CYP2B6 gene single nucleotide polymorphisms and leukemia susceptibility

An Updated Overview of the Role of CYP450 during Xenobiotic Metabolization in Regulating the Acute Myeloid Leukemia Microenvironment

Oxidative stress is associated with several acute and chronic disorders, including hematological malignancies such as acute myeloid leukemia, the most prevalent acute leukemia in adults. Xenobiotics are usually harmless compounds that may be detrimental, such as pharmaceuticals, environmental pollutants, cosmetics, and even food additives. The storage of xenobiotics can serve as a defense mechanism or a means of bioaccumulation, leading to adverse effects. During the absorption, metabolism, and cellular excretion of xenobiotics, three steps may be distinguished: (i) inflow by transporter enzymes, (ii) phases I and II, and (iii) phase III. Phase I enzymes, such as those in the cytochrome P450 superfamily, catalyze the conversion of xenobiotics into more polar compounds, contributing to an elevated acute myeloid leukemia risk. Furthermore, genetic polymorphism influences the variability and susceptibility of related myeloid neoplasms, infant leukemias associated with mixed-lineage leukemia (MLL) gene rearrangements, and a subset of de novo acute myeloid leukemia. Recent research has shown a sustained interest in determining the regulators of cytochrome P450, family 2, subfamily E, member 1 (CYP2E1) expression and activity as an emerging field that requires further investigation in acute myeloid leukemia evolution. Therefore, this review suggests that CYP2E1 and its mutations can be a therapeutic or diagnostic target in acute myeloid leukemia.

Association between CYP2B6 c.516G >T variant and acute leukaemia: A protocol for systematic review and meta-analysis

BACKGROUND

Acute leukemia (AL) is a kind of malignant tumor of hematopoietic system. A number of studies have suggested that Single Nucleotide Polymorphisms are significantly associated with risk of AL. Present study performs meta-analysis to evaluate the association between CYP2B6 c.516G>T variant and AL risk.

METHODS

Databases including PubMed, EMBASE, Chinese National Knowledge Infrastructure (CNKI), and Wanfang were searched for literatures to September 30, 2019, both in English and Chinese. Relative risk and its 95% confidence intervals were used to assess the associations. Statistical analyses of this meta-analysis were conducted by using STATA 13.0. software.

RESULTS

A total of 7 studies, including 1038 cases and 1648 controls, were analyzed. Our results indicated that CYP2B6 c.516G>T variant was significantly related to an increased the risk of AL under dominant model, recessive model, homozygote model, and allelic model. In addition, subgroup analyses were also performed by disease classification, country, and study design. No significant associations were obtained between CYP2B6 c.516G>T variant and the risk of AL under the recessive model in the design of hospital-based (relative risk = 0.98; 95% confidence interval: 0.95-1.01; P  = 0.118).

CONCLUSION

Our meta-analysis indicated that the CYP2B6 variant is significantly associated with AL risk, in which CYP2B6 c.516G>T is related to an increased risk of AL.

Impact of Cytochromes P450 3A4 and 2B6 gene polymorphisms on predisposition and prognosis of acute myeloid leukemia: an Egyptian case-control study

Background

It has been postulated that the interaction between environmental risk factors and genetic susceptibility is a possible cause for the development of acute myeloid leukemia (AML). Cytochrome P450 (CYP) detoxification enzymes are responsible for the elimination of oxidative stress. Genetic polymorphisms in these enzymes may cause AML due to enhanced accumulation of reactive oxygen species. To study the association between CYP3A4 (A290G) and CYP2B6 (G516T) gene polymorphisms and the predisposition and prognosis of AML, 50 upfront AML patients and 50 healthy individuals were genotyped for CYP2B6 (G516T) and CYP3A4 (A290G) single-nucleotide polymorphisms (SNPs) using polymerase chain reaction (PCR)-based restriction fragment length polymorphism (RFLP) technique. The polymorphisms were evaluated in relation to the response to chemotherapy and survival.

Results

CYP2B6 gene mutation carries a threefold risk of developing AML (odds ratio [OR], 3.0; 95% confidence interval [CI], 1.3–6.9), whereas CYP3A4 gene mutation carries approximately fourfold risk (OR, 3.8; 95% CI, 1.4–10.1). The presence of combined gene mutation conferred about 15-fold increased risk of developing AML compared with the presence of a single gene mutation (OR, 14.8; 95% CI, 1.8–124.2). CYP3A4 gene mutation is associated with worse overall survival (P = 0.030).

Conclusion

CYP enzyme gene polymorphisms are associated with the development of AML. Elimination of oxidative stress in genetically susceptible individuals may decrease the risk of AML and may improve survival.

Association between CYP2B6 polymorphism and acute leukemia in a Han population of Northwest China

Background

The aim of this study was to investigate potential associations between CYP2B6 c.516G>T polymorphism and the occurrence and prognosis of acute leukemias (AL) in the Han population of Northwest China.

Methods

The CYP2B6 gene polymorphism was analyzed by PCR‐RFLP and Sanger DNA sequencing in 126 patients with AL and 161 healthy controls.

Results

Compared with controls, there were significantly higher frequencies of GT and TT genotypes and T alleles in AL patients (p < .05), particularly in fusion gene‐positive AL patients. There was no significant difference in CYP2B6 polymorphic genotypes and T alleles between AL patients with complete remission after the first course of chemotherapy and controls (p > .05), while the frequencies in AL patients with partial remission and no remission were significantly higher. The CYP2B6 allele frequency in Han Chinese in Northwest China was significantly different to that reported in Han Chinese and other ethnic minorities in southern China, Uygur Chinese, Vietnamese, African, German, British, Spanish, Turkish, and Argentinian populations; however, there was no significant difference compared with allele frequencies reported in Tibetan and Mongolian Chinese, Japanese, Korean, and American populations.

Conclusion

Our findings show a strong correlation of the CYP2B6 c.516G>T polymorphism in the Han population of Northwest China with AL, especially fusion gene‐positive AL, and indicate a poor prognosis after the first course of chemotherapy. Our findings also implicate the T allele in AL susceptibility and indicate the existence of racial and geographical differences in allele frequencies of CYP2B6 c.516G>T polymorphism.

Inter-Individual Variability in Xenobiotic-Metabolizing Enzymes: Implications for Human Aging and Longevity

Xenobiotic-metabolizing enzymes (XME) mediate the body’s response to potentially harmful compounds of exogenous/endogenous origin to which individuals are exposed during their lifetime. Aging adversely affects such responses, making the elderly more susceptible to toxics. Of note, XME genetic variability was found to impact the ability to cope with xenobiotics and, consequently, disease predisposition. We hypothesized that the variability of these genes influencing the interaction with the exposome could affect the individual chance of becoming long-lived. We tested this hypothesis by screening a cohort of 1112 individuals aged 20–108 years for 35 variants in 23 XME genes. Four variants in different genes (CYP2B6/rs3745274-G/T, CYP3A5/rs776746-G/A, COMT/rs4680-G/A and ABCC2/rs2273697-G/A) differently impacted the longevity phenotype. In particular, the highest impact was observed in the age group 65–89 years, known to have the highest incidence of age-related diseases. In fact, genetic variability of these genes we found to account for 7.7% of the chance to survive beyond the age of 89 years. Results presented herein confirm that XME genes, by mediating the dynamic and the complex gene–environment interactions, can affect the possibility to reach advanced ages, pointing to them as novel genes for future studies on genetic determinants for age-related traits.

Association of SLC28A3 Gene Expression and CYP2B6*6 Allele with the Response to Fludarabine Plus Cyclophosphamide in Chronic Lymphocytic Leukemia Patients

Fludarabine plus cyclophosphamide (FC) chemotherapy is the basis of treatment protocols used in management of chronic lymphocytic leukemia (CLL). In some patients, response to therapy may be affected by aberrant function of genes involved in pharmacokinetics and pharmacodynamics of the drugs. The aim of this research was to assess the impact of pharmacogenetic variability, namely expression of SLC28A3 gene and the presence of CYP2B6*6 variant allele, on the FC treatment efficacy. Forty-four CLL patients with functional TP53 gene at the time of FC initiation were enrolled in this study. CYP2B6 genotyping was performed by polymerase chain reaction and direct sequencing. SLC28A3 expression was measured by quantitative reverse-transcriptase polymerase chain reaction. Significantly higher pretreatment levels of SLC28A3 mRNA were detected in patients who failed to respond to FC in comparison to patients who achieved complete and partial response (p = 0.01). SLC28A3 high-expressing cases were almost ten times more likely not to respond to FC than low-expressing cases (OR = 9.8; p = 0.046). However, association of SLC28A3 expression with progression-free survival (PFS) and overall survival (OS) was not observed. CYP2B6*6 allele, detected in 24 patients (54.6%), exerted no association with the attainment of response to FC, as well as with PFS and OS. The results of this study demonstrate that SLC28A3 expression is a significant predictor of FC efficacy in CLL patients with intact TP53. Elevated SLC28A3 mRNA levels are associated with inferior short-term response to FC, suggesting that, if validated on larger cohorts, SLC28A3 expression may become a biomarker useful for pretreatment stratification of patients.

Polymorphisms and haplotypes of the CYP2B6 detoxification gene in the predisposition of Acute Myeloid Leukemia (AML) and induction of its cytogenetic abnormalities

CYP2B6 is a polymorphic detoxification gene which plays a vital role in the degradation of genotoxic compounds. In this study we hypothesized that inadequate detoxification due to CYP2B6 polymorphisms may contribute to AML. To evaluate the potential impact of CYP2B6 polymorphisms on AML development and induction of its specific chromosomal abnormalities we studied C⁷⁷⁷A and A⁷⁸⁵G polymorphisms for the first time in AML. Furthermore, we investigated the co-existence of the above polymorphisms with G⁵¹⁶T polymorphism to determine the CYP2B6 high-risk haplotypes in AML susceptibility. Our study included 619 AML patients and 430 healthy donors. Concerning C⁷⁷⁷A CYP2B6 polymorphism, no significant difference was found between patients and controls. However, A⁷⁸⁵G CYP2B6 polymorphism showed a statistically higher frequency of the variant genotypes in patients (48.2%), mainly in secondary AML patients (49.1%) than in controls (26.1%). Moreover, an increased frequency of the variant genotypes was found in those with abnormal karyotypes, especially with -7/del(7q), -5/del(5q), +8, inv(16) and t(8;21). The combination of the three CYP2B6 polymorphisms (G⁵¹⁶T, C⁷⁷⁷A & A⁷⁸⁵G) revealed seven haplotypes. Four out of six haplotypes with at least one mutant allele were significantly associated with an increased risk for AML. Interestingly, T₅₁₆A₇₇₇G₇₈₅ haplotype, where the three mutant alleles co-existed, had ~3-fold increased risk to be found in patients than controls. The association between haplotypes and cytogenetic aberrations revealed a positive correlation between specific CYP2B6 haplotypes and AML cytogenetic abnormalities. Our data suggest that A⁷⁸⁵G CYP2B6 gene polymorphism and specific CYP2B6 haplotypes may contribute to AML and its specific chromosomal aberrations.

Prognostic Value of a CYP2B6 Gene Polymorphism in Patients with Acute Myeloid Leukemia

BACKGROUND

The objectives of this study aimed to detect a CYP2B6 polymorphism in de novo cases of acute myeloid leukemia patients and identify any role in disease progression and outcome.

MATERIALS AND METHODS

DNA was isolated from peripheral blood of 82 newly diagnosed acute myeloid leukemia cases and the CYP2B6 G15631T gene polymorphism was assayed by PCR restriction fragment length polymorphism (PCR-RFLP).

RESULTS

The frequency of the GG genotype (wild type) was 48 (58.5%) and that of the mutant type T allele was 34 (41.9%). GT genotype heterozygous variants were found in 28 (34%), and TT genotype homozygous variants in 6 (7.3%) cases. We found no significant association between the CYP2B6 G15631T polymorphism and complete response (CR) (p-value=0.768), FAB classification (p-value=0.51), cytogenetic analysis (p-value=0.673), and overall survival (p-value=0.325). Also, there were no significant links with early toxic death (p-value=0.92) or progression- free survival (PFS) (p-value=0.245).

CONCLUSIONS

Our results suggest that the CYP2B6 polymorphism has no role in disease progression, therapeutic outcome, patient free survival, early toxic death and overall survival in acute myeloid leukemia patients.

Associations Between CYP2B6 rs707265, rs1042389, rs2054675, and Hirschsprung Disease in a Chinese Population

BACKGROUND

Previous studies suggested that cytochrome P450 participated in the tumor metastasis and migration. CYP2B6 also acts as an important enzyme which metabolize partially or primarily metabolism of drugs, environmental contaminants, and mutagens. The objective of this study was to investigate the influence of CYP2B6 polymorphism on susceptibility of Hirschsprung disease.

METHODS

TaqMan assay was performed to determine the genotypes of CYP2B6 rs707265, rs1042389, rs2054675 in 262 cases and 290 control subjects. Logistic regression was used to assess the associations between these polymorphisms and HSCR.

RESULTS

We observed a significant association of CYP2B6 rs707265 (G>A) polymorphism and HSCR susceptibility (p < 0.001). Besides, rs707265 A presented a significant risk of HSCR (p < 0.001).

CONCLUSIONS

Our result suggested that CYP2B6 rs707265 modified the risk of HSCR.

Genetic variation in the CYP2B6 gene is related to circulating 2,2',4,4'-tetrabromodiphenyl ether (BDE-47) concentrations: an observational population-based study

BACKGROUND

Since human CYP2B6 has been identified as the major CYP enzyme involved in the metabolism of 2,2',4,4'-tetrabromodiphenyl ether (BDE-47) and that human 2B6 is a highly polymorphic CYP, with known functional variants, we evaluated if circulating concentrations of a major brominated flame retardant, BDE-47, were related to genetic variation in the CYP2B6 gene in a population sample.

METHODS

In the population-based Prospective Investigation of the Vasculature in Uppsala Seniors (PIVUS) study (men and women all aged 70), 25 single nucleotide polymorphisms (SNPs) in the CYP2B6 gene were genotyped. Circulating concentrations of BDE-47 were analyzed by high-resolution gas chromatography coupled to high-resolution mass spectrometry (HRGC/ HRMS).

RESULTS

Several SNPs in the CYP2B6 gene were associated with circulating concentrations of BDE-47 (P = 10-4 to 10-9). The investigated SNPs came primarily from two haplotypes, although the correlation between the haplotypes was rather high. Conditional analyses adjusting for the SNP with the strongest association with the exposure (rs2014141) did not provide evidence for independent signals.

CONCLUSION

Circulating concentrations of BDE-47 were related to genetic variation in the CYP2B6 gene in an elderly population.

The G⁵¹⁶T CYP2B6 germline polymorphism affects the risk of acute myeloid leukemia and is associated with specific chromosomal abnormalities

The etiology of acute myeloid leukemia (AML) underlies the influence of genetic variants in candidate genes. The CYP2B6 enzyme detoxifies many genotoxic xenobiotics, protecting cells from oxidative damage. The CYP2B6 gene is subjected to a single-nucleotide polymorphism (G⁵¹⁶T) with heterozygotes (GT) and homozygotes (TT) presenting decreased enzymatic activity. This case-control study aimed to investigate the association of CYP2B6 G⁵¹⁶T polymorphism with the susceptibility of AML and its cytogenetic and clinical characteristics. Genotyping was performed on 619 AML patients and 430 healthy individuals using RCR-RFLP and a novel LightSNip assay. The major finding was a statistically higher frequency of the variant genotypes (GT and TT) in patients compared to the controls (GT:38.8% vs 29.8% and TT:9.3% vs 5.3% respectively) (p<0.001). More specifically, a significantly higher frequency of GT+TT genotypes in de novo AML patients (46.6%) and an immensely high frequency of TT in secondary AML (s-AML) (20.5%) were observed. The statistical analysis showed that the variant T allele was approximately 1.5-fold and 2.4-fold higher in de novo and s-AML respectively than controls. Concerning FAB subtypes, the T allele presented an almost 2-fold increased in AML-M2. Interestingly, a higher incidence of the TT genotype was observed in patients with abnormal karyotypes. In particular, positive correlations of the mutant allele were found in patients carrying specific chromosomal aberrations [-7/del(7q), -5/del(5q), +8, +21 or t(8;21)], complex or monosomal karyotypes. Finally, a strikingly higher frequency of TT genotype was also observed in patients stratified to the poor risk group. In conclusion, our results provide evidence for the involvement of the CYP2B6 polymorphism in AML susceptibility and suggest a possible role of the CYP2B6 genetic background on the development of specific chromosomal aberrations.

Functional polymorphism of CYP2B6 G15631T is associated with hematologic and cytogenetic response in chronic myeloid leukemia patients treated with imatinib

In the spite of the impressive results achieved with imatinib in chronic myeloid leukemia (CML) patients, differences in patient's response are observed, which may be explained by interindividual genetic variability. It is known that cytochrome P450 enzymes play a major role in the metabolism of imatinib. The present study aimed to understand the functional impact of CYP2B6 15631G>T polymorphism on the response of imatinib in CML patients and its relation to CML susceptibility. We have genotyped CYP2B6 G15631T in 48 CML patients and 64 controls by PCR-RFLP. CYP2B6 15631G>T was not found to be a risk factor for CML (OR 95 % CI, 1.12, 0.6-2, p > 0.05). Hematologic response loss was higher in patients with 15631GG/TT genotype when compared with 15631GT (36.8 vs. 13.8 %; X (2) = 3.542, p = 0.063). Complete cytogenetic response was higher in 15631GG/GT genotype groups when compared with 15631TT (X (2) = 3.298, p = 0.024). Primary cytogenetic resistance was higher in patients carrying 15631GG/TT genotype when compared with 15631GT carriers (52.6 vs. 17.2 %; X (2) = 6.692, p = 0.010). Furthermore, side effects were more common for patients carrying 15631GG genotypes when compared with GT/TT carriers (36 vs. 13.8 %; X (2) = 8.3, p = 0.004). In light of our results, identification of 15631G>T polymorphism in CML patients might be helpful to predict therapeutic response to imatinib.

CYP2B6*6 is associated with increased breast cancer risk

The cytochrome P450 2B6 (CYP2B6) is involved in the metabolism of testosterone. Functional changes in this enzyme may influence endogenous hormone exposure, which has been associated with risk of breast cancer. To assess potential associations between two functional polymorphisms CYP2B6_516_G>T (rs3745274) and CYP2B6_785_A>G (rs2279343) and breast cancer risk, we established a specific matrix-assisted laser desorption/ionization time-of-flight mass spectrometry assay. The GENICA breast cancer case-control study showed associations between the variant genotypes CYP2B6_516_TT and CYP2B6_785_GG and breast cancer risk with odds ratios (ORs) of 1.34 (p = 0.001) and 1.31 (p = 0.002), respectively. A similar effect was observed for carriers of the CYP2B6_516_T allele in a validation study including four independent studies from Germany, Sweden and USA. In a pooled analysis of all five studies involving 4,638 breast cancer cases and 3,594 controls of European ancestry, carriers of the CYP2B6_516_G and the CYP2B6_785_G variant had an increased breast cancer risk with ORs of 1.10 (p = 0.027) and 1.10 (p = 0.031), respectively. We conclude that the genetic variants CYP2B6_516_G and CYP2B6_785_G (designated CYP2B6*6), which are known to decrease activity of the CYP2B6 enzyme, contribute to an increased breast cancer risk.

MDR-1 and GST polymorphisms are involved in myelodysplasia progression

Myelodysplastic syndromes (MDS) are a heterogeneous group of clonal stem cell disorders characterized by abnormal hematopoietic differentiation and maturation, which progress toward acute leukemia in approximately 30% of the cases. Drug metabolism polymorphisms in Cytochrome P450 2B6 (CYP2B6), Glutathione S-transferase (GST) and Dehydrogenase Quinone 1 (NQO1) enzymes and P-glycoprotein (MDR-1) could modify enzyme activity. Thus, the aim of this study was to identify the influence of CYP2B6 G15631T, GSTT1, GSTM1, NQO1 C609T and MDR-1 C3435T polymorphisms on MDS progression. We analyzed 78 MDS patients using the PCR-RFLP and multiplex method. The frequency of GST deletions and MDR-1 CC genotype was lower in progression-free patients compared to patients with progression; GST: 17% vs. 35% (P=0.018); MDR-1 gene: 19% vs. 48% (P=0.012). We also verified the influence of GST deletions and MDR-1 C3435T on patient overall survival and found no significant difference (RR=0.75; P=0.599 and RR=0.79; P=0.594 respectively). We concluded that GSTM1 deletion may contribute toward MDS progression probably due to toxic metabolite accumulation which generates cell toxicity and DNA damage. Moreover, MDR-1 C3435T may have a protective effect against MDS progression because the expected lower expression of P-glycoprotein would lead to a higher degree of cell death. To the best of our knowledge, this is the first study showing the relationship of these polymorphisms with MDS progression.

Association between cytochrome P450 promoter polymorphisms and ischemic stroke

The human cytochrome P450 (CYP) superfamily includes at least 57 genes that encode enzymes with diverse metabolic and biosynthetic functions. This study was conducted in order to investigate the associations between polymorphisms in CYP superfamily genes (CYP11B2, CYP17A1, CYP2B6, CYP2C9, CYP2E1 and CYP7A1) and ischemic stroke (IS). Six single nucleotide polymorphisms (SNPs) of CYP superfamily genes were selected and genotyped by direct sequencing in 121 patients with IS and 321 control subjects. The genetic data were analyzed using SNPStats and SPSS 18.0. Multiple logistic regression models (codominant 1, codominant 2, dominant, recessive and log-additive) were used to evaluate odds ratios (ORs), 95% confidence intervals (CIs) and p-values. The rs179998 SNP of CYP11B2 was significantly associated with IS (p=0.0336 in a log-additive model). The rs3813867 SNP of CYP2E1 was significantly associated with smoking in IS (p=0.0336 in a log-additive model). The rs1799998 SNP of CYP11B2 and rs3808607 of CYP7A1 were related to diabetes mellitus in IS (p<0.05). CYP11B2, CYP2E1 and CYP7A1 SNPs were associated with IS in the population studied. Further study is required to confirm these associations and to determine their biological significance.

Cytochrome P450 CYP2B6 genotypes and haplotypes in a Colombian population: identification of novel variant CYP2B6 alleles

OBJECTIVE

Information on CYP2B6 allele frequencies and detrimental genotypes in mixed human populations is scarce. The aim of this study was to analyze the frequencies and haplotypes of nonsynonymous CYP2B6 single nucleotide polymorphisms (SNPs) in a Colombian population.

METHODS

One hundred and fifty-two healthy individuals were analyzed for five nonsynonymous CYP2B6 SNPs, namely rs8192709, rs3745274, rs2279343 rs28399499, and rs3211371.

RESULTS

Besides eight known variant alleles, we identified two as yet unknown variant alleles combining, respectively, the SNPs rs3745274 and rs3211371 and rs8192709 and rs3745274. Comparison of Colombian mestizo individuals with other mestizo population indicates statistically significant differences (P<0.001) for the gain-of-function CYP2B6*4 allele and for combined detrimental CYP2B6 alleles. In addition, we observed a low linkage between the SNPs rs3745274 and rs2279343, which are often assumed as linked.

CONCLUSION

In conclusion, large interethnic and intraethnic variability exists for CYP2B6 polymorphisms, thus reinforcing the need for tailored genotyping protocols for CYP2B6 testing as a biomarker of drug response.

Distribution of polymorphisms in cytochrome P450 2B6, histocompatibility complex P5, chemokine coreceptor 5, and interleukin 28B genes in inhabitants from the central area of Argentina

AIMS

The selection of the most appropriate treatment for several diseases relies on a number of factors such as environment, age, gender, and nutrition. Additionally, the contribution of different genetic polymorphisms to treatment efficacy has been largely recognized. The lack of information on the pharmacogenetic profile of our population prompted us to analyze the frequency of polymorphisms known to be relevant to achieve treatment efficacy with different therapeutic agents in viral infectious diseases, such as Hepatitis C and AIDS.

RESULTS

The allelic frequencies for the wild-type variant of the genes analyzed were cytochrome P450 2B6 (CYP2B6; rs3745274; 516G) 0.618 (95% confidence interval [CI]: 0.523, 0.711), chemokine coreceptor 5 (CCR5; rs333) 0.961 (95% CI: 0.942, 0.98), histocompatibility complex P5 (HCP5; rs2395029; 335T) 0.971 (95% CI: 0.937, 1), and interleukin 28B (IL28B; rs12979860; 12007005C) 0.656 (95% CI: 0.564, 0.747), respectively.

CONCLUSIONS

Our data indicate that the genetic profile of the population studied is similar to that reported for other Caucasian populations, with only slight differences for CYP2B6. Noteworthy, the considerable number of patients carrying CYP2B6 (516T) and IL28B (12007005T) alleles underlies the importance of considering pharmacogenetic testing before starting drug therapy protocols to prevent toxicity and/or lack of effectiveness in AIDS or hepatitis C virus infections.