Gene Therapy for Spinal Muscular Atrophy (SMA): A Review of Current Challenges and Safety Considerations for Onasemnogene Abeparvovec (Zolgensma).

Spinal Muscular Atrophy (SMA) is a genetic disease that causes weakness and wasting in the voluntary muscles of infants and children. SMA has been the leading inherited cause of infant death. More specifically, SMA is caused by the absence of the SMN1 gene. In May 2019, the Food and Drug Administration (FDA) approved onasemnogene abeparvovec, SMN1 gene replacement therapy, for all children with SMA younger than two years of age, without end-stage weakness. The objective of the study is to review the safety and efficacy of a novel gene therapy, onasemnogene abeparvovec (Zolgensma), for SMA and assess current challenges for gene therapy. For this, we have conducted a literature search on PubMed, MEDLINE, and Ovid (2019 to 2022) in the English language using the terms SMA, onasemnogene, and gene therapy. The search included articles, websites, and published papers from reputable health organizations, hospitals, and global organizations dedicated to bringing awareness to Spinal Muscular Atrophy. We found the first gene therapy for SMA to be onasemnogene, directly providing the survival motor neuron 1 (SMN1) gene to produce the survival motor neuron (SMN) protein. Onasemnogene is approved by the Food and Drug Administration and has the added benefit of being a one-time dose. On the downside, a major side effect of this treatment is hepatotoxicity. There is substantial evidence that the efficacy of therapy is increased when administered early to children under three months of age. Therefore, we concluded that onasemnogene appears to be an efficacious therapy for younger pediatric patients with SMA type 1. Drug cost and potential hepatotoxicity are major concerns. Long-term benefits and risks have not been determined, but it is more cost-effective and requires less time of treatment compared to the other used drug, nusinersen. Therefore, the combined safety, cost, and effectiveness of onasemnogene abeparvovec make it a reliable treatment option for treating SMA Type 1.

Towards sustainability and affordability of expensive cell and gene therapies? Applying a cost-based pricing model to estimate prices for Libmeldy and Zolgensma.

BACKGROUND AIMS: Drug prices are regarded as one of the most influential factors in determining accessibility and affordability to novel therapies. Cell and gene therapies such as OTL-200 (brand name: Libmeldy) and AVXS-101 (brand name: Zolgensma) with (expected) list prices of 3.0 million EUR and 1.9 million EUR per treatment, respectively, spark a global debate on the affordability of such therapies. The aim of this study was to use a recently published cost-based pricing model to calculate prices for cell and gene therapies, with OTL-200 and AVXS-101 as case study examples. METHODS: Using the pricing model proposed by Uyl-de Groot and Löwenberg, we estimated a price for both therapies. We searched the literature and online public sources to estimate (i) research and development (R&D) expenses adjusted for risk of failure and cost of capital, (ii) the eligible patient population and (iii) costs of drug manufacturing to calculate a base-case price for OTL-200 and AVXS-101. All model input parameters were varied in a stepwise, deterministic sensitivity analysis and scenario analyses to assess their impact on the calculated prices. RESULTS: Prices for OTL-200 and AVXS-101 were estimated at 1 048 138 EUR and 380 444 EUR per treatment, respectively. In deterministic sensitivity analyses, varying R&D estimates had the greatest impact on the price for OTL-200, whereas for AVXS-101, changes in the profit margin changed the calculated price substantially. Highest prices in scenario analyses were achieved when assuming the lowest number of patients for OTL-200 and highest R&D expenses for AVXS-101. The lowest R&D expenses scenario resulted in lowest prices for either therapy. CONCLUSIONS: Our results show that, using the proposed model, prices for both OTL-200 and AVXS-101 lie substantially below the currently (proposed) list prices for both therapies. Nevertheless, the uncertainty of the used model input parameters is considerable, which translates in a wide range of estimated prices. This is mainly because of a lack of transparency from pharmaceutical companies regarding R&D expenses and the costs of drug manufacturing. Simultaneously, the disease indications for both therapies remain heavily understudied in terms of their epidemiological profile. Despite the considerable variation in the estimated prices, our results may support the public debate on value-based and cost-based pricing models, and on "fair" drug prices in general.

Short-term clinical outcomes of onasemnogene abeparvovec treatment for spinal muscular atrophy.

INTRODUCTION: Spinal muscular atrophy (SMA) is a degenerative neuromuscular disorder long recognized as the most common genetic cause of infantile mortality described so far. However, the emergence of some innovative therapies, such as nusinersen and onasemnogene abeparvovec (AVXS-101), have made it possible to change the disease course of SMA. METHODS: In this study, five SMA type 1 and one SMA type 2 patients who received AVXS-101 were enrolled (7-24 months of age when administered). They were all previously treated with nusinersen, 4-5 times including loading doses, but stopped nusinersen maintenance after injection of AVXS-101. Patients were regularly followed up with laboratory tests and functional assessments after administration. RESULTS: Liver enzymes (aspartate aminotransferase, alanine aminotransferase, and gamma-glutamyl transferase) and monocyte count tended to be elevated but normalized after several weeks. Platelets and white blood cells were transiently decreased for a few weeks after injection. Prolonged elevation of liver enzymes was associated with steroid tapering earlier than 1 month post treatment. During the follow-up period (ranging from 5 to 17 months after injection), all patients showed improved motor function and there was no case of mortality or requirement for permanent ventilatory support. For one patient, use of bilevel positive airway pressure could be reduced from 16 h to 8 h a day during sleep at 6 months post treatment. CONCLUSION: Our experience of AVXS-101 treatment has shown that a single intravenous dose could be safe and effective for SMA patients without the need for any maintenance treatment.

Onasemnogene Abeparvovec (AVXS-101) for the Treatment of Spinal Muscular Atrophy.

Spinal muscular atrophy (SMA) is a debilitating disorder characterized by degeneration of large motor neurons. It is a heterogeneous group of disorders caused by a homozygous deletion in the survival motor neuron (SMN) gene on chromosome 5, resulting in a SMN protein deficiency. Small amounts of SMN protein are also produced by the SMN2 gene, which that differs from SMN1 by a single nucleotide. Spinal muscular atrophy types and phenotypic severity depend on the number of variations of the SMN2 gene and the amount of SMN2 protein produced. Because the SMN protein deficiency is the root cause of the disease, treatment strategies for SMA revolve around increasing SMN protein production. Nusinersen (Spinraza, Biogen, Cambridge, MA) was the only treatment option available for SMA until the FDA approved onasemnogene abeparvovec-xioi (Zolgensma, AveXis Inc, Bannockburn, IL), a one-time-administered adeno-associated viral vector-based gene therapy that delivers the SMN gene to the motor neuron cells. Data from clinical studies show significant improvement in motor milestone achievements and ventilator-free survival but are limited by approximately 5 years' worth of results. This one-time intravenous injection of this new gene therapy also bears a hefty price tag; however, it may be more cost effective in the long run versus the multiple intrathecal administrations needed with nusinersen. Drug access and use are hindered by drug cost, payer reimbursement issues, and lack of long-term data from clinical studies. Questions also remain regarding the safety and efficacy of repeated drug administration for patients with advanced disease.

Early Cost-Effectiveness of Onasemnogene Abeparvovec-xioi (Zolgensma) and Nusinersen (Spinraza) Treatment for Spinal Muscular Atrophy I in The Netherlands With Relapse Scenarios.

OBJECTIVES: Onasemnogene Abeparvovec-xioi (AVXS-101) is a gene therapy intended for curative treatment of spinal muscular atrophy (SMA) with an expected price of around €2 000 000. The goal of this study is to perform a cost-effectiveness analysis of treatment of SMA I patients with AVXS-101 in The Netherlands including relapse scenarios. METHODS: An individual-based state-transition model was used to model treatment effect and survival of SMA I patients treated with AVXS-101, nusinersen and best supportive care (BSC). The model included five health states: three health states according to SMA types, one for permanent ventilation and one for death. Deterministic and probabilistic sensitivity analyses were performed. Effects of relapsing to lower health states in the years following treatment was explored. RESULTS: The base-case incremental cost-effectiveness ratio (ICER) for AVXS-101 versus BSC is €138 875/QALY, and €53 447/QALY for AVXS-101 versus nusinersen. If patients relapse within 10 years after treatment with AVXS-101, the ICER can increase up to 6-fold, with effects diminishing thereafter. Only relapses occurring later than 50 years after treatment have a negligible effect on the ICER. To comply with Dutch willingness-to-pay reference values, the price of AVXS-101 must decrease to €680 000. CONCLUSIONS: Based on this model, treatment with AVXS-101 is unlikely to be cost-effective under Dutch willingness-to-pay reference values. Uncertainty regarding the long-term curative properties of AVXS-101 can result in multiplication of the ICER. Decision-makers are advised to appropriately balance these uncertainties against the price they are willing to pay now.

Onasemnogene Abeparvovec-xioi: Gene Therapy for Spinal Muscular Atrophy.

OBJECTIVE: To review the efficacy and safety of onasemnogene abeparvovec-xioi (Zolgensma) in the treatment of spinal muscular atrophy (SMA). DATA SOURCES: An English-language literature search of PubMed, MEDLINE, and Ovid (1946 to December 2019) was completed using the terms onasemnogene, AVXS-101, and spinal muscular atrophy. Manufacturer prescribing information, article bibliographies, and data from ClinicalTrials.gov were incorporated in the reviewed data. STUDY SELECTION/DATA EXTRACTION: All studies registered on ClinicalTrials.gov were incorporated in the reviewed data. DATA SYNTHESIS: Onasemnogene is the first agent for SMA utilizing gene therapy to directly provide survival motor neuron 1 (SMN1) gene to produce SMN protein. Four publications of 1 clinical trial, 1 comparison study of treatment effects, and 1 combination therapy case series have been published. RELEVANCE TO PATIENT CARE AND CLINICAL PRACTICE: Onasemnogene is a one time dose approved by the Food and Drug Administration for SMA patients <2 years old who possess mutations in both copies of the SMN1 gene. CONCLUSION: Onasemnogene appears to be an efficacious therapy for younger pediatric patients with SMA type 1. Concerns include drug cost and potential liver toxicity. Long-term benefits and risks have not been determined.

From Clinical Trials to Clinical Practice: Practical Considerations for Gene Replacement Therapy in SMA Type 1.

Spinal muscular atrophy is a devastating neurodegenerative autosomal recessive disease that results from survival of motor neuron 1 (SMN1) gene mutation or deletion. Patients with spinal muscular atrophy type 1 utilizing supportive care, which focuses on symptom management, never sit unassisted, and 75% die or require permanent ventilation by age 13.6 months. Onasemnogene abeparvovec (Zolgensma, formerly AVXS-101) is a gene replacement therapy comprising an adeno-associated viral vector containing the human SMN gene under control of the chicken beta-actin promoter. This therapy addresses the genetic root cause of the disease by increasing functional SMN protein in motor neurons and preventing neuronal cell death, resulting in improved neuronal and muscular function as previously demonstrated in transgenic animal models. In an open-label, one-arm, dose-escalation phase 1 trial, systemic administration of onasemnogene abeparvovec via a one-time infusion over one hour demonstrated improved motor function and survival in all infants symptomatic for spinal muscular atrophy type 1. Of the 12 patients who received the proposed therapeutic dose, 11 achieved independent sitting, two achieved independent standing, and two are able to walk. Most of these 12 patients remained free of respiratory supportive care. The only treatment-related adverse event observed was transient asymptomatic transaminasemia that resolved with a short course of prednisolone treatment. This review discusses the biological rationale underlying gene replacement therapy for spinal muscular atrophy, describes the onasemnogene abeparvovec clinical trial experience, and provides expert recommendations as a reference for the real-world use of onasemnogene abeparvovec in clinical practice. As of May 24, 2019, the Food and Drug Administration approved onasemnogene abeparvovec, the first gene therapy approved to treat children younger than two years with spinal muscular atrophy.

Impact of Age and Motor Function in a Phase 1/2A Study of Infants With SMA Type 1 Receiving Single-Dose Gene Replacement Therapy.

BACKGROUND: This study characterizes motor function responses after early dosing of AVXS-101 (onasemnogene abeparvovec) in gene replacement therapy in infants with severe spinal muscular atrophy type 1 (SMA1). METHODS: This study is a follow-up analysis of 12 infants with SMA1 who received the proposed therapeutic dose of AVXS-101 in a Phase 1 open-label study (NCT02122952). Infants were grouped according to age at dosing and baseline Children's Hospital of Philadelphia Infant Test of Neuromuscular Disorders scores: (1) early dosing/low motor, dosed age less than three months with scores <20 (n = 3), (2) late dosing, dosed at age three months or greater (n = 6), and (3) early dosing/high motor, dosed age less than three months with scores ≥20 (n = 3). RESULTS: Early dosing/low motor group demonstrated a mean gain of 35.0 points from a mean baseline of 15.7, whereas the late dosing group had a mean gain of 23.3 from a mean baseline of 26.5. The early dosing/high motor group quickly reached a mean score of 60.3, near the scale maximum (64), from a mean baseline of 44.0. Despite a lower baseline motor score, the early dosing/low motor group achieved sitting unassisted earlier than the late dosing group (mean age: 17.0 vs 22.0 months). The early dosing/high motor group reached this milestone earliest (mean age: 9.4 months). CONCLUSIONS: The rapid, significant motor improvements among infants with severe SMA1 treated with AVXS-101 at an early age highlight the importance of newborn screening and early treatment and demonstrate the therapeutic potential of AVXS-101 regardless of baseline motor function.

Cost-effectiveness analysis of using onasemnogene abeparvocec (AVXS-101) in spinal muscular atrophy type 1 patients.

Background: Spinal muscular atrophy type 1 (SMA1) is a devastating genetic disease for which gene-replacement therapy may bring substantial survival and quality of life benefits. Objective: This study investigated the cost-effectiveness of onasemnogene abeparvovec (AVXS-101) gene-replacement therapy for SMA1. Study design: A Markov model was used to estimate the incremental cost-effectiveness ratio (ICER), expressed as cost/quality-adjusted life year ($/QALY), of AVXS-101 versus nusinersen over a lifetime. Survival, healthcare costs and QALYs were estimated using natural history data for SMA patients who achieved motor milestones (sitting/walking). Health utility weights were obtained from the CHERISH trial. Setting: USA; commercial payer perspective Participants: SMA1 infants Interventions: AVXS-101 was compared to nusinersen. Main outcome measure: The primary outcome was the ICER. Results: Expected survival (undiscounted) over a lifetime predicted by the model was 37.20 life years for AVXS-101 and 9.68 for nusinersen (discounted QALYs, 15.65 and 5.29, respectively). Using a potential AVXS-101 price range ($2.5-5.0M/treatment), the average lifetime cost/patient was $4.2-6.6M for AVXS-101 and $6.3M for nusinersen. The ICER range was (-$203,072) to $31,379 per QALY gained for AVXS-101 versus nusinersen, indicating that AVXS-101 was cost-effective with prices of ≤$5M. Conclusion: Single-dose AVXS-101 was cost-effective compared to chronic nusinersen for SMA1 patients.

Survival, Motor Function, and Motor Milestones: Comparison of AVXS-101 Relative to Nusinersen for the Treatment of Infants with Spinal Muscular Atrophy Type 1.

INTRODUCTION: Infants with spinal muscular atrophy (SMA) type 1 typically face a decline in motor function and a severely shortened life expectancy. Clinical trials for SMA type 1 therapies, onasemnogene abeparvovec (AVXS-101) and nusinersen, demonstrated meaningful improvements in efficacy (e.g., overall survival) but there were no head-to-head clinical trials assessing comparative efficacy. This study estimated the treatment effects of AVXS-101 relative to nusinersen for the treatment of SMA type 1. METHODS: Overall survival, event-free survival (no death or need to use permanent assisted ventilation), improvement in motor function [increase of ≥ 4 points in Children's Hospital of Philadelphia Infant Test of Neuromuscular Disorders (CHOP-INTEND) score from baseline], and motor milestone achievements (head control, rolling over, and sitting unassisted) reported in the onasemnogene abeparvovec (AVXS-101-CL-101; NCT02122952) and nusinersen (ENDEAR; NCT02193074) clinical trials were indirectly compared using frequentist and Bayesian approaches. RESULTS: Among symptomatic infants with SMA type 1, the number needed to treat (NNT) to prevent one more death with AVXS-101 instead of nusinersen was 6.2 [95% confidence intervals (CI) = 4.1-12.2], and the probability of preventing death was 20% higher for patients treated with AVXS-101 than nusinersen [risk ratio (RR) = 1.2, 95% CI 1.1-1.3]. For event-free survival, the NNT to prevent one more event was 2.6 (95% CI 2.0-3.6) and RR was 1.6 (95% CI 1.4-1.9). For improvement in motor function, NNT was 3.5 (95% CI 2.6-5.3) and RR was 1.4 (95% CI 1.2-1.6). For milestone achievements, the NNTs were 1.4 (95% CI 1.1-1.9), 1.5 (95% CI 1.1-2.5), and 1.2 (95% CI 1.0-1.5); RRs 4.2 (95% CI 2.6-6.7), 7.8 (95% CI 3.6-17.0), and 11.2 (95% CI 5.1-24.5) for head control, rolling over, and sitting unassisted, respectively. Results were similar using the Bayesian approach. CONCLUSION: This indirect comparison (AVXS-101-CL-101 vs. ENDEAR) among symptomatic SMA type 1 infants suggests that AVXS-101 may have an efficacy advantage relative to nusinersen for overall survival, independence from permanent assisted ventilation, motor function, and motor milestones. FUNDING: AveXis.

Health outcomes in spinal muscular atrophy type 1 following AVXS-101 gene replacement therapy.

BACKGROUND: Spinal Muscular Atrophy type 1 (SMA1) is a rare genetic neuromuscular disease where 75% of SMA1 patients die/require permanent-ventilation by 13.6 months. This study assessed the health outcomes of SMA1 infants treated with AVXS-101 gene replacement therapy. METHODS: Twelve genetically confirmed SMA1 infants with homozygous deletions of the SMN1 gene and two SMN2 gene copies received a one-time intravenous proposed therapeutic dose of AVXS-101 in an open label study conducted between December 2014 and 2017. Patients were followed for 2-years post-treatment for outcomes including (1) pulmonary interventions; (2) nutritional interventions; (3) swallow function; (4) hospitalization rates; and (5) motor function. RESULTS: All 12 patients completed the study. Seven infants did not require noninvasive ventilation (NIV) by study completion. Eleven patients had stable or improved swallow function, demonstrated by the ability to feed orally; 11 patients were able to speak. The mean proportion of time hospitalized was 4.4%; the mean unadjusted annualized hospitalization rate was 2.1 (range = 0, 7.6), with a mean length of stay/hospitalization of 6.7 (range = 3, 12.1) days. Eleven patients achieved full head control and sitting unassisted and two patients were walking independently. CONCLUSIONS: AVXS-101 treatment in SMA1 was associated with reduced pulmonary and nutritional support requirements, improved motor function, and decreased hospitalization rate over the follow-up period. This contrasts with the natural history of progressive respiratory failure and reduced survival. The reduced healthcare utilization could potentially alleviate patient and caregiver burden, suggesting an overall improved quality of life following gene replacement therapy. TRIAL REGISTRATION: ClinicalTrials.gov number, NCT02122952.

American Academy of Neurology - 69th Annual Meeting (April 22-28, 2017 - Boston, Massachusetts, USA).

The Annual Meeting of the American Academy of Neurology (AAN) is the largest conference convening neurology professionals from all over the world to share and discuss the latest breakthroughs in neurology treatment. The conference covers basic scientific research to clinical application through a wide range and interesting programs. This report covers some of the therapeutic highlights presented during the conference.