Drug interactions with the taxanes: clinical implications

Concomitant medication, comorbidity and survival in patients with breast cancer

Between 30% and 70% of patients with breast cancer have pre-existing chronic conditions, and more than half are on long-term non-cancer medication at the time of diagnosis. Preliminary epidemiological evidence suggests that some non-cancer medications may affect breast cancer risk, recurrence, and survival. In this nationwide cohort study, we assessed the association between medication use at breast cancer diagnosis and survival. We included 235,368 French women with newly diagnosed non-metastatic breast cancer. In analyzes of 288 medications, we identified eight medications positively associated with either overall survival or disease-free survival: rabeprazole, alverine, atenolol, simvastatin, rosuvastatin, estriol (vaginal or transmucosal), nomegestrol, and hypromellose; and eight medications negatively associated with overall survival or disease-free survival: ferrous fumarate, prednisolone, carbimazole, pristinamycin, oxazepam, alprazolam, hydroxyzine, and mianserin. Full results are available online from an interactive platform ( https://adrenaline.curie.fr ). This resource provides hypotheses for drugs that may naturally influence breast cancer evolution.

Potential Drug Interactions Between Psychotropics and Intravenous Chemotherapeutics Used by Patients With Cancer

Introduction: Patients undergoing cancer treatment usually have comorbidities, and psychiatric disorders are commonly seen in these patients. For the treatment of these psychiatric disorders, the use of psychotropic drugs is common, turning these patients susceptible to untoward drug interactions. Therefore, the aim of this study was to estimate the prevalence of clinically relevant drug-drug interactions (DDI) between chemotherapeutic and psychotropic agents in patients with cancer treated at an oncology service in southern Brazil. Methods: An observational epidemiological study with a cross-sectional census-type design was carried out between October and December 2020. The drug-drug interactions were identified through consultation and analysis of the Medscape Drug Interaction Check and Micromedex databases. The interactions were classified as major, when the interaction can be fatal and/or require medical intervention to avoid or minimize serious adverse effects and moderate, when the interaction can exacerbate the patient's condition and/or requires changes in therapy. Results: A total of 74 patients was included in the study among the 194 patients seen in the oncology service during the period studied. A total of 24 (32.4%) DDIs were found, 21 (87.5%) of which were classified as being of major risk and 3 (12.5%) as moderate risk. According to the mechanism of action, 19 (79.1%) were classified as pharmacodynamic interactions and 5 (20.9%) as pharmacokinetic interactions. Conclusion: It was shown that a considerable percentage of patients undergoing intravenous chemotherapy are at risk of pharmacological interaction with psychotropic drugs. Thus, it is essential that the oncologist considers all psychotropic drugs and other drugs used by patients in order to avoid drug-drug interactions.

Cisapride induced hypoglycemia via the KCNH6 potassium channel

Mutations in KCNH6 has been proved to cause hypoinsulinemia and diabetes in human and mice. Cisapride is a stomach-intestinal motility drug used to treat gastrointestinal dysfunction. Cisapride has been reported to be a potential inhibitor of the KCNH family, but it remained unclear whether cisapride inhibited KCNH6. Here, we discovered the role of cisapride on glucose metabolism, focusing on the KCNH6 potassium channel protein. Cisapride reduced blood glucose level and increased serum insulin secretion in wild-type (WT) mice fed standard normal chow/a high-fat diet or in db/db mice, especially when combined with tolbutamide. This effect was much stronger after 4 weeks of intraperitoneal injection. Whole-cell patch-clamp showed that cisapride inhibited KCNH6 currents in transfected HEK293 cells in a concentration-dependent manner. Cisapride induced an increased insulin secretion through the disruption of intracellular calcium homeostasis in a rat pancreatic β-cell line, INS-1E. Further experiments revealed that cisapride did not decrease blood glucose or increase serum insulin in KCNH6 β-cell knockout (Kcnh6-β-KO) mice when compared with WT mice. Cisapride also ameliorated glucose-stimulated insulin secretion (GSIS) in response to high glucose in WT but not Kcnh6-β-KO mice. Thus, our data reveal a novel way for the effect of KCNH6 in cisapride-induced hypoglycemia.

Geminal Diheteroatomic Motifs: Some Applications of Acetals, Ketals, and Their Sulfur and Nitrogen Homologues in Medicinal Chemistry and Drug Design

Acetals and ketals and their nitrogen and sulfur homologues are often considered to be unconventional and potentially problematic scaffolding elements or pharmacophores for the design of orally bioavailable drugs. This opinion is largely a function of the perception that such motifs might be chemically unstable under the acidic conditions of the stomach and upper gastrointestinal tract. However, even simple acetals and ketals, including acyclic molecules, can be sufficiently robust under acidic conditions to be fashioned into orally bioavailable drugs, and these structural elements are embedded in many effective therapeutic agents. The chemical stability of molecules incorporating geminal diheteroatomic motifs can be modulated by physicochemical design principles that include the judicious deployment of proximal electron-withdrawing substituents and conformational restriction. In this Perspective, we exemplify geminal diheteroatomic motifs that have been utilized in the discovery of orally bioavailable drugs or drug candidates against the backdrop of understanding their potential for chemical lability.

Onco-cardiology: Drug-drug interactions of antineoplastic and cardiovascular drugs

Cardiovascular diseases (CVD) and cancer are still the leading causes of death. There are many common etiologic factors, especially smoking and obesity. Therefore, it is not uncommon for CVD and cancer to coexist. Drug-drug interactions (DDIs) inevitably occur in this group of patients, where polypharmacy is increasing due to older age and multiple comorbidities. However, multidisciplinary studies, especially close collaboration of medical oncologists and cardiologists, who deals with the diagnosis and treatment of these diseases, awareness and preventive approaches to DDIs may reduce serious morbidity and mortality. In this review, information about the common treatments used in cardiology and oncology and possible DDIs are discussed.

Cardiovascular Ion Channel Inhibitor Drug-Drug Interactions with P-glycoprotein

P-glycoprotein (Pgp) is an ATP-binding cassette (ABC) transporter that plays a major role in cardiovascular drug disposition by effluxing a chemically and structurally diverse range of cardiovascular therapeutics. Unfortunately, drug-drug interactions (DDIs) with the transporter have become a major roadblock to effective cardiovascular drug administration because they can cause adverse drug reactions (ADRs) or reduce the efficacy of drugs. Cardiovascular ion channel inhibitors are particularly susceptible to DDIs and ADRs with Pgp because they often have low therapeutic indexes and are commonly coadministered with other drugs that are also Pgp substrates. DDIs from cardiovascular ion channel inhibitors with the transporter occur because of inhibition or induction of the transporter and the transporter's tissue and cellular localization. Inhibiting Pgp can increase absorption and reduce excretion of drugs, leading to elevated drug plasma concentrations and drug toxicity. In contrast, inducing Pgp can have the opposite effect by reducing the drug plasma concentration and its efficacy. A number of in vitro and in vivo studies have already demonstrated DDIs from several cardiovascular ion channel inhibitors with human Pgp and its animal analogs, including verapamil, digoxin, and amiodarone. In this review, Pgp-mediated DDIs and their effects on pharmacokinetics for different categories of cardiovascular ion channel inhibitors are discussed. This information is essential for improving pharmacokinetic predictions of cardiovascular therapeutics, for safer cardiovascular drug administration and for mitigating ADRs emanating from Pgp.

The role of docetaxel in the treatment of non-small cell lung cancer lung cancer: an update

INTRODUCTION

Non-small cell lung cancer lung cancer (NSCLC) is a devastating disease, with poor prognosis for patients with metastatic disease. The management of these patients has evolved during the past decade, challenging the role of cytotoxic chemotherapy as the only available treatment option. Nevertheless, chemotherapy still retains a dominant position for the majority of both treatment naïve and pretreated patients. Among the chemotherapeutic agents, docetaxel is one of the most commonly used in 1st and subsequent treatment lines, even in the current era of precision medicine. Areas covered: We searched Medline, Embase, Scopus and Cochrane Library for randomized phase III trials that evaluated docetaxel in various clinical settings of NSCLC and for meta-analyses of such trials and we present all relevant data regarding the pharmacology and clinical use of docetaxel in NSCLC. Expert commentary: Despite its diminishing role, docetaxel in combination with novel targeted agents remains an important option of the therapeutic armamentarium in advanced NSCLC.

Drug interactions with mitotane by induction of CYP3A4 metabolism in the clinical management of adrenocortical carcinoma

Mitotane [1-(2-chlorophenyl)-1-(4-chlorophenyl)-2,2-dichloroethane, (o,p'-DDD)] is the only drug approved for the treatment for adrenocortical carcinoma (ACC) and has also been used for various forms of glucocorticoid excess. Through still largely unknown mechanisms, mitotane inhibits adrenal steroid synthesis and adrenocortical cell proliferation. Mitotane increases hepatic metabolism of cortisol, and an increased replacement dose of glucocorticoids is standard of care during mitotane treatment. Recently, sunitinib, a multityrosine kinase inhibitor (TKI), has been found to be rapidly metabolized by CYP3A4 during mitotane treatment, indicating clinically relevant drug interactions with mitotane. We here summarize the current evidence concerning mitotane-induced changes in hepatic monooxygenase expression, list drugs potentially affected by mitotane-related CYP3A4 induction and suggest alternatives. For example, using standard doses of macrolide antibiotics is unlikely to reach sufficient plasma levels, making fluoroquinolones in many cases a superior choice. Similarly, statins such as simvastatin are metabolized by CYP3A4, whereas others like pravastatin are not. Importantly, in the past, several clinical trials using cytotoxic drugs but also targeted therapies in ACC yielded disappointing results. This lack of antineoplastic activity may be explained in part by insufficient drug exposure owing to enhanced drug metabolism induced by mitotane. Thus, induction of CYP3A4 by mitotane needs to be considered in the design of future clinical trials in ACC.

Clinical trials and progress with paclitaxel in ovarian cancer

Paclitaxel is a front-line agent for ovarian cancer chemotherapy, along with the platinum agents. Derived from the Pacific yew tree, Taxus brevifolia, paclitaxel has covered significant ground from the initial discovery of its antineoplastic properties to clinical applications in many forms of human cancers, including ovarian cancer. Although much has been published about the unique mechanism of action of this agent, several issues remain to be resolved. Finding the appropriate dosage schedule for paclitaxel in chemo-naïve and recurrent ovarian cancer, defining the role of paclitaxel in maintenance chemotherapy, and elucidating the mechanisms of taxane resistance are areas of intense research. Newer forms of taxanes are being manufactured to avoid troublesome adverse effects and to improve clinical efficacy. These issues are reviewed in detail in this paper with an emphasis on clinically relevant evidence-based information.

Seizures in patients with low-grade gliomas--incidence, pathogenesis, surgical management, and pharmacotherapy

Seizures complicate the clinical course of > 80% of patients with low-grade gliomas. Patients with some tumor variants almost always have epilepsy. Diffuse low-grade gliomas (LGG) are believed to cause epilepsy through partial deafferentiation of nearby brain cortex (denervation hypersensitivity). Glioneural tumors may interfere with local neurotransmitter levels and are sometimes associated with structural abnormalities of the brain which may produce seizures. The severity of tumor associated epilepsy varies considerably between patients. Some cases may present with a first seizure. Others suffer from long-standing pharmacoresistant epilepsy. Seizure control rates of > 70-80% can be expected after complete tumor resections. Patients with drug-resistant epilepsy require a comprehensive preoperative epileptological work-up which may include the placement of subdural (and intraparenchymal) electrodes or intraoperative electrocorticography (ECoG) for the delineation of extratumoral seizure foci. Partial and subtotal tumor resections are helpful in selected cases, i.e. for gliomas involving the insula. In one series, 40% of patients presented for surgery with uncontrolled seizures, i.e. medical therapy alone often fails to control tumor-related epilepsy. Use of the newer (second generation) non-enzyme inducing antiepileptic drugs (non-EIAED) is encouraged since they seem to have lesser interactions with other medications (e.g. chemotherapy). Chemotherapy and irradiation may have some minor beneficial effects on the patients' seizure disorder. Overall 60-70% of patients may experience recurrent epilepsy during long-term follow-up. Recurrent seizures (not infrequently heralding tumor recurrence) after surgery continue to pose significant clinical problems.

Tumor Priming Enhances Delivery and Efficacy of Nanomedicines

We have shown that high epithelial cell density is a major barrier to the distribution of protein-bound drugs in solid tumors, and tumor priming (expansion of interstitial space using an apoptosis-inducing pretreatment) can promote drug delivery. This study evaluated the optimal conditions of paclitaxel tumor priming (time window, particle size) and its effects on the delivery and efficacy of nanomedicines. Paclitaxel tumor priming was applied to mice bearing human xenograft tumors. The kinetics of paclitaxel-induced apoptosis was evaluated to identify the time window of tumor priming. The effects of tumor priming on the tumor delivery and interstitial dispersion of fluorescence-labeled nanoparticles of various sizes, the perfusion of tumor and normal tissues, the delivery of doxorubicin HCl liposomes to tumor and host tissues, and the antitumor activity and host toxicity were studied. Tumor priming by a single i.v. injection of paclitaxel induced apoptosis, expanded the interstitial space, vessel diameter and blood-perfused area, and promoted the delivery and interstitial dispersion of nanoparticles (100- and 200-nm diameter, administered 48 h after paclitaxel) in a tumor-selective manner. Tumor priming also enhanced the tumor delivery and antitumor activity of doxorubicin HCl liposomes (85 nm) without affecting the delivery to noncancerous host tissues or enhancing host toxicity. Tumor priming represents a potentially useful means to promote tumor-selective delivery and efficacy of nanomedicines. The current study will have significant impact on enhancing delivery and efficacy of nanomedicines and dosing regimen optimization of combination chemotherapy in the clinical setting.

Determination of paclitaxel in human and rat blood samples after administration of low dose paclitaxel by HPLC-UV detection

A simple and sensitive HPLC-UV method was developed for the determination of paclitaxel (TXL) in human and rat blood samples. 4-Hydroxybenzoic acid n-hexyl ester was used as an internal standard. TXL was extracted by a liquid-liquid extraction with tert-butylmethyl ether. The disturbing peaks in the case of serum sample were removed by pre-extraction with hexane. The separation of TXL was achieved within 25 min using an ODS column with 50% acetonitrile aqueous solution as a mobile phase at a flow rate of 1.0 mL/min. The eluent was monitored at 230 nm, and the resulted retention times of TXL and IS were 11.2 and 20.4 min. The detection limits of TXL for human plasma, serum and rat plasma samples at a signal-to-noise ratio of 3 were 10, 9.5 and 7.5 ng/mL, respectively. The proposed methods were applicable to the determination of TXL in human patients' plasma ranging from 15 to 27 ng/mL. Furthermore, monitoring of the time course of TXL after its single administration to rat could be demonstrated.

Drug interactions in cancer therapy

Drug interactions in oncology are of particular importance owing to the narrow therapeutic index and the inherent toxicity of anticancer agents. Interactions with other medications can cause small changes in the pharmacokinetics or pharmacodynamics of a chemotherapy agent that could significantly alter its efficacy or toxicity. Improvements in in vitro methods and early clinical testing have made the prediction of potentially clinically significant drug interactions possible. We outline the types of drug interaction that occur in oncology, the mechanisms that underlie these interactions and describe select examples.

Potential synergism of natural products in the treatment of cancer

Cancer is the second leading cause of death worldwide. There is thus increased interest in alternative treatment modalities that include chemotherapy, hormonal supplements, surgery, radiation therapy, complementary or alterative medicine, used alone or in combination. Therefore patients who are subjected to combination treatments such as hormonal supplements or alternative medicine face considerable risk of drug-drug interactions. The administration of herbal drugs by patients without a physician's prior counseling is increasing globally and there is a possibility of herb-drug interactions too. Herbal drugs or extracts themselves contain a combination of active constituents, which interact within themselves and also between other prescribed pharmaceutical drugs to either enhance (synergize) or decrease (antagonize) the therapeutic effect. This review focuses on a number of reports of herb-drug interactions, their mechanism of action with a special emphasis on dietetic phytochemicals such as quercetin, genistein, curcumin and catechins. All phytochemicals tend to increase the therapeutic effect by blocking one or more targets of the signal transduction pathway, by increasing the bioavailability of the other drug or, by stabilizing the other drug in the system.

Monthly paclitaxel and carboplatin with oral estramustine phosphate in patients with hormone-refractory prostate cancer

BACKGROUND

We aimed to determine the safety and efficacy of monthly paclitaxel and carboplatin with oral estramustine phosphate in patients with hormone-refractory prostate cancer (HRPC).

METHODS

Patients with prostate cancer that was progressing despite androgen ablation therapy were treated with i.v. paclitaxel, 175 mg/m2, over 3 h, followed by carboplatin (area under the curve, 5) on day 1, with oral estramustine phosphate, 280 mg twice daily, for a 28-day treatment cycle. Estramustine phosphate was precluded in those patients who had experienced adverse effects during prior chemotherapies. Patients were evaluated for response every cycle, and the treatment was continued until the cancer progressed.

RESULTS

Twenty-one patients with progressive hormone-refractory disease were treated for a median of 4 cycles (range, 1 to 11 cycles). Estramustine phosphate was precluded in seven patients. Post-therapy decreases in serum prostate-specific antigen levels of 50% and 75%, respectively, were seen in 43% and 19% of the patients (95% confidence intervals, 22% to 64% and 2% to 36%). Of the nine patients with measurable disease, 1 (11%) had a complete response and 2 (22%) had a partial response. The overall median time to progression was 4 months, and the median survival time for all patients was 11 months. Major grade 3 or 4 adverse effects were anemia (29%), neutropenia (48%), and thrombocytopenia (24%). Mild peripheral neuropathy and myalgia/arthralgia were observed in 11 (52%) and 9 (43%) patients, respectively.

CONCLUSION

Monthly paclitaxel and carboplatin with oral estramustine phosphate has significant antitumor activity and is well tolerated in patients with progressive HRPC.

Drug–drug interactions in oncology: Why are they important and can they be minimized?

Adverse drug-drug interactions are a major cause of morbidity and mortality. Cancer patients are at particularly high risk of such interactions because they commonly receive multiple medications, including cytotoxic chemotherapy, hormonal agents and supportive care drugs. In addition, the majority of cancer patients are elderly, and so require medications for co-morbid conditions such as cardiovascular, gastrointestinal, and rheumatological diseases. Furthermore, the age-related decline in hepatic and renal function reduces their ability to metabolize and clear drugs and so increases the potential for toxicity. Not all drug-drug interactions can be predicted, and those that are predictable are not always avoidable. However, increased awareness of the potential for these interactions will allow healthcare providers to minimize the risk by choosing appropriate drugs and also by monitoring for signs of interaction. This review considers the basic principles of drug-drug interactions, and presents specific examples that are relevant to oncology.

Increased Feasibility of Weekly Epirubicin and Paclitaxel as Neoadjuvant Chemotherapy for Locally Advanced Breast Carcinoma

BACKGROUND

Primary systemic therapy (PST) with a combination of epirubicin and paclitaxel achieves high response rates in locally advanced breast cancer (LABC), but considerable toxicity occurs and the patient's compliance is poor. In this open-label phase II trial toxicity of a weekly administration schedule was evaluated.

PATIENTS AND METHODS

On days 1 and 8 of each 3-week cycle, 45 patients with non-inflammatory breast cancer received epirubicin (35 mg/m(2), intravenous bolus) followed by paclitaxel (80 mg/m(2) in 500 ml of normal saline infused over 3 h) for 3 cycles. Surgery was done 2 weeks after primary chemotherapy, followed by another 6 cycles of adjuvant CEF (cyclophosphamide 500 mg/m(2), epirubicin 70 mg/m(2), 5-fluorouracil 500 mg/m(2)) chemotherapy.

RESULTS

The median tumor size before and after PST was 6.0 and 2.0 cm, respectively. The clinical response rate was 96%, including 24% complete remission; 5 patients (11%) achieved pathologically complete response (pCR) including 3 patients with carcinoma in situ. Only 5 (11%) patients underwent breast conserving surgery although there were 15 patients suitable. Axillary nodes were negative in 16 (36%) of the 45 patients. Febrile neutropenia was found in 1 patient. There was no severe cardiac toxicity or serious adverse events.

CONCLUSIONS

PST with weekly epirubicin and paclitaxel was an effective and well-tolerated combination for LABC, although only few patients underwent breast conserving surgery.

Paclitaxel chemotherapy: from empiricism to a mechanism-based formulation strategy

Paclitaxel is an anticancer agent effective for the treatment of breast, ovarian, lung, and head and neck cancer. Because of water insolubility, paclitaxel is formulated with the micelle-forming vehicle Cremophor EL to enhance drug solubility. However, the addition of Cremophor EL results in hypersensitivity reactions, neurotoxicity, and altered pharmacokinetics of paclitaxel. To circumvent these unfavorable effects resulting from the addition of Cremophor EL, efforts have been made to develop new delivery systems for paclitaxel administration. For example, ABI-007 is a Cremophor-free, albumin-stabilized, nanoparticle paclitaxel formulation that was found to have significantly less toxicity than Cremophor-containing paclitaxel in mice. Pharmacokinetic studies indicate that in contrast to Cremophor-containing paclitaxel, ABI-007 displays linear pharmacokinetics over the clinically relevant dose range of 135-300 mg/m(2). In a phase III study conducted in patients with metastatic breast cancer, patients treated with ABI-007 achieved a significantly higher objective response rate and time to progression than those treated with Cremophor-containing paclitaxel. Together these findings suggest that nanoparticle albumin-bound paclitaxel may enable clinicians to administer paclitaxel at higher doses with less toxicity than is seen with Cremophor-containing paclitaxel. The role of this novel paclitaxel formulation in combination therapy with other antineoplastic agents needs to be determined.

Optimal seizure management in brain tumor patients

The mechanism of epilepsy in brain tumor patients is probably multifactorial, and its incidence depends on tumor type and location. Refractory epilepsy is common in patients with a structural brain lesion, and a role for multidrug resistance proteins has been suggested. Until now, the medical treatment of epilepsy in brain tumor patients has only been studied retrospectively. Therefore, the optimal seizure management by antiepileptic drugs (AEDs) in this patient category is essentially unsure. Choices depend on the outcome of retrospective studies, a few nonrandomized series, extrapolation from other studies in symptomatic epilepsy, and anticipated interactions, most notably between AEDs and anticancer agents. The newly developed AEDs levetiracetam and gabapentin are recommended because of good results in preliminary studies and because they do not show interactions with anticancer agents. The use of prophylactic AEDs in brain tumor patients is disputable and generally not advised.

Dexamethasone-induced methylprednisolone hemisuccinate hydrolase: Its identification as a member of the rat carboxylesterase 2 family and its unique existence in plasma

Carboxylesterases (CESs) play important roles in the metabolism of many ester-drugs. In the present study, we identified and characterized dexamethasone-induced methylprednisolone hemisuccinate (MPHS) hydrolase in rat liver microsomes. Intraperitoneal injection of dexamethasone resulted in a significant increase in the level of MPHS hydrolase activity accompanied by induction of a specific CES isozyme. Since the biochemical characteristics of the induced CES isozyme were very similar to those of rat CES RL4, we hypothesized that these were the same enzymes. The results of nano-electrospray ionization tandem mass spectrometry analysis revealed that both dexamethasone-induced CES isozyme and CES RL4 possessed identical peptide fragments to those of , a rat CES2 isozyme, supporting our hypothesis. Furthermore, the results of reverse transcription-polymerase chain reaction showed that the amount of mRNA in dexamethasone-treated liver was greater than that in control liver. To confirm that encodes dexamethasone-induced CES isozyme, cDNA cloning was performed and the obtained cDNA was expressed in Sf9 cells by using a baculovirus-mediated expression system. The recombinant CES protein could hydrolyze MPHS and exhibited biochemical characteristics similar to those of CES RL4. Collectively, the results indicated that dexamethasone-induced MPHS hydrolase in liver microsomes is a rat CES2 isozyme. Interestingly, the results also showed that this rat CES2 isozyme exists in plasma and that the amount of this protein is increased by dexamethasone. These findings, together with the findings described above, provide important information for the study of phramacokinetics and pharmacodynamics of ester-drugs as well as for the study of CESs.

A simultaneous assessment of CYP3A4 metabolism and induction in the DPX-2 cell line

The DPX-2 cell line, a derivative of HepG2 cells, harbors human PXR and a luciferase-linked CYP3A4 promoter. These cells were used in a panel of cell-based assays for a parallel assessment of CYP3A4 induction, metabolism, and inhibition at the cellular level. CYP3A4 induction in the DPX-2 cell line by various agents was monitored in 96-well plates by a luciferase-based transcriptional activation assay. Of the prototypical CYP3A4 inducers examined, all exhibited elevated luciferase activity in DPX-2 cells. CYP3A4 enzyme activity in noninduced and rifampicin-induced DPX-2 cells was also assessed using Vivid fluorogenic substrates. Significantly elevated CYP3A4 activity levels (2.8-fold +/- 0.2-fold above DMSO-treated cells) were found in DPX-2 cells after 48 hours of exposure to rifampicin, but were undetectable in parental HepG2 cells. Rifampicin-induced activity levels were found to be suitable for assessing the inhibitory potential of new chemical entities in downstream CYP3A4 inhibition assays. The elevated CYP3A4 activity was inhibited 85% by 10 microM ketoconazole. In addition, a cytotoxicity assay to correct for possible toxic effects of compounds at the cellular level was applied. The comparative data obtained with a combination of the above assays suggests that the application of several independent in vitro technologies used in DPX-2 cells is the best possible strategy for the assessment of the complex phenomena of CYP3A4 induction and inhibition.

The immunopharmacology of paclitaxel (Taxol®), docetaxel (Taxotere®), and related agents

Paclitaxel (Taxol) and docetaxel (Taxotere) are among the most unique, and successful, chemotherapeutic agents used for the treatment of breast and ovarian cancer. Both agents have anti-mitotic properties derived from binding to tubulin and excessive stabilization of microtubules. Their anti-neoplastic effects derive from this mechanism. Distinct from their effects on microtubule stabilization, paclitaxel, docetaxel, and related taxanes display immunopharmacological traits. In this review, we discuss their induction of pro-inflammatory genes and proteins; the current hypotheses on the molecular mechanism for this induction, especially its relationship to the lipopolysaccharide (LPS) signaling pathway. We also discuss the structure-activity relationships (SAR) that govern gene induction, especially the striking differences between the SAR for murine and human cells in vitro. Lastly, we discuss the immunopharmacological traits of paclitaxel and docetaxel in terms of their relevance to human clinical pharmacology and toxicology and their activity in animal models of autoimmune disorders.

Phase I dose and sequencing study of pegylated liposomal doxorubicin and docetaxel in patients with advanced malignancies

BACKGROUND

Pegylated liposomal doxorubicin (PEG-LD) and docetaxel have single-agent activity in several malignancies. The authors conducted a Phase I trial to evaluate the maximum tolerated dose (MTD), toxicities, and effect of dose sequencing of this combination in patients with advanced malignancies.

METHODS

Twenty-two patients were enrolled in this two-arm, accelerated, dose escalation trial. Both drugs were administered on Days 1 and 15 of a 28 day cycle. In Arm A, dose escalation proceeded from a sequence and starting dose of 15 mg/m(2) PEG-LD and 30 mg/m(2) docetaxel. In Arm B, dose escalation proceeded from a sequence and starting dose of 30 mg/m(2) docetaxel and 15 mg/m(2)PEG-LD. In both arms, the dose of each drug was increased alternately by 5 mg/m(2) at each dose level.

RESULTS

The MTD for Arm A was 20 mg/m(2) PEG-LD and 40 mg/m(2) docetaxel, both of which were administered on Days 1 and 15 of a 28-day cycle. The MTD for Arm B was 35 mg/m(2) docetaxel and 20 mg/m(2) PEG-LD, both of which were administered on Days 1 and 15 of a 28-day cycle. Dose-limiting toxicities were Grade 3 (according to the National Cancer Institute Common Toxicity Criteria) skin toxicity and thrombocytopenia. One partial response was observed and stable disease was documented for three patients.

CONCLUSIONS

The recommended sequence and dose is 20 mg/m(2) PEG-LD followed by 40 mg/m(2) docetaxel on Days 1 and 15 of a 28-day cycle in Phase II trials for patients with breast and ovarian carcinoma to establish the efficacy of this well tolerated regimen.

Interactions between antiepileptic and chemotherapeutic drugs

Cancer and epilepsy commonly co-occur, and concomitant administration of antiepileptic (AEDS) and chemotherapeutic drugs (CTDs) is necessary in many cases. Many drugs are metabolised by the hepatic cytochrome P450 (CYP) isoenzyme system, and coadministration of AEDs and CTDs can lead to clinically relevant interactions by induction or inhibition of enzymes in shared metabolic pathways. These interactions can cause insufficient tumour and seizure control or lead to unforeseen toxicity. Enzyme-inducing AEDs reduce the effects of taxanes, vinca alkaloids, methotrexate, teniposide, and camptothecin analogues. Inhibition of the metabolism of nitrosoureas or etoposide by valproic acid can lead to CTD toxicity. Poor seizure control may result from the combinations of phenytoin with cisplatin or corticosteroids, and valproic acid with methotrexate. Increased toxicity of AEDs can occur when phenytoin is combined with 5-fluorouracil. Use of enzyme-inducing AEDs should be avoided in patients with cancer, particularly in association with chemotherapy. Generally, valproic acid-although not free from interactions-would be the agent of first choice. Some of the newer AEDs not metabolised by the P450 system may prove to be good alternatives.

Drug interactions of paclitaxel metabolism in human liver microsomes

The human liver metabolism of paclitaxel (Taxol), an anticancer drug, leads to three metabolites: 6alpha-hydroxypaclitaxel, 3'-p-hydroxypaclitaxel and 6alpha,3'-p-dihydroxypaclitaxel. The inter-individual variability of paclitaxel metabolism was investigated first in vitro using 22 human liver microsomes. Three metabolites have been detected by HPLC. This preliminary work revealed marked inter-individual differences in paclitaxel metabolism. The amount of major metabolite 6alpha-hydroxypaclitaxel formed varied 16-fold (0.7 to 11.5 nmol/mg/h). We next studied the effect of 29 compounds (antineoplastics, antiemetics, histamine-2 receptor antagonist, antalgics, antifungals, antivirals, psychotropics, antibiotic, corticoid, antiarrhythmic, calcium channel blocker) on paclitaxel metabolism in human liver microsomes. Among the compounds studied, quercetin, antifungal drugs such as ketoconazole and miconazole, and the antineoplastic drug doxorubicin inhibited formation of 6alpha-hydroxypaclitaxel. Dixon plots indicated that quercetin and doxorubicin inhibited 6alpha-hydroxypaclitaxel formation through a competitive mechanism with a Ki of 10.1 microM and 64.8 microM, respectively. The inhibition of this metabolite by ketoconazole was through a noncompetitive mechanism with a Ki of 11.8 microM. Our data thus suggest that special attention should be paid when these drugs are combined in clinical practice.