Key Pharmacogenomic Considerations for Sickle Cell Disease Patients

Pharmacogenomics of Drugs Used in β-Thalassemia and Sickle-Cell Disease: From Basic Research to Clinical Applications

In this short review we have presented and discussed studies on pharmacogenomics (also termed pharmacogenetics) of the drugs employed in the treatment of β-thalassemia or Sickle-cell disease (SCD). This field of investigation is relevant, since it is expected to help clinicians select the appropriate drug and the correct dosage for each patient. We first discussed the search for DNA polymorphisms associated with a high expression of γ-globin genes and identified this using GWAS studies and CRISPR-based gene editing approaches. We then presented validated DNA polymorphisms associated with a high HbF production (including, but not limited to the HBG2 XmnI polymorphism and those related to the BCL11A, MYB, KLF-1, and LYAR genes). The expression of microRNAs involved in the regulation of γ-globin genes was also presented in the context of pharmacomiRNomics. Then, the pharmacogenomics of validated fetal hemoglobin inducers (hydroxyurea, butyrate and butyrate analogues, thalidomide, and sirolimus), of iron chelators, and of analgesics in the pain management of SCD patients were considered. Finally, we discuss current clinical trials, as well as international research networks focusing on clinical issues related to pharmacogenomics in hematological diseases.

Sickle Cell Anemia: Variants in the CYP2D6, CAT, and SLC14A1 Genes Are Associated With Improved Hydroxyurea Response

Differences in hydroxyurea response in sickle cell anemia may arise due to a series of factors with genetic factors appearing to be predominant. This study aims to investigate the effects of single nucleotide polymorphisms in genes encoding drug-metabolizing enzymes and solute carriers on hydroxyurea response, in patients with sickle cell anemia. For that purpose, a total number of 90 patients with sickle cell anemia were recruited, 45 were undergoing hydroxyurea treatment, while 45 were not under the treatment. Association analyses were performed between CYP3A4 (rs2740574), CYP2D6 (rs3892097), CAT (rs7943316 and rs1001179), and SLC14A1 (rs2298720) variants and laboratory parameters. According to our findings, patients with hydroxyurea treatment demonstrated higher HbF levels and a significant improvement in hemolytic, hepatic, inflammatory, and lipid parameters in comparison to those without the treatment. We also found significant associations between the CYP2D6 (rs3892097), CAT (rs7943316 and rs1001179), and SLC14A1 (rs2298720) variants and an improvement of the therapeutic effects, specifically the hemolytic, hepatic, inflammatory, lipid, and renal parameters. In conclusion, our results highlight the importance of the investigated variants, and their strong association with hydroxyurea efficacy in patients with sickle cell anemia, which may be considered in the future as genetic markers.

Impact of ZBTB7A hypomethylation and expression patterns on treatment response to hydroxyurea

BACKGROUND

We aimed to clarify the emerging epigenetic landscape in a group of genes classified as "modifier genes" of the β-type globin genes (HBB cluster), known to operate in trans to accomplish the two natural developmental switches in globin expression, from embryonic to fetal during the first trimester of conception and from fetal to adult around the time of birth. The epigenetic alterations were determined in adult sickle cell anemia (SCA) homozygotes and SCA/β-thalassemia compound heterozygotes of Greek origin, who are under hydroxyurea (HU) treatment. Patients were distinguished in HU responders and HU non-responders (those not benefited from the HU) and both, and in vivo and in vitro approaches were implemented.

RESULTS

We examined the CpG islands' DNA methylation profile of BCL11A, KLF1, MYB, MAP3K5, SIN3A, ZBTB7A, and GATA2, along with γ-globin and LRF/ZBTB7A expression levels. In vitro treatment of hematopoietic stem cells (HSCs) with HU induced a significant DNA hypomethylation pattern in ZBTB7A (p*, 0.04) and GATA2 (p*, 0.03) CpGs exclusively in the HU non-responders. Also, this group of patients exhibited significantly elevated baseline methylation patterns in ZBTB7A, before the HU treatment, compared to HU responders (p*, 0.019) and to control group of healthy individuals (p*, 0.021), which resembles a potential epigenetic barrier for the γ-globin expression. γ-Globin expression in vitro matched with detected HbF levels during patients' monitoring tests (in vivo) under HU treatment, implying a good reproducibility of the in vitro HU epigenetic effect. LRF/ZBTB7A expression was elevated only in the HU non-responders under the influence of HU.

CONCLUSIONS

This is one of the very first pharmacoepigenomic studies indicating that the hypomethylation of ZBTB7A during HU treatment enhances the LRF expression, which by its turn suppresses the HbF resumption in the HU non-responders. Its role as an epigenetic regulator of hemoglobin switching is also supported by the wide distribution of ZBTB7A-binding sites within the 5' CpG sequences of all studied human HBB cluster "modifier genes." Also, the baseline methylation level of selective CpGs in ZBTB7A and GATA2 could be an indicator of the negative HU response among the β-type hemoglobinopathy patients.

Pharmacoproteomics Profiling of Plasma From β-Thalassemia Patients in Response to Hydroxyurea Treatment

β-Thalassemia is a genetic disorder caused by defects in the β-globin gene resulting in the absence or reduced synthesis of adult hemoglobin (HbA). Hydroxyurea is an effective drug to increase fetal γ-globin (HbF) expression, replacing the missing adult β-globin. The mechanism of HbF induction by hydroxyurea and improvement in clinical symptoms are still poorly understood. In the present study we performed comparative analysis of plasma proteome in pre- and post-hydroxyurea-treated β-thalassemia major transfusion-dependent children (n = 10, mean age = 3.2 years) as well as responders versus nonresponders to hydroxyurea treatment. Plasma was collected before and after 6 months of hydroxyurea treatment, with patients subcategorized on the basis of their response to hydroxyurea. Among 400 identified proteins using a label-free quantitative proteomics approach, 28 proteins were found to be significantly different in pre- versus post-hydroxyurea-treated groups, with transferrin receptor protein-1 being most downregulated and hemopexin and haptoglobin the most upregulated proteins after treatment. In responder versus nonresponder comparison, 26 proteins were found to be differentially expressed, with carbonic anhydrase 1, hemoglobin subunit γ-1, and peroxiredoxin-2 showing the significant changes. The mechanism of hydroxyurea treatment in β-thalassemia patients appears to be complex, requiring a large sample size and a longer period of treatment to reveal its details.