38.8 months vs 21.4 months, respectively. CONCLUSION: Data mining identified a large number of patients with ICI-induced DT, which was associated with improved OS accounting for immortal time bias.

Therapies for RYR1-Related Myopathies: Where We Stand and the Perspectives.

RyR1-related myopathies are a family of genetic neuromuscular diseases due to mutations in the RYR1 gene. No treatment exists for any of these myopathies today, which could change in the coming years with the growing number of studies dedicated to the pre-clinical assessment of various approaches, from pharmacological to gene therapy strategies, using the numerous models developed up to now. In addition, the first clinical trials for these rare diseases have just been completed or are being launched. We review the most recent results obtained for the treatment of RyR1-related myopathies, and, in view of the progress in therapeutic development for other myopathies, we discuss the possible future therapeutic perspectives for RyR1-related myopathies.

Development of Knock-Out Muscle Cell Lines using Lentivirus-Mediated CRISPR/Cas9 Gene Editing.

One important application of clustered regulatory interspaced short palindromic repeats (CRISPR)/Cas 9 is the development of knock-out cell lines, specifically to study the function of new genes/proteins associated with a disease, identified during the genetic diagnosis. For the development of such cell lines, two major issues have to be untangled: insertion of the CRISPR tools (the Cas9 and the guide RNA) with high efficiency into the chosen cells, and restriction of the Cas9 activity to the specific deletion of the chosen gene. The protocol described here is dedicated to the insertion of the CRISPR tools in difficult to transfect cells, such as muscle cells. This protocol is based on the use of lentiviruses, produced with plasmids publicly available, for which all the cloning steps are described to target a gene of interest. The control of Cas9 activity has been performed using an adaptation of a previously described system called KamiCas9, in which the transduction of the cells with a lentivirus encoding a guide RNA targeting the Cas9 allows the progressive abolition of Cas9 expression. This protocol has been applied to the development of a RYR1-knock out human muscle cell line, which has been further characterized at the protein and functional level, to confirm the knockout of this important calcium channel involved in muscle intracellular calcium release and in excitation-contraction coupling. The procedure described here can easily be applied to other genes in muscle cells or in other difficult to transfect cells and produce valuable tools to study these genes in human cells.

Cabazitaxel activity in men with metastatic castration-resistant prostate cancer with and without DNA damage repair defects.

BACKGROUND: Cabazitaxel was shown to improve overall survival (OS) in patients with metastatic castration-resistant prostate cancer (mCRPC) after abiraterone/enzalutamine and docetaxel failure, though benefit by the presence of DNA damage repair (DDR) defects is unknown. With the advent of poly(adenosine diphosphate-ribose) polymerase inhibitors (PARPi) in partially overlapping indications with cabazitaxel, we aimed to determine cabazitaxel activity in men with mCRPC according to their DDR status. METHODS: This is a retrospective multicenter study that enrolled patients with mCRPC treated with cabazitaxel who had undergone DDR tumour tissue profiling. Patients with at least one deleterious germline or somatic alterations were considered DDR positive (DDR+). Each DDR + patient has been matched with a DDR negative (DDR-) from the same institution who underwent the same test. An exploratory cohort of patients found to be DDR + by liquid biopsy was also included. Prostate specific antigen (PSA) decline≥50% (PSA50), PSA progression-free survival (PFS, PSA-PFS), radiographic PFS (rPFS), clinical PFS or radiographic PFS (c/rPFS) and OS were evaluated. RESULTS: Among 190 men (95 DDR+, 95 DDR-) with tissue sequencing, PSA50 was achieved with cabazitaxel in 29/92 (32%) and 33/92 (36%) in patients with DDR+ and DDR- (P = 0.64). The median rPFS was 5.33 months [95%CI 4.34-7.04] versus 5.75 months [95%CI 4.67-7.27] (P = 0.55). The median OS was 15.4 months [95%CI 12.16-26.6] and 11.5 months [95%CI 9.76-14.4] (P = 0.036), respectively. No PSA50 responses on cabazitaxel were observed in BRCA1/2 patients previously treated with PARPi (n = 10). Similar outcomes with cabazitaxel were observed in the liquid biopsy cohort (n = 63 DDR+). CONCLUSIONS: Our study suggests that cabazitaxel is active in patients with mCRPC regardless of their DDR status, although its activity in men pretreated with a PARPi may be lower.

In vivo RyR1 reduction in muscle triggers a core-like myopathy.

Mutations in the RYR1 gene, encoding the skeletal muscle calcium channel RyR1, lead to congenital myopathies, through expression of a channel with abnormal permeability and/or in reduced amount, but the direct functional whole organism consequences of exclusive reduction in RyR1 amount have never been studied. We have developed and characterized a mouse model with inducible muscle specific RYR1 deletion. Tamoxifen-induced recombination in the RYR1 gene at adult age resulted in a progressive reduction in the protein amount reaching a stable level of 50% of the initial amount, and was associated with a progressive muscle weakness and atrophy. Measurement of calcium fluxes in isolated muscle fibers demonstrated a reduction in the amplitude of RyR1-related calcium release mirroring the reduction in the protein amount. Alterations in the muscle structure were observed, with fibers atrophy, abnormal mitochondria distribution and membrane remodeling. An increase in the expression level of many proteins was observed, as well as an inhibition of the autophagy process. This model demonstrates that RyR1 reduction is sufficient to recapitulate most features of Central Core Disease, and accordingly similar alterations were observed in muscle biopsies from Dusty Core Disease patients (a subtype of Central Core Disease), pointing to common pathophysiological mechanisms related to RyR1 reduction.