Anti-rasburicase antibodies induce clinical refractoriness by inhibiting the enzyme catalytic activity

Use of rasburicase to improve kidney function in children with hyperuricemia and acute kidney injury

BACKGROUND

Hyperuricemia contributes to decrease in kidney function and induces additional renal damage in children with acute kidney injury (AKI). Rasburicase oxidizes uric acid (UA), decreasing its serum quantities in less than 24 h.

METHODS

This is a retrospective study involving hospitalized patients under 18 years of age with underlying pathology diagnosed with AKI and severe hyperuricemia treated with rasburicase over a 4-year period.

RESULTS

We describe 15 patients from 4 days of life to 18 years (median: 4.4 years). Seventy-three percent had known underlying pathologies. All presented worsening of basal renal function or AKI data. All received the usual medical treatment for AKI without response. Twenty percent received an extrarenal depuration technique. All had hyperuricemia with a mean (± SD) of 13.1 (± 2.19) mg/dl. After rasburicase administration UA levels fell to a mean (± SD) of 0.76 (± 0.62) mg/dl (p < 0.001) in less than 24 h. In parallel, a decrease in the mean plasma creatinine was observed (2.92 mg/dl to 1.93 mg/dl (p = 0.057)) together with a significant improvement of the mean glomerular filtration rate (16.3 ml/min/1.73 m2 to 78.6 ml/min/1.73 m2) (p = 0.001)). No side effects were recorded. Kidney function normalized in all cases or returned to baseline levels.

CONCLUSIONS

Although the use of rasburicase is not routinely approved in pediatric patients with severe hyperuricemia and AKI, it has been used successfully without complications, and helped prevent progressive kidney damage. This study could serve as a basis for suggesting the off-label use of rasburicase for the management of complex pediatric patients in whom UA plays an important role in the development of AKI.

Pegloticase efficacy and safety in kidney transplant recipients; results of the phase IV, open-label PROTECT clinical trial

INTRODUCTION

Kidney transplant (KT) recipients have a high prevalence and severity of gout. Pegloticase (pegylated recombinant uricase) rapidly metabolizes serum uric acid (sUA), and its efficacy is not impacted by kidney function.

METHODS

This open-label, Phase 4 trial (PROTECT NCT04087720) examined safety and efficacy of pegloticase in 20 participants with KT > 1 year prior to enrollment and with uncontrolled gout (sUA ≥7 mg/dL, intolerance/inefficacy to urate lowering therapy, and ≥1 of the following: tophi, chronic gouty arthritis, ≥2 flares in past year) and functioning KT (estimated glomerular filtration rate [eGFR] ≥15 mL/min/1.73 m2 ) on stable immunosuppression therapy.

RESULTS

The primary endpoint was sUA response during month 6 (sUA < 6 mg/dL for ≥80% of time). The study enrolled 20 participants (mean ± SD); age: 53.9 ± 10.9 years, time since KT: 14.7 ± 6.9 years, sUA: 9.4 ± 1.5 mg/dL, gout duration: 8.4 ± 11.6 years; all on ≥2 stable doses of immunosuppression agents. Pegloticase (8 mg intravenous every 2 weeks) in KT recipients with uncontrolled gout showed a high response rate of 89% (16/18 responders). Two participants discontinued treatment solely due to COVID-19 concerns prior to month 6 were not included in the primary analysis. Pegloticase exposures were higher than those historically observed with pegloticase monotherapy, and no anaphylaxis or infusion reaction events occurred during the study.

CONCLUSIONS

This improved response rate to pegloticase in the KT population reflects observations from other trials and reports on immunomodulation with pegloticase. As the KT population has a high prevalence of gout and limitations with oral urate lowering medication options, these findings suggest a potential option for uncontrolled gout therapy in KT participants.

A Randomized, Placebo-Controlled Study of Methotrexate to Increase Response Rates in Patients with Uncontrolled Gout Receiving Pegloticase: Primary Efficacy and Safety Findings

OBJECTIVE

To assess efficacy, safety, pharmacokinetics, and immunogenicity of pegloticase plus methotrexate (MTX) versus pegloticase plus placebo cotreatment for uncontrolled gout in a randomized, placebo-controlled, double-blind trial.

METHODS

This study included adults with uncontrolled gout, defined as serum urate ≥7 mg/dl, oral urate-lowering therapy failure or intolerance, and presence of ongoing gout symptoms including ≥1 tophus, ≥2 flares in the past 12 months, or gouty arthritis. Key exclusion criteria included MTX contraindication, current immunosuppressant use, G6PDH deficiency, and estimated glomerular filtration rate <40 ml/minute/1.73 m² . Patients were randomized 2:1 to 52 weeks of pegloticase (8 mg biweekly) with either oral MTX (15 mg/week) or placebo. The primary end point was the proportion of treatment responders during month 6 (defined as serum urate <6 mg/dl for ≥80% of visits during weeks 20-24). Efficacy was evaluated in all randomized patients (intent-to-treat population), and safety was evaluated in all patients receiving ≥1 blinded MTX or placebo dose.

RESULTS

A total of 152 patients were randomized, 100 to receive pegloticase plus MTX, 52 to receive pegloticase plus placebo. Significantly higher treatment response occurred during month 6 in the MTX group versus the placebo group (71.0% [71 of 100 patients] versus 38.5% [20 of 52 patients], respectively; between-group difference 32.3% [95% confidence interval 16.3%, 48.3%]) (P < 0.0001 for between-group difference). During the first 6 months of pegloticase plus MTX or pegloticase plus placebo treatment, 78 (81.3%) of 96 MTX patients versus 47 (95.9%) of 49 placebo patients experienced ≥1 adverse event (AE), most commonly gout flare (64 [66.7%] of 96 MTX patients and 34 [69.4%] of 49 placebo patients). Reports of AEs and serious AEs were comparable between groups, but the infusion reaction rate was considerably lower with MTX cotherapy (4.2% [4 of 96 MTX patients, including 1 patient who had anaphylaxis]) than with placebo cotherapy (30.6% [15 of 49 placebo patients, 0 who had anaphylaxis]) (P < 0.001). Antidrug antibody positivity was also lower in the MTX group.

CONCLUSION

MTX cotherapy markedly increased pegloticase response rate over placebo (71.0% versus 38.5%) during month 6 with no new safety signals. These findings verify higher treatment response rate, lower infusion reaction incidence, and lower immunogenicity when pegloticase is coadministered with MTX.

Enhancing the Response Rate to Recombinant Uricases in Patients with Gout

Refractory, or uncontrolled, gout is a chronic, progressive, inflammatory arthropathy resulting from continued urate deposition after failed attempts to lower serum uric acid below the therapeutic threshold with oral urate-lowering therapies such as allopurinol and febuxostat. Recombinant uricase is increasingly being used to treat refractory gout; however, the immunogenicity of uricase-based therapies has limited the use of these biologic therapies. Antidrug antibodies against biologic therapies, including uricase and PEGylated uricase, can lead to loss of urate-lowering response, increased risk of infusion reactions, and subsequent treatment failure. However, co-therapy with an immunomodulator can attenuate antidrug antibody development, potentially increasing the likelihood of sustained urate lowering, therapy course completion, and successful treatment outcomes. This review summarizes evidence surrounding the use of immunomodulation as co-therapy with recombinant uricases.

Enzyme Replacement Therapy for Genetic Disorders Associated with Enzyme Deficiency

Mutations in human genes might lead to loss of functional proteins, causing diseases. Among these genetic disorders, a large class is associated with the deficiency in metabolic enzymes, resulting in both an increase in the concentration of substrates and a loss in the metabolites produced by the catalyzed reactions. The identification of therapeutic actions based on small molecules represents a challenge to medicinal chemists because the target is missing. Alternative approaches are biology-based, ranging from gene and stem cell therapy, CRISPR/Cas9 technology, distinct types of RNAs, and enzyme replacement therapy (ERT). This review will focus on the latter approach that since the 1990s has been successfully applied to cure many rare diseases, most of them being lysosomal storage diseases or metabolic diseases. So far, a dozen enzymes have been approved by FDA/EMA for lysosome storage disorders and only a few for metabolic diseases. Enzymes for replacement therapy are mainly produced in mammalian cells and some in plant cells and yeasts and are further processed to obtain active, highly bioavailable, less degradable products. Issues still under investigation for the increase in ERT efficacy are the optimization of enzymes interaction with cell membrane and internalization, the reduction in immunogenicity, and the overcoming of blood-brain barrier limitations when neuronal cells need to be targeted. Overall, ERT has demonstrated its efficacy and safety in the treatment of many genetic rare diseases, both saving newborn lives and improving patients' life quality, and represents a very successful example of targeted biologics.