Pharmacokinetic and neuroimmune pharmacogenetic impacts on slow-release morphine cancer pain control and adverse effects.

The aim was to determine if opioid neuroimmunopharmacology pathway gene polymorphisms alter serum morphine, morphine-3-glucuronide and morphine-6-glucuronide concentration-response relationships in 506 cancer patients receiving controlled-release oral morphine. Morphine-3-glucuronide concentrations (standardised to 11 h post-dose) were higher in patients without pain control (median (interquartile range) 1.2 (0.7-2.3) versus 1.0 (0.5-1.9) µM, P = 0.006), whereas morphine concentrations were higher in patients with cognitive dysfunction (40 (20-81) versus 29 (14-60) nM, P = 0.02). TLR2 rs3804100 variant carriers had reduced odds (adjusted odds ratio (95% confidence interval) 0.42 (0.22-0.82), P = 0.01) of opioid adverse events. IL2 rs2069762 G/G (0.20 (0.06-0.52)), BDNF rs6265 A/A (0.15 (0.02-0.63)) and IL6R rs8192284 carrier (0.55 (0.34-0.90)) genotypes had decreased, and IL6 rs10499563 C/C increased (3.3 (1.2-9.3)), odds of sickness response (P ≤ 0.02). The study has limitations in heterogeneity in doses, sampling times and diagnoses but still suggests that pharmacokinetics and immune genetics co-contribute to morphine pain control and adverse effects in cancer patients.

Population Pharmacokinetics and Pharmacodynamics of the Therapeutic and Adverse Effects of Ketamine in Patients With Treatment-Refractory Depression.

We aimed to develop population pharmacokinetic/pharmacodynamic (PK/PD) models that can effectively describe ketamine and norketamine PK/PD relationships for Montgomery-Åsberg Depression Rating Scale (MADRS) scores, blood pressure (BP), and heart rate (HR) following i.v., s.c., and i.m. ketamine administration in patients with treatment-refractory depression. Ketamine PK/PD data were collected from 21 treatment-refractory depressed participants who received ketamine (dose titration 0.1-0.5 mg/kg as single doses) by i.v., s.c., or i.m. administration. Model development used nonlinear mixed effect modeling. Ketamine and norketamine PK were best described using two-compartment models with first-order absorption after s.c. and i.m. administration. Estimated ketamine bioavailability after i.m. and s.c. was ~ 64% with indistinguishable first-order absorption rate constants. Allometric scaling of body weight on all clearance and volumes of distribution improved the model fit. The delay in the concentration-response relationship for MADRS scores was best described using a turnover model (turnover time ~ 42 hours), whereas for the BP and HR rates this was an immediate effect model. For all PD effects, ketamine alone was superior to models with norketamine concentration linked to an effect. No covariates were identified for PD effects. The estimated half-maximal effective concentration from the MADRS score, BP, and HR were 0.44, 468, and 7,580 ng/mL, respectively. The integrated population models were able to effectively describe the PK/PD relationships for MADRS scores, BP, and HR after i.v., s.c., and i.m. ketamine administration. These findings allow for a deeper understanding of the complex relationships between route of ketamine administration and clinical response and safety.

New pharmacological perspectives and therapeutic options for opioids: Differences matter.

Opioids remain the major drug class for the treatment of acute, chronic and cancer pain, but have major harmful effects such as dependence and opioid-induced ventilatory impairment. Although no new typical opioids have come onto the market in the past almost 50 years, a plethora of new innovative formulations has been developed to meet the clinical need. This review is intended to shed light on new understanding of the molecular pharmacology of opioids, which has arisen largely due to the genomic revolution, and what new drugs may become available in the coming years. Atypical opioids have and are being developed which not only target the mu opioid receptor but other targets in the pain pathway. Biased mu agonists have been developed but remain 'unbiased' clinically. The contribution of drugs targeting non-mu opioid receptors either alone or as heterodimers shows potential promise but remains understudied. That gene splice variants of the mu opioid receptor produce multiple receptor isoforms in different brain regions, and may change with pain chronicity and phenotype, presents new challenges but also opportunities for precision pain medicine. Finally, that opioids also have pro-inflammatory effects not aligned with mu opioid receptor binding affinity implicates a fresh understanding of their role in chronic pain, whether cancer or non-cancer. Hopefully, a new understanding of opioid analgesic drug action may lead to new drug development and better precision medicine in acute and chronic pain relief with less patient harm.

Instability of Efavirenz Metabolites Identified During Method Development and Validation.

Accurate quantification of efavirenz metabolites in patient samples is required to investigate their potential contribution to efavirenz adverse events. This study aimed to validate a LC-MS/MS method to quantify and investigate the stability of efavirenz and metabolites in human plasma. Compounds were extracted from plasma by supported liquid extraction and resolved on a C18 column. Validation was performed following FDA bioanalytical method validation guidelines. Stability under common conditions of sample pre-treatment and storage were assessed. Efavirenz and 8-hydroxyefavirenz were stable for all conditions tested. 7-Hydroxyefavirenz and 8,14-dihydroxyefavirenz were not stable in plasma at room temperature for 24 h (46%-69% loss), -20°C for 90 days (17%-50% loss), or 60°C for 1 h (90%-95% loss). Efavirenz and 8-hydroxyefavirenz concentrations in HIV/AIDS patient (n=5) plasma prepared from pre-treated (60°C for 1 h) whole blood varied from 517-8564 ng/mL and 131-813 ng/mL, respectively. 7-Hydroxyefavirenz and 8,14-dihydroxyefavirenz concentrations were below validated lower limits of quantification (0.25 and 0.5 ng/mL, respectively), most likely due to sample pre-treatment. This is the first report of 7-hydroxyefavirenz and 8,14-dihydroxyefavirenz instability under conditions commonly used in preparation of samples from HIV/AIDS patients. Alternative biosafety measures to heat pre-treatment must therefore be used for accurate quantification of plasma 7-hydroxyefavirenz and 8,14-dihydroxyefavirenz.

Innate Immune and Neuronal Genetic Markers Are Highly Predictive of Postoperative Pain and Morphine Patient-Controlled Analgesia Requirements in Indian but Not Chinese or Malay Hysterectomy Patients.

OBJECTIVE: Pain severity and opioid requirements in the postoperative period show substantial and clinically significant inter-patient variation due mainly to factors such as age, surgery type, and duration. Genetic factors have not been adequately assessed except for the neuronal OPRM1 rs1799971 and COMT rs4680, whereas the contribution of innate immune signaling pathway genetics has seldom been investigated. SETTING: Hospital surgical ward. SUBJECTS: Women (107 Indian, 184 Malay, and 750 Han Chinese) undergoing total hysterectomy surgery. METHODS: Morphine consumption, preoperative pain, and postoperative pain were evaluated in relation to genetic variability comprising 19 single-nucleotide polymorphisms (SNPs) in 14 genes involved in glial activation, inflammatory signaling, and neuronal regulation, plus OPRM1 (1 SNP) and COMT (3 SNPs). RESULTS: Pre- and postoperative pain and age were associated with increased and decreased morphine consumption, respectively. In Chinese patients, only 8% of the variability in consumption could be explained by these nongenetic and genetic (BDNF, IL1B, IL6R, CRP, OPRM1, COMT, MYD88) factors. However, in Indian patients, 41% of morphine consumption variability could be explained by age (explaining <3%) and variants in OPRM1 rs1799971, CRP rs2794521, TLR4 rs4986790, IL2 rs2069762, COMT rs4818, TGFB1 rs1800469, and IL6R rs8192284 without controlling for postoperative pain. CONCLUSIONS: This is the highest known value reported for genetic contributions (38%) to morphine use in the acute postoperative pain setting. Our findings highlight the need to incorporate both genetic and nongenetic factors and consider ethnicity-dependent and nonadditive genotypic models in the assessment of factors that contribute to variability in opioid use.

Tacrolimus dose, blood concentrations and acute nephrotoxicity, but not CYP3A5/ABCB1 genetics, are associated with allograft tacrolimus concentrations in renal transplant recipients.

AIMS: Long-term use of the immunosuppressant tacrolimus is limited by nephrotoxicity. Following renal transplantation, the risk of nephrotoxicity may be determined more by allograft than by blood tacrolimus concentrations, and thus may be affected by donor CYP3A5 and ABCB1 genetics. Little is known regarding factors that determine tacrolimus intrarenal exposure. METHODS: This study investigated the relationship between trough blood (C0Blood ) and allograft (CGraft ) tacrolimus concentrations and tacrolimus dose, haematocrit, genetics, acute nephrotoxicity, rejection status, delayed graft function, and time post-transplant. C0Blood and CGraft were quantified in 132 renal transplant recipients together with recipient and donor CYP3A5 (rs776746) and ABCB1 3435 (rs1045642) genotypes. RESULTS: C0Blood ranged from 2.6 to 52.3 ng/mL and CGraft from 33 to 828 pg/mg tissue. Adjusting for dose, recipients who were CYP3A5 expressors had lower C0Blood compared to nonexpressors, whilst delayed graft function was associated with higher C0Blood . Linear regression showed that the significant predictors of CGraft were C0Blood (point-wise P = 7 × 10-10 ), dose (P = .004) acute nephrotoxicity (P = .002) and an interaction between C0Blood and acute tacrolimus nephrotoxicity (P = .0002), with an adjusted r2  = 0.35 and no contribution from donor or recipient CYP3A5 or ABCB1 genotype. The association between CGraft and acute nephrotoxicity depended on one very high CGraft (828 pg/mg tissue). CONCLUSIONS: Recipient and donor CYP3A5 and ABCB1 3435C>T genotypes are not determinants of allograft tacrolimus exposure in kidney transplant recipients. However, tacrolimus dose and C0Blood were significant predictors of CGraft , and the relationship between C0Blood and CGraft appeared to differ in the presence or absence of acute nephrotoxicity.

Is There a Temporal Relationship Between Trough Whole Blood Tacrolimus Concentration and Acute Rejection in the First 14 Days After Kidney Transplantation?

BACKGROUND: There are inconsistent findings regarding the relationship between trough whole blood tacrolimus concentration (TAC C0) and acute kidney rejection in recipients undergoing TAC therapeutic drug monitoring (TDM). However, studies have not always assessed TAC C0 at the time of rejection or accounted for variability in hematocrit. Therefore, this study aimed to investigate the temporal relationship between TAC C0 and acute rejection, including when accounting for variation in hematocrit. METHODS: For 38 recipients who developed biopsy-proven acute rejection (BPAR) in the first 14 days after kidney transplantation, daily TAC C0 from TDM and hematocrit was collected from case notes. Differences in log10-transformed TAC C0 between the day of BPAR (log Cr), 1 day before BPAR (log Cr-1), and 2 days before BPAR (log Cr-2) and the combined median concentrations for the days preceding these (log Cprior) were examined by repeated-measures analysis of variance with Dunnett post hoc testing. Generalized linear mixed-effects regression (glmer) examined the ability of TAC C0 to predict acute rejection episodes with and without controlling for hematocrit. RESULTS: Log Cr-1 [mean difference (95% confidence interval) = -0.13 (-0.21 to -0.048), post hoc P = 0.002] and log Cr [-0.13 (-0.24 to -0.025), post hoc P = 0.013] were significantly lower than log Cprior. TAC C0 was a significant (P = 0.0078) predictor of rejection episodes (area under the receiver operating characteristic curve = 0.79) only in glmer models accounting for variability in hematocrit. CONCLUSIONS: In recipients who developed BPAR, there was a significant temporal relationship between TAC C0 and BPAR incidence under TAC TDM that may not be detected in cross-sectional studies, especially if variability in hematocrit is not addressed. This supports a TAC C0-rejection relationship, which differs between recipients, and may explain why some recipients do or do not experience rejection within or below the TDM range, respectively. However, studies with larger sample sizes are needed to confirm this finding.

High and variable population prevalence of HLA-B*56:02 in indigenous Australians and relation to phenytoin-associated drug reaction with eosinophilia and systemic symptoms.

Phenytoin drug reaction with eosinophilia and systemic symptoms (DRESS) in 3 Aboriginal Australians positive for HLA-B*56:02 has been previously reported. We report the allele frequency of HLA-B*56:02 in 2 South Australian populations, 1 Aboriginal (4.8%, 95% confidence interval 2.4-7.8%) and the other European (0%). We compared the frequency with publicly available information on HLA-B*56:02 status in other Indigenous Australian (n = 4) and European Australian cohorts (n = 1). In the Indigenous Australian cohorts, HLA-B*56:02 allele frequency ranged from 1.3 to 19%. We also describe an additional case of phenytoin DRESS (RegiSCAR DRESS score 7) in an Aboriginal Australian that was associated with HLA-B*56:02 and with CYP2C9*1/*3 genotype. In Aboriginal Australians, phenytoin DRESS appears distinctly linked to HLA-B*56:02 with an allele carriage rate substantially higher than in Europeans, but also with considerable regional variation. Investigations of human leucocyte antigen and other contributing genes and severe adverse drug reactions in understudied non-European populations are required to optimize safe medication use and inform risk mitigation strategies.

No Major Effect of Innate Immune Genetics on Acute Kidney Rejection in the First 2 Weeks Post-Transplantation.

BACKGROUND: Innate immunity contributes to acute rejection after kidney transplantation. Genetic polymorphisms affecting innate immunity may therefore influence patients' risk of rejection. IL2 -330T > G, IL10 -1082G > A, -819C > T, and -592C > A, and TNF -308G > A are not associated with acute rejection incidence in Caucasian kidney transplant recipients receiving a calcineurin inhibitor, ciclosporin or tacrolimus (TAC). However, other important innate immune genetic polymorphisms have not yet been extensively studied in recipients and donors. In addition, innate immunogenetics have not been investigated in kidney transplant cohorts receiving only TAC as the calcineurin inhibitor. OBJECTIVE: To investigate the effect of recipient and donor CASP1, CRP, IL1B, IL2, IL6, IL6R, IL10, MYD88, TGFB, TLR2, TLR4, and TNF genetics on acute kidney rejection in the first 2 weeks post-transplant in TAC-treated kidney transplant recipients. METHODS: This study included 154 kidney transplant recipients and 81 donors successfully genotyped for 17 polymorphisms in these genes. All recipients were under triple immunosuppressant therapy of TAC, mycophenolate mofetil, and prednisolone. Recipient and donor genotype differences in acute rejection incidence within the first 2 weeks post-transplantation were assessed by logistic regression, adjusting for induction therapy, human leukocyte antigen mismatches, kidney transplant number, living donor, and peak panel-reactive antibody scores. RESULTS: A trend (Cochran-Armitage P = 0.031) of increasing acute rejection incidence was observed from recipient IL6 -6331 T/T (18%) to T/C (25%) to C/C (46%) genotype [C/C versus T/T odds ratio (95% confidence interval) = 6.6 (1.7 to 25.8) (point-wise P = 0.017)]. However, no genotype differences were significant after Bonferroni correction for multiple comparisons. CONCLUSIONS: This study did not detect any statistically significant effects of recipient or donor innate immune genetics on acute rejection incidence in the first 2 weeks post-transplantation. However, the sample size was small, and future larger studies or meta-analyses are required to demonstrate conclusively if innate immune genetics such as IL6 influence the risk of acute rejection after kidney transplantation.

Effect of tacrolimus dispositional genetics on acute rejection in the first 2 weeks and estimated glomerular filtration rate in the first 3 months following kidney transplantation.

BACKGROUND: CYP3A4/5 and P-glycoprotein (P-gp, ABCB1) affect tacrolimus (TAC) exposure in T cells and kidney cells. Genetic variability of these genes has been widely studied for effects on acute rejection and kidney function after transplantation, but findings remain contradictory. In addition, cytochrome P450 reductase (POR) is important for CYP3A4/5 activity, and the pregnane X receptor (NR1I2) regulates CYP3A4/5 and P-gp expression. However, the relationship between POR and NR1I2 genetics and acute rejection and kidney function has not been extensively investigated. OBJECTIVE: The aim of this study was to investigate the effect of ABCB1 (61A>G, 1199G>A, 1236C>T, 2677G>T, 3435C>T), CYP3A4*22, CYP3A5*3, NR1I2 (8055C>T, 63396C>T) and POR*28 genotypes/haplotypes on acute rejection and kidney function in the first 3 months after transplant. PARTICIPANTS AND METHODS: The study included 165 kidney transplant recipients, who received TAC, mycophenolate and prednisolone, and 129 donors. TAC dose was adjusted to target trough blood concentrations of 8-15 ng/ml by therapeutic drug monitoring. Recipient and donor genotype/haplotype differences in acute rejection incidence within the first 2 weeks after transplant were assessed by logistic regression, adjusting for induction therapy, human leucocyte antigen mismatches, kidney transplant number, peak panel-reactive antibodies and donor type. Recipient and donor genotype/haplotype differences in estimated glomerular filtration rate in the first 3 months after transplant were assessed by linear mixed effects analysis, adjusting for acute rejection, delayed graft function and donor type. RESULTS: No genetic factors significantly affected acute rejection or estimated glomerular filtration rate after correction for multiple comparisons (P>0.004). CONCLUSION: Recipient and donor dispositional genetics had no significant effect on short-term clinical outcomes in kidney transplant patients receiving TAC therapeutic drug monitoring.

Pharmacogenomics in Papua New Guineans: unique profiles and implications for enhancing drug efficacy while improving drug safety.

Papua New Guinea (PNG) can be roughly divided into highland, coastal and island peoples with significant mitochondrial DNA differentiation reflecting early and recent distinct migrations from Africa and East Asia, respectively. Infectious diseases such as tuberculosis, malaria and HIV severely impact on the health of its peoples for which drug therapy is the major treatment and pharmacogenetics has clinical relevance for many of these drugs. Although there is generally little information about known single nucleotide polymorphisms in the population, in some instances, their frequencies have been shown to be higher than anywhere worldwide. For example, CYP2B6*6 is over 50%, and CYP2C19*2 and *3 are over 40 and 25%, respectively. Conversely, CYP2A6*9, 2B6*2, *3, *4 and *18, and 2C8*3 appear to be much lower than in Whites. CYP2D6 known variants are unclear, and for phase II enzymes, only UGT2B7 and UGT1A9 data are available, with variant frequencies either slightly lower than or similar to Whites. Although almost all PNG people tested are rapid acetylators, but which variant(s) define this phenotype is not known. For HLA-B*13:01, HLA-B*35:05 and HLA-C*04:01, the frequencies show some regioselectivity, but the clinical implications with respect to adverse drug reactions are not known. There are minimal phenotype data for the CYPs and nothing is known about drug transporter or receptor genetics. Determination of genetic variants that are rare in Whites or Asians but common in PNG people is a topic of both scientific and clinical importance, and further research needs to be carried out. Optimizing the safety and efficacy of infectious disease drug therapy through pharmacogenetic studies that have translation potential is a priority.

CYP3A5*3 and ABCB1 61A>G Significantly Influence Dose-adjusted Trough Blood Tacrolimus Concentrations in the First Three Months Post-Kidney Transplantation.

Tacrolimus (TAC) is a first-line immunosuppressant used to prevent organ rejection after kidney transplantation. There is large inter-individual variability in its pharmacokinetics. Single nucleotide polymorphisms (SNPs) in genes encoding TAC metabolizing enzymes cytochromes P450 3A4/5 (CYP3A4/5), P-glycoprotein efflux transporter (ABCB1), their expression regulator pregnane X receptor (NR1I2) and CYP3A co-factor cytochrome P450 reductase (POR) have been studied for their effects on tacrolimus disposition. However, except for CYP3A5*3, controversies remain about their roles in predicting dose-adjusted trough blood TAC concentrations (C0 /D). This study aimed to investigate the effects of ABCB1 (61A>G, 1199G>A, 1236C>T, 2677G>T and 3435C>T), CYP3A4*22, CYP3A5*3, NR1I2 (8055C>T, 63396C>T and -25385C>T) and POR*28 SNPs on TAC C0 /D. In total, 165 kidney transplant recipients were included in this study. SNPs were genotyped by probe-based real-time polymerase chain reaction. Associations between log-transformed whole blood TAC C0 /D (measured at 1 and 3 months post-transplant) and genotypes/haplotypes were assessed by linear mixed effects analysis, controlling for age, sex and haematocrit. It was observed that CYP3A5 expressors (*1/*1 + *1/*3) (p = 5.5 × 10-16 ) and ABCB1 61G allele carriers (p = 0.001) had lower log-transformed TAC C0 /D (56% and 26% lower geometric mean TAC C0 /D, respectively) and accounted for approximately 30% and 4%, respectively, of log-transformed TAC C0 /D variability in the first 3 months post-transplant. In conclusion, CYP3A5*3 is a major, and ABCB1 61A>G is a novel, although minor, genetic factor affecting TAC C0 /D in kidney transplant recipients.

CYP2C8 Genotype Significantly Alters Imatinib Metabolism in Chronic Myeloid Leukaemia Patients.

OBJECTIVE: The aims of this study were to determine the effects of the CYP2C8*3 and *4 polymorphisms on imatinib metabolism and plasma imatinib concentrations in chronic myeloid leukaemia (CML) patients. METHODS: We genotyped 210 CML patients from the TIDELII trial receiving imatinib 400-800 mg/day for CYP2C8*3 (rs11572080, rs10509681) and *4 (rs1058930). Steady-state trough total plasma N-desmethyl imatinib (major metabolite):imatinib concentration ratios (metabolic ratios) and trough total plasma imatinib concentrations were compared between genotypes (one-way ANOVA with Tukey post hoc). RESULTS: CYP2C8*3 (n = 34) and *4 (n = 15) carriers had significantly higher (P < 0.01) and lower (P < 0.01) metabolic ratios, respectively, than CYP2C8*1/*1 (n = 147) patients (median ± standard deviation: 0.28 ± 0.08, 0.18 ± 0.06 and 0.22 ± 0.08, respectively). Plasma imatinib concentrations were consequently > 50% higher for CYP2C8*1/*4 than for CYP2C8*1/*1 and CYP2C8*3 carriers (2.18 ± 0.66 vs. 1.45 ± 0.74 [P < 0.05] and 1.36 ± 0.98 µg/mL [P < 0.05], respectively). CONCLUSIONS: CYP2C8 genotype significantly alters imatinib metabolism in patients through gain- and loss-of-function mechanisms.

Ethnicity-dependent influence of innate immune genetic markers on morphine PCA requirements and adverse effects in postoperative pain.

Although several genetic factors have been associated with postsurgical morphine requirements, those involving the innate immune system and cytokines have not been well investigated. The aim of this study was to investigate the contribution of genetic variability in innate immune signalling pathways to variability in morphine dosage after elective caesarean section under spinal anaesthesia in 133 Indian, 230 Malay, and 598 Han Chinese women previously studied. Twenty single nucleotide polymorphisms in 14 genes involved in glial activation (TLR2, TLR4, MYD88, MD2), inflammatory signalling (IL2, IL6, IL10, IL1B, IL6R, TNFA, TGFB1, CRP, CASP1), and neuronal regulation (BDNF) were newly investigated, in addition to OPRM1, COMT, and ABCB1 genetic variability identified previously. Postsurgical patient-controlled analgesia morphine use (mg/24 hours) was binned into 6 normally distributed groups and scored 0 to 5 to facilitate step-down multiple linear regression analysis of genetic predictors, controlling for ethnicity and nongenetic variables. Ethnicity, OPRM1 rs1799971 (increased), TLR2 rs3804100 (decreased), and an interaction between ethnicity and IL1B rs1143634 (increased), predicted 9.8% of variability in morphine use scores in the entire cohort. In the Indian cohort, 14.5% of the variance in morphine use score was explained by IL1B rs1143634 (increased) and TGFB1 rs1800469 (decreased). In Chinese patients, the incidence of postsurgical pain was significantly higher in variant COMT rs4680 genotypes (P = 0.0007) but not in the Malay or Indian cohorts. Innate immune genetics may contribute to variability in postsurgical opioid requirements in an ethnicity-dependent manner.

Impact of CYP2C8*3 polymorphism on in vitro metabolism of imatinib to N-desmethyl imatinib.

1. Imatinib is metabolized to N-desmethyl imatinib by CYPs 3A4 and 2C8. The effect of CYP2C8*3 genotype on N-desmethyl imatinib formation was unknown. 2. We examined imatinib N-demethylation in human liver microsomes (HLMs) genotyped for CYP2C8*3, in CYP2C8*3/*3 pooled HLMs and in recombinant CYP2C8 and CYP3A4 enzymes. Effects of CYP-selective inhibitors on N-demethylation were also determined. 3. A single-enzyme Michaelis-Menten model with autoinhibition best fitted CYP2C8*1/*1 HLM (n = 5) and recombinant CYP2C8 kinetic data (median ± SD Ki = 139 ± 61 µM and 149 µM, respectively). Recombinant CYP3A4 showed two-site enzyme kinetics with no autoinhibition. Three of four CYP2C8*1/*3 HLMs showed single-enzyme kinetics with no autoinhibition. Binding affinity was higher in CYP2C8*1/*3 than CYP2C8*1/*1 HLM (median ± SD Km = 6 ± 2 versus 11 ± 2 µM, P=0.04). CYP2C8*3/*3 (pooled HLM) also showed high binding affinity (Km = 4 µM) and single-enzyme weak autoinhibition (Ki = 449 µM) kinetics. CYP2C8 inhibitors reduced HLM N-demethylation by 47-75%, compared to 0-30% for CYP3A4 inhibitors. 4. In conclusion, CYP2C8*3 is a gain-of-function polymorphism for imatinib N-demethylation, which appears to be mainly mediated by CYP2C8 and not CYP3A4 in vitro in HLM.

Innate Immune Signalling Genetics of Pain, Cognitive Dysfunction and Sickness Symptoms in Cancer Pain Patients Treated with Transdermal Fentanyl.

Common adverse symptoms of cancer and chemotherapy are a major health burden; chief among these is pain, with opioids including transdermal fentanyl the mainstay of treatment. Innate immune activation has been implicated generally in pain, opioid analgesia, cognitive dysfunction, and sickness type symptoms reported by cancer patients. We aimed to determine if genetic polymorphisms in neuroimmune activation pathways alter the serum fentanyl concentration-response relationships for pain control, cognitive dysfunction, and other adverse symptoms, in cancer pain patients. Cancer pain patients (468) receiving transdermal fentanyl were genotyped for 31 single nucleotide polymorphisms in 19 genes: CASP1, BDNF, CRP, LY96, IL6, IL1B, TGFB1, TNF, IL10, IL2, TLR2, TLR4, MYD88, IL6R, OPRM1, ARRB2, COMT, STAT6 and ABCB1. Lasso and backward stepwise generalised linear regression were used to identify non-genetic and genetic predictors, respectively, of pain control (average Brief Pain Inventory < 4), cognitive dysfunction (Mini-Mental State Examination ≤ 23), sickness response and opioid adverse event complaint. Serum fentanyl concentrations did not predict between-patient variability in these outcomes, nor did genetic factors predict pain control, sickness response or opioid adverse event complaint. Carriers of the MYD88 rs6853 variant were half as likely to have cognitive dysfunction (11/111) than wild-type patients (69/325), with a relative risk of 0.45 (95% CI: 0.27 to 0.76) when accounting for major non-genetic predictors (age, Karnofsky functional score). This supports the involvement of innate immune signalling in cognitive dysfunction, and identifies MyD88 signalling pathways as a potential focus for predicting and reducing the burden of cognitive dysfunction in cancer pain patients.

Pharmacogenomics of methadone maintenance treatment.

Methadone is the major opioid substitution therapy for opioid dependence. Dosage is highly variable and is often controlled by the patient and prescriber according to local and national policy and guidelines. Nevertheless many genetic factors have been investigated including those affecting its metabolism (CYP2B6-consistent results), efflux transport (P-gp-inconsistent results), target µ-opioid receptor (µ-opioid receptor-inconsistent results) and a host of other receptors (DRD2) and signaling elements (GIRK2 and ARRB2; not replicated). None by themselves have been able to substantially explain dosage variation (the major but not sole end point). When multiple genes have been combined such as ABCB1, CYP2B6, OPRM1 and DRD2 a greater contribution to dosage variation was found but not as yet replicated. As stabilization of dosage needs to be made rapidly, it is imperative that larger internationally based studies be instigated so that genetic contribution to dosage can be properly assessed, which may or may not tailor to different ethnic groups and each country's policy towards an outcome that benefits all.

Genetic, pathological and physiological determinants of transdermal fentanyl pharmacokinetics in 620 cancer patients of the EPOS study.

OBJECTIVE: This study aimed to investigate whether CYP3A4/5 genetic variants, together with clinical and patient factors, influence serum fentanyl and norfentanyl concentrations and their ratio in cancer pain patients receiving transdermal fentanyl. METHODS: CYP3A4*22 and CYP3A5*3 polymorphisms were analysed in 620 cancer pain patients receiving transdermal fentanyl (12.5-700 µg/h) from the European Pharmacogenetic Opioid Study. Using stepwise linear regression, CYP3A4/5 genetic variability was examined in combination with patient factors relating to organ drug elimination function and ABCB1 genetics for their association with serum fentanyl and norfentanyl concentrations and metabolic ratio (MR) (norfentanyl : fentanyl). RESULTS: Delivery rate-adjusted serum fentanyl concentrations (0.0012-1.1 nmol/l/µg.h) and MRs (0.08-499) varied widely. Only 43% of variability in serum fentanyl concentrations was accounted for by delivery rate and less than 50% by CYP3A4/5 genotypes and clinical variables (delivery rate, sex, comedications, kidney disease, BMI, serum albumin). CYP3A4*22 and CYP3A5*3 variants, CYP3A inhibitors and variables relating to liver and kidney function (serum albumin, glomerular filtration rate, kidney disease, BMI) were associated with MR, but accounted for only 14% of variability. CONCLUSION: Serum fentanyl concentrations and MR vary considerably between cancer pain patients on transdermal fentanyl patches. CYP3A4*22 and CYP3A5*3 genotypes, and multiple clinical factors, combine to influence transdermal fentanyl pharmacokinetics, but accounted for only a small proportion of variability in this study. Identification of the remaining factors determining serum fentanyl concentrations, and their relationship to efficacy and adverse effects may aid in improving the safety and effectiveness of transdermal fentanyl.

ABCB1 haplotype and OPRM1 118A > G genotype interaction in methadone maintenance treatment pharmacogenetics.

BACKGROUND: Genetic variability in ABCB1, encoding the P-glycoprotein efflux transporter, has been linked to altered methadone maintenance treatment dose requirements. However, subsequent studies have indicated that additional environmental or genetic factors may confound ABCB1 pharmacogenetics in different methadone maintenance treatment settings. There is evidence that genetic variability in OPRM1, encoding the mu opioid receptor, and ABCB1 may interact to affect morphine response in opposite ways. This study aimed to examine whether a similar gene-gene interaction occurs for methadone in methadone maintenance treatment. METHODS: Opioid-dependent subjects (n = 119) maintained on methadone (15-300 mg/day) were genotyped for five single nucleotide polymorphisms of ABCB1 (61A > G; 1199G > A; 1236C > T; 2677G > T; 3435C > T), as well as for the OPRM1 118A > G single nucleotide polymorphism. Subjects' methadone doses and trough plasma (R)-methadone concentrations (C(trough)) were compared between ABCB1 haplotypes (with and without controlling for OPRM1 genotype), and between OPRM1 genotypes (with and without controlling for ABCB1 haplotype). RESULTS: Among wild-type OPRM1 subjects, an ABCB1 variant haplotype group (subjects with a wild-type and 61A:1199G:1236C:2677T:3435T haplotype combination, or homozygous for the 61A:1199G:1236C:2677T:3435T haplotype) had significantly lower doses (median ± standard deviation 35 ± 5 versus 180 ± 65 mg/day, P < 0.01) and C(trough) (78 ± 22 versus 177 ± 97 ng/mL, P < 0.05) than ABCB1 wild-type subjects. Among subjects with the most common ABCB1 haplotype combination (wild-type with 61A:1199G:1236T:2677T:3435T), the OPRM1 118 A/G genotype was associated with a significantly higher C(trough) than 118 A/A (250 ± 126 versus 108 ± 36 ng/mL, P = 0.016). No ABCB1 haplotype group or OPRM1 genotype was associated with dose or C(trough) without taking into account confounding genetic variability at the other locus. Therefore, two interacting pharmacogenetic determinants of methadone maintenance treatment response were identified, ie, ABCB1, where variants are associated with lower methadone requirements, and OPRM1, where the variant is associated with higher methadone requirements. CONCLUSION: These opposing pharmacogenetic effects therefore need to be considered in combination when assessing methadone maintenance treatment pharmacogenetics.

Harnessing pain heterogeneity and RNA transcriptome to identify blood-based pain biomarkers: a novel correlational study design and bioinformatics approach in a graded chronic constriction injury model.

A quantitative, peripherally accessible biomarker for neuropathic pain has great potential to improve clinical outcomes. Based on the premise that peripheral and central immunity contribute to neuropathic pain mechanisms, we hypothesized that biomarkers could be identified from the whole blood of adult male rats, by integrating graded chronic constriction injury (CCI), ipsilateral lumbar dorsal quadrant (iLDQ) and whole blood transcriptomes, and pathway analysis with pain behavior. Correlational bioinformatics identified a range of putative biomarker genes for allodynia intensity, many encoding for proteins with a recognized role in immune/nociceptive mechanisms. A selection of these genes was validated in a separate replication study. Pathway analysis of the iLDQ transcriptome identified Fcγ and Fcε signaling pathways, among others. This study is the first to employ the whole blood transcriptome to identify pain biomarker panels. The novel correlational bioinformatics, developed here, selected such putative biomarkers based on a correlation with pain behavior and formation of signaling pathways with iLDQ genes. Future studies may demonstrate the predictive ability of these biomarker genes across other models and additional variables.