Psoriasis is an immune-mediated, chronic inflammatory skin condition. It manifests with a wide array of skin symptoms and also includes systemic inflammation. Psoriasis conveys a significant physical, psychological and social burden, which significantly affects patient’s quality of life. A comprehensive and timely approach to treatment is crucial. Mild psoriasis can usually be managed with topical treatment. About a third of patients experience moderate to severe disease. They require systemic treatment, which aims at improving skin manifestations, control of systemic inflammation and improvement in quality of life. Systemic treatment options comprise of conventional agents, such as methotrexate, and biological therapies, which inhibit specific targets in the pathogenetic pathways of psoriasis. Despite the growing use of biologicals, methotrexate still represents the first-line treatment option for treatment of moderate to severe psoriasis. The clinical utility of methotrexate is, however, hampered by inter-individual variability in treatment outcomes. Genetic factors contribute to the observed variability in treatment response. Pharmacogenetics of methotrexate in patients with psoriasis are relatively scarcely investigated. Results of available studies currently do not allow for prediction of treatment outcomes or for treatment individualization. The main purpose of this doctoral dissertation was to investigate the influence of single nucleotide polymorphisms in genes coding for methotrexate transporters ang genes coding for enzymes of the folate-methionine pathway on the efficacy and safety of methotrexate treatment in patients with psoriasis. Additionally, we aimed to investigate whether the polymorphisms identified as markers of methotrexate treatment outcomes also influence methotrexate drug survival. We conducted a retrospective clinical study, which included 211 patients with moderate to severe psoriasis receiving systemic treatments at the Dermatovenerology department of the University Medical Centre Maribor. We described a cohort of 199 patients with moderate to severe plaque psoriasis, which we consider representative of the Slovenian population of patients with such disease. We recorded treatment patterns and response to systemic therapy. The most commonly used medicines in this cohort were the conventional agent methotrexate and biologics adalimumab, ustekinumab and etanercept. Methotrexate was the most frequently prescribed treatment, which confirms the importance of this medication in the management of psoriasis. We also noticed a step-wise approach, whereby treatment with biologics is preceded by conventional therapies. We conclude that management and treatment of patients in our cohort follow the recommendations of international guidelines. Treatment outcomes recorded for methotrexate, adalimumab, ustekinumab and etanercept were compared to literature data; the recorded efficacy and safety were in line with results of randomized clinical trials, as well as real-life studies. In the pharmacogenetic part of our research we describe the genetic variability in genes coding for methotrexate transporters and genes coding for enzymes of the folate-methionine pathway in 137 patients with plaque psoriasis treated with methotrexate. To the best of our knowledge, this was the first pharmacogenetic study in patients with psoriasis conducted in Slovenia. We identified novel potential biomarkers of methotrexate treatment response. The most pronounced association identified in the present study was between GNMT rs10948059 and MTX efficacy. The presence of at least one copy of the variant allele was associated with an increased risk of insufficient clinical response. Another risk factor associated with insufficient treatment responses was DNMT3b rs2424913. Additionally, we identified an interaction between the genes for both methyltransferases by means of classification and regression tree analysis. We observed an increased risk of treatment failure in patients with the variant GNMT genotype when they were also carriers of the variant DNMT3b allele. Furthermore, we discovered an association between methotrexate efficacy and the activity of methotrexate transporters ABCC2 and OATP1B1. We detected a higher chance of a good treatment response in carriers of the variant ABCC2 rs717620 allele or patients with SLCO1B1 haplotypes coding for low activity versions of the transporter. We further identified an association between the polymorphism rs3733890 coding for BHMT and the onset of methotrexate hepatotoxicity. We detected an increased risk of hepatotoxicity in patients with at least one copy of the variant allele as compared to patients with the wild-type genotype. To the best of our knowledge, this is the first time polymorphisms in genes for enzymes of the methionine cycle have been investigated in a pharmacogenetic study of methotrexate in patients with psoriasis. Our results indicate the importance of the cell methylation potential for the efficacy and safety of methotrexate in the treatment of psoriasis. In the last part of our research we investigated whether the polymorphisms previously associated with methotrexate treatment response were also important for the duration of successful treatment with this agent. We described methotrexate drug survival in our cohort and identified a significant influence of the year of treatment introduction. After restricting the observation time we noted a relatively low median methotrexate drug survival time of 11 months. We also found most treatment discontinuations were associated with inadequate efficacy of methotrexate. The reason for treatment discontinuation significantly impacted methotrexate drug survival in women, while this effect was not observed in men. We identified the ABCC2 rs717620 genotype as a determinant of methotrexate drug survival. The variant allele was associated with a lower risk of treatment discontinuation, or, in other words, it was associated with a longer methotrexate drug survival. ABCC2 rs717620 genotype is thus the first pharmacogenetic determinant of methotrexate drug survival in patients with psoriasis. Our findings suggest pharmacogenetic markers might have further applications in treatment of psoriasis. In this doctoral dissertation we show psoriasis patients in Slovenia benefit from similar management strategies and achieve similar treatment success as their counterparts in other countries. These findings support the extrapolation of results from relevant international literature to our setting. We identified novel pharmacogenetic markers of methotrexate treatment outcomes, i.e., treatment efficacy, adverse events occurence and methotrexate drug survival. These findings contribute to the understanding of the observed variability of methotrexate treatment response in patients with psoriasis. The predictive value of the identified pharmacogenetic factors is yet to be determined and further validation in prospective, randomized, controlled trials is needed. Despite this, our results emerge as a starting point for prediction of methotrexate efficacy, safety and drug survival in patients with psoriasis. In this way, we are one step closer to the individualization of treatment, safer and rational use of medication and consequently, to better quality of life in patients with psoriasis.
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