Comparison of two screening methods for in-house genotyping in clinical pharmacology units

Two genetic screening methods, the fluorescence resonance energy transfer (FRET) technique on the LightCycler and the real-time pyrophosphate detection technique on the Pyrosequencer have been compared with regard to their usefulness as screening methods for subject recruitment in clinical studies in pharmacology units. Two SNPs of possible clinical relevance were selected, namely the 118A>G SNP of the OPRM1 gene and the 3435C>T SNP of the ABCB1 gene. Genotypes diagnosed using conventional sequencing served as control. The allelic frequency of the mutated 118G allele of the OPRM1 gene was 12.7% and that of the mutated 3435T allele of the ABCB1 gene was 50.7%. All results obtained with the Pyrosequencer were in accord with those obtained using conventional sequencing. With the LightCycler, an incorrect genotype was assigned to 1 of the 130 DNA samples corresponding to an error rate of 0.8%. Although both methods were found suitable for rapid SNP detection, Pyrosequencing was the preferred method since it provides the nucleotide sequence directly thus facilitating interpretation.

Single-step identification of all length polymorphisms in the UGT1A1 gene promoter

AIM

To provide a sensitive genetic screening method for rapid identification of all known length polymorphisms in the promoter region of the uridine 5'-diphosphoglucose glucuronosyltransferase (UGT) 1A1 gene comprising (TA)5, (TA)7 and (TA)8 repeats as opposed to the non-mutated (TA)6 allele.

METHODS

The UGT1A1 promoter genotype was assessed in 115 subjects by means of a newly developed pyrosequencing method. PCR-generated DNA templates of heterozygous (TA)5 and (TA)7 carriers were cloned into a TOPO TA vector and verified by sequencing. In addition, a (TA)8 segment was produced by cloning to demonstrate the ability of the method to detect this mutation.

RESULTS

All length polymorphisms of the UGT1A1 promoter described in the literature were clearly identified. Fifteen subjects had Gilbert's syndrome with elevated serum bilirubin associated with a homozygous (TA)7TAA/(TA)7TAA genotype. Two subjects with the rare genotypes (TA)5TAA/(TA)6TAA and (TA)5TAA/(TA)7TAA were found, where only the latter one displayed elevated serum bilirubin levels. Allelic frequencies were 0.9%, 66.1% and 33% for the (TA)5TAA, (TA)6TAA and (TA)7TAA allele, respectively.

CONCLUSION

Our method enables reliable genetic single-step screening for all known length polymorphisms in the UGT1A1 gene promoter that cause Gilbert's syndrome. This facilitates pharmacogenetic-guided dosing of drugs with known toxicity metabolized by UGT1A1.

BER, MGMT, and MMR in defense against alkylation-induced genotoxicity and apoptosis

Methylating carcinogens and cytostatic drugs induce different methylation products in DNA. In cells not expressing the repair protein MGMT or expressing it at a low level, O6-methylguanine is the major genotoxic, recombinogenic, and apoptotic lesion. Genotoxicity and apoptosis triggered by O6-methylguanine require mismatch repair (MMR). In cells expressing O6-methylguanine-DNA methyl transferase (MGMT) at a high level or for agents producing low amounts of O6-methylguanine, N-alkylations become the major genotoxic lesions. N-Alkylations are repaired by base excision repair (BER). In mammalian cells, naturally occurring mutants of BER have not been detected, which points to the importance of BER for viability. In order to ascertain the role of BER in cellular defense, BER was modulated either by transfection or mutational inactivation. It has been shown that overexpression of N-methylpurine-DNA glycosylase (MPG) does not protect, but rather sensitizes cells to SN2 agents. This has been interpreted in terms of an imbalance in BER. Regarding abasic site endonuclease (APE), transient but not stable overexpression of the enzyme was achieved upon transfection in CHO cells, which indicates that unphysiologic APE levels are not tolerated by the cell. Besides the repair function, APE (alias Ref-1) exerts redox capability by which the activity of various transcription factors is modulated. Therefore, it is possible that stable overexpression of mammalian APE impairs transcriptional regulation of genes, whereas transient overexpression may exert some protective effect. DNA polymerase beta (Pol beta) transfection was ineffective in conferring resistance to methylmethane sulfonate (MMS). On the other hand, Pol beta-deficient cells proved to be highly sensitive to methylation-induced chromosomal aberrations and reproductive cell death. The dramatic hypersensitivity in the killing response is largely due to induction of apoptosis. Obviously, nonrepaired BER intermediates are clastogenic and act as a strong trigger of the apoptotic pathway. The elements of this pathway are currently under investigation.

The transfer half-life of morphine-6-glucuronide from plasma to effect site assessed by pupil size measurement in healthy volunteers

BACKGROUND

Clinical and experimental data suggested a long delay between the plasma concentration versus time course of morphine-6-glucuronide and the time course of its central opioid effects. This study was aimed at the quantification of the transfer half-life (t(1/2,ke0)) of this delay.

METHODS

Pupil size was used as a measure of central opioid effect. Eight healthy volunteers (four men, four women) participated in that single-blind randomized crossover study. Median dosages administered intravenously were 0.5 mg morphine as loading dose followed by 10.7 mg given as infusion over a period of 4.7 h, and 10.2 mg M6G as loading dose followed by 39.1 mg M6G given over a period of 3.7 h. The duration of the infusion was tailored to achieve submaximum pupil constriction. The pupil diameter was assessed every 20 min for approximately 18 h. Values of t(1/2,ke0) were obtained by semiparametric pharmacokinetic-pharmacodynamic modeling.

RESULTS

The estimated median t(1/2,ke0) of M6G was 6.4 h (range, 2.9-16.2 h), and that of morphine was 2.8 h (range, 1.8-4.4 h). The individual t(1/2,ke0) of M6G was always longer than that of morphine. Judged by the concentration at half-maximun effect (EC50) values of the sigmoid pupil size at maximum constriction (Emax) model describing concentration-response relation, M6G was apparently 22 times less potent than morphine (EC50 = 740.5 nm [range, 500-1,520 nm] for M6G and 36.2 nm [range, 19.7-43.3 nm] for morphine). The steepness of the sigmoid Emax model did not significantly differ between morphine and M6G (gamma = 1.9 and 2.6, respectively). To produce similar pupil effects, the M6G dose had to be 2.8 times greater than the morphine dose.

CONCLUSIONS

The reported numerical value of the t(1/2,ke0) of M6G in humans obtained after direct administration of M6G is a step toward a complete modeling approach to the prediction of the clinical effects of morphine. The study raises questions about the high interindividual variability of the transfer half-life between plasma and effect site (ke0) values and the apparent low potency of M6G.

A rapid screening method for a single nucleotide polymorphism (SNP) in the human MOR gene

AIMS

Genetic association studies have suggested that the single nucleotide polymorphism (SNP) at position 118 of the human mu-opioid receptor (MOR) gene could be a potential risk factor for drug treatment variability in patients. Therefore, we wanted to develop a fast and reliable detection method for this SNP which is applicable in a clinical setting.

METHODS

To detect the polymorphism at position A118-->G in the human MOR gene we used the fluorescence resonance energy transfer (FRET)-PCR technique with subsequent melting curve analysis.

RESULTS

The polymorphism at position A118-->G in the human MOR gene could be clearly discriminated with melting peak temperatures of 69.8 degrees C and 63.8 degrees C, corresponding to the wild type and mutated MOR allele, respectively. The results from FRET-PCR were validated by sequencing and restriction-fragment length polymorphism (RFLP). Screening of blood samples from 100 subjects showed an allelic distribution for the human MOR alleles of 79% (homozygous wild type), 20% (heterozygous) and 0.9% (homozygous mutated).

CONCLUSIONS

The FRET-PCR protocol for detection of the human MOR gene polymorphism at position 118 offers a rapid and reliable method which could be used for population screening of this and other genes.

COX-2 independent induction of cell cycle arrest and apoptosis in colon cancer cells by the selective COX-2 inhibitor celecoxib

The regular use of various nonsteroidal anti-inflammatory drugs (NSAIDs) was shown to decrease the incidence of colorectal cancer. This effect is thought to be caused predominantly by inhibition of cyclooxygenase-2 (COX-2) and, subsequently, prostaglandin synthesis. However, recent studies have suggested that COX-independent pathways may contribute considerably to these antiproliferative effects. To evaluate the involvement of COX-dependent and COX-independent mechanisms further, we assessed the effects of celecoxib (selective COX-2 inhibitor) and SC560 (selective COX-1 inhibitor) on cell survival, cell cycle distribution, and apoptosis in three colon cancer cell lines, which differ in their expression of COX-2. Both drugs induced a G0/G1 phase block and reduced cell survival independent of whether or not the cells expressed COX-2. Celecoxib was more potent than SC560. The G0/G1 block caused by celecoxib could be attributed to a decreased expression of cyclin A, cyclin B1, and cyclin-dependent kinase-1 and an increased expression of the cell cycle inhibitory proteins p21Waf1 and p27Kip1. In addition, celecoxib, but not SC560, induced apoptosis, which was also independent of the COX-2 expression of the cells. In vivo, celecoxib as well as SC560 reduced the proliferation of HCT-15 (COX-2 deficient) colon cancer xenografts in nude mice, but both substances had no significant effect on HT-29 tumors, which express COX-2 constitutively. Thus, our in vitro and in vivo data indicate that the antitumor effects of celecoxib probably are mediated through COX-2 independent mechanisms and are not restricted to COX-2 over-expressing tumors.

A rapid screening method for a single nucleotide polymorphism (SNP) in the human MOR gene

AIMS

Genetic association studies have suggested that the single nucleotide polymorphism (SNP) at position 118 of the human mu-opioid receptor (MOR) gene could be a potential risk factor for drug treatment variability in patients. Therefore, we wanted to develop a fast and reliable detection method for this SNP which is applicable in a clinical setting.

METHODS

To detect the polymorphism at position A118-->G in the human MOR gene we used the fluorescence resonance energy transfer (FRET)-PCR technique with subsequent melting curve analysis.

RESULTS

The polymorphism at position A118-->G in the human MOR gene could be clearly discriminated with melting peak temperatures of 69.8 degrees C and 63.8 degrees C, corresponding to the wild type and mutated MOR allele, respectively. The results from FRET-PCR were validated by sequencing and restriction-fragment length polymorphism (RFLP). Screening of blood samples from 100 subjects showed an allelic distribution for the human MOR alleles of 79% (homozygous wild type), 20% (heterozygous) and 0.9% (homozygous mutated).

CONCLUSIONS

The FRET-PCR protocol for detection of the human MOR gene polymorphism at position 118 offers a rapid and reliable method which could be used for population screening of this and other genes.

Inhibition of NF-kappaB and AP-1 activation by R- and S-flurbiprofen

R-flurbiprofen is considered the 'inactive' isomer of the nonsteroidal anti-inflammatory drug (NSAID), flurbiprofen, because it does not inhibit cyclooxygenase (COX) activity. However, previous studies have revealed that it has antinociceptive and antitum or effects not due to epimerization to the cyclooxygenase-inhibiting S-isomer. Here, we show that R-flurbiprofen has additional anti-inflammatory activity comparable with that of dexamethasone in the zymosan-induced paw inflammation model in rats. Different criteria suggest that the observed effects are mediated at least in part through inhibition of NF-kB activation: R-flurbiprofen inhibited i) LPS-induced NF-kB DNA binding activity in RAW 264.7 macrophages, ii) translocation of the p65 subunit of NF-kB into the nucleus of these cells, and iii) zymosan-induced NF-kB-dependent gene transcription in the inflamed paw and spinal cord of rats. S-flurbiprofen produced similar effects but was less potent. In addition, R-flurbiprofen inhibited DNA binding activity of AP-1, another key regulatory transcription factor in inflammatory processes. Because R-flurbiprofen does not cause gastrointestinal mucosal damage or other side effects associated with long-term NSAID or glucocorticoid use, it might be a useful drug in inflammatory or other diseases in which increased or constitutive NF-kB and AP-1 activation are involved in the pathophysiological processes.

Transcriptional activation of apurinic/apyrimidinic endonuclease (Ape, Ref-1) by oxidative stress requires CREB

Apurinic/apyrimidinic endonuclease (APE alias Ref-1) is a multifunctional enzyme involved in DNA repair and redox regulation of transcription factors (e.g., AP-1). It also acts as a repressor of its own and other genes. Recently, it was shown that the level of APE mRNA and protein is enhanced upon treatment of cells with oxidative agents, such as hydrogen peroxide (H(2)O(2)), which gives rise to an adaptive response of cells to oxidative stress. Induction of APE is due to APE promoter activation. To elucidate the mechanism of transcriptional activation of APE by oxidative agents, we introduced mutations into the cloned human APE promoter and checked its activity in transient transfection assays. Here we demonstrate that mutational inactivation of a CREB binding site (CRE) present within the promoter completely abolished APE promoter activation by H(2)O(2), indicating that CREB is required for APE induction. The CRE element in the context of the APE promoter sequence binds c-Jun and ATF-2, which was shown in gel retardation experiments. Under conditions of induction of APE by H(2)O(2), the expression of c-Jun was significantly enhanced, which supports the view that induction of c-Jun is involved in signaling leading to APE promoter activation by oxidative stress.

Apurinic endonuclease (Ref-1) is induced in mammalian cells by oxidative stress and involved in clastogenic adaptation

Apurinic endonuclease (APE; also known as Ref-1 protein) is a key enzyme in base excision repair, cleaving apurinic sites that arise spontaneously because of the activity of DNA glycosylases. To address the question of whether APE can be modulated by genotoxic stress affecting cellular protection, we analyzed the expression of APE in Chinese hamster ovary (CHO) cells after treatment with various genotoxic agents. We show that treatment of CHO cells with hydrogen peroxide (H2O2) or sodium hypochlorite (NaOCl) increases the levels of APE mRNA and protein. APE induction was observed 3-9 h after treatment and was accompanied by an increase in APE activity. We also show that the cloned human APE promoter transfected into CHO cells is stimulated by the oxidants, indicating transcriptional activation of the APE gene. When cells were pretreated with NaOCl, inducing APE, and then challenged with H2O2, the clastogenic effect of the challenge dose was significantly reduced, suggesting clastogenic adaptation due to APE induction. To further prove the involvement of APE in adaptation against induced chromosomal breakage, we transfected human APE cDNA driven by an inducible promoter into CHO cells and observed that transient induction of APE reduced the clastogenic effect of H2O2. Overall, the data demonstrate that the APE gene can be activated by oxidative agents, resulting in a transient increase in APE repair activity, which reduces the clastogenic response of cells to an oxidative agent. The protection of cells from chromosomal aberrations seen after prior exposure to oxidants is attributed to an adaptive response to oxidative stress.

Regulation of expression of the DNA repair gene O6-methylguanine-DNA methyltransferase via protein kinase C-mediated signaling

O6-Alkylguanine is the major mutagenic and cytotoxic DNA lesion induced by alkylating agents, including 2-chloroethyl-N-nitrosourea-based antitumor drugs. This lesion is repaired by O6-methylguanine-DNA methyltransferase (MGMT), the expression of which is highly variable in both normal tissues and in tumor cells. The promoter of the human MGMT gene was found to contain two putative activator protein (AP)-1 sites. Here, we show that the level of MGMT mRNA in HeLa S3 cells was increased 3-5-fold by phorbol-12-myristate-13-acetate (TPA) and 1,2-diacyl-sn-glycerol (DAG), which are activators of protein kinase C (PKC), as well as by okadaic acid, an inhibitor of protein phosphatases. The PKC inhibitor 1-(5-isoquinoline sulfonyl)-2-methylpiperazine-HCl eliminated MGMT activation by TPA and DAG but not by OA. Prior down-regulation of PKC abolished subsequent effects of TPA or DAG. The results indicate AP-1 to be involved in regulation of MGMT expression. This hypothesis was supported by showing AP-1 binding to two target sequences of the MGMT promoter and transactivation of the MGMT promoter upon cotransfection with c-fos and c-jun in F9 cells. That TPA-mediated induction of MGMT caused increased cellular resistance to 2-chloroethyl-N-nitrosourea suggests a therapeutic significance for PKC-mediated MGMT modulation.