Quantitative modeling of tumor dynamics and development of drug resistance in non-small cell lung cancer patients treated with erlotinib

Insight into the development of treatment resistance can support the optimization of anticancer treatments. This study aims to characterize the tumor dynamics and development of drug resistance in patients with non-small cell lung cancer treated with erlotinib, and investigate the relationship between baseline circulating tumor DNA (ctDNA) data and tumor dynamics. Data obtained for the analysis included (1) intensively sampled erlotinib concentrations from 29 patients from two previous pharmacokinetic (PK) studies, and (2) tumor sizes, ctDNA measurements, and sparsely sampled erlotinib concentrations from 18 patients from the START-TKI study. A two-compartment population PK model was first developed which well-described the PK data. The PK model was subsequently applied to investigate the exposure-tumor dynamics relationship. To characterize the tumor dynamics, models accounting for intra-tumor heterogeneity and acquired resistance with or without primary resistance were investigated. Eventually, the model assumed acquired resistance only resulted in an adequate fit. Additionally, models with or without exposure-dependent treatment effect were explored, and no significant exposure-response relationship for erlotinib was identified within the observed exposure range. Subsequently, the correlation of baseline ctDNA data on EGFR and TP53 variants with tumor dynamics' parameters was explored. The analysis indicated that higher baseline plasma EGFR mutation levels correlated with increased tumor growth rates, and the inclusion of ctDNA measurements improved model fit. This result suggests that quantitative ctDNA measurements at baseline have the potential to be a predictor of anticancer treatment response. The developed model can potentially be applied to design optimal treatment regimens that better overcome resistance.

Therapeutic Drug Monitoring of Erlotinib in Non-Small Cell Lung Carcinoma: A Case Study

ABSTRACT

We describe a clinical case of an 84-year-old man diagnosed with non-small cell lung carcinoma and epidermal growth factor receptor mutation, who was treated with erlotinib, with doses adjusted by therapeutic drug monitoring. This case involved a clearance fluctuation leading to over-therapeutic drug concentrations of erlotinib and toxicity. The intrapatient and interpatient variability of erlotinib, in addition to other factors such as age or variations in liver clearance, create situations that are challenging in clinical practice. During treatment, erlotinib serum concentrations were measured, and the dose was accordingly adjusted. The erlotinib dose required to reduce toxicity (rash grade III) and maintain effective plasma concentrations, as well as clinical and radiological responses, was 50% of the initial dose, underscoring the relevance of therapeutic drug monitoring for tyrosine kinase inhibitors in routine clinical practice.

Pharmacokinetic Profiles Determine Optimal Combination Treatment Schedules in Computational Models of Drug Resistance

Identification of optimal schedules for combination drug administration relies on accurately estimating the correct pharmacokinetics, pharmacodynamics, and drug interaction effects. Misspecification of pharmacokinetics can lead to wrongly predicted timing or order of treatments, leading to schedules recommended on the basis of incorrect assumptions about absorption and elimination of a drug and its effect on tumor growth. Here, we developed a computational modeling platform and software package for combination treatment strategies with flexible pharmacokinetic profiles and multidrug interaction curves that are estimated from data. The software can be used to compare prespecified schedules on the basis of the number of resistant cells where drug interactions and pharmacokinetic curves can be estimated from user-provided data or models. We applied our approach to publicly available in vitro data of treatment with different tyrosine kinase inhibitors of BT-20 triple-negative breast cancer cells and of treatment with erlotinib of PC-9 non-small cell lung cancer cells. Our approach is publicly available in the form of an R package called ACESO (https://github.com/Michorlab/aceso) and can be used to investigate optimum dosing for any combination treatment. SIGNIFICANCE: These findings introduce a computational modeling platform and software package for combination treatment strategies with flexible pharmacokinetic profiles and multidrug interaction curves that are estimated from data.

Safety and CSF distribution of high-dose erlotinib and gefitinib in patients of non-small cell lung cancer (NSCLC) with brain metastases

PURPOSE

Patients of non-small cell lung cancer (NSCLC) with brain metastases have limited treatment options. High-dose erlotinib (HDE) and gefitinib (HDG) have been tried in the past. This study investigates the cerebrospinal fluid (CSF) disposition and safety of both, high-dose erlotinib and gefitinib regimens.

METHODS

Eleven and nine patients were treated with erlotinib and gefitinib, respectively. All patients received 1 week of standard dose of erlotinib (150 mg OD) or gefitinib (250 mg OD), followed by the high dose (1500 mg weekly for erlotinib and 1250 mg OD for gefitinib) from day 8. Blood and CSF samples were collected on days 7 and 15, 4 h after the morning dose and drug levels determined using LC-MS/MS. Adverse events were documented as per CTCAE 4.03 till day 15.

RESULTS

Pulsatile HDE and daily HDG resulted in 1.4- and 1.9-fold increase in CSF levels, respectively. A constant 2% CSF penetration rate was observed across both doses of erlotinib, while for gefitinib the penetration rate for high dose was half that of the standard dose suggesting a nonlinear disposition. Three patients on HDE treatment discontinued treatment after the first dose due to intolerable toxicities, whereas HDG was better tolerated with no treatment discontinuations. Since CSF disposition of gefitinib followed saturable kinetics, a lower dose of 750 mg was found to achieve CSF concentrations comparable to that of the 1250 mg dose.

CONCLUSIONS

HDG was better tolerated than HDE. CSF disposition of gefitinib was found to be saturable at a higher dose. Based on these findings, the dose of 750 mg OD should be considered for further evaluation in this setting.

Dual functionalized liposomes for efficient co-delivery of anti-cancer chemotherapeutics for the treatment of glioblastoma

Glioblastoma is a hostile brain tumor associated with high infiltration leading to poor prognosis. Anti-cancer chemotherapeutic agents have limited access into the brain due to the presence of the blood brain barrier (BBB). In this study, we designed a dual functionalized liposomal delivery system, surface modified with transferrin (Tf) for receptor mediated transcytosis and a cell penetrating peptide-penetratin (Pen) for enhanced cell penetration. We loaded doxorubicin and erlotinib into liposomes to enhance their translocation across the BBB to glioblastoma tumor. In vitro cytotoxicity and hemocompatibility studies demonstrated excellent biocompatibility for in vivo administration. Co-delivery of doxorubicin and erlotinib loaded Tf-Pen liposomes revealed significantly (p < 0.05) higher translocation (~15%) across the co-culture endothelial barrier resulting in regression of tumor in the in vitro brain tumor model. The biodistribution of Tf-Pen liposomes demonstrated ~12 and 3.3 fold increase in doxorubicin and erlotinib accumulation in mice brain, respectively compared to free drugs. In addition, Tf-Pen liposomes showed excellent antitumor efficacy by regressing ~90% of tumor in mice brain with significant increase in the median survival time (36 days) along with no toxicity. Thus, we believe that this study would have high impact for treating patients with glioblastoma.

Towards Improved Pharmacokinetic Models for the Analysis of Transporter-Mediated Hepatic Disposition of Drug Molecules with Positron Emission Tomography

Positron emission tomography (PET) imaging with radiolabeled drugs holds great promise to assess the influence of membrane transporters on hepatobiliary clearance of drugs. To exploit the full potential of PET, quantitative pharmacokinetic models are required. In this study, we evaluated the suitability of different compartment models to describe the hepatic disposition of [11C]erlotinib as a small-molecule model drug which undergoes transporter-mediated hepatobiliary excretion. We analyzed two different, previously published data sets in healthy volunteers, in which a baseline [11C]erlotinib PET scan was followed by a second PET scan either after oral intake of unlabeled erlotinib (300 mg) or after intravenous infusion of the prototypical organic anion-transporting polypeptide inhibitor rifampicin (600 mg). We assessed a three-compartment (3C) and a four-compartment (4C) model, in which either a sampled arterial blood input function or a mathematically derived dual input function (DIF), which takes the contribution of the portal vein to the liver blood supply into account, was used. Both models provided acceptable fits of the observed PET data in the liver and extrahepatic bile duct and gall bladder. Changes in model outcome parameters between scans were consistent with the involvement of basolateral hepatocyte uptake and canalicular efflux transporters in the hepatobiliary clearance of [11C]erlotinib. Our results demonstrated that inclusion of a DIF did not lead to substantial improvements in model fits. The models developed in this work represent a step forward in applying PET as a tool to assess the impact of hepatic transporters on drug disposition and their involvement in drug-drug interactions.

Erlotinib-Valproic Acid Liquisolid Formulation: Evaluating Oral Bioavailability and Cytotoxicity in Erlotinib-Resistant Non-small Cell Lung Cancer Cells

Lung cancer patients develop acquired resistance to tyrosine kinase inhibitors including erlotinib (ERL) after few months of primary treatment. Evidently, new chemotherapy strategies to delay or overcome the resistance are urgently needed to improve the clinical outcome in non-small cell lung cancer (NSCLC) patients. In this paper, we have investigated the cytotoxic interaction of ERL and valproic acid (VA) in ERL-resistant NSCLC cells and developed a liquisolid formulation of ERL-VA for improving oral bioavailability of ERL. ERL is weakly basic, biopharmaceutical classification system (BCS) class II drug with extremely poor aqueous solubility while VA is a branched chain fatty acid. Ionic interaction between ERL and VA (1:2 M ratio) resulted in significant enhancement in saturation solubility of ERL at different pH range. Liquisolid formulation of ERL-VA (EVLF) developed using PEG 400 and mesoporous calcium silicate was characterized for solid state and in vitro dissolution in biorelevant dissolution medium (FaSSIF and FeSSIF). Cytotoxicity of ERL was enhanced by 2-5 folds on co-incubation with VA in HCC827/ERL cell line. Flow cytometry analysis using AnnexinV-FITC assay demonstrated that VA and ERL alone have poor apoptotic effect on HCC827/ERL cells while combination showed around 69% apoptotic cells. Western blot analysis confirmed the role of survivin in overcoming resistance. In vivo pharmacokinetic studies of EVLF in rats demonstrated a 199% relative bioavailability compared to ERL suspension. Thus, EVLF could be a promising alternative to current ERL formulations in the treatment of NSCLC.

Integrated mapping of pharmacokinetics and pharmacodynamics in a patient-derived xenograft model of glioblastoma

Therapeutic options for the treatment of glioblastoma remain inadequate despite concerted research efforts in drug development. Therapeutic failure can result from poor permeability of the blood-brain barrier, heterogeneous drug distribution, and development of resistance. Elucidation of relationships among such parameters could enable the development of predictive models of drug response in patients and inform drug development. Complementary analyses were applied to a glioblastoma patient-derived xenograft model in order to quantitatively map distribution and resulting cellular response to the EGFR inhibitor erlotinib. Mass spectrometry images of erlotinib were registered to histology and magnetic resonance images in order to correlate drug distribution with tumor characteristics. Phosphoproteomics and immunohistochemistry were used to assess protein signaling in response to drug, and integrated with transcriptional response using mRNA sequencing. This comprehensive dataset provides simultaneous insight into pharmacokinetics and pharmacodynamics and indicates that erlotinib delivery to intracranial tumors is insufficient to inhibit EGFR tyrosine kinase signaling.

Design of a Multicompartment Hydrogel that Facilitates Time-Resolved Delivery of Combination Therapy and Synergized Killing of Glioblastoma

There is significant current interest in identifying new combination therapies that synergize to treat disease, and it is becoming increasingly clear that the temporal resolution of their administration greatly impacts efficacy. To facilitate effective delivery, a multicompartment hydrogel material was developed that is composed of spherical vesicles interlaced within a self-assembled peptide-based network of physically crosslinked fibrils that allows time-resolved independent co-delivery of small molecules. This material architecture effectively delivers the EGFR kinase inhibitor Erlotinib (ERL) and Doxorubicin (DOX, DNA intercalator) in an ERL→DOX sequential manner to synergistically kill glioblastoma, the most aggressive form of brain cancer.

HA/HSA co-modified erlotinib-albumin nanoparticles for lung cancer treatment

BACKGROUND

Aim of this study was to prepare the hyaluronic acid and human serum albumin modified erlotinib nanoparticles (ERT-HSA-HA NPs) delivery system by a precipitation method.

METHODS

ERT-HSA-HA NPs were characterized for physical properties, such as morphology and particle size, and in vitro drug release. Moreover, the cytotoxicity, cellular uptake, in vivo studies of ERT-HSA-HA nanoparticle were investigated and compared in A549 cells.

RESULTS

The ERT-HSA-HA NPs showed spherical morphology, and their hydrodynamic diameter was 112.5±2.8 nm. The drug loading amount and encapsulation efficiency were 5.6% and 81.2%, respectively. After 3 months of storage, no dramatic change, such as visible aggregation, drug content changes, and precipitation, in the appearance of ERT-HSA-HA NPs occurred. In vitro release showed that the release of ERT from HSA-HA NPs was slow, without obvious burst effects at an early stage. In in vivo studies, ERT-HSA-HA NPs showed a superior antiproliferative effect on A549 cells, and the HA modification strategy can also facilitate the high-efficiency uptake of ERT-HSA NPs by A549 cells. Pharmacokinetic studies showed that the form of NPs could significantly extend the role of ERT in vivo (provided higher bioavailability). However, there was no significant difference in the pharmacokinetic parameters between ERT-HSA NPs and ERT-HSA-HA NPs after intravenous administration. In terms of in vivo antitumor activity, ERT-HSA-HA NP-treated mice showed a significantly suppressed tumor growth and no relapse after 30 d of treatment.

CONCLUSION

HA/HSA co-modified erlotinib albumin nanoparticles was expected to be a new strategy in the treatment of lung cancer.

A Phase I Dose-Escalation Study of the Safety and Pharmacokinetics of Pictilisib in Combination with Erlotinib in Patients with Advanced Solid Tumors

BACKGROUND

Epidermal growth factor receptor (EGFR) and phosphatidylinositol 3-kinase (PI3K) are involved in the proliferation and survival of many cancer types. Enhanced antitumor activity may be achieved through combined inhibition of these pathways. We report results for pictilisib (GDC-0941, a class I pan-PI3K inhibitor) plus erlotinib (an EGFR tyrosine kinase inhibitor) in patients with advanced solid tumors.

MATERIALS AND METHODS

A 3 + 3 dose-escalation study was carried out at a starting daily dose of 60 mg pictilisib on days 1-21 of a 28-day cycle and 150 mg erlotinib from day 2 of cycle 1. The primary objectives of the study were to assess safety and tolerability, identify dose-limiting toxicities (DLTs), estimate the maximum tolerated dose, and identify the recommended phase II dose (RP2D). Evaluation of a dose-expansion cohort at the RP2D was performed.

RESULTS

Fifty-seven patients were treated in the study. All patients experienced at least one adverse event (AE). Grade ≥3 AEs, serious AEs, and deaths were reported in 38 (66.7%), 19 (33.3%), and 4 (7.0%) patients, respectively. DLTs occurred in nine patients across eight cohorts and the RP2D was determined to be 340 mg pictilisib on a "5 days on, 2 days off" schedule plus 100 mg erlotinib. Two patients (3.5%) experienced partial response and 19 (33.3%) had stable disease.

CONCLUSION

Combining pictilisib with erlotinib in patients with advanced solid tumors is feasible; however, antitumor activity is limited. Additional studies may identify patients likely to benefit from combined inhibition of EGFR and PI3K pathways.

IMPLICATIONS FOR PRACTICE

Combining drugs targeting different signaling pathways in cancer growth and survival could overcome drug resistance and improve antitumor activity. In this first-in-human study for the combination, addition of the PI3K inhibitor pictilisib to the EGFR tyrosine kinase inhibitor erlotinib resulted in toxicity that led to dose and schedule modifications to identify a tolerable recommended phase II dose of 340 mg pictilisib on a "5 days on, 2 days off" schedule plus 100 mg erlotinib daily. The limited antitumor activity observed, however, suggests that additional studies are needed to identify patients most likely to benefit from combined EGFR and PI3K inhibition.

Phase 1 study of twice weekly pulse dose and daily low-dose erlotinib as initial treatment for patients with EGFR-mutant lung cancers

Background

Patients with EGFR-mutant lung cancers treated with EGFR tyrosine kinase inhibitors (TKIs) develop clinical resistance, most commonly with acquisition of EGFR T790M. Evolutionary modeling suggests that a schedule of twice weekly pulse and daily low-dose erlotinib may delay emergence of EGFR T790M. Pulse dose erlotinib has superior central nervous system (CNS) penetration and may result in superior CNS disease control.

Methods

We evaluated toxicity, pharmacokinetics, and efficacy of twice weekly pulse and daily low-dose erlotinib. We assessed six escalating pulse doses of erlotinib.

Results

We enrolled 34 patients; 11 patients (32%) had brain metastases at study entry. We observed 3 dose-limiting toxicities in dose escalation: transaminitis, mucositis, and rash. The MTD was erlotinib 1200 mg days 1-2 and 50 mg days 3-7 weekly. The most frequent toxicities (any grade) were rash, diarrhea, nausea, fatigue, and mucositis. 1 complete and 24 partial responses were observed (74%, 95% CI 60-84%). Median progression-free survival was 9.9 months (95% CI 5.8-15.4 months). No patient had progression of an untreated CNS metastasis or developed a new CNS lesion while on study (0%, 95% CI 0-13%). Of the 18 patients with biopsies at progression, EGFR T790M was identified in 78% (95% CI 54-91%).

Conclusion

This is the first clinical implementation of an anti-cancer TKI regimen combining pulse and daily low-dose administration. This evolutionary modeling-based dosing schedule was well-tolerated but did not improve progression-free survival or prevent emergence of EGFR T790M, likely due to insufficient peak serum concentrations of erlotinib. This dosing schedule prevented progression of untreated or any new central nervous system metastases in all patients.

Phase I Study of Oral Vinorelbine in Combination with Erlotinib in Advanced Non-Small Cell Lung Cancer (NSCLC) Using Two Different Schedules

Purpose

This study aimed to evaluate the safety, tolerability and pharmacokinetics of the combination of oral vinorelbine with erlotinib using the conventional (CSV) and metronomic (MSV) dosing schedules in patients with advanced non-small cell lung cancer (NSCLC).

Methods

This was an open-label, multiple dose-escalation phase I study. An alternating 3+3 phase I design was employed to allow each schedule to enroll three patients sequentially at each dose level. Thirty patients with Stage IIIB/IV NSCLC were treated with escalating doses of oral vinorelbine starting at 40 mg/m² on day 1 and 8 in the CSV group (N = 16) and at 100 mg/week in the MSV group (N = 14). Erlotinib was administered orally daily.

Results

The maximum tolerated dose was vinorelbine 80 mg/m² with erlotinib 100 mg in the CSV group and vinorelbine 120 mg/week with erlotinib 100 mg in the MSV group. Grade 3/4 toxicities included neutropenia (N = 2; 13%) and hyponatremia (N = 1; 6%) in the CSV group, and neutropenia (N = 5; 36%) in the MSV group. Objective response was achieved in 38% and 29% in the CSV and MSV groups respectively. Vinorelbine co-administration did not significantly affect the pharmacokinetics of erlotinib and OSI-420 after initial dose. However, at steady-state, significantly higher C_max, higher C_min and lower CL/F of erlotinib were observed with increasing dose levels of vinorelbine in the CSV group. Significantly higher steady-state C_min, C_avg and AUC_ss of erlotinib were observed with increasing dose levels of vinorelbine in the MSV group.

Conclusions

Combination of oral vinorelbine with erlotinib is feasible and tolerable in both the CSV and MSV groups.

Trial Registration

ClinicalTrials.gov NCT00702182

Development of Solid Self-Emulsifying Formulation for Improving the Oral Bioavailability of Erlotinib

To improve the solubility and oral bioavailability of erlotinib, a poorly water-soluble anticancer drug, solid self-emulsifying drug delivery system (SEDDS) was developed using solid inert carriers such as dextran 40 and Aerosil® 200 (colloidal silica). The preliminary solubility of erlotinib in various oils, surfactants, and co-surfactants was determined. Labrafil M2125CS, Labrasol, and Transcutol HP were chosen as the oil, surfactant, and co-surfactant, respectively, for preparation of the SEDDS formulations. The ternary phase diagram was evaluated to show the self-emulsifying area. The formulations were optimized using the droplet size and polydispersity index (PDI) of the resultant emulsions. Then, the optimized formulation containing 5% Labrafil M2125CS, 65% Labrasol, and 30% Transcutol was spray dried with dextran or Aerosil® and characterized for surface morphology, crystallinity, and pharmacokinetics in rats. Powder X-ray diffraction (PXRD) and differential scanning calorimetry (DSC) exhibited the amorphous form or molecular dispersion of erlotinib in the formulations. The pharmacokinetic parameters of the optimized formulations showed that the maximum concentration (C max) and area under the curve (AUC) of erlotinib were significantly increased, compared to erlotinib powder (p < 0.05). Thus, this SEDDS could be a promising method for enhancing the oral bioavailability of erlotinib.

Preclinical assessment of the interactions between the antiretroviral drugs, ritonavir and efavirenz, and the tyrosine kinase inhibitor erlotinib

PURPOSE

Prevalence of non-AIDS-defining cancers (NADCs) has increased in the era of potent antiretroviral treatments. Incidence rates of NADCs now exceed AIDS-defining cancers in HIV-positive patients. Treatment of NADCs may be complicated by interactions between antiretrovirals and chemotherapy mostly via inhibition or induction of CYP3A4. Erlotinib is used to treat non-small cell lung and pancreatic cancer and is primarily metabolized by CYP3A4 into multiple products including the active metabolite (OSI-420). Preclinical in vivo assessment was performed to gain a better understanding of CYP3A4-mediated interactions between antiretrovirals and erlotinib.

METHODS

Erlotinib (50 mg/kg p.o.) was administered to male FVB mice in the presence and absence of dexamethasone (10 mg/kg p.o. QDx4), efavirenz (25 mg/kg p.o. QDx4), ketoconazole (50 mg/kg p.o.), or ritonavir (12.5 mg/kg p.o.). Blood samples were collected to characterize exposure (AUC).

RESULTS

Administration of erlotinib with CYP3A4 inducers (dexamethasone) and inhibitors (ketoconazole and ritonavir) resulted in significant alterations in erlotinib exposure. Ketoconazole and ritonavir resulted in a 1.7- and 3.0-fold increase in erlotinib AUC, respectively, while dexamethasone results in a 0.6-fold decrease in erlotinib AUC. The CYP3A4 inducer efavirenz did not have a significant effect on erlotinib exposure.

CONCLUSION

CYP3A4 inducers and inhibitors altered the exposure of erlotinib. Until a definitive clinical trial is performed, erlotinib should be used with caution in patients on a ritonavir-containing antiretroviral regimen, while standard doses may be appropriate for patients on an efavirenz-containing antiretroviral regimen.

A phase I/II study combining erlotinib and dasatinib for non-small cell lung cancer

BACKGROUND

EGFR and Src are frequently activated in non-small cell lung cancer (NSCLC). In preclinical models, combining EGFR and Src inhibition has additive synergistic effects. We conducted a phase I/II trial of the combination of Src inhibitor dasatinib with EGFR inhibitor erlotinib to determine the maximum tolerated dose (MTD), pharmacokinetic drug interactions, biomarkers, and efficacy in NSCLC.

METHODS

The phase I 3+3 dose-escalation study enrolled patients with solid tumors to determine the MTD. The phase II trial enrolled patients with advanced NSCLC who had undergone no previous treatments to determine progression-free survival (PFS) and response. Pharmacokinetic and tissue biomarker analyses were performed.

RESULTS

MTD was 150 mg of erlotinib and 70 mg of dasatinib daily based on 12 patients treated in the phase I portion. No responses were observed in phase I. The 35 NSCLC patients treated in phase II had an overall disease control rate of 59% at 6 weeks. Five patients (15%) had partial responses; all had activating EGFR mutations. Median PFS was 3.3 months. Epithelial-mesenchymal transition markers did not correlate with outcomes.

CONCLUSION

The combination of erlotinib and dasatinib is safe and feasible in NSCLC. The results of this study do not support use of this combination in molecularly unselected NSCLC.

[Clinical pharmacokinetics of small molecule tyrosine kinase inhibitors]

Human protein tyrosine kinases play an essential role in carcinogenesis and have been recognized as promising drug targets. By the end of 2012, eight small molecule tyrosine kinase inhibitors (TKIs) have been approved by State Food and Drug Administration of China for cancer treatment. In this paper, the pharmacokinetic characteristics (absorption, distribution, metabolism and excretion) and drug-drug interactions of the approved TKIs are reviewed. Overall, these TKIs reach their peak plasma concentrations relatively fast; are extensively distributed and highly protein bound (> 90%); are primarily metabolized by CYP3A4; most are heavily influenced by CYP3A4 inhibitors or inducers except for sorafenib; are mainly excreted with feces and only a minor fraction is eliminated with the urine; and are substrate of the efflux transporters ABCB1 (P-gp) and ABCG2 (BCRP). Additionally, many of the TKIs can inhibit some CYP450 enzymes, UGT enzymes, and transporters. Gefitinib, erlotinib, dasatinib, and sunitinib are metabolized to form reactive metabolites capable of covalently binding to biomolecules.