Tumours modulate the systemic vascular response to anti-angiogenic therapy.

Toxicologic evaluation of new drug candidates routinely utilizes healthy animals. In oncology, there remains a limited understanding of the effects of novel test candidates in a diseased host. For vascular modulating agents (VMAs), an increased understanding of preclinical tumour-host interaction, and its potential to exacerbate or alleviate 'off-target' effects of anti-angiogenic administration, could aid in the prediction of adverse clinical outcomes in a defined cancer patient. We have previously reported that the implantation and growth of a range of human- and mouse-derived tumours leads to structural vascular and, potentially, functional signalling changes within host mouse endocrine tissues, indicating possible roles for tumour- and host-derived cytokines/growth factors and the liberation of myeloid-derived suppressor cells in this phenomenon. Here, we further demonstrate that the growth of the Calu-6 xenograft is associated with a resistance to VMA-induced mouse peripheral endocrine vascular rarefaction (toxicity), with potential functional impact, notably with respect to mixed tyrosine kinase inhibition. The pathogenesis of these findings indicates a potential role for both tumour- and host-derived basic fibroblast growth factor (bFGF), with associated upregulation in the intra-tumoural autotaxin-lysophosphatic acid signalling axis.

Tumors modulate fenestrated vascular beds and host endocrine status.

Allograft and xenograft transplantation into a mouse host is frequently utilized to study cancer biology, tumor behavior, and response to treatment. Preclinical studies employing these models often focus solely upon the intra-tumoral effects of a given treatment, without consideration of systemic toxicity or tumor-host interaction, nor whether this latter relationship could modulate the toxicologic response to therapy. Here it is demonstrated that the implantation and growth of a range of human- and mouse-derived cell lines leads to structural vascular and, potentially, functional changes within peripheral endocrine tissues, a process that could conceivably ameliorate the severity of anti-angiogenic-induced fenestrated vessel attenuation. Observations suggest a multifactorial process, which may involve host- and tumor-derived cytokines/growth factors, and the liberation of myeloid-derived suppressor cells. Further investigation revealed a structurally comparable response to the administration of exogenous estrogen. These findings, in addition to providing insight into the development of clinical anti-angiogenic "adaptation," may be of significance within the "cancer-cachexia" and cancer-related anemia syndromes in man.

Automated image analysis of intra-tumoral and peripheral endocrine organ vascular bed regression using 'Fibrelength' as a novel structural biomarker.

The study of vascular modulation has received a great deal of attention in recent years as knowledge has increased around the role of angiogenesis within disease contexts such as cancer. Despite rapidly expanding insights into the molecular processes involved and the concomitant generation of a number of anticancer vascular modulating chemotherapeutics, techniques used in the measurement of structural vascular change have advanced more modestly, particularly with regard to the preclinical quantification of off-target vascular regression within systemic, notably endocrine, blood vessels. Such changes translate into a number of major clinical side effects and there remains a need for improved preclinical screening and analysis. Here we present the generation of a novel structural biomarker, which can be incorporated into a number of contemporary image analysis platforms and used to compare tumour versus systemic host tissue vascularity. By contrasting the measurements obtained, the preclinical efficacy of vascular modulating chemotherapies can be evaluated in light of the predicted therapeutic window. Copyright © 2017 John Wiley & Sons, Ltd.

Leptin, BMI, and a Metabolic Gene Expression Signature Associated with Clinical Outcome to VEGF Inhibition in Colorectal Cancer.

VEGF (vascular endothelial growth factor) signaling inhibitors are widely used in different cancer types; however, patient selection remains a challenge. Analyses of samples from a phase III clinical trial in metastatic colorectal cancer testing chemotherapy versus chemotherapy with the small molecule VEGF receptors inhibitor cediranib identified circulating leptin levels, BMI, and a tumor metabolic and angiogenic gene expression signature associated with improved clinical outcome in patients treated with cediranib. Patients with a glycolytic and hypoxic/angiogenic profile were associated with increased benefit from cediranib, whereas patients with a high lipogenic, oxidative phosphorylation and serine biosynthesis signature did not gain benefit. These findings translated to pre-clinical tumor xenograft models where the same metabolic gene expression profiles were associated with in vivo sensitivity to cediranib as monotherapy. These findings suggest a link between patient physiology, tumor biology, and response to antiangiogenics, which may guide patient selection for VEGF therapy in the future.

Therapeutic targeting of integrin αvß6 in breast cancer.

BACKGROUND: Integrin αvß6 promotes migration, invasion, and survival of cancer cells; however, the relevance and role of αvß6 has yet to be elucidated in breast cancer. METHODS: Protein expression of integrin subunit beta6 (ß6) was measured in breast cancers by immunohistochemistry (n > 2000) and ITGB6 mRNA expression measured in the Molecular Taxonomy of Breast Cancer International Consortium dataset. Overall survival was assessed using Kaplan Meier curves, and bioinformatics statistical analyses were performed (Cox proportional hazards model, Wald test, and Chi-square test of association). Using antibody (264RAD) blockade and siRNA knockdown of ß6 in breast cell lines, the role of αvß6 in Human Epidermal Growth Factor Receptor 2 (HER2) biology (expression, proliferation, invasion, growth in vivo) was assessed by flow cytometry, MTT, Transwell invasion, proximity ligation assay, and xenografts (n ≥ 3), respectively. A student's t-test was used for two variables; three-plus variables used one-way analysis of variance with Bonferroni's Multiple Comparison Test. Xenograft growth was analyzed using linear mixed model analysis, followed by Wald testing and survival, analyzed using the Log-Rank test. All statistical tests were two sided. RESULTS: High expression of either the mRNA or protein for the integrin subunit ß6 was associated with very poor survival (HR = 1.60, 95% CI = 1.19 to 2.15, P = .002) and increased metastases to distant sites. Co-expression of ß6 and HER2 was associated with worse prognosis (HR = 1.97, 95% CI = 1.16 to 3.35, P = .01). Monotherapy with 264RAD or trastuzumab slowed growth of MCF-7/HER2-18 and BT-474 xenografts similarly (P < .001), but combining 264RAD with trastuzumab effectively stopped tumor growth, even in trastuzumab-resistant MCF-7/HER2-18 xenografts. CONCLUSIONS: Targeting αvß6 with 264RAD alone or in combination with trastuzumab may provide a novel therapy for treating high-risk and trastuzumab-resistant breast cancer patients.

Tumor stromal architecture can define the intrinsic tumor response to VEGF-targeted therapy.

PURPOSE: The aim of the study was to investigate the vascular and stromal architecture of preclinical tumor models and patient tumor specimens from malignancies with known clinical outcomes to VEGFi treatment, to gain insight into potential determinants of intrinsic sensitivity and resistance. EXPERIMENTAL DESIGN: The tumor stroma architecture of preclinical and clinical tumor samples were analyzed by staining for CD31 and α-smooth muscle actin (α-SMA). Tumor models representative of each phenotype were then tested for sensitivity to the VEGFR2-blocking antibody DC101. RESULTS: Human tumor types with high response rates to VEGF inhibitors (e.g., renal cell carcinoma) have vessels distributed amongst the tumor cells (a "tumor vessel" phenotype, TV). In contrast, those malignancies where single-agent responses are lower, such as non-small cell lung cancer (NSCLC), display a complex morphology involving the encapsulation of tumor cells within stroma that also supports the majority of vessels (a "stromal vessel" phenotype). Only 1 of 31 tumor xenograft models displayed the stromal vessel phenotype. Tumor vessel models were sensitive to VEGFR2-blocking antibody DC101, whereas the stromal vessel models were exclusively refractory. The tumor vessel phenotype was also associated with a better Response Evaluation Criteria in Solid Tumors (RECIST) response to bevacizumab + chemotherapy in metastatic colorectal cancer (CRC). CONCLUSION: The tumor stromal architecture can differentiate between human tumor types that respond to a VEGF signaling inhibitor as single-agent therapy. In addition to reconciling the clinical experience with these agents versus their broad activity in preclinical models, these findings may help to select solid tumor types with intrinsic sensitivity to a VEGFi or other vascular-directed therapies.

Anti-tumour and anti-vascular effects of cediranib (AZD2171) alone and in combination with other anti-tumour therapies.

PURPOSE: Cediranib (AZD2171) is a highly potent inhibitor of all three vascular endothelial growth factor receptors. The aim of this preclinical study was to examine the effect of combining cediranib with mechanistically distinct anti-tumour therapies. METHODS: Cediranib (1.5 or 3 mg/kg/day) was evaluated alone and in combination with either gefitinib, imatinib, ZD6126, saracatinib, selumetinib, bevacizumab, 5-fluorouracil (5-FU), docetaxel, oxaliplatin, gemcitabine, pemetrexed, irinotecan or cisplatin in human tumour xenograft models. Anti-tumour activity was measured by assessing the change in tumour volume following treatment compared with vehicle-treated time-matched controls. RESULTS: In all cases, the combination regimens, at tolerated doses and schedules, inhibited tumour growth to a greater extent than the corresponding monotherapy treatments. Compared with cediranib alone, statistically significant enhancements in anti-tumour activity were observed with all combination regimens. Notably, after 14 days of treatment, the combination of cediranib with ZD6126 induced substantial tumour regression (60 % compared with pre-treatment volume), whilst treatment with each agent alone led only to partial growth inhibition. A combination of cediranib with gefitinib also induced tumour regressions, and cediranib combined with either gemcitabine or irinotecan was found to inhibit tumour growth profoundly (by 99 and 98 %, respectively). CONCLUSIONS: Combining cediranib with selected cytotoxic or targeted agents proved efficacious in a range of human tumour xenograft models.

MEDI0639: a novel therapeutic antibody targeting Dll4 modulates endothelial cell function and angiogenesis in vivo.

The Notch signaling pathway has been implicated in cell fate determination and differentiation in many tissues. Accumulating evidence points toward a pivotal role in blood vessel formation, and the importance of the Delta-like ligand (Dll) 4-Notch1 ligand-receptor interaction has been shown in both physiological and tumor angiogenesis. Disruption of this interaction leads to a reduction in tumor growth as a result of an increase in nonfunctional vasculature leading to poor perfusion of the tumor. MEDI0639 is an investigational human therapeutic antibody that targets Dll4 to inhibit the interaction between Dll4 and Notch1. The antibody cross-reacts to cynomolgus monkey but not mouse species orthologues. In vitro MEDI0639 inhibits the binding of Notch1 to Dll4, interacting via a novel epitope that has not been previously described. Binding to this epitope translates into MEDI0639 reversing Notch1-mediated suppression of human umbilical vein endothelial cell growth in vitro. MEDI0639 administration resulted in stimulation of tubule formation in a three-dimensional (3D) endothelial cell outgrowth assay, a phenotype driven by disruption of the Dll4-Notch signaling axis. In contrast, in a two-dimensional endothelial cell-fibroblast coculture model, MEDI0639 is a potent inhibitor of tubule formation. In vivo, MEDI0639 shows activity in a human endothelial cell angiogenesis assay promoting human vessel formation and reducing the number of vessels with smooth muscle actin-positive mural cells coverage. Collectively, the data show that MEDI0639 is a potent modulator of Dll4-Notch signaling pathway.

Structure-activity relationship of a series of non peptidic RGD integrin antagonists targeting α5ß1: part 1.

Potent antagonists of the integrin α(5)ß(1), which are RGD mimetics built from tyrosine are described. This letter describes the optimization of in vitro potency obtained by variation of two parts of the molecule, the basic group and the linker between the basic group and the phenyl central core.

Structure-activity relationship of a series of non peptidic RGD integrin antagonists targeting α5ß1: part 2.

Potent antagonists of the integrin α(5)ß(1), which are RGD mimetics built from tyrosine are described. This paper describes the optimization of in vitro potency obtained by variation of two parts of the molecule, the central aromatic core and the amide moiety.

An antibody targeted to VEGFR-2 Ig domains 4-7 inhibits VEGFR-2 activation and VEGFR-2-dependent angiogenesis without affecting ligand binding.

Inhibition of VEGFR-2 signaling reduces angiogenesis and retards tumor growth. Current biotherapeutics that inhibit VEGFR-2 signaling by either sequestering VEGF ligand or inhibiting VEGF binding to VEGFR-2 may be compromised by high VEGF concentrations. Here we describe a biotherapeutic that targets VEGFR-2 signaling by binding to Ig domains 4-7 of VEGFR-2 and therefore has the potential to work independently of ligand concentration. 33C3, a fully human VEGFR-2 antibody, was generated using XenoMouse technology. To elucidate the mechanism of action of 33C3, we have used a number of competition and binding assays. We show that 33C3 binds VEGFR-2 Ig domains 4-7, has no impact on VEGF-A binding to VEGFR-2, and does not compete with an antibody that interacts at the ligand binding site. 33C3 has a high affinity for VEGFR-2 (K(D) < 1 nmol/L) and inhibits VEGF-A induced phosphorylation of VEGFR-2 with an IC(50) of 99 ± 3 ng/mL. In vitro, in a 2D angiogenesis assay, 33C3 potently inhibits both tube length and number of branch points, and endothelial tubule formation in a 3D assay. In vivo, 33C3 is a very effective inhibitor of angiogenesis in both a human endothelial angiogenesis assay and in a human skin chimera model. These data show targeting VEGFR-2 outside of the ligand binding domain results in potent inhibition of VEGFR-2 signaling and inhibition of angiogenesis in vitro and in vivo.

Assessing the activity of cediranib, a VEGFR-2/3 tyrosine kinase inhibitor, against VEGFR-1 and members of the structurally related PDGFR family.

Cediranib is a potent inhibitor of the VEGF receptor (VEGFR)-2 and VEGFR-3 tyrosine kinases. This study assessed the activity of cediranib against the VEGFR-1 tyrosine kinase and the platelet-derived growth factor receptor (PDGFR)-associated kinases c-Kit, PDGFR-α, and PDGFR-ß. Cediranib inhibited VEGF-A-stimulated VEGFR-1 activation in AG1-G1-Flt1 cells (IC(50) = 1.2 nmol/L). VEGF-A induced greatest phosphorylation of VEGFR-1 at tyrosine residues Y1048 and Y1053; this was reversed by cediranib. Potency against VEGFR-1 was comparable with that previously observed versus VEGFR-2 and VEGFR-3. Cediranib also showed significant activity against wild-type c-Kit in cellular phosphorylation assays (IC(50) = 1-3 nmol/L) and in a stem cell factor-induced proliferation assay (IC(50) = 13 nmol/L). Furthermore, phosphorylation of wild-type c-Kit in NCI-H526 tumor xenografts was reduced markedly following oral administration of cediranib (≥1.5 mg/kg/d) to tumor-bearing nude mice. The activity of cediranib against PDGFR-ß and PDGFR-α was studied in tumor cell lines, vascular smooth muscle cells (VSMC), and a fibroblast line using PDGF-AA and PDGF-BB ligands. Both receptor phosphorylation (IC(50) = 12-32 nmol/L) and PDGF-BB-stimulated cellular proliferation (IC(50) = 32 nmol/L in human VSMCs; 64 nmol/L in osteosarcoma cells) were inhibited. In vivo, ligand-induced PDGFR-ß phosphorylation in murine lung tissue was inhibited by 55% following treatment with cediranib at 6 mg/kg but not at 3 mg/kg or less. In contrast, in C6 rat glial tumor xenografts in mice, ligand-induced phosphorylation of both PDGFR-α and PDGFR-ß was reduced by 46% to 61% with 0.75 mg/kg cediranib. Additional selectivity was showed versus Flt-3, CSF-1R, EGFR, FGFR1, and FGFR4. Collectively, these data indicate that cediranib is a potent pan-VEGFR kinase inhibitor with similar activity against c-Kit but is significantly less potent than PDGFR-α and PDGFR-ß.

A human monoclonal anti-ANG2 antibody leads to broad antitumor activity in combination with VEGF inhibitors and chemotherapy agents in preclinical models.

Localized angiopoietin-2 (Ang2) expression has been shown to function as a key regulator of blood vessel remodeling and tumor angiogenesis, making it an attractive candidate for antiangiogenic therapy. A fully human monoclonal antibody (3.19.3) was developed, which may have significant pharmaceutical advantages over synthetic peptide-based approaches in terms of reduced immunogenicity and increased half-life to block Ang2 function. The 3.19.3 antibody potently binds Ang2 with an equilibrium dissociation constant of 86 pmol/L, leading to inhibition of Tie2 receptor phosphorylation in cell-based assays. In preclinical models, 3.19.3 treatment blocked blood vessel formation in Matrigel plug assays and in human tumor xenografts. In vivo studies with 3.19.3 consistently showed broad antitumor activity as a single agent across a panel of diverse subcutaneous and orthotopic xenograft models. Combination studies of 3.19.3 with cytotoxic drugs or anti-vascular endothelial growth factor agents showed significant improvements in antitumor activity over single-agent treatments alone with no apparent evidence of increased toxicity. Initial pharmacokinetic profiling studies in mice and nonhuman primates suggested that 3.19.3 has a predicted human half-life of 10 to 14 days. These studies provide preclinical data for 3.19.3 as a potential new antiangiogenic therapy as a single agent or in combination with chemotherapy or vascular endothelial growth factor inhibitors for the treatment of cancer.

Inhibition of vascular endothelial growth factor-a signaling induces hypertension: examining the effect of cediranib (recentin; AZD2171) treatment on blood pressure in rat and the use of concomitant antihypertensive therapy.

PURPOSE: Inhibition of vascular endothelial growth factor-A (VEGF) signaling is a key therapeutic approach in oncology given the role of VEGF in angiogenesis and vascular permeability in solid tumors. Clinical trials examining VEGF signaling inhibitors commonly report hypertension. We examined the effect of cediranib, a highly potent VEGF signaling inhibitor, on the blood pressure of rats and the ability of standard antihypertensive agents to modulate the consequences of VEGF signaling inhibition. EXPERIMENTAL DESIGN: The ability of cediranib to induce hypertensive changes and the effect of giving antihypertensive therapy were investigated in conscious, unrestrained telemetered rats. Two antihypertensive agents were studied: captopril, an angiotensin-converting enzyme inhibitor, and nifedipine, a dihydropyridine calcium channel blocker. The antitumor activity of cediranib, alone and in combination with nifedipine, was also evaluated in a LoVo human colorectal tumor xenograft model in nude rats. All treatments were given orally. RESULTS: Administration of 0.1 to 1.5 mg/kg/d of cediranib for 4 consecutive days induced a relatively mild hypertensive effect, elevating diastolic blood pressure by 10 to 14 mmHg. Dosing 3 mg/kg/d cediranib for 4 days induced a marked hypertension of 35 to 50 mmHg. Captopril (30 mg/kg, qd) was effective at lowering a 10 mmHg increase in blood pressure but not a 35 to 50 mmHg increase. However, the latter was rapidly reversed by administration of nifedipine (10 mg/kg, bd). Coadministration of nifedipine did not negatively affect the antitumor activity of cediranib (1.5 mg/kg/d). CONCLUSIONS: Hypertension is a direct consequence of inhibiting VEGF signaling but can be controlled with appropriately selected, standard antihypertensive medication.

Acute pharmacodynamic and antivascular effects of the vascular endothelial growth factor signaling inhibitor AZD2171 in Calu-6 human lung tumor xenografts.

The vascular endothelial growth factor-A (VEGF-A) signaling pathway, a key stimulant of solid tumor vascularization, is primarily dependent on the activation of the endothelial cell surface receptor VEGF receptor-2 (VEGFR-2). AZD2171 is an oral, highly potent small-molecule inhibitor of VEGFR tyrosine kinase activity that inhibits angiogenesis and the growth of human tumor xenografts in vivo. Here, we show pharmacodynamic changes in VEGFR-2 phosphorylation induced by AZD2171. In mouse lung tissue, a single dose of AZD2171 at 6 mg/kg inhibited VEGF-A-stimulated VEGFR-2 phosphorylation by 87% at 2 h with significant inhibition (>or=60%) maintained to 24 h. To examine inhibition of VEGFR-2 phosphorylation in tumor vasculature by immunohistochemistry, a comprehensive assessment of antibodies to various phosphorylation sites on the receptor was undertaken. Antibodies to the phosphotyrosine epitopes pY1175/1173 and pY1214/1212 were found suitable for this application. Calu-6 human lung tumor xenografts, from mice receiving AZD2171 or vehicle treatment (p.o., once daily), were examined by immunohistochemistry. A significant reduction in tumor vessel staining of phosphorylated VEGFR-2 (pVEGFR-2) was evident within 28 h of AZD2171 treatment (6 mg/kg). This effect preceded a significant reduction in tumor microvessel density, which was detectable following 52 h of AZD2171 treatment. These data show that AZD2171 is a potent inhibitor of VEGFR-2 activation in vivo and suggest that AZD2171 delivers therapeutic benefit in Calu-6 tumors by targeting vessels dependent on VEGFR-2 signaling for survival. In addition, this work highlights the utility of measuring either pY1175/1173 or pY1214/1212 on VEGFR-2 as a pharmacodynamic marker of VEGFR-2 activation.

Inhibitors of epidermal growth factor receptor tyrosine kinase: optimisation of potency and in vivo pharmacokinetics.

The structure-activity and structure-property relationships of anilinoquinazoline inhibitors of EGFR were investigated. Strategies to lower volume of distribution and shorten half-life through structure and pKa modulation are discussed.

Novel 4-anilinoquinazolines with C-6 carbon-linked side chains: synthesis and structure-activity relationship of a series of potent, orally active, EGF receptor tyrosine kinase inhibitors.

The structure-activity relationship of a novel subseries of 4-anilinoquinazoline EGFR inhibitors substituted at the C-6 position with carbon-linked side chains has been investigated. This exploration has led to the discovery of novel aminomethyl carboxamides with good biological, pharmacokinetic and physical properties.

AZD2171: a highly potent, orally bioavailable, vascular endothelial growth factor receptor-2 tyrosine kinase inhibitor for the treatment of cancer.

Inhibition of vascular endothelial growth factor-A (VEGF) signaling is a promising therapeutic approach that aims to stabilize the progression of solid malignancies by abrogating tumor-induced angiogenesis. This may be accomplished by inhibiting the kinase activity of VEGF receptor-2 (KDR), which has a key role in mediating VEGF-induced responses. The novel indole-ether quinazoline AZD2171 is a highly potent (IC50 < 1 nmol/L) ATP-competitive inhibitor of recombinant KDR tyrosine kinase in vitro. Concordant with this activity, in human umbilical vein endothelial cells, AZD2171 inhibited VEGF-stimulated proliferation and KDR phosphorylation with IC50 values of 0.4 and 0.5 nmol/L, respectively. In a fibroblast/endothelial cell coculture model of vessel sprouting, AZD2171 also reduced vessel area, length, and branching at subnanomolar concentrations. Once-daily oral administration of AZD2171 ablated experimental (VEGF-induced) angiogenesis in vivo and inhibited endochondral ossification in bone or corpora luteal development in ovary; physiologic processes that are highly dependent upon neovascularization. The growth of established human tumor xenografts (colon, lung, prostate, breast, and ovary) in athymic mice was inhibited dose-dependently by AZD2171, with chronic administration of 1.5 mg per kg per day producing statistically significant inhibition in all models. A histologic analysis of Calu-6 lung tumors treated with AZD2171 revealed a reduction in microvessel density within 52 hours that became progressively greater with the duration of treatment. These changes are indicative of vascular regression within tumors. Collectively, the data obtained with AZD2171 are consistent with potent inhibition of VEGF signaling, angiogenesis, neovascular survival, and tumor growth. AZD2171 is being developed clinically as a once-daily oral therapy for the treatment of cancer.

Tumor penetration of gefitinib (Iressa), an epidermal growth factor receptor tyrosine kinase inhibitor.

The relative distribution of gefitinib-related material in nude mice bearing s.c. human tumor xenografts and in an orthotopic rat lung tumor model was investigated following oral administration (50 mg/kg) of [14C]-gefitinib. Selected tissue samples were monitored for radioactivity by liquid scintillation counting, whereas plasma and tumor extracts were assayed for gefitinib and its major metabolites (M523595 and M537194) by high-performance liquid chromatography with tandem mass spectrometric detection. Tissue distribution was also determined by whole body autoradiography. Gefitinib was extensively distributed into the tissues of tumor-bearing mice and unchanged gefitinib was shown to account for most of the tumor radioactivity. Concentrations of gefitinib in mouse s.c. tumor xenografts were similar to skin concentrations and substantially greater (up to 12-fold based on area under the concentration-time curve) than plasma. Concentrations of gefitinib-related material in an orthotopic rat lung tumor were similar to those in healthy lung tissue and were much higher than corresponding blood levels. Following treatment of breast cancer patients with oral gefitinib (Iressa) 250 mg/d for > or = 14 days, gefitinib concentrations (mean, 7.5 microg/g, 16.7 micromol/L) in breast tumor tissue were 42 times higher than plasma, confirming the preferential distribution of gefitinib from blood into tumor tissue in the clinical situation. These gefitinib tumor concentrations are considerably higher than those reportedly required in vitro to achieve complete inhibition of epidermal growth factor receptor autophosphorylation in both epidermal growth factor receptor mutant (0.2 micromol/L) and wild-type cells (2 micromol/L).