Optimization of Pediatric Rheumatology Therapeutics

Metabolomic Profiling Identifies Exogenous and Microbiota-Derived Metabolites as Markers of Methotrexate Efficacy in Juvenile Idiopathic Arthritis

Variability in methotrexate (MTX) efficacy represents a barrier to early and effective disease control in the treatment of juvenile idiopathic arthritis (JIA). This work seeks to understand the impact of MTX on the plasma metabolome and to identify metabolic biomarkers of MTX efficacy in a prospective cohort of children with JIA. Plasma samples from a cohort of children with JIA (n = 30) collected prior to the initiation of MTX and after 3 months of therapy were analyzed using a semi-targeted global metabolomic platform detecting 673 metabolites across a diversity of biochemical classes. Disease activity was measured using the 71-joint count juvenile arthritis disease activity score (JADAS-71) and clinical response to MTX was based on achievement of ACR Pedi 70 response. Metabolomic analysis identified 50 metabolites from diverse biochemical classes that were altered following the initiation of MTX (p < 0.05) with 15 metabolites reaching a false-discovery rate adjusted p-value (q-value) of less than 0.05. Enrichment analysis identified a class-wide reduction in unsaturated triglycerides following initiation of MTX (q = 0.0009). Twelve of the identified metabolites were significantly associated with disease activity by JADAS-71. Reductions in three metabolites were found to be associated with clinical response by ACR Pedi 70 response criteria and represented several microbiota and exogenously derived metabolites including: dehydrocholic acid, biotin, and 4-picoline. These findings support diverse metabolic changes following initiation of MTX in children with JIA and identify metabolites associated with microbial metabolism and exogenous sources associated with MTX efficacy.

Cytokine Biomarkers of Disease Activity and Therapeutic Response after Initiating Methotrexate Therapy in Patients with Juvenile Idiopathic Arthritis

STUDY OBJECTIVE

To evaluate the relationship between plasma cytokine levels with disease activity and therapeutic response in patients with juvenile idiopathic arthritis (JIA) after initiating methotrexate (MTX) therapy.

DESIGN

Single-center observational prospective cohort study.

SETTING

Outpatient pediatric rheumatology clinic at a tertiary care academic pediatric hospital.

PATIENTS

The study included 61 patients diagnosed with JIA who started therapy with standard-dose MTX 15 mg/m² /week. At 3 months, treating physicians were given the option of maintaining the MTX dose, increasing the MTX dose, or adding etanercept (ETN), based on their clinical judgment.

MEASUREMENTS AND MAIN RESULTS

Patients were evaluated at baseline, 3 months (51 patients), and 6 months (35 patients). Plasma samples from each visit were analyzed for interleukin (IL)-1α, IL-1β, IL-1Ra, IL-6, and tumor necrosis factor-α (TNF-α). Cytokine concentrations were evaluated for relationships with disease activity using the 71-joint count Juvenile Arthritis Disease Activity Score (JADAS). Therapeutic response was assessed by changes in JADAS. Failure to respond to standard-dose MTX was defined as the need for the addition of ETN or a MTX dose increase at or before the 3-month visit. Increased disease severity at baseline was associated with increased IL-6 (p=0.01) and TNF-α (p=0.008) levels. Initiation of MTX was associated with reductions in IL-1α (p=0.009), IL-1β (p=0.01), IL-1Ra (p=0.007), and IL-6 (p=0.03) levels; however, reductions in JADAS were only associated with reductions in IL-6 (p=0.009) and TNF-α levels (p=0.02). Compared with responders, patients failing to respond to standard-dose MTX had increased TNF-α levels at baseline (p=0.02) and at 3 months (p=0.005). Reductions in JADAS by 6 months were observed following either the addition of ETN (p=0.009) or an increase in MTX dose (p=0.007), but the addition of ETN was associated with a median 7-fold increase in TNF-α levels (p=0.003) that corresponded with clinical response.

CONCLUSION

Plasma cytokine levels were responsive to MTX therapy in patients with JIA, but only TNF-α and IL-6 levels were consistently associated with disease activity and therapeutic response. Increased TNF-α levels at baseline were associated with failure to respond to standard-dose MTX and the need for more aggressive drug therapy. Initiation of ETN resulted in increased TNF-α levels that corresponded with therapeutic response, suggesting a potential clinical benefit of monitoring TNF-α levels as a pharmacodynamic marker of etanercept activity.

Nicotinamide Phosphoribosyltransferase Attenuates Methotrexate Response in Juvenile Idiopathic Arthritis and In Vitro

Variability in response to methotrexate (MTX) in the treatment of juvenile idiopathic arthritis (JIA) remains unpredictable and poorly understood. Based on previous studies implicating an interaction between nicotinamide phosphoribosyltransferase (NAMPT) expression and MTX therapy in inflammatory arthritis, we hypothesized that increased NAMPT expression would be associated with reduced therapeutic response to MTX in patients with JIA. A significant association was found between increased plasma concentrations of NAMPT and reduced therapeutic response in patients with JIA treated with MTX. Inhibition of NAMPT in cell culture by either siRNA‐based gene silencing or pharmacological inhibition with FK‐866 was found to result in a fourfold increase in the pharmacological activity of MTX. Collectively, these findings provide evidence that NAMPT inhibits the pharmacological activity of MTX and may represent a predictive biomarker of response, as well as a therapeutic target, in the treatment of JIA with MTX.

Genetic determinants for methotrexate response in juvenile idiopathic arthritis

Juvenile idiopathic arthritis (JIAs) is the most common chronic rheumatic disease of childhood and is an important cause of disability. The folic acid analog methotrexate is the first choice disease-modifying anti-rheumatic drug in this disease, however, 35–45% of patients fail to respond. Molecular elements, such as variants in genes of pharmacological relevance, influencing response to methotrexate in JIA, would be important to individualize treatment strategies. Several studies have evaluated the effects of candidate genetic variants in the complex pathway of genes involved in methotrexate pharmacodynamics and pharmacokinetics, however, results are still contrasting and no definitive genetic marker of methotrexate response useful for the clinician to tailor therapy of children with JIA has been identified. Recently, genome-wide approaches have been applied, identifying new potential biological processes involved in methotrexate response in JIA such as TGF-beta signaling and calcium channels. If these genomic results are properly validated and integrated with innovative analyses comprising deep sequencing, epigenetics, and pharmacokinetics, they will greatly contribute to personalize therapy with methotrexate in children with JIA.

5-Aminoimidazole-4-carboxamide ribonucleotide-transformylase and inosine-triphosphate-pyrophosphatase genes variants predict remission rate during methotrexate therapy in patients with juvenile idiopathic arthritis

For children with juvenile idiopathic arthritis (JIA) who fail to respond to methotrexate, the delay in identifying the optimal treatment at an early stage of disease can lead to long-term joint damage. Recent studies indicate that relevant variants to predict methotrexate response in JIA are those in 5-aminoimidazole-4-carboxamide ribonucleotide-transformylase (ATIC), inosine-triphosphate-pyrophosphatase (ITPA) and solute-liquid-carrier-19A1 genes. The purpose of the study was, therefore, to explore the role of these candidate genetic factors on methotrexate response in an Italian cohort of children with JIA. Clinical response to methotrexate was evaluated as clinical remission stable for a 6-month period, as ACRPed score and as change in Juvenile Arthritis Disease score. The most relevant SNPs for each gene considered were assayed on patients' DNA. ITPA activity was measured in patients' erythrocytes. Sixty-nine patients with JIA were analyzed: 52.2 % responded to therapy (ACRPed70 score), while 37.7 % reached clinical remission stable for 6 months. ATIC rs2372536 GG genotype was associated with improved clinical remission (adjusted p value = 0.0090). For ITPA, rs1127354 A variant was associated with reduced clinical remission: (adjusted p value = 0.028); this association was present even for patients with wild-type ITPA and low ITPA activity. These preliminary results indicate that genotyping of ATIC rs2372536 and ITPA rs1127354 variants or measuring ITPA activity could be useful to predict methotrexate response in children with JIA after validation by further prospective studies on a larger patient cohort.

Therapeutic advancements in juvenile idiopathic arthritis

The treatment of juvenile idiopathic arthritis (JIA) has substantially evolved over the past two decades. Research has been conducted and is ongoing on how therapies can best be utilized either as monotherapy or in combination for enhanced efficacy. The introduction of biologic therapies that selectively target specific cytokines has changed the acceptable clinical course of childhood arthritis. In addition to the development and utilization of new therapeutic agents, the pediatric rheumatology community has made vital progress toward defining disease activity, developing validated outcome measures, and establishing collaborative networks to assess both clinical outcomes and the long-term side effects related to therapeutics for juvenile arthritis. In this chapter, we will discuss the therapeutic evolution in JIA over the past two decades. Although the largest strides have been made with biologic agents, and these newer drugs have more rigorous data to support their use, select commonly used non-biologic therapies are included, with the discussion focused on more recent updated literature.

Pediatric perspective on pharmacogenomics

The advances in high-throughput genomic technologies have improved the understanding of disease pathophysiology and have allowed a better characterization of drug response and toxicity based on individual genetic make up. Pharmacogenomics is being recognized as a valid approach used to identify patients who are more likely to respond to medication, or those in whom there is a high probability of developing severe adverse drug reactions. An increasing number of pharmacogenomic studies are being published, most include only adults. A few studies have shown the impact of pharmacogenomics in pediatrics, highlighting a key difference between children and adults, which is the contribution of developmental changes to therapeutic responses across different age groups. This review focuses on pharmacogenomic research in pediatrics, providing examples from common pediatric conditions and emphasizing their developmental context.

Pharmacogenomics and pharmacoepigenomics in pediatric medicine

In the past several years, human genetics studies have progressed from monogenic to complex and common diseases because of the advancement in technologies. There is increased knowledge of the pharmacokinetics and pharmacogenomics of the drugs in adults as well as in children. These technological developments provided new diagnostic, prognostic, and therapeutic opportunities. We are now in a position to address many additional ambitious questions. For instance, in clinical medicine, interindividual variation in drug response is a major problem. Some of the heterogeneity of drug safety and efficacy among individuals can be explained by pharmacogenomics. It has also the potential to improve the treatment in both adults and children. In pediatrics however, there is ontogeny and metabolic capacity in children is different compared to adults. Several specific developmental changes may underlie some of the variability in drug response seen in children. They may also be responsible for adverse drug reactions (ADRs). Therefore, much of the diversity in drug effects cannot be explained by studying the genomic diversity alone. It is necessary to include the effect of growth (involves variations in gene expression) along with genetic differences when explaining the variability in treatment response. In this respect epigenomics may expand the scope of pharmacogenomics towards optimization of drug therapy. Future studies must focus on periods of maturation of the drug-metabolizing enzymes and polymorphisms in their genes by using candidate gene approach, gene expression analysis, genome-wide haplotype mapping, and proteomics. The integration of genetic data and clinical phenotypes along with the role of other factors is necessary to evaluate both efficacy and ADRs of any drug. It may require extensive genetic epidemiological studies spanning over many years.

Pharmacogenomics in pediatric rheumatology

PURPOSE OF REVIEW

Despite major advancements in therapeutics, variability in drug response remains a challenge in both adults and children diagnosed with rheumatic disease. The genetic contribution to interindividual variability has emerged as a promising avenue of exploration; however, challenges remain in making this knowledge relevant in the clinical realm.

RECENT FINDINGS

New genetic associations in patients with rheumatic disease have been reported for disease modifying antirheumatic drugs, antimetabolites and biologic drugs. However, many of these findings are in need of replication, and few have taken into account the concept of ontogeny, specific to pediatrics.

SUMMARY

In the current era in which we practice, genetic variation will undoubtedly contribute to variability in therapeutic response and may be a factor that will ultimately impact individualized care. However, preliminary studies have shown that there are many hurdles that need to be overcome as we explore pharmacogenomic associations specifically in the field of pediatric rheumatology.