Pharmacogenetics and rheumatology: Molecular mechanisms contributing to variability in drug response

Efficacy and tolerability of celecoxib and naproxen versus placebo in Hispanic patients with knee osteoarthritis

Background

Celecoxib is an effective treatment for osteoarthritis (OA). However, information on its efficacy and safety profile in different racial/ethnic groups is limited. Noticeable differences among racial groups are found in other disease states, but a thorough investigation of OA is lacking. The objective of this study was to determine if celecoxib 200 mg once daily is as effective as naproxen 500 mg twice daily in the treatment of OA of the knee in Hispanic patients.

Methods

Hispanic patients aged ≥45 years with knee OA were randomized to receive celecoxib 200 mg once daily, naproxen 500 mg twice daily, or placebo for 6 weeks. The primary efficacy variable was the change in Patient’s Assessment of Arthritis Pain at 6 weeks compared with baseline. Secondary variables were change in Patient’s and Physician’s Global Assessments of Arthritis from baseline to week 6/early termination, change in Western Ontario and McMaster Universities OA Index (WOMAC) from baseline to week 6/early termination, change in American Pain Society pain score, Pain Satisfaction Scale, Patient Health Questionnaire (PHQ-9), and measurements of upper gastrointestinal tolerability.

Results

In total, 239 patients completed the trial (96 celecoxib, 96 naproxen, 47 placebo). Celecoxib was as effective as naproxen in reducing OA pain (least squares mean change from baseline [standard error] −39.7 [2.7] for celecoxib and −36.9 [2.6] for naproxen). Patient’s and Physician’s Global Assessments of Arthritis, WOMAC scores, upper gastrointestinal tolerability, Pain Satisfaction Scale, and PHQ-9 showed no statistically significant differences between the celecoxib and naproxen groups. The incidence of adverse events and treatment-related adverse events were similar among the treatment groups.

Conclusion

Celecoxib 200 mg once daily was as effective as naproxen 500 mg twice daily in the treatment of signs and symptoms of knee OA in Hispanic patients. Celecoxib was shown to be safe and well tolerated in this patient population.

Role of the MTHFR polymorphisms in cancer risk modification and treatment

The role of folate, a water-soluble B vitamin, and single nucleotide polymorphisms (SNPs) in the folate metabolic pathway in human health and disease has been rapidly expanding. Recently, functionally significant SNPs in 5,10-methylenetetrahydrofolate reductase (MTHFR), a critical enzyme for intracellular folate homeostasis and metabolism, have been identified and characterized. The MTHFR SNPs are ideal candidates for investigating the role of SNPs in cancer risk modification and treatment because of their well-defined and highly relevant biochemical effects on intracellular folate composition and one-carbon transfer reactions. Indeed, a large body of molecular epidemiologic evidence suggests that the MTHFR 677 variant T allele is associated with cancer risk in a site-specific manner. Furthermore, biologically plausible mechanisms based on the functional consequences of changes in intracellular folate cofactors resulting from the MTHFR 677T variant exist to readily explain cancer risk modification associated with this variant. In addition, a growing body of in vitro and clinical evidence suggests that the MTHFR SNPs may be an important pharmacogenetic determinant of response to and toxicity of 5-fluorouracil (5FU) and methotrexate (MTX)-based cancer and anti-inflammatory chemotherapy. Furthermore, studies suggest that MTHFR inhibition may be a potential target for increasing chemosensitvity of cancer cells to 5FU-based chemotherapy. Because the MTHFR SNPs are prevalent and MTX and 5FU are widely used for the treatment of common cancers and inflammatory conditions, the pharmacogenetic role of the MTHFR SNPs has significant clinical implications. MTHFR SNPs may play an important role in providing rational, effective and safe tailored treatment to patients with cancer and inflammatory disorders requiring 5FU and MTX-based therapy. As such, largescale human studies and in vitro mechanistic studies are warranted to clarify the pharmacogenetic role of the MTHFR SNPs.

Update on nonsteriodal anti-inflammatory drugs

PURPOSE OF REVIEW

This review addresses recent concerns about the cardiovascular safety of nonsteroidal anti-inflammatory drugs, the disease-modifying role of these drugs in ankylosing spondylitis, and their use in the understudied pediatric population.

RECENT FINDINGS

Several recent observational and controlled studies highlight the cardiovascular toxicity of rofecoxib, celecoxib, parecoxib, valdecoxib and naproxen. Concerns about cardiovascular safety raise questions about the chronic use of nonsteroidal anti-inflammatory drugs in patients with rheumatic diseases, including children. The risks of these drugs in the pediatric population are not well known and this review addresses the limited data available concerning nonsteroidal anti-inflammatory drug use in children. A recent trial in ankylosing spondylitis patients demonstrated continuous nonsteroidal anti-inflammatory drug use reduced the rate of syndesmophyte formation, suggesting that they may have a disease-modifying role in these patients.

SUMMARY

Nonsteroidal anti-inflammatory drugs have been in the spotlight this year. While preliminary evidence has supported novel roles for these drugs in ankylosing spondylitis and in cancer prevention, accumulating evidence shows that some cyclooxygenase-2 and perhaps all nonsteroidal anti-inflammatory drugs are associated with cardiovascular toxicity. Further research is needed to understand the magnitude and mechanism of this risk. Clinicians are compelled to weigh carefully the benefits and risks of therapy. Concerns about safety are balanced by optimism about their potential role in delaying the progression of ankylosing spondylitis.

Impact of thiopurine methyltransferase activity and 6-thioguanine nucleotide concentrations in patients with chronic inflammatory diseases

As azathioprine is one of the standard immunosuppressive drugs used for treatment of patients with different chronic inflammatory diseases, the effect of the azathioprine metabolizing enzyme thiopurine methyltransferase (TPMT) activity on incidence of adverse events (AE) was examined. In addition, potential correlations between the concentration of the azathioprine metabolite 6-thioguanine nucleotide (6-TGN) in erythrocytes (RBC) and inflammatory disease activity as well as hematological AE were investigated. TPMT activities were investigated prospectively in 139 patients (35 male, 104 female) with chronic inflammatory diseases [systemic lupus erythematosus (SLE, 38), progressive systemic sclerosis (PSS, 13), Wegener's granulomatosis (4), rheumatoid arthritis (RA, 5), and other chronic inflammatory diseases (79)]. In addition, 6-TGN concentrations were investigated in a second cohort of 58 patients (17 patients with SLE, 5 with PSS, 5 with vasculitides, 4 with undifferentiated connective tissue diseases, 1 with dermatomyositis, 1 with Sjögren's syndrome, 1 with RA, 20 with Crohn's disease, and 4 with ulcerative colitis) prior to and during therapy with azathioprine. The distribution of activities of TPMT in 139 patients showed a normal Gaussian distribution in the Caucasian population. Within the group of 96 patients taking azathioprine, known azathioprine-related AE could be observed: minor AE (sickness, rash, and increase in cholestasis parameters) in 11 patients (11.4%), and severe AE (bone marrow toxicity) in 7 patients (7.3%). Below a "cutoff" value of 11.9 nmol/mL RBC x h of TPMT activity, AE were significantly more frequent. In the second cohort of patients, no significant correlations could be observed between 6-TGN concentrations and parameters of disease activity. Reduced activity of TPMT in patients with chronic inflammatory diseases requiring immunosuppressive therapy with azathioprine, especially below a distinct cutoff, appears to inherit a substantial risk for development of AE.

Pharmacogenomics steps toward personalized medicine

The goal of personalized medicine is to maximize the likelihood of therapeutic efficacy and to minimize the risk of drug toxicity for an individual patient. One of the major contributors to this concept is pharmacogenomics. Marked interindividual genetic variation contributes significantly to both susceptibility to diseases, and response to drugs. Even though pharmacogenomics is not a new science, the translation of pharmacogenomics into clinical practice (i.e., personalized medicine) has not taken place at the same pace as science is delivering new results. It is felt that a large number of recent pharmacogenomic findings allow bold steps to be taken toward personalized medicine. This review collates a variety of examples that have great potential for immediate and effective introduction into clinical practice. In addition, other exploratory examples with a particular focus on drug safety and targeted cancer therapy are summarized.