Clinical potential of microdystrophin as a surrogate endpoint.

Accelerated approval based on a likely surrogate endpoint can be life-changing for patients suffering from a rare progressive disease with unmet medical need, as it substantially hastens access to potentially lifesaving therapies. In one such example, antisense morpholinos were approved to treat Duchenne muscular dystrophy (DMD) based on measurement of shortened dystrophin in skeletal muscle biopsies as a surrogate biomarker. New, promising therapeutics for DMD include AAV gene therapy to restore another form of dystrophin termed mini- or microdystrophin. AAV-microdystrophins are currently in clinical trials but have yet to be accepted by regulatory agencies as reasonably likely surrogate endpoints. To evaluate microdystrophin expression as a reasonably likely surrogate endpoint for DMD, this review highlights dystrophin biology in the context of functional and clinical benefit to support the argument that microdystrophin proteins have a high probability of providing clinical benefit based on their rational design. Unlike exon-skipping based strategies, the approach of rational design allows for functional capabilities (i.e. quality) of the protein to be maximized with every patient receiving the same optimized microdystrophin. Therefore, the presence of rationally designed microdystrophin in a muscle biopsy is likely to predict clinical benefit and is consequently a strong candidate for a surrogate endpoint analysis to support accelerated approval.

Online Rehabilitation Protocols for Medial Patellofemoral Ligament Reconstruction With and Without Tibial Tubercle Osteotomy Are Variable Among Institutions.

PURPOSE: To compare and contrast the various rehabilitation protocols for medial patellofemoral ligament (MPFL) reconstruction and MPFL reconstruction plus tibial tubercle osteotomy (TTO) published online by academic orthopaedic surgery residency programs and private practice institutions throughout the United States. METHODS: We performed a systematic electronic search of MPFL reconstruction rehabilitation protocols in academic orthopaedic surgery residency programs in the United States using Google's search engine (www.google.com) based on the Fellowship and Residency Electronic Interactive Database Access System (FREIDA). Private practice organizations publishing MPFL reconstruction or MPFL reconstruction-TTO rehabilitation protocols that were found on the first page of search results were also included, but no comprehensive search for private practice protocols was performed. Protocols specifying an MPFL reconstruction with TTO were included for separate review because of altered weight-bearing status postoperatively. A list of comparative criteria was created to assess the protocols for the presence and timing of the various rehabilitation components. RESULTS: From the list of 189 U.S. academic residency programs, as well as additional private practice protocols found in the Google search, 38 protocols were included for review (31 protocols for isolated MPFL reconstruction and 7 protocols for MPFL reconstruction plus TTO). A return to full range of motion by week 6 was recommended by 15 (48.4%) of the isolated MPFL reconstruction protocols and 6 (85.7%) of the MPFL reconstruction-TTO protocols. Six weeks of knee brace wear was recommended by 13 isolated MPFL reconstruction protocols (43.3%) and 4 MPFL reconstruction-TTO protocols (57.1%). Moreover, 6 isolated MPFL reconstruction protocols (19.4%) and 3 MPFL reconstruction-TTO protocols (42.9%) recommended use of a patellar stabilizing brace postoperatively. CONCLUSIONS: There is substantial variability among rehabilitation protocols after MPFL reconstruction, as well as MPFL reconstruction plus TTO, including postoperative range of motion, weight-bearing status, and time until return to sport. Furthermore, many online protocols from academic orthopaedic surgery residency programs and private practices in the United States fail to mention several of these parameters, most notably functional testing to allow patients to return to sport. CLINICAL RELEVANCE: Proper rehabilitation after MPFL reconstruction with or without TTO is an important factor to a patient's postoperative outcome. This study outlines the variability in online rehabilitation protocols after MPFL reconstruction with or without TTO published online by academic residency programs and private practice institutions.

A Review of Online Rehabilitation Protocols Designated for Rotator Cuff Repairs.

PURPOSE: To compare publicly available rehabilitation protocols designated for rotator cuff (RTC) repairs published online by academic residency programs and private practice institutions. METHODS: A systematic electronic search using the Fellowship and Residency Electronic Interactive Database Access System (FREIDA) was performed for RTC repair rehabilitation protocols. Private practice programs with published rehabilitation protocols that were discovered during the Google search were also included for review, but no comprehensive search for private practice protocols was performed. The main exclusion criteria consisted of non-English-language protocols and protocols without any of the time-based components in question. Included protocols were assessed independently based on the specified RTC tear size (small [≤1 cm], medium [1-4 cm], large or massive [≥5 cm], or no mention of size). Protocols were compared based on the inclusion, exclusion, and timing of certain rehabilitation components. RESULTS: A total of 96 rehabilitation protocols were included for review, from 39 academic institutions and 28 private practice programs. Specific instructions for concomitant biceps tenodesis were included in 26 protocols (27.1%). Of the 96 protocols, 88 (91.7%) did not place restrictions on early postoperative passive range of motion (PROM) of the shoulder. Isolated PROM with restrictions on active range of motion was most commonly recommended for the first 4 or 6 weeks postoperatively (80.2%). Use of a sling or immobilizer was most frequently recommended for the first 4 or 6 weeks postoperatively (78.1%). Wide variation was noted in recommendations for returning to resistance strengthening, with the highest incidence being 27 protocols recommending returning at 12 weeks (28.1%); this further varied based on the size of the tear. A total of 21 protocols (21.9%) recommended the use of cryotherapy postoperatively. CONCLUSIONS: Although certain rehabilitation components were common, such as duration of PROM and sling or immobilizer use, a large degree of variation remains among published rehabilitation protocols after RTC repair, and this variability is still seen even when subdividing by the size or severity of the RTC tear. CLINICAL RELEVANCE: Rehabilitation after RTC repair is crucial to patient outcomes. This study summarizes the variability among online rehabilitation protocols for RTC repair in the United States and emphasizes the importance of appropriate rehabilitation after RTC surgery.

Membrane recruitment of nNOSµ in microdystrophin gene transfer to enhance durability.

Several gene transfer clinical trials are currently ongoing with the common aim of delivering a shortened version of dystrophin, termed a microdystrophin, for the treatment of Duchenne muscular dystrophy (DMD). However, one of the main differences between these trials is the microdystrophin protein produced following treatment. Each gene transfer product is based on different selections of dystrophin domain combinations to assemble microdystrophin transgenes that maintain functional dystrophin domains and fit within the packaging limits of an adeno-associated virus (AAV) vector. While domains involved in mechanical function, such as the actin-binding domain and ß-dystroglycan binding domain, have been identified for many years and included in microdystrophin constructs, more recently the neuronal nitric oxide synthase (nNOS) domain has also been identified due to its role in enhancing nNOS membrane localization. As nNOS membrane localization has been established as an important requirement for prevention of functional ischemia in skeletal muscle, inclusion of the nNOS domain into a microdystrophin construct represents an important consideration. The aim of this mini review is to highlight what is currently known about the nNOS domain of dystrophin and to describe potential implications of this domain in a microdystrophin gene transfer clinical trial.

CysLT1 receptor antagonists pranlukast and zafirlukast inhibit LRRC8-mediated volume regulated anion channels independently of the receptor.

Volume-regulated anion channels (VRACs) encoded by the leucine-rich repeat containing 8 (LRRC8) gene family play critical roles in myriad cellular processes and might represent druggable targets. The dearth of pharmacological compounds available for studying VRAC physiology led us to perform a high-throughput screen of 1,184 of US Food and Drug Administration-approved drugs for novel VRAC modulators. We discovered the cysteinyl leukotriene receptor 1 (CysLT1R) antagonist, pranlukast, as a novel inhibitor of endogenous VRAC expressed in human embryonic kidney 293 (HEK293) cells. Pranlukast inhibits VRAC voltage-independently, reversibly, and dose-dependently with a maximal efficacy of only ~50%. The CysLT1R pathway has been implicated in activation of VRAC in other cell types, prompting us to test whether pranlukast requires the CysLT1R for inhibition of VRAC. Quantitative PCR analysis demonstrated that CYSLTR1 mRNA is virtually undetectable in HEK293 cells. Furthermore, the CysLT1R agonist leukotriene D4 had no effect on VRAC activity and failed to stimulate Gq-coupled receptor signaling. Heterologous expression of the CysLT1R reconstituted LTD4-CysLT1R- Gq-calcium signaling in HEK293 cells but had no effect on VRAC inhibition by pranlukast. Finally, we show the CysLT1R antagonist zafirlukast inhibits VRAC with an IC50 of ~17 µM and does so with full efficacy. Our data suggest that both pranlukast and zafirlukast are likely direct channel inhibitors that work independently of the CysLT1R. This study provides clarifying insights into the putative role of leukotriene signaling in modulation of VRAC and identifies two new chemical scaffolds that can be used for development of more potent and specific VRAC inhibitors.