Metabolism Of Docetaxel Research Articles

Effects of tesmilifene, a substrate of CYP3A and an inhibitor of P-glycoprotein, on the pharmacokinetics of intravenous and oral docetaxel in rats

It has been reported that docetaxel is a P-glycoprotein substrate and is metabolized via the cytochrome P450 (CYP) 3A subfamily in rats. Tesmilifene is a substrate of the CYP3A subfamily and is an inhibitor of P-glycoprotein. Thus, the effects of various doses of tesmilifene on the pharmacokinetics of intravenous and orally administered docetaxel have been investigated in rats. Docetaxel (20 mg/kg as base) was administered intravenously and orally without and with tesmilifene (5, 10, and 20 mg/kg) in rats. After intravenous administration of docetaxel with tesmilifene, the values of nonrenal clearance (CL(NR)) and area under the plasma concentration-time (AUC) for docetaxel were comparable with those without tesmilifene. Tesmilifene did not increase the values of AUC or of absolute oral bioavailability (F) for docetaxel after oral administration of docetaxel with tesmilifene. The inhibition for the metabolism of docetaxel via hepatic and intestinal CYP3A subfamily, and inhibition of P-glycoprotein-mediated efflux of docetaxel in the intestine by tesmilifene were almost negligible. The extremely low value of F for docetaxel was due to the incomplete absorption from the gastrointestinal tract and considerable first-pass metabolism of docetaxel in rats.

Efficacy versus toxicity of docetaxel in Asian and Caucasian cancer patients from the pharmacogenomics perspectives: a review of the literature

Docetaxel is a common anticancer agent in the treatment of breast and lung cancers. Metabolism of docetaxel occurs through cytochrome P450 (CYP) and the function of the enzyme can be altered by genetic, environmental and physiological factors. Interindividual differences in pharmacokinetic profiles of anticancer agents due to changes in CYP function lead to variations in drug efficacy and/or toxicity. Unpredictable toxicities of taxanes have been reported, related to interindividual variability of pharmacokinetics of the drugs. It is evident from multiple studies that adverse events, which are mainly haematological amongst Asian patients receiving docetaxel are higher than as reported in the Caucasian population. Most clinicians who treat Asian patients thus prophylactically support patients with growth factors or reduce the dose of docetaxel. Polymorphisms in genes encoding transporters involved in the uptake of docetaxel will lead to accumulation of the drug in the circulation e.g. ABCB1. Polymorphisms in β‐tubulin (target of docetaxel) affect the taxane chemotherapy results. Presently we have embarked on a project to study the pharmacogenomics of docetaxel in Malaysian breast cancer patients for the very first time to address the above issues. This project is funded by UPM and Al‐Malak Universality, Iraq.

Is There a Place for Drug Combination Strategies Using Clinical Pharmacology Attributes? – Review of Current Trends in Research

Drug discovery is the main flag ship of the pharmaceutical industry in order to ensure that innovations constantly occur in the identification and development of novel therapeutic options for the management of diseases. Recently, research trends that take advantage of the safety and efficacy of marketed products by combining such products with other agents to influence certain clinical pharmacology attribute(s) have emerged. The focus of the review is to evaluate ongoing research trends that have considered leveraging on certain clinical pharmacology attributes in the areas of viral infection (HIV and influenza) and oncology. Case studies discussed in this review include: a) the use of probenecid to block the organic anion renal transport of oseltamivir carboxylate (a key active metabolite of oseltamivir phosphate) to reduce the oral dose of oseltamivir phosphate; b) the use of rifampicin to induce the CYP2C19 enzyme and thereby, promote the formation of a potent active metabolite M8 (nelfinavir hydroxyl-t-butylamide) and achieve sustained blood levels to combat HIV infection along with ritonavir; c) the use of CYP3A4 inhibitors such as ketoconazole, cyclosporin A, ritonavir etc to overcome the extensive presystemic metabolism of docetaxel and enhance the oral bioavailability of docetaxel. Along with the case studies, several hurdles for drug development such as dose selection, frequency of dosing, and duration of the clinical studies, picking the right surrogate(s) for efficacy, evaluation of drug-drug interaction potential with other co-substrates have been discussed in line with the current day requirements for a sound clinical and regulatory strategy. In summary, based on the collated information, a pragmatic approach would render feasibility for a balanced therapy management using combined clinical pharmacology attributes of drugs.

Association of the CYP1B1*3 allele with survival in patients with prostate cancer receiving docetaxel

Using a single nucleotide polymorphism association study in 52 men with prostate cancer receiving docetaxel, we found that individuals carrying two copies of the CYP1B1*3 polymorphic variant had a poor prognosis after docetaxel-based therapies compared with individuals carrying at least one copy of the CYP1B1*1 allele (30.6 versus 12.8 months; P=0.0004). The association between CYP1B1*3 and response to therapy was not observed in similar subjects receiving non-taxane-based therapy (P=0.18). The systemic clearance of docetaxel was also unrelated to CYP1B1 genotype status (P=0.39), indicating that the association of CYP1B1*3 with clinical response is not due to docetaxel metabolism. To explain these results, we hypothesized that an indirect gene-drug interaction was interfering with the primary mechanism of action of docetaxel, tubulin polymerization. We therefore conducted tubulin polymerization experiments with taxanes in the presence or absence of certain CYP1B1 estrogen metabolites, which are known to bind to nucleophilic sites in proteins and DNA, that revealed the primary estrogen metabolite of CYP1B1, 4-hydroxyestradiol (4-OHE2), when oxidized to estradiol-3,4-quinone strongly inhibits tubulin polymerization. The 4-OHE2 is also formed more readily by the protein encoded by the CYP1B1*3 allele, validating further our data in patients. Furthermore, estradiol-3,4-quinone reacted in vitro with docetaxel to form the 4-OHE2-docetaxel adduct. This pilot study provides evidence that CYP1B1*3 may be an important marker for estimating docetaxel efficacy in patients with prostate cancer. This link is likely associated with CYP1B1*3 genotype-dependent estrogen metabolism.

Hoosier Oncology Group Randomized Phase II Study of Docetaxel, Vinorelbine, and Estramustine in Combination in Hormone-Refractory Prostate Cancer with Pharmacogenetic Survival Analysis

To determine the safety and efficacy of two docetaxel doublets in hormone-refractory prostate cancer (HRPC) patients and to examine the prognostic role of polymorphisms in host genes important to docetaxel metabolism and transport. Sixty-four chemotherapy-naive patients with HRPC were randomized to docetaxel and vinorelbine (D, 20 mg/m2 i.v. days 1 and 8; V, 25 mg/m2 i.v. days 1 and 8) or docetaxel and estramustine phosphate (D, 60-70 mg/m2 i.v. day 1; E, 280 mg oral thrice daily days 1-5) administered q21d. Primary end point was clinically significant toxicity. A pharmacogenetic analysis of host genes was done in patients who received at least one cycle of docetaxel therapy. Grade 3/4 toxicity occurred in 15.6% of DV patients and in 28.6% DE patients. Neither arm exceeded the threshold of clinically significant toxicity. In the DV arm, objective response rate was 33%, prostate-specific antigen response rate was 20%, and median survival was 16.2 months. In the DE arm, objective response rate was 67%, prostate-specific antigen response rate was 43%, and median survival was 19.7 months. Pharmacogenetic analyses showed a significant association between survival beyond 15 months and the ABCG2 421 C > A (Q141K) polymorphism compared with the wild-type (C/C) genotype (66% versus 27%; P = 0.05). DV and DE doublets are active with a tolerable toxicity profile in patients with HRPC; however, efficacy does not seem superior to standard single-agent docetaxel. The ABCG2 421 C > A (Q141K) polymorphism may be an important predictor of response and survival in HRPC patients treated with docetaxel-based chemotherapy.

Effects of paclitaxel, docetaxel and their combinations on subcutaneous lymphomas in inbred Sprague–Dawley/Cub rats

We investigated, whether the effects on paclitaxel, docetaxel or their combinations on T-cell lymphomas in Sprague–Dawley/Cub rats were mainly caused by their different efficiency or combination of different mechanism of action, or limited by metabolic inactivation by P450 enzymes or drug efflux caused by P-glycoprotein (P-gp). Docetaxel most effectively prolonged the survival of rats and the time of lymphoma appearance, inhibited their intravital size and weight after sacrifice. Paclitaxel was poorly effective and combined administration had intermediate effects. Blood levels of both drugs were similar. Repeated administration of paclitaxel, but not docetaxel, decreased its area under concentration, but the effect disappeared 6 h after dosing and was not sufficient to explain lower effects of paclitaxel. The faster metabolism of docetaxel than paclitaxel in vitro did not limit its higher efficiency and repeated administration of paclitaxel did not induce its metabolism to decrease its blood levels sufficiently. Likewise, undetectable expression of P-gp protein in tumours could not explain lower effects of paclitaxel, which is a better substrate of P-gp. Docetaxel was three-fold more effective than paclitaxel against P388D1 lymphoma cell line, used as a model of the T-cell lymphoma and combined action was dominated by the effects of docetaxel. Thus, docetaxel was effective against T-cell lymphomas and may be a potential anticancer drug in similar indications.

Influence of high-dose ketoconazole on the pharmacokinetics of docetaxel

Objective: The pharmacokinetics (PK) of docetaxel are characterized by large inter-individual variability in systemic drug exposure (AUC) and drug clearance. The PK variability is thought to be largely related to differences in the catalytic function of CYP3A, involved in docetaxel metabolism and elimination. As variability in efficacy and toxicity is associated with variability in docetaxel AUC and clearance, reducing inter-individual PK variability may help improve the risk-benefit ratio of docetaxel therapy. We investigated if high-dose ketoconazole, a potent CYP3A inhibitor, could result in a uniform reduction of docetaxel clearance and reduce the inter-individual variability in docetaxel AUC and clearance.Methods: Seven patients were treated in a randomized-cross over design with intravenous docetaxel (100 mg/m2) followed 3 weeks later by docetaxel (15 mg/m2) given in combination with orally administered ketoconazole (400 mg 3 times daily, up to 47 hours after docetaxel infusion) or vice versa. Docetaxel plasma concentration-time data were described by a three-compartment PK model. Ketoconazole plasma concentration-time data were described by a one-compartment PK model. Results: Docetaxel clearance was reduced by 50% (P = .018) from 32.8 ± 13.7 L/hr to 16.5 ± 8.15 L/hr upon ketoconazole co-administration, albeit with large inter-individual variability (fractional change in clearance, range 0.31 – 0.66). In the presence of ketoconazole, inter-individual variability in clearance and AUC, expressed as coefficient of variation, was increased from 41.6 to 49.5% and from 28.0 to 35.1%, respectively, and not, as we had hypothesized, reduced.Conclusion: Inhibition of CYP3A by concomitant high-dose ketoconazole administration does not result in a uniform reduction of docetaxel clearance and does not reduce the inter-individual variability in docetaxel AUC or clearance. This approach is unsuitable as method to achieve a uniform docetaxel PK profile.

Taxane pharmacogenetics.

The taxanes paclitaxel and docetaxel exert their anticancer activity by stabilizing microtubules during cell division. There is significant interindividual variability in response and toxicity between paclitaxel and docetaxel. Interpatient variability also exists for response and toxicity from each drug. Variability within genes involved in paclitaxel and/or docetaxel metabolism and transport exists. However, to date there is little evidence to suggest useful markers for the selection of individualized therapy. Epigenetic regulation of taxane pathway genes may play a large role in explaining the variability in toxicity and response.

Clinical Pharmacokinetics of Docetaxel

Docetaxel belongs to the class of taxane antineoplastic agents that act by inducing microtubular stability and disrupting the dynamics of the microtubular network. The drug has shown a broad spectrum of antitumour activity in preclinical models as well as clinically, with responses observed in various disease types, including advanced breast cancer and non-small cell lung cancer. The pharmacokinetics and metabolism of docetaxel are extremely complex and have been the subject of intensive investigation in recent years. Docetaxel is subject to extensive metabolic conversion by the cytochrome P450 (CYP) 3A isoenzymes, which results in several pharmacologically inactive oxidation products. Elimination routes of docetaxel are also dependent on the presence of drug-transporting proteins, notably P-glycoprotein, present on the bile canalicular membrane. The various processes mediating drug elimination, either through metabolic breakdown or excretion, impact substantially on interindividual variability in drug handling. Strategies to individualise docetaxel administration schedules based on phenotypic or genotype-dependent differences in CYP3A expression are underway and may ultimately lead to more selective chemotherapeutic use of this agent.

Phase I study of docetaxel and topotecan in patients with advanced malignancies

Docetaxel and topotecan are drugs with different mechanisms of action and significant activity against various tumour types. Topotecan may influence docetaxel metabolism by inhibiting the CYP3A4 enzyme. We designed a phase I study to evaluate the maximum tolerated dose of this combination and to assess the impact of pharmacokinetic interactions of the two drugs on toxicity. Docetaxel and topotecan were administered intravenously on day 1, and days 1 - 5 respectively, using a phase I dose escalation design. Plasma samples were analysed to determine docetaxel and topotecan concentration by HPLC with subsequent pharmacokinetic analysis using NONMEM. Of the 17 patients enrolled in the trial, 11 had grade 3 and 4 neutropenia and 1 had grade 4 thrombocytopenia. Nonhaematological toxicities were less frequent. The maximum tolerated dose for docetaxel and topotecan were 60 mg/m(2) on day 1 and 0.75 mg/m(2) days 1 - 5, respectively. One patient had stable disease. Subjects with grade >or= 3 haematologic toxicity had higher plasma docetaxel or topotecan area under the curve (AUC) (docetaxel 1.03 +/- 0.11 mg-hr/L versus 0.73 +/- 0.13 mg-hr/L; topotecan 65.8 +/- 14.6 mcg-hr/L versus 41.6 +/- 13.9 mcg-hr/L). There was no additive effect of the AUC of the two drugs on the likelihood of grade >or= 3 haematologic toxicity by multiple logistic regression. The dose-limiting toxicity seen with the combination of docetaxel and topotecan was myelosuppression. Future trials will require growth factor support if this combination is pursued.

Effect of the St. John's Wort Constituent Hyperforin on Docetaxel Metabolism by Human Hepatocyte Cultures

St. John's wort is a commonly used herbal medication that increases cytochrome P450 3A (CYP3A) activity. Because docetaxel is inactivated by CYP3A, we studied the effects of the St. John's wort constituent hyperforin on docetaxel metabolism in a human hepatocyte model. Hepatocytes, isolated from three donor livers, were exposed to hyperforin (0.1, 0.5, or 1.5 micromol/L) or rifampin (10 micromol/L) for 48 hours. After 48 hours, hyperforin- or rifampin-containing medium was replaced with medium containing 100 micromol/L docetaxel. After 1 hour, docetaxel metabolism was characterized by liquid chromatography-tandem mass spectrometry. Subsequent incubations characterized the specific cytochrome P450s that produced the docetaxel metabolites observed in hepatocyte incubations. Rifampin induced docetaxel metabolism 6.8- to 32-fold above docetaxel metabolism in control cultures. Hyperforin induced docetaxel metabolism in all three hepatocyte preparations. Hyperforin induction was dose-dependent and, at maximum, was 2.6- to 7-fold greater than that in controls. Docetaxel metabolites identified in rifampin- and hyperforin-treated hepatocyte preparations included the previously described tert-butyl-hydroxylated metabolite and two previously unidentified metabolites involving hydroxylation on the baccatin ring. CYP3A4 produced the tert-butyl-hydroxylated metabolite and the two ring-hydroxylated metabolites. CYP2C8 produced one of the newly described ring-hydroxylated metabolites. Exposure to the St. John's wort constituent hyperforin induces docetaxel metabolism in vitro. This implies that subtherapeutic docetaxel concentrations may result when docetaxel is administered to patients using St. John's wort on a chronic basis. The results also show induction of previously undescribed metabolic pathways for docetaxel, one of which may be analogous to the known 6-alpha-hydroxylation of paclitaxel by CYP2C8.

A Phase I/II Study of Exisulind in Combination with Docetaxel/Carboplatin in Patients with Metastatic Non–Small-Cell Lung Cancer

Exisulind is a sulfone derivative of sulindac that induces apoptosis and demonstrates synergy with docetaxel in lung cancer models. This study evaluated the safety, efficacy, and pharmacokinetic interactions of exisulind and docetaxel/carboplatin in patients with metastatic non–small-cell lung cancer (NSCLC). Fifty-seven patients received 218 cycles of docetaxel (75 mg/m2) and carboplatin (area under the curve, 5.0) in combination with exisulind (125-250 mg orally twice daily). Two complete responses and 9 partial responses were observed among the 47 patients assessable for response (overall response rate, 23%). The median duration of response was 5.9 months and median survival was 9.4 months. The 1- and 2-year survival rates are 35% and 14%, respectively. The hematologic toxicities were consistent with those previously reported with docetaxel/carboplatin. The most common nonhematologic toxicities were mild to moderate fatigue, anorexia, nausea, and vomiting. The addition of exisulind to the chemotherapy regimen did not interfere with the metabolism or elimination of docetaxel and vice versa, and docetaxel did not interfere with the pharmacokinetic parameters of exisulind. This trial did not allow direct comparison of patients receiving docetaxel/carboplatin with and without exisulind, but when compared with historical data of docetaxel/carboplatin alone, the addition of exisulind does not appear to enhance antitumor activity, duration of response, or survival. Although preclinical data demonstrate increased apoptosis and prolonged survival for the combination of exisulind and docetaxel, multiple clinical trials do not support further clinical development of this combination regimen in patients with advanced NSCLC.

Metabolism of docetaxel in mice

Previous studies have shown by quantification of the parent drug and the known metabolites M-1, M-2, M-3 and M-4 that the mass balance of docetaxel in mice and humans is not complete. We therefore used reversed-phase high-performance liquid chromatography (HPLC) with photodiode array (PDA) detection and tandem mass spectrometry to trace and identify putative metabolites in the feces and bile of mice injected intravenously with docetaxel. HPLC-PDA revealed two metabolic products in the feces and more than ten potential new metabolites in the bile. Mass spectrometry was performed on docetaxel reference compound, on the known metabolites M-1, M-2, M-3 and M-4, and on HPLC eluate fractions containing metabolic products, six fractions originating from the bile and two from the feces. The mass spectra of the most abundant unknown metabolite in the bile and the feces were identical, and indicated that this structure contained a carboxyl moiety at the tert-butyl group. Under the conditions of storage this product degraded to metabolite M-4. All other unknown metabolites found in the bile samples were oxidized products, with the oxidations in both the C-13 side chain and the baccatin structure, the latter being a new finding.

The effect of granisetron on in vitro metabolism of paclitaxel and docetaxel.

Paclitaxel and docetaxel are effective anticancer agents; however, these agents can be associated with the debilitating side effects of nausea and vomiting, thereby necessitatingthe administration of concomitant antiemetic agents. This increases the potential fordrug-drug interactionsthrough inhibition or induction of the cytochrome P450 (CYP) enzymes. The 5-HT3-receptor antagonists are currently regarded as the antiemetic 'gold standard' and this study was undertaken to investigate the effects of granisetron on the metabolism of paclitaxel and docetaxel in human liver microsomal preparations in vitro. Paclitaxel, 5 nM, and docetaxel, 1.25 nM, were incubated in the presence of granisetron, 0, 10, 100, and 1000 pM, in human liver microsomal preparations (500 microg). The levels of unchanged paclitaxel and docetaxel in the incubation mixture were determined by high-performance liquid chromatography. Ketoconazole, 10 nM, a potent inhibitor of CYP3A metabolism, served as a positive control. In the absence of granisetron, unchanged paclitaxel and docetaxel levels measured were 27.2 +/- 2.8% and 44.3 +/- 4.0% of control, respectively. Ketoconazole prevented the breakdown of both paclitaxel and docetaxel, to the degree that no unchanged paclitaxel or docetaxel was detected in the incubation mixture. Granisetron had no effect on the rate of reduction of either paclitaxel or docetaxel; unchanged paclitaxel and docetaxel decreased to 25.0 +/- 1.5%, 26.4 +/- 1.0%, and 27.6 +/- 6.4%, and 44.2 +/- 1.5%, 41.2 +/- 4.1%, and 43.1 +/- 0.5%, respectively. The results from this study suggest that granisetron neither inhibits nor induces the enzymes involved in the metabolism of paclitaxel or docetaxel. Thus, granisetron can be used safely as a supportive care agent to treat paclitaxel or docetaxel chemotherapy-induced nausea and vomiting with minimal risk of drug-drug interactions.

Docetaxel (Taxotere) Is Not Metabolized by Recombinant Human CYP1B1 in Vitro, but Acts as an Effector of This Isozyme.

The objective of this study was to determine whether recombinant human cytochrome P450 1B1 (rhCYP1B1) metabolizes the anticancer agent docetaxel (Taxotere) in vitro. First, the catalytic activities of Supersomes-expressed rhCYP1B1 toward 17beta-estradiol and of rhCYP3A4 toward docetaxel in our conditions were determined. Second, [(14)C]docetaxel at 0.1 and 1 microM was incubated with rhCYP1B1 in the presence of NADPH up to 60 min. No metabolism of docetaxel was detected. Third, several activators of P450 isoenzymes were added to docetaxel incubations with rhCYP1B1, such as 2-chloro 3-pyridine 3-yl 5,6,7,8-tetrahydroindolizine 1-carboxamide, alpha-naphthoflavone, and organic solvents. Again, no metabolism of docetaxel was detected. As a forth step, 10 incubation factors were tested at two levels each in 16 different combinations, using a fractional factorial statistical experimental design. Docetaxel was not metabolized by rhCYP1B1 under any of the combinations. As a final step, the effect of docetaxel on the rhCYP1B1-mediated 7-ethoxyresorufin O-deethylase (EROD) activity was studied, to evaluate if docetaxel can bind to CYP1B1. Alpha-Naphthoflavone (1 microM), a CYP1B1 inhibitor, totally inhibited the EROD activity. Docetaxel at 3, 10, and 30 microM did not show major effects on EROD activity. At 100 microM, docetaxel increased EROD activity by 3.8-fold. Additionally, it was shown that 7-epidocetaxel, which is in equilibrium with docetaxel as a minor compound in solutions, was a potent activator of rhCYP1B1, with a >7-fold increase of EROD activity at 10 microM. In conclusion, docetaxel was not metabolized by recombinant human CYP1B1 in vitro, under any of the conditions tested. Docetaxel was shown to bind to recombinant human CYP1B1 and to act as an effector of this enzyme.

Cytochromes P450 Involved in Cyclophosphamide, Paclitaxel and Docetaxel Metabolism in Rats

We investigated involvement of cytochromes P450 (CYPs) of rat liver microsomes in metabolism of two anticancer drugs, paclitaxel (PCT) and docetaxel (DTX), by an indirect method. This method is based on the presumption that the compound competitively inhibiting oxidation of the CYP-selective substrate should also be a substrate for the CYP enzyme. The validity of this approach was confirmed using the model drug, cyclophosphamide (CPA). Indeed, CPA competitively inhibited oxidation of substrates specific for CYP2B1 and CYP3A1/2, enzymes previously reported to be capable of metabolizing CPA. Using this method, we identified CYP enzymes participating in PCT and DTX metabolism. The CYP2D1/2/3 and CYP3A1/2 are enzymes oxidizing PCT while CYP3A1/2 and CYP2E1 are responsible for metabolism of DTX. Here, we report a suitable method serving for easy and fast estimation of CYP enzymes involved in drug metabolism.

Preclinical pharmacokinetics of paclitaxel and docetaxel.

The taxanes paclitaxel and docetaxel represent a novel class of antineoplastic agents. A major problem of both drugs is their low aqueous solubility and the design of suitable formulations has been a difficult step in the process of therapeutic development. The formulations currently used are mixtures of Cremophor EL:ethanol for paclitaxel (Taxol) and Tween 80:ethanol for docetaxel (Taxotere), but many new approaches have been tested or are under investigation. Paclitaxel and docetaxel have a similar mechanism of action, which is based on promotion of tubulin assembly and inhibition of microtubule disassembly. Pharmacokinetic studies revealed a marked non-linearity of paclitaxel in mice, which appeared to result exclusively from Cremophor EL, the major component present in the pharmaceutical formulation. An almost linear pharmacokinetic behavior was observed in the case of docetaxel. The reported plasma protein binding of both compounds ranged from 76 to 97% in different animal species. Paclitaxel and docetaxel widely distribute into most tissues of mice and rats, including tumor tissue, but only low concentrations were detected in the central nervous system. Despite the great similarity in the chemical structures of paclitaxel and docetaxel, their metabolic profile is very distinct. Furthermore, whereas paclitaxel metabolism is largely species dependent, docetaxel metabolism is similar across species in both isolated hepatic microsomal fractions and in vivo models. For both taxanes, hepatobiliary excretion is the major pathway of elimination and a major fraction of the dose is excreted in feces as parent drug or hydroxylated metabolites.