Differential metabolism of gefitinib and erlotinib by human cytochrome P450 enzymes

Modeling of rifampicin-induced CYP3A4 activation dynamics for the prediction of clinical drug-drug interactions from in vitro data

Induction of cytochrome P450 3A4 (CYP3A4) expression is often implicated in clinically relevant drug-drug interactions (DDI), as metabolism catalyzed by this enzyme is the dominant route of elimination for many drugs. Although several DDI models have been proposed, none have comprehensively considered the effects of enzyme transcription/translation dynamics on induction-based DDI. Rifampicin is a well-known CYP3A4 inducer, and is commonly used as a positive control for evaluating the CYP3A4 induction potential of test compounds. Herein, we report the compilation of in vitro induction data for CYP3A4 by rifampicin in human hepatocytes, and the transcription/translation model developed for this enzyme using an extended least squares method that can account for inherent inter-individual variability. We also developed physiologically based pharmacokinetic (PBPK) models for the CYP3A4 inducer and CYP3A4 substrates. Finally, we demonstrated that rifampicin-induced DDI can be predicted with reasonable accuracy, and that a static model can be used to simulate DDI once the blood concentration of the inducer reaches a steady state following repeated dosing. This dynamic PBPK-based DDI model was implemented on a new multi-hierarchical physiology simulation platform named PhysioDesigner.

Drug interactions with solid tumour-targeted therapies

Drug interactions are an on-going concern in the treatment of cancer, especially when targeted therapies, such as tyrosine kinase inhibitors (TKI) or mammalian target of rapamycin (mTOR) inhibitors, are being used. The emergence of elderly patients and/or patients with both cancer and other chronic co-morbidities leads to polypharmacy. Therefore, the risk of drug-drug interactions (DDI) becomes a clinically relevant issue, all the more so as TKIs and mTOR inhibitors are essentially metabolised by cytochrome P450 enzymes. These DDIs can result in variability in anticancer drug exposure, thus favouring the selection of resistant cellular clones or the occurrence of toxicity. This review provides a comprehensive overview of DDIs that involve targeted therapies approved by the FDA for the treatment of solid tumours for more than 3 years (sorafenib, sunitinib, erlotinib, gefitinib, imatinib, lapatinib, everolimus, temsirolimus) and medicinal herb or drugs. This review also provides some guidelines to help oncologists and pharmacists in their clinical practice.

Moving towards molecular-guided treatments: erlotinib and clinical outcomes in non-small-cell lung cancer patients

Erlotinib is an orally administered small-molecule inhibitor of EGF receptor (EGFR) tyrosine kinase that is approved for the treatment of non-small-cell lung cancer (NSCLC) and pancreatic cancer. Erlotinib was first approved for the treatment of unselected NSCLC patients with advanced disease after failure of at least one prior chemotherapy regimen, and it was subsequently demonstrated to also confer a significant clinical benefit as maintenance therapy after first-line platinum-based chemotherapy. In all clinical studies, erlotinib treatment was associated with a good safety profile. Activating mutations in the EGFR gene have emerged as the strongest predictive marker of response to tyrosine kinase inhibitors, erlotinib and gefitinib, independently of other clinical and molecular features. Results from recently published, randomized Phase III trials showed that first-line erlotinib significantly prolongs progression-free survival in patients with advanced EGFR mutation-positive NSCLC with favorable tolerability, compared with standard chemotherapy. EGFR mutation testing is a crucial factor in the decision-making process regarding the most appropriate initial treatment option for patients. Specific molecular alterations in crucial genes have been discovered and associated with resistance to erlotinib, limiting its efficacy. New targeted agents and combined-treatment strategies are now under evaluation in clinical trials of NSCLC patients following progression to tyrosine kinase inhibitors.

Polymorphisms of CYP2D6 gene and gefitinib-induced hepatotoxicity

INTRODUCTION

Gefitinib induces severe hepatotoxicity in approximately a quarter of Japanese patients with epidermal growth factor receptor (EGFR) mutation-positive non-small-cell lung cancer (NSCLC). Gefitinib is metabolized by cytochrome P450 (CYP) enzymes--including CYP3A4/5, CYP1A1, and CYP2D6--in the liver. We hypothesized that polymorphisms of the CYP2D6 gene may account for gefitinib-induced hepatotoxicity.

PATIENTS AND METHODS

Polymorphisms of the CYP2D6 gene were analyzed in 55 patients with NSCLC who experienced grade ≥ 2 transaminase elevation from gefitinib. The distribution of the CYP2D6 genotype was compared with that of the healthy Japanese population. The correlations between the nonfunctional allele *5 or the reduced-function allele *10 and hepatotoxicity-related clinical factors were also examined.

RESULTS

The distribution of the CYP2D6 genotype in the study participants was not different from that of the general Japanese population, reported previously. Existence of allele *5 or *10 did not correlate with clinical factors such as onset of hepatotoxicity within 2 months, grade ≥ 3 serum transaminase elevation, and tolerability to dose reduction or rechallenge of gefitinib. However, in 7 patients taking CYP3A4-inhibitory drugs, rechallenge of gefitinib again caused hepatotoxicity in 4 patients with allele *5 or *10 but not in 3 patients with normal alleles (P = .029). Moreover, switching to erlotinib did not cause hepatotoxicity in any of 17 patients with allele *5 or *10 but did in 3 of 8 patients without these alleles (P = .024).

CONCLUSION

Reduced function of CYP2D6 may partly account for gefitinib-induced hepatotoxicity when CYP3A4 is inhibited. Erlotinib could be safely used in patients with decreased CYP2D6 activity even after they experienced gefitinib-induced hepatotoxicity.

Successful treatment with erlotinib of severe neutropenia induced by gefitinib in a patient with advanced non-small cell lung cancer

Neutropenia is a rare side effect of gefitinib and was scarcely reported in many large-scale randomized phase III trials using gefitinib monotherapy as first-line treatment. A 77-year-old female was referred to our institution due to abnormal shadow of the right lung, diagnosed by CT scan and biopsy histopathology as adenocarcinoma of the lung (cT3N1M1b). Mutation analysis with PCR-Invader assay of tumor DNA samples revealed short in-frame deletion in exon 19. Based on the diagnosis, first-line treatment was initiated using oral gefitinib (250 mg, daily). During the initial 27 days of gefitinib therapy, the only side effect was a mild skin rash. After 28 days, there was marked tumor shrinkage, indicative of a partial response to gefitinib; however, grade 4 neutropenia was also detected. The patient was switched to the oral erlotinib monotherapy (150 mg/day) as second-line chemotherapy with careful monitoring of neutropenia. Discontinuation of the gefitinib, without the need for granulocyte colony-stimulating factor support, was successful in allowing the neutrophils and leukocytes counts to recover to normal by day 47. The patient continued oral erlotinib for more than 9 months and there has been no evidence of neutropenia, leukopenia, or disease progression. Clinicians should be aware that gefitinib-induced neutropenia in patients with non-small cell lung cancer can be treated successful by switching to erlotinib.

A phase I study of erlotinib and hydroxychloroquine in advanced non-small-cell lung cancer

INTRODUCTION

This investigator-initiated study explores the safety, maximum tolerated dose, clinical response, and pharmacokinetics of hydroxychloroquine (HCQ) with and without erlotinib in patients with advanced non-small-cell lung cancer.

METHODS

Patients with prior clinical benefit from an epidermal growth factor receptor (EGFR) tyrosine kinase inhibitor were randomized to HCQ or HCQ plus erlotinib in a 3 + 3 dose-escalation schema.

RESULTS

Twenty-seven patients were treated, eight with HCQ (arm A) and 19 with HCQ plus erlotinib (arm B). EGFR mutations were detected in 74% of the patients and 85% had received two or more prior therapies. Arm A had no dose-limiting toxicities, but the maximum tolerated dose was not reached as this arm closed early to increase overall study accrual. In arm B, one patient each experienced grade 3 rash, nail changes, skin changes, nausea, dehydration, and neutropenia; one had grade 4 anemia; and one developed fatal pneumonitis, all considered unrelated to HCQ. There were no dose-limiting toxicities, therefore the highest tested dose for HCQ with erlotinib 150 mg was 1000 mg daily. One patient had a partial response to erlotinib/HCQ, for an overall response rate of 5% (95% confidence interval, 1-25). This patient had an EGFR mutation and remained on therapy for 20 months. Administration of HCQ did not alter the pharmacokinetics of erlotinib.

CONCLUSIONS

HCQ with or without erlotinib was safe and well tolerated. The recommended phase 2 dose of HCQ was 1000 mg when given in combination with erlotinib 150 mg.

A phase I study of erlotinib and hydroxychloroquine in advanced non-small-cell lung cancer

INTRODUCTION

This investigator-initiated study explores the safety, maximum tolerated dose, clinical response, and pharmacokinetics of hydroxychloroquine (HCQ) with and without erlotinib in patients with advanced non-small-cell lung cancer.

METHODS

Patients with prior clinical benefit from an epidermal growth factor receptor (EGFR) tyrosine kinase inhibitor were randomized to HCQ or HCQ plus erlotinib in a 3 + 3 dose-escalation schema.

RESULTS

Twenty-seven patients were treated, eight with HCQ (arm A) and 19 with HCQ plus erlotinib (arm B). EGFR mutations were detected in 74% of the patients and 85% had received two or more prior therapies. Arm A had no dose-limiting toxicities, but the maximum tolerated dose was not reached as this arm closed early to increase overall study accrual. In arm B, one patient each experienced grade 3 rash, nail changes, skin changes, nausea, dehydration, and neutropenia; one had grade 4 anemia; and one developed fatal pneumonitis, all considered unrelated to HCQ. There were no dose-limiting toxicities, therefore the highest tested dose for HCQ with erlotinib 150 mg was 1000 mg daily. One patient had a partial response to erlotinib/HCQ, for an overall response rate of 5% (95% confidence interval, 1-25). This patient had an EGFR mutation and remained on therapy for 20 months. Administration of HCQ did not alter the pharmacokinetics of erlotinib.

CONCLUSIONS

HCQ with or without erlotinib was safe and well tolerated. The recommended phase 2 dose of HCQ was 1000 mg when given in combination with erlotinib 150 mg.

Smoking cessation interventions for lung cancer patients

SUMMARY Worldwide, lung cancer contributes to over 1.4 million deaths per year. Smoking cessation is strongly recommended in clinical practice guidelines for lung cancer management, yet evidence suggests a translational gap between evidence and practice. There are significant health benefits following smoking cessation even after a short period of time. Long-term implications for lung cancer patients include improvements in quality of life, reductions in postoperative complications and reductions in 12-month mortality. Evidence suggests that combining pharmacotherapy, in particular varenicline tartrate (varenicline), with cognitive and behavioral interventions offers the best opportunity for successful long-term abstinence. This review summarizes the latest evidence for smoking cessation interventions in lung cancer patients, identifies gaps in current clinical practice and highlights priority areas for future research.

Review of the treatment of non-small cell lung cancer with gefitinib

In the past decade, molecular-targeted drugs have been focused upon for the treatment of cancer. In 2002, gefitinib, an epidermal growth factor receptor (EGFR) tyrosine kinase inhibitor became available in Japan for the treatment of non-small cell lung cancer (NSCLC). Over 80% of selected patients, such as EGFR mutation-positive patients, respond to gefitinib treatment; however, most patients develop acquired resistance to gefitinib within a few years. Recently, many studies have been performed to determine precisely how to select patients who will respond to gefitinib, the best timing for its administration, and how to avoid the development of acquired resistance as well as adverse drug effects. This article reviews the use of gefitinib for the treatment of NSCLC from a pharmaceutical viewpoint.

Reduced CYP2D6 function is associated with gefitinib-induced rash in patients with non-small cell lung cancer

Background

Rash, liver dysfunction, and diarrhea are known major adverse events associated with erlotinib and gefitinib. However, clinical trials with gefitinib have reported different proportions of adverse events compared to trials with erlotinib. In an in vitro study, cytochrome P450 (CYP) 2D6 was shown to be involved in the metabolism of gefitinib but not erlotinib. It has been hypothesized that CYP2D6 phenotypes may be implicated in different adverse events associated with gefitinib and erlotinib therapies.

Methods

The frequency of each adverse event was evaluated during the period in which the patients received gefitinib or erlotinib therapy. CYP2D6 phenotypes were determined by analysis of CYP2D6 genotypes using real-time polymerase chain reaction techniques, which can detect single-nucleotide polymorphisms. The CYP2D6 phenotypes were categorized into 2 groups according to functional or reduced metabolic levels. In addition, we evaluated the odds ratio (OR) of the adverse events associated with each factor, including CYP2D6 activities and treatment types.

Results

A total of 232 patients received gefitinib therapy, and 86 received erlotinib therapy. Reduced function of CYP2D6 was associated with an increased risk of rash of grade 2 or more (OR, 0.44; 95% confidence interval [CI], 0.21–0.94; *p = 0.03), but not diarrhea ≥ grade 2 (OR, 0.49; 95% CI, 0.17–1.51; *p = 0.20) or liver dysfunction ≥ grade 2 (OR, 1.08; 95% CI, 0.52–2.34; *p = 0.84) in the gefitinib cohort. No associations were observed between any adverse events in the erlotinib cohort and CYP2D6 phenotypes (rash: OR, 1.77; 95% CI, 0.54–6.41; *p = 0.35/diarrhea: OR, 1.08; 95% CI, 0.21–7.43; *p = 0.93/liver dysfunction: OR, 0.93; 95% CI, 0.20–5.07; *p = 0.93).

Conclusions

The frequency of rash was significantly higher in patients with reduced CYP2D6 activity who treated with gefitinib compared to patients with functional CYP2D6. CYP2D6 phenotypes are a risk factor for the development of rash in response to gefitinib therapy.

Treatment of Non-Small-Cell Lung Cancer with Erlotinib following Gefitinib-Induced Hepatotoxicity: Review of 8 Clinical Cases

Objective. Gefitinib often induces liver damage. A few reports have described that the subsequent administration of erlotinib was associated with less hepatotoxicity, but the safety and efficacy of this treatment are still not fully investigated. Therefore, we evaluated retrospectively the patients with erlotinib following gefitinib-induced hepatotoxicity. Methods and Patients. We retrospectively reviewed the medical records between December 2007 and March 2010. The patients were evaluated including the following information: age, gender, histology of lung cancer, performance status, smoking status, epidermal growth factor receptor (EGFR) mutation status, liver metastasis, viral hepatitis, alcoholic liver injury, clinical response, and hepatotoxicity due to EGFR tyrosine kinase inhibitors. Results. We identified 8 patients with erlotinib following gefitinib-induced hepatotoxicity. All achieved disease control by gefitinib. Hepatotoxicity was grades 2 and 3 in 3 and 5 patients, respectively. The median duration of treatment with gefitinib was 112.5 days and the median time to gefitinib-induced hepatotoxicity was 51.5 days. The median duration of treatment with erlotinib was 171.5 days. Grade 1 and 2 erlotinib-induced hepatotoxicity was observed in 2 and 1 patient, respectively. Conclusions. Erlotinib administration with careful monitoring is thought to be a good alternative strategy for patients who respond well to gefitinib treatment but experience hepatotoxicity.

Molecular mechanisms of lung-specific toxicity induced by epidermal growth factor receptor tyrosine kinase inhibitors

Lung-specific toxicity induced by epidermal growth factor receptor (EGFR) tyrosine kinase inhibitors (TKIs) for the treatment of non-small cell lung cancer (NSCLC) has emerged as a critical side-effect. Although the clinical features of the pulmonary side-effects of TKIs have been characterized, the details of the molecular mechanisms in the development of this lung-specific toxicity remain to be elucidated. EGFR-dependent epithelial regeneration and restoration plays an important role in the recovery process from lung injury. The lung comprises a unique environment where epithelial cells are exposed to internal agents in the systemic circulation and to airborne particles through the mouth and nose. This unique environment may also be associated with the development of lung-specific toxicity induced by EGFR-TKIs. Therefore, the aim of this review was to provide further insight into the molecular mechanisms of lung-specific toxicity in the context of treatment with EGFR-TKIs.

EGF receptor-targeted therapy in non-small-cell lung cancer: role of germline polymorphisms in outcome and toxicity

Conventional chemotherapeutic regimens have limited impact against most solid tumors and deal with significant toxicity. Over the last 10 years, novel anticancer treatments targeting specific molecules or genes involved in cancer progression have been developed to improve outcome and reduce side effects. In particular, the tyrosine kinase inhibitors gefitinib and erlotinib have been approved for the treatment of non-small-cell lung cancer. Their clinical activity has been related to different clinical and biological parameters, such as EGFR-activating mutations. However, not all clinical outcomes, including tolerability, are explained, and the identification/validation of novel biomarkers is a viable area of research. Germline polymorphisms can be easily assessed in blood samples, and candidate polymorphisms in EGFR and ABCG2 have been correlated with outcome and toxicity in non-small-cell lung cancer patients treated with gefitinib or erlotinib. However, differences in study population and design resulted in several controversial findings, while the prognostic versus predictive role of the polymorphisms still needs to be validated within larger prospective studies. More studies on the relationship of the genotype with drug pharmacokinetics and mechanism of action are also warranted. These future studies, as well as further development and application of novel technologies to decipher genetic alterations, might contribute to the validation of selected polymorphisms as molecular markers predictive of drug activity and help in the selection of tyrosine kinase inhibitors best suited to the individual patient.

Liver kidney microsomal type 1 antibodies reduce the CYP2D6 activity in patients with chronic hepatitis C virus infection

Liver kidney microsomal type 1 (LKM-1) antibodies have been shown to decrease the CYP2D6 activity in vitro and are present in a minority of patients with chronic hepatitis C infection. We investigated whether LKM-1 antibodies might reduce the CYP2D6 activity in vivo. All patients enrolled in the Swiss Hepatitis C Cohort Study and tested for LKM-1 antibodies were assessed (n = 1723): 10 eligible patients were matched with patients without LKM-1 antibodies. Patients were genotyped for CYP2D6 variants to exclude individuals with a poor metabolizer genotype. CYP2D6 activity was measured by a specific substrate using the dextromethorphan/dextrorphan metabolic ratio to classify patients into four activity phenotypes. All patients had a CYP2D6 extensive metabolizer genotype. The observed phenotype was concordant with the CYP2D6 genotype in most LKM-negative patients, whereas only three LKM-1 positive patients had a concordant phenotype (six presented an intermediate and one a poor metabolizer phenotype). The median DEM/DOR ratio was sixfold higher in LKM-1 positive than in LKM-1 negative patients (0.096 vs. 0.016, P = 0.004), indicating that CYP2D6 metabolic function was significantly reduced in the presence of LKM-1 antibodies. In chronic hepatitis C patients with LKM-1 antibodies, the CYP2D6 metabolic activity was on average reduced by 80%. The impact of LKM-1 antibodies on CYP2D6-mediated drug metabolism pathways warrants further translational studies.

A phase II trial of erlotinib in combination with gemcitabine and capecitabine in previously untreated metastatic/recurrent pancreatic cancer: combined analysis with translational research

BACKGROUND

To confirm the efficacy and toxicity of Erlotinib in combination with Gemcitabine and Capecitabine when used as a first-line therapy in metastatic/recurrent pancreatic cancer (PC).

METHODS

Locally advanced PC was excluded. Erlotinib was given at a dose of 100 mg daily from D1 to D28. 1000 mg/m(2) of gemcitabine was given on D1,8,15 and 1660 mg/m(2)/day of capecitabine was given from D1 to 21, repeated every 4 weeks. Response was assessed every 8 weeks.

RESULTS

A total of 47 patients were enrolled. Response rate and disease control rate was 32.6% (95% CI, 18.6-46.6%) and 83.7% (95% CI, 72.7-94.7%) respectively. The PFS was 6.5 months (95% CI, 3.4-9.7) and OS was 12.0 months (95% CI, 8.6-15.9). The Gr 3/4 toxicities were: neutropenia (6.8%), thrombocytopenia (3.2%), anemia (1.6%). nausea (1.6%), vomiting (1.6%), anorexia (5.3%), rash (2.4%). The EGFR expression was associated with shorter OS and ERCC2 expression was associated with longer PFS and OS. PFS and OS were not different according to K-RAS mutation or polymorphism of RRM1 and CDA.

CONCLUSIONS

Erlotinib, gemcitabine and capecitabine combination showed promising efficacy and good tolerability in metastatic PC. This efficacy was observed irrespective of K-RAS mutation, and EGFR expression was poor prognostic factor for OS.

Tyrosine kinase inhibitors in lung cancer

Identification of driver mutations in growth related protein kinases, especially tyrosine kinases, has led to clinical development of an array of tyrosine kinase inhibitors in various malignancies, including lung cancer. Improved understanding of tyrosine kinase biology has led to faster drug development, identification of resistance mechanisms, and ways to overcome resistance. This review discusses the clinical data supporting the use and practical aspects of management of patients on epidermal growth factor receptor and anaplastic lymphoma kinase tyrosine kinase inhibitors.

N-Isopropyl-p-iodoamphetamine hydrochloride Is predominantly metabolized by CYP2C19

[(123)I]N-Isopropyl-p-iodoamphetamine hydrochloride ([(123)I]IMP) is clinically used to evaluate blood flow in the brain on single photon emission-computed tomography. This is a rare radiopharmaceutical that undergoes metabolism. The first step is reported to be [(123)I]p-iodoamphetamine formation. The drug-metabolizing enzyme(s) involved remain(s) unclear. This study examined the roles of human cytochrome P450 (P450) in the metabolism of nonradiolabeled IMP with the use of human liver microsomes (HLM) and recombinant human CYP1A1, -1A2, -1B1, -2A6, -2B6, -2C8, -2C9, -2C19, -2D6, -2E1, -3A4, and -3A5. Disappearance of IMP was examined because p-iodoamphetamine was not available. IMP (0.5 μM) time-dependently disappeared when HLM and NADPH-generating system were added to the reaction mixture. (S)-Mephenytoin (1 mM) inhibited the IMP disappearance by approximately 90%. The disappearance of IMP was predominantly catalyzed by recombinant CYP2C19, with K(m) and V(max) of 8.6 μM and 9.7 nmol · min(-1) · nmol P450(-1), respectively. IMP disappearance in CYP2C19-deficient HLM (CYP2C19*2/*2) was approximately 30% of that in the presence of HLM harboring wild-type CYP2C19, indicating that IMP is polymorphically metabolized by CYP2C19. High-performance liquid chromatography of the incubation mixture of IMP and CYP2C19 revealed an unidentified peak. As the area of the IMP peak decreased, the area of this unidentified peak increased in a time-dependent fashion. The peak was also detectable on incubation of IMP with HLM. Mass spectrometry revealed that the molecular weight of a compound in this unidentified peak was the same as that of p-iodoamphetamine. Thus, we demonstrated that IMP was predominantly metabolized by CYP2C19 to form p-iodoamphetamine.

A phase I/II, non-randomized, feasibility/safety and efficacy study of the combination of everolimus, cetuximab and capecitabine in patients with advanced pancreatic cancer

BACKGROUND

Improvements in knowledge of molecular mechanisms in cancer are the basis for new studies combining chemotherapy with targeted drugs. Inhibition of the epidermal growth factor receptor (EGFR) by erlotinib or cetuximab has limited or no activity, respectively, in pancreatic cancer. The crosstalk between EGFR and mammalian target of rapamycin (mTOR) pathways is a potential mechanism of resistance; therefore we conducted a study to explore safety and efficacy of multiple pathway inhibition by cetuximab and everolimus in combination with capecitabine.

METHODS

Safety and efficacy of fixed standard dose cetuximab in combination with various dose levels of everolimus (5-10 mg/day) and capecitabine (600-800 mg/m(2) bid, 2 weeks every 3 weeks) were investigated in a phase I/II study in patients with advanced pancreatic cancer. The primary endpoint was objective response.

RESULTS

Sixteen patients were treated in the phase I part at two dose levels. Mucositis, rash and hand-foot syndrome were dose-limiting toxicities. Dose level 1 (everolimus 5 mg/day, capecitabine 600 mg/m(2) bid for 2 weeks every 3 weeks and cetuximab 250 mg/m(2) weekly) was considered the maximum tolerated dose (MTD). Of 31 patients in the phase II part, partial response was documented in two patients (6.5%) and five (16.1%) had stable disease. Median overall survival was 5.0 months (CI 3.1-6.8).

CONCLUSION

The schedule of capecitabine, everolimus and cetuximab resulted in considerable epidermal and mucosal toxicities and prevented escalation to optimal dose levels. Because of toxicity and low efficacy this treatment combination cannot be recommended for treatment in pancreatic cancer patients.

Salvage treatment with erlotinib after gefitinib failure in advanced non-small-cell lung cancer patients with poor performance status: A matched-pair case-control study

PURPOSE

Gefitinib plays an important role in non-small-cell lung cancer (NSCLC) treatment; however, progression of the disease occurs in most patients even after an initial response. The role of erlotinib after gefitinib failure has been investigated but continues to be debated, especially in heavily treated patients with poor performance status (PS). Therefore, a retrospective matched-pair case-control study was carried out to evaluate the role of erlotinib after gefitinib failure in advanced NSCLC patients.

METHODS

A total of 58 patients were identified. The two groups were balanced with demographic and baseline clinical characteristics. All patients had PS ≥2 and most of them (89.7%) had received more than two systemic therapies before erlotinib or best supportive care (BSC). The epidermal growth factor receptor (EGFR) and KRAS genotypes were analyzed in 36 (62.1%) patients, 19 of them were in the erlotinib group.

RESULTS

Median overall survival (OS) for all patients was 6 months. Median OS for patients who received erlotinib and BSC was 10 and 3 months, respectively (P= 0.001). Disease control rate (DCR) and objective response rate (ORR) were 51.7% and 10.3% in patients receiving erlotinib, respectively, while median time to progression (TTP) was 3 months. Among the 19 patients in the erlotinib group with biomarker results available, those with EGFR mutation achieved longer median TTP (P= 0.016) and better DCR (P= 0.177) than those with wild-type EGFR.

CONCLUSIONS

A switch to erlotinib after gefitinib failure may represent a better therapeutic option for advanced NSCLC patients with poor PS, and an EGFR mutation seemed to be associated with better survival rate.

Effectiveness of erlotinib in advanced non-small cell lung cancer in cases of gefitinib resistance after treatment of more than 6 months

BACKGROUND

There have been reports on the use of erlotinib in non-small cell lung cancer (NSCLC) patients after gefitinib resistance occurs, and it has been stated that erlotinib may be beneficial in patients with long stable disease (SD) previously treated with gefitinib.

PATIENTS AND METHODS

We retrospectively studied gefitinib-resistant NSCLC patients with favorable clinical features, who received erlotinib following disease progression after gefitinib treatment of more than 6 months.

RESULTS

A total of 21 patients with NSCLC were included. Partial response was seen in 2 cases (9%), SD in 6 cases (19%), and progressive disease (PD) in 13 cases (62%). Disease control (DC) was achieved with erlotinib in 8 cases (36%). The median survival time (MST) was 369 days in DC cases and 133 days in PD cases. There were no statistical differences between DC cases and PD cases in terms of MST relative to sex, smoking and skin rash.

CONCLUSION

Subsequent erlotinib therapy is one of the therapeutic options in the treatment of gefitinib-resistant NSCLC in which prior gefitinib has shown long-term SD of more than 6 months.

Successful treatment of non-small cell lung cancer with gefitinib after severe erlotinib-related hepatotoxicity

Gefitinib and erlotinib are first-generation small molecular inhibitors of EGFR tyrosine kinase activity. To the best of our knowledge, to date, two reports have stated that patients with NSCLC who develop severe hepatotoxicity secondary to gefitinib treatment can be safely switched to erlotinib. However, the reverse situation has not been reported. Here, we present the first case with non-small cell lung cancer harboring EGFR mutation who developed grade 3/4 hepatotoxicity after initiation of erlotinib, which resolved when therapy was changed to gefitinib. As far as we know, this is the first report showing the efficacy of gefitinib for a non-small cell lung cancer patient who developed severe hepatotoxicity while under erlotinib therapy.

Lung cancer in HIV Infection

Lung cancer is the most prevalent non-AIDS-defining malignancy in the highly active antiretroviral therapy era. Smoking plays a significant role in the development of HIV-associated lung cancer, but the cancer risk is two to four times greater in HIV-infected persons than in the general population, even after adjusting for smoking intensity and duration. Lung cancer is typically diagnosed a decade or more earlier among HIV-infected persons (mean age, 46 years) compared to those without HIV infection. Adenocarcinoma is the most common histological subtype, and the majority of patients are diagnosed with locally advanced or metastatic carcinoma. Because pulmonary infections are common among HIV-infected individuals, clinicians may not suspect lung cancer in this younger patient population. Surgery with curative intent remains the treatment of choice for early-stage disease. Although there is increasing experience in using radiation and chemotherapy for HIV-infected patients who do not have surgical options, there is a need for prospective studies because this population is frequently excluded from participating in cancer trials. Evidence-based treatments for smoking-cessation with demonstrated efficacy in the general population must be routinely incorporated into the care of HIV-positive smokers.

Treatment with gefitinib after erlotinib-induced liver injury: a case report

INTRODUCTION

Gefitinib and erlotinib have minor differences in their chemical structures, and thus it remains unclear whether the hepatotoxicity induced by one compound is affected by the other. The case of a patient who developed erlotinib-induced liver injury and was then treated with gefitinib without hepatic toxicity or disease progression is presented.

CASE PRESENTATION

A 31-year-old Japanese woman, who never smoked and who was diagnosed as having lung adenocarcinoma with carcinomatous meningitis, was treated with erlotinib. She developed erlotinib-induced liver injury after four weeks of treatment. The treatment was stopped right away, but the symptoms of meningitis re-appeared immediately. Gefitinib treatment was started and continued without recurrence of drug-induced liver injury.

CONCLUSION

Gefitinib appears to be a potential treatment option after erlotinib-induced liver injury.

A phase I dose-escalation and pharmacokinetic study of enzastaurin and erlotinib in patients with advanced solid tumors

Purpose

Enzastaurin, an oral serine/threonine kinase inhibitor, targets the protein kinase C and AKT pathways with anti-tumor and anti-angiogenic effects. Erlotinib, an oral epidermal growth factor receptor (EGFR) inhibitor, has activity in solid tumors. Based on the promising combination of EGFR inhibitors and anti-angiogenic agents, this phase I trial was initiated.

Methods

This single-institution, open-label, non-randomized trial used a standard 3 + 3 dose-escalation model in patients with advanced solid malignancies including non-small-cell lung cancer (NSCLC). Two dose levels of enzastaurin (with loading doses) were explored: 250 mg daily and 500 mg daily. Erlotinib was given at 150 mg daily.

Results

Sixteen patients were enrolled in this study (median age, 64 years). Most patients were heavily pre-treated, female, and Caucasian and had NSCLC. The highest dose of enzastaurin, 500 mg daily, was tolerated with no unexpected adverse events and no alteration in the pharmacokinetics of either drug at this dose level. The mean clearance was 5.75 L/h for erlotinib and 53.8 L/h for enzastaurin. The most common possibly drug-related grade 3–4 adverse events included diarrhea (25.0%), neurologic symptoms (18.8%), and vomiting (18.8%). Activity was noted, with a partial response in one patient and prolonged disease stability for >12 cycles in three patients.

Conclusion

The combination of enzastaurin 500 mg daily and erlotinib 150 mg daily is well tolerated and does not alter the pharmacokinetics of the individual drugs, with clinical activity seen. A phase II trial of this combination has been initiated in patients with advanced-stage NSCLC.

Smoking history as a predictive factor of treatment response in advanced non-small-cell lung cancer: a systematic review

Recent trials in patients with advanced non-small-cell lung cancer (NSCLC) suggest that nonsmokers may benefit more from epidermal growth factor receptor (EGFR) tyrosine kinase inhibitor (TKI) therapy than will smokers. The aim of this systematic review was to assess smoking history as a predictive factor for treatment outcomes in patients with NSCLC. Relevant published literature was identified through systematic searches of databases (MEDLINE, EMBASE, Cochrane Library), oncology and thoracic journals, and abstracts from major oncology conferences using prespecified criteria. Articles reporting treatment outcomes (overall survival [OS], progression-free survival [PFS], and/or response rate) in smoking history subgroups from randomized controlled trials of targeted therapy and/or chemotherapy were reviewed. Data from 30 trials (32 articles, 4 abstracts) were included. Of these, 23 trials tested first-line therapy. Treatment arms included EGFR TKIs (13 trials), EGFR monoclonal antibodies (2 trials), non-EGFR targeted treatments (9 trials), chemotherapy (27 trials), and placebo or best supportive care only (3 trials). Smoking history definitions and analyses of its effect on treatment outcomes varied widely. Only 11 trials reported testing for a treatment-by-smoking history interaction. The available evidence supports but does not confirm smoking history as a predictive factor for the response to TKIs, particularly in previously treated patients. The evidence does not support smoking history as a predictor of response to non-EGFR-targeted therapies or chemotherapy. Smoking history and its effect on treatment response are inadequately reported. More rigorous collection, analysis, and reporting may clarify whether smoking history is a predictor of treatment response in advanced NSCLC.

Metabolism of the EGFR tyrosin kinase inhibitor gefitinib by cytochrome P450 1A1 enzyme in EGFR-wild type non small cell lung cancer cell lines

Background

Gefitinib is a tyrosine kinase inhibitor (TKI) of the epidermal growth factor receptor (EGFR) especially effective in tumors with activating EGFR gene mutations while EGFR wild-type non small cell lung cancer (NSCLC) patients at present do not benefit from this treatment.

The primary site of gefitinib metabolism is the liver, nevertheless tumor cell metabolism can significantly affect treatment effectiveness.

Results

In this study, we investigated the intracellular metabolism of gefitinib in a panel of EGFR wild-type gefitinib-sensitive and -resistant NSCLC cell lines, assessing the role of cytochrome P450 1A1 (CYP1A1) inhibition on gefitinib efficacy. Our results indicate that there is a significant difference in drug metabolism between gefitinib-sensitive and -resistant cell lines. Unexpectedly, only sensitive cells metabolized gefitinib, producing metabolites which were detected both inside and outside the cells. As a consequence of gefitinib metabolism, the intracellular level of gefitinib was markedly reduced after 12-24 h of treatment. Consistent with this observation, RT-PCR analysis and EROD assay showed that mRNA and activity of CYP1A1 were present at significant levels and were induced by gefitinib only in sensitive cells. Gefitinib metabolism was elevated in crowded cells, stimulated by exposure to cigarette smoke extract and prevented by hypoxic condition. It is worth noting that the metabolism of gefitinib in the sensitive cells is a consequence and not the cause of drug responsiveness, indeed treatment with a CYP1A1 inhibitor increased the efficacy of the drug because it prevented the fall in intracellular gefitinib level and significantly enhanced the inhibition of EGFR autophosphorylation, MAPK and PI3K/AKT/mTOR signalling pathways and cell proliferation.

Conclusion

Our findings suggest that gefitinib metabolism in lung cancer cells, elicited by CYP1A1 activity, might represent an early assessment of gefitinib responsiveness in NSCLC cells lacking activating mutations. On the other hand, in metabolizing cells, the inhibition of CYP1A1 might lead to increased local exposure to the active drug and thus increase gefitinib potency.

Human immunodeficiency virus infection and non-small cell lung cancer: survival and toxicity of antineoplastic chemotherapy in a cohort study

OBJECTIVES

To describe factors associated with survival in human immunodeficiency virus (HIV)-infected subjects with non-small cell lung cancer (NSCLC) and analyze toxicities induced by cytotoxic chemotherapy and antiretroviral compounds.

DESIGN

Retrospective analyses of HIV-infected subjects with NSCLC enrolled in the Dat'Aids cohort. A toxicity substudy included subjects treated by at least one cycle of cytotoxic chemotherapy.

METHODS

Survival was analyzed using Cox models. In the toxicity substudy, factors associated with grade 4 hematological toxicity of each episode of combination of antiretroviral drugs and cytotoxic chemotherapy were analyzed using marginal logistic regression models.

RESULTS

Fifty-two subjects were included in the study: 42 were men, median age was 48 years, 98% were smokers, with a median of 30 pack years, median CD4 was 300 cells/μl, and median survival time was 12 months. CD4 levels ≥200 cells/μl at NSCLC diagnosis (hazard ratio [HR] = 0.29, 95% confidence interval [CI] [0.10-0.89]), performance status less than 2 (HR = 0.32, 95% CI [0.15-0.68]) and highly active antiretroviral therapy (HR = 0.26, 95% CI [0.09-0.74]) were significantly associated with increased survival in the multivariable model. Forty subjects were included in the toxicity substudy, and 14 among 68 different combinations were complicated by a grade 4 hematological toxicity. Protease inhibitor use (odds ratio = 5.22, 95% CI [1.07-25.38]) was significantly associated with grade 4 hematological toxicity in the multivariable analyses.

CONCLUSIONS

In HIV-infected patients, CD4 levels at NSCLC diagnosis may be a predictive factor of survival. Use of highly active antiretroviral therapy during NSCLC chemotherapy is warranted, but protease inhibitors should be used with caution, as they may enhance severe hematological toxicities.

An update on ethnic differences in drug metabolism and toxicity from anti-cancer drugs

INTRODUCTION

Based on recent emerging evidence of inter-ethnic differences in drug response and toxicity, ethnic diversity in pharmacokinetics, pharmacogenomics and clinical outcomes are being increasingly investigated. Ultimately, this will promote improved understanding of inter-individual differences in the pharmacokinetics and tolerance of cytotoxic drugs.

AREAS COVERED

This article reviews potential explanations for the observed ethnic differences in treatment outcomes and provides clinical data to support this concept. A literature search was implemented on PubMed and PharmGKB to investigate the areas of ethnic differences in pharmacogenomics, pharmacogenetics and clinical outcomes of cancer therapies.

EXPERT OPINION

There has been a relative paucity of clinical evidence linking genetic polymorphisms of genes encoding drug-metabolizing enzymes to the pharmacokinetics, pharmacodynamics and tolerance of anti-cancer drugs. Future research should focus on studies using large sample sizes, in the hope that they will provide results of high clinical significance. Due to the potential for ethnic differences to impact on both toxicities and benefits of systemic cancer therapies, the development of new therapeutic agents should include patients from diverse geographical ancestries in each phase of drug development.

Off-target serine/threonine kinase 10 inhibition by erlotinib enhances lymphocytic activity leading to severe skin disorders

Skin disorders are among the most common adverse events related to treatment with epidermal growth factor receptor (EGFR) kinase inhibitors, and of these, erlotinib is known to cause more frequent and severe skin disease than other agents in this class. Although previous reports have shown that cutaneous manifestations are triggered by the inhibition of multiple EGFR-related homeostatic functions of the skin, this mechanism alone cannot explain the differences in frequency and severity of skin disorders caused by different kinase inhibitors. In this study, we focused on the relationship between the off-target kinase inhibition and aggravation of skin disorders. Based on calculations using reported K(d) values and plasma drug concentrations, serine/threonine kinase 10 (STK10) and Ste20-like kinase (SLK) were selected as candidates preferentially inhibited by erlotinib over gefitinib. In vitro experiments confirmed that STK10 and SLK kinase activity are inhibited by erlotinib at clinical concentrations, whereas only STK10 is slightly inhibited by gefitinib. It was also shown that erlotinib up-regulated lymphocytic responses such as interleukin (IL)-2 secretion and cell migration at clinical concentrations, whereas gefitinib did not affect lymphocyte activity. Moreover, small interfering RNA experiments revealed that STK10 plays a major role in up-regulation of the lymphocytic responses induced by erlotinib treatment. Finally, the role of erlotinib-induced lymphocyte activation was assessed in vivo using irritant hypersensitivity models. The results indicated that erlotinib aggravates cutaneous inflammatory reactions through the activation of lymphocytic responses such as IL-2 secretion and cell migration. These results demonstrated that off-target inhibition of STK10 by erlotinib enhances lymphocytic responses, which lead to the aggravation of skin inflammation.

Safety and pharmacokinetics of motesanib in combination with gemcitabine and erlotinib for the treatment of solid tumors: a phase 1b study

BACKGROUND

This phase 1b study assessed the maximum tolerated dose (MTD), safety, and pharmacokinetics of motesanib (a small-molecule antagonist of VEGF receptors 1, 2, and 3; platelet-derived growth factor receptor; and Kit) administered once daily (QD) or twice daily (BID) in combination with erlotinib and gemcitabine in patients with solid tumors.

METHODS

Patients received weekly intravenous gemcitabine (1000 mg/m2) and erlotinib (100 mg QD) alone (control cohort) or in combination with motesanib (50 mg QD, 75 mg BID, 125 mg QD, or 100 mg QD; cohorts 1-4); or erlotinib (150 mg QD) in combination with motesanib (100 or 125 mg QD; cohorts 5 and 6).

RESULTS

Fifty-six patients were enrolled and received protocol-specified treatment. Dose-limiting toxicities occurred in 11 patients in cohorts 1 (n = 2), 2 (n = 4), 3 (n = 3), and 6 (n = 2). The MTD of motesanib in combination with gemcitabine and erlotinib was 100 mg QD. Motesanib 125 mg QD was tolerable only in combination with erlotinib alone. Frequently occurring motesanib-related adverse events included diarrhea (n = 19), nausea (n = 18), vomiting (n = 13), and fatigue (n = 12), which were mostly of worst grade < 3. The pharmacokinetics of motesanib was not markedly affected by coadministration of gemcitabine and erlotinib, or erlotinib alone. Erlotinib exposure, however, appeared lower after coadministration with gemcitabine and/or motesanib. Of 49 evaluable patients, 1 had a confirmed partial response and 26 had stable disease.

CONCLUSIONS

Treatment with motesanib 100 mg QD plus erlotinib and gemcitabine was tolerable. Motesanib 125 mg QD was tolerable only in combination with erlotinib alone.

TRIAL REGISTRATION

ClinicalTrials.gov NCT01235416.

[Inhibitors of the epidermal growth factor receptor (EGFR) tyrosine kinase: similarity and differences]

Tyrosine kinase inhibitors (TKI) of EGFR are used in advanced non-small cell lung cancer (NSCLC) in 2(nd) and 3(rd) line, and for gefitinib in first line in case of EGFR mutations. These drugs are particularly active in presence of these mutations, with response rate around 60-70%. Pharmacological data suggest an equivalent effect of erlotinib and gefitinib. One phase II study has directly compared the two drugs in 2(nd) line, with a non significant advantage for gefitinib in term of response and progression-free survival. However, skin tolerance profile was statistically better with gefitinib. Indirect comparisons between erlotinib and gefitinib in the phase III trials vs chemotherapy 1(st) line have to be interpreted, with caution and take under consideration the impact of the chemotherapy arm on the Hazard Ratio for Progression-free and overall survival. However, response rates seem to be equivalent. Cohort and phase IV studies have shown no significant difference for response and survival, and a similar tolerance profile.

Part 2: pharmacogenetic variability in drug transport and phase I anticancer drug metabolism

Equivalent drug doses in anticancer chemotherapy may lead to wide interpatient variability in drug response reflected by differences in treatment response or in severity of adverse drug reactions. Differences in the pharmacokinetic (PK) and pharmacodynamic (PD) behavior of a drug contribute to variation in treatment outcome among patients. An important factor responsible for this variability is genetic polymorphism in genes that are involved in PK/PD processes, including drug transporters, phase I and II metabolizing enzymes, and drug targets, and other genes that interfere with drug response. In order to achieve personalized pharmacotherapy, drug dosing and treatment selection based on genotype might help to increase treatment efficacy while reducing unnecessary toxicity. We present a series of four reviews about pharmacogenetic variability in anticancer drug treatment. This is the second review in the series and is focused on genetic variability in genes encoding drug transporters (ABCB1 and ABCG2) and phase I drug-metabolizing enzymes (CYP2B6, CYP2C8, CYP2C9, CYP2C19, CYP2D6, CYP3A4, CYP3A5, DPYD, CDA and BLMH) and their associations with anticancer drug treatment outcome. Based on the literature reviewed, opportunities for patient-tailored anticancer therapy are presented.

Clinically relevant drug interactions between anticancer drugs and psychotropic agents

Drug interactions are commonly seen in the treatment of cancer patients. Psychotropics are often indicated for these patients since they may also suffer from pre-existing psychological disorders or experience insomnia and anxiety associated with cancer therapy. Thus, the risk of anticancer drug (ACD)-psychotropic drug-drug interactions (DDIs) is high. Drug interactions were compiled from the British National Formulary (53rd edn), Lexi-Comp's Drug Information Handbook (15th edn), Micromedex (v5.1), Hansten & Horn's Drug Interactions (2000) and Drug Interaction Facts (2008 edn). Product information of the individual drugs, as well as documented literature on ACD-psychotropic interactions from PubMed and other databases was also incorporated. This paper identifies clinically important ACD-psychotropic DDIs that are frequently observed. Pharmacokinetic DDIs were observed for tyrosine kinase inhibitors, corticosteroids and antimicrotubule agents due to their inhibitory or inductive effects on cytochrome P450 isoenzymes. Pharmacodynamic DDIs were identified for thalidomide with central nervous system depressants, procarbazine with antidepressants, myelosuppressive ACDs with clozapine and anthracyclines with QT-prolonging psychotropics. Clinicians should be vigilant when psychotropics are prescribed concurrently with ACDs. Close monitoring of plasma drug levels should be carried out to avoid toxicity in the patient, as well as to ensure adequate chemotherapeutic and psychotropic coverage.

Sorafenib and sunitinib, two anticancer drugs, inhibit CYP3A4-mediated and activate CY3A5-mediated midazolam 1'-hydroxylation

Sorafenib and sunitinib are novel small-molecule molecularly targeted anticancer drugs that inhibit multiple tyrosine kinases. These medicines have shown survival benefits in advanced renal cell carcinomas as well as in advanced hepatocellular carcinomas and gastrointestinal stromal tumors, respectively. The effects of sorafenib and sunitinib on midazolam 1'-hydroxylation catalyzed by human CYP3A4 or CYP3A5 were investigated. Sorafenib and sunitinib inhibited metabolic reactions catalyzed by recombinant CYP3A4. Midazolam hydroxylation was also inhibited in human liver microsomes harboring the CYP3A5*3/*3 genotype (poor CYP3A5 expressor). In contrast, midazolam 1'-hydroxylation catalyzed by recombinant CYP3A5 was enhanced by the coexistence of sorafenib or sunitinib in a concentration-dependent manner, with saturation occurring at approximately 10 μM. Midazolam hydroxylation was also enhanced in human liver microsomal samples harboring the CYP3A5*1/*1 genotype (extensive CYP3A5 expressor). Sorafenib N-oxidation and sunitinib N-deethylation, the primary routes of metabolism, were predominantly catalyzed by CYP3A4 but not by CYP3A5. The preincubation period of sorafenib and sunitinib before the midazolam addition in the reaction mixture did not affect the enhancement of CYP3A5-catalyzed midazolam hydroxylation, indicating that the enhancement was caused by parent sorafenib and sunitinib. Docking studies with a CYP3A5 homology model based on the structure of CYP3A4 revealed that midazolam closely docked to the heme of CYP3A5 compared with sorafenib or sunitinib, suggesting that these anticancer drugs act as enhancers, not as substrates. Our results thus showed that sorafenib and sunitinib activated midazolam 1'-hydroxylation by CYP3A5 but inhibited that by CYP3A4. Unexpected drug interactions involving sorafenib and sunitinib might occur via heterotropic cooperativity of CYP3A5.

Dosing modifications of targeted cancer therapies in patients with special needs: evidence and controversies

Targeted therapies have revolutionized the treatment of malignancies over the past decade. These agents are generally regarded to posses fewer systemic side effects than traditional cytotoxic chemotherapies. However, patients manifesting organ dysfunction or drug interactions with concurrent medications may require dosing modifications of their targeted therapies in order to reduce the risk of systemic toxicities or reduction of drug efficacies. Studies have shown that wide variations and controversies exist with regard to dosing modifications of drugs, due to the lack of well conducted studies and consensus. Hence, this review was conducted to review the literature on the dosing modification strategies, for 30 commercially available targeted cancer drugs, and to evaluate the current mainstay recommendations and controversies.

Treatment of non-small-cell lung cancer with erlotinib or gefitinib

A 64-year-old woman receives the diagnosis of metastatic non-small-cell lung cancer (NSCLC), which has progressed during treatment with carboplatin, paclitaxel, and bevacizumab. Erlotinib therapy is recommended.

Substrate-dependent modulation of the catalytic activity of CYP3A by erlotinib

AIM

To ascertain the effects of erlotinib on CYP3A, to investigate the amplitude and kinetics of erlotinib-mediated inhibition of seven major CYP isoforms in human liver microsomes (HLMs) for evaluating the magnitude of erlotinib in drug-drug interaction in vivo.

METHODS

The activities of 7 major CYP isoforms (CYP1A2, CYP2A6, CYP3A, CYP2C9, CYP2D6, CYP2C8, and CYP2E1) were assessed in HLMs using HPLC or UFLC analysis. A two-step incubation method was used to examine the time-dependent inhibition of erlotinib on CYP3A.

RESULTS

The activity of CYP2C8 was inhibited with an IC(50) value of 6.17±2.0 μmol/L. Erlotinib stimulated the midazolam 1'-hydroxy reaction, but inhibited the formation of 6β-hydroxytestosterone and oxidized nifedipine. Inhibition of CYP3A by erlotinib was substrate-dependent: the IC(50) values for inhibiting testosterone 6β-hydroxylation and nifedipine metabolism were 31.3±8.0 and 20.5±5.3 μmol/L, respectively. Erlotinib also exhibited the time-dependent inhibition on CYP3A, regardless of the probe substrate used: the value of K(I) and k(inact) were 6.3 μmol/L and 0.035 min(-1) for midazolam; 9.0 μmol/L and 0.045 min(-1) for testosterone; and 10.1 μmol/L and 0.058 min(-1) for nifedipine.

CONCLUSION

The inhibition of CYP3A by erlotinib was substrate-dependent, while its time-dependent inhibition on CYP3A was substrate-independent. The time-dependent inhibition of CYP3A may be a possible cause of drug-drug interaction, suggesting that attention should be paid to the evaluation of erlotinib's safety, especially in the context of combination therapy.