Iressa Mechanism of Action





Zuellig Pharma
Full Prescribing Info
Pharmacology: Pharmacodynamics: Gefitinib is a selective inhibitor of the epidermal growth factor receptor (EGFR) tyrosine kinase, commonly expressed in solid human tumours of epithelial origin. Inhibition of EGFR tyrosine kinase activity inhibits tumour growth, metastasis and angiogenesis and increases tumour cell apoptosis.
Patients that have never smoked, have adenocarcinoma histology, are female gender or are of Asian ethnicity, are more like to benefit from treatment with IRESSA. These clinical characteristics are also associated with a higher rate of EGFR mutation positive tumours.
Resistance: Most NSCLC tumours with sensitizing EGFR kinase mutations eventually develop resistance to IRESSA treatment with a median time to disease progression of 1 year. In about 60% of cases, resistance is associated with a secondary T790M mutation for which T790M targeted EGFR TKIs may be considered as a next line treatment option. Other potential mechanisms of resistance have been reported following treatment with EGFR signal blocking agents including bypass signaling such as HER2 and MET gene amplification and PIK3CA mutations. Phenotypic switch to small cell lung cancer has also been reported in 5-10% of cases.
IPASS Study: In a phase III clinical trial conducted in Asia in 1217 patients with advanced (stage IIIB or IV) NSCLC of adenocarcinoma histology who were ex-light (ceased smoking > 15 years ago and smoked < 10 pack years) or never smokers and had not received previous chemotherapy, IRESSA was proven to be superior to carboplatin (AUC 5.0 or 6.0)/paclitaxel (200 mg/m2) in terms of Progression Free Survival (PFS) (Hazard Ratio [HR] 0.741, 95% CI 0.651 to 0.845, p < 0.0001) which was the primary endpoint of the trial. The effect was not constant over time, initially favouring carboplatin/paclitaxel and then favouring IRESSA, driven by differences in PFS outcomes by EGFR mutation status. EGFR mutation status was a strong predictive biomarker for the effect of IRESSA compared to carboplatin/paclitaxel.
Objective Response Rates (ORR) were superior for IRESSA (43.0%) vs. carboplatin/paclitaxel (32.2%) (Odds Ratio [OR] 1.59, 95% CI 1.25 to 2.01, p = 0.0001). Significantly more IRESSA-treated patients experienced a clinically important improvement in Quality of Life (QOL) vs. carboplatin/paclitaxel (Functional Assessment of Cancer Therapy for Lung Cancer [FACT-L] total score; 48% vs. 41%, OR 1.34, 95% CI 1.06 to 1.69, p = 0.0148; Trial Outcome Index [TOI]) 46% vs. 33%, OR 1.78, 95% CI 1.40 to 2.26, p < 0.0001). Similar proportions of patients on both treatments experienced an improvement in lung cancer symptoms (FACT-L Lung Cancer Subscale [LCS]) 52% for IRESSA vs. 49% for carboplatin/paclitaxel (OR 1.13, 95% CI 0.90 to 1.42, p = 0.3037).
Pre-planned exploratory analyses were conducted on the biomarker data at the time of the primary analysis. A total of 437 patients had evaluable data for EGFR mutation analysis. PFS was significantly longer for IRESSA than carboplatin/paclitaxel in EGFR mutation positive patients (n = 261, HR 0.48, 95% CI 0.36 to 0.64, p < 0.0001), and significantly longer for carboplatin/paclitaxel than IRESSA in EGFR mutation negative patients (n = 176, HR 2.85, 95% CI 2.05 to 3.98, p < 0.0001). Patients were considered EGFR mutation positive if one of 29 EGFR mutations was detected by Amplification Refractory Mutation System (ARMS) using DxS EGFR 29 mutation detection kit. Patients were deemed EGFR mutation negative if samples were successfully analysed and none of the 29 EGFR mutations was detected. PFS results in the subgroup with unknown EGFR-mutation status (hazard ratio with gefitinib, 0.68; 95% CI, 0.58 to 0.81; P<0.0001) were similar to those for the overall population.
In EGFR mutation positive patients, ORR was superior for IRESSA (71.2%) vs. carboplatin/paclitaxel (47.3%) (OR 2.751, 95% CI 1.646 to 4.596, p = 0.0001). In EGFR mutation negative patients, ORR was superior for carboplatin/paclitaxel (23.5%) vs. IRESSA (1.1%) (OR 0.036, 95% CI 0.005 to 0.273, p = 0.0013).
In EGFR mutation positive patients, significantly more IRESSA treated patients experienced an improvement in QOL and lung cancer symptoms vs. carboplatin/paclitaxel (FACT-L total score; 70.2% vs. 44.5%, p < 0.0001) (TOI 70.2% vs. 38.3%, p < 0.0001) (LCS 75.6% vs. 53.9%, p = 0.0003). In EGFR mutation negative patients, significantly more carboplatin/paclitaxel treated patients experienced an improvement in QOL and lung cancer symptoms vs. IRESSA (FACT-L total score; 36.3% vs. 14.6%, p = 0.0021) (TOI 28.8% vs. 12.4%, p = 0.0111), (LCS 47.5% vs. 20.2%, p = 0.0002).
An analysis of overall survival (OS) was performed after 954 deaths (78% maturity), which demonstrated no statistically significant difference in OS for IRESSA versus carboplatin/paclitaxel in the overall study population (HR 0.901, 95% CI 0.793 to 1.023; p=0.1087). Median OS: IRESSA, 18.8 months; carboplatin/paclitaxel, 17.4 months.
Subgroup analyses of OS by EGFR mutation status showed no significant difference in OS for IRESSA versus carboplatin/paclitaxel in the subgroup of patients with known mutation positive (HR 1.002, 95% CI 0.756 to 1.328; median OS 21.6 months vs. 21.9 months) or negative (HR 1.181, 95% CI 0.857 to 1.628; median OS 11.2 months vs. 12.7 months) tumours. The OS outcome in the subgroup of patients with unknown mutation status (HR 0.818, 95% CI 0.696 to 0.962; median OS 18.9 months vs. 17.2 months) was consistent with the overall population.
In the IPASS trial, IRESSA demonstrated superior PFS, ORR, QOL and symptom relief with no significant difference in overall survival compared to carboplatin/paclitaxel in previously untreated patients, with locally advanced or metastatic NSCLC, whose tumours harboured activating mutations of the EGFR tyrosine kinase.
INTEREST Study: In a phase III clinical trial of 1466 patients with locally advanced or metastatic NSCLC who had previously received platinum-based chemotherapy and were eligible for further chemotherapy, IRESSA was proven to be non-inferior to docetaxel (75 mg/m2) in terms of overall survival (Hazard Ratio [HR] 1.020, 96% Confidence Interval [CI] 0.905 to 1.150 [CI entirely below non-inferiority limit of 1.154], median 7.6 vs. 8.0 months).
IRESSA also had similar Progression-Free Survival (HR 1.04, 95% CI 0.93 to 1.18, p = 0.466, median 2.2 vs. 2.7 months) and similar Objective Response Rates (9.1% vs. 7.6%, odds ratio [OR] 1.22, 95% CI 0.82 to 1.84, p = 0.3257) compared to docetaxel. Significantly more IRESSA-treated patients experienced clinically important improvements in QOL compared with docetaxel (Functional Assessment of Cancer Therapy for Lung Cancer [FACTL] Trial Outcome Index [TOI]: 17% vs. 10%, p = 0.0026; FACT-L total score: 25% vs. 15%, p < 0.0001). Similar proportions of patients on both treatments experienced an improvement in lung cancer symptoms (FACT-L Lung Cancer Subscale [LCS] 20% vs. 17%, p = 0.1329).
The co-primary analysis evaluating overall survival in 174 patients with high EGFR gene copy number did not demonstrate superiority of IRESSA over docetaxel. Survival outcomes in patients with high EGFR gene copy number were similar for both treatments (HR 1.087, 95% CI 0.782 to 1.510, p = 0.6199, median 8.4 vs. 7.5 months).
ISEL Study: In a phase III double blind clinical trial of 1692 patients comparing IRESSA plus BSC to placebo plus BSC in patients with advanced NSCLC who had received 1 or 2 prior chemotherapy regimens and were refractory or intolerant to their most recent regimen, IRESSA did not significantly prolong survival in the overall population (HR 0.89, CI 0.77 to 1.02, p = 0.09, Median 5.6 vs. 5.1 months for IRESSA and placebo respectively), or in patients with adenocarcinoma (HR 0.84, CI 0.68 to 1.03, p = 0.09, Median 6.3 vs. 5.4 months for IRESSA and placebo respectively). Pre-planned subgroup analyses showed a statistically significant increase in survival for patients of Oriental ethnicity treated with IRESSA compared to placebo (HR = 0.66, CI 0.48 to 0.91, p = 0.01, Median 9.5 vs. 5.5 months), and for patients that had never smoked treated with IRESSA compared to placebo (HR = 0.67, CI 0.49 to 0.92, p = 0.01, Median 8.9 vs. 6.1 months).
Exploratory analysis of EGFR gene copy number data showed that the treatment effect, IRESSA compared to placebo, on survival was larger in patients with high EGFR gene copy number compared to patients with low EGFR gene copy number (interaction p-value = 0.0448). The hazard ratio, IRESSA to placebo, in patients with high EGFR gene copy number was 0.61 (N = 114; 95% CI 0.36 to 1.04, p = 0.067) and the hazard ratio in patients with low EGFR gene copy number was 1.16 (N = 256; 95% CI 0.81 to 1.64, p = 0.42). For patients in whom EGFR gene copy number was not tested (N = 1322, HR = 0.85, CI 0.73 to 0.99, p = 0.032), the HR was similar to that seen for the overall study population as would be expected.
IFUM Study: The IFUM study was a single arm, multicentre study conducted in Caucasian patients (n=106) with activating, sensitizing EGFR mutation positive NSCLC to confirm that the activity of gefitinib is similar in Caucasian and Asian populations. The ORR according to investigator review was 70% and the median PFS was 9.7 months. These data are similar to those reported in the IPASS study.
Circulating Tumour DNA (ctDNA): In the IFUM trial, mutation status was assessed in tumour and ctDNA samples derived from plasma, using the Therascreen EGFR RGQ PCR kit. Both ctDNA and tumour samples were evaluable for 652 patients out of 1060 screened. The sensitivity of EGFR mutation testing in ctDNA using the Qiagen Therascreen EGFR RGQ PCR kit was 65.7%, with a specificity of 99.8%. The positive and negative predictive values of ctDNA were 98.6% and 93.8%, respectively (Table 1). Objective response rate in the IFUM FAS population was 69.8% (95% CI: 60.5% to 77.7%). The ORR in those patients within the FAS population who were ctDNA mutation positive was 77.3% (95% CI: 65.8 to 85.7). (See Table 1.)

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These data are consistent with the pre-planned exploratory Japanese subgroup analysis in IPASS. In that study ctDNA derived from serum, not plasma was used for EGFR mutation analysis using the EGFR Mutation Test Kit (DxS) (N = 86). In that study, concordance was 66%, sensitivity was 43.1%, specificity was 100%. The positive and negative predictive values were 100% and 54.7%, respectively.
Pharmacokinetics: Following intravenous administration, gefitinib is rapidly cleared, extensively distributed and has a mean elimination half-life of 48 hours. Following oral dosing in cancer patients, absorption is moderately slow and the mean terminal half-life is 41 hours. Administration of gefitinib once daily results in 2 to 8-fold accumulation with steady state exposures achieved after 7 to 10 doses. At steady state, circulating plasma concentrations are typically maintained within a 2 to 3-fold range over the 24-hour dosing interval.
Absorption: Following oral administration of IRESSA, peak plasma concentrations of gefitinib typically occur at 3 to 7 hours after dosing. Mean absolute bioavailability is 59% in cancer patients. Exposure to gefitinib is not significantly altered by food. In a trial in healthy volunteers where gastric pH was maintained above pH 5, gefitinib exposure was reduced by 47% (see Precautions and Interactions).
Distribution: Mean volume of distribution at steady state of gefitinib is 1400 L indicating extensive distribution into tissue. Plasma protein binding is approximately 90%. Gefitinib binds to serum albumin and α1-acid glycoprotein.
Metabolism: In vitro data indicate that CYP3A4 is the major P450 isozyme involved in the oxidative metabolism of gefitinib.
In vitro studies have shown that gefitinib has limited potential to inhibit CYP2D6. In a clinical trial in patients, gefitinib was co-administered with metoprolol (a CYP2D6 substrate). This resulted in a small (35%) increase in exposure to metoprolol, which is not considered to be clinically relevant.
Gefitinib shows no enzyme induction effects in animal studies and no significant inhibition (in vitro) of any other cytochrome P450 enzyme.
Three sites of biotransformation have been identified in the metabolism of gefitinib: metabolism of the N-propylmorpholino-group, demethylation of the methoxy-substituent on the quinazoline and oxidative defluorination of the halogenated phenyl group. Five metabolites have been fully identified in faecal extracts and the major component was O-desmethyl gefitinib, although this only accounted for 14% of the dose.
In human plasma 8 metabolites were fully identified. The major metabolite identified was O-desmethyl gefitinib, which was 14-fold less potent than gefitinib at inhibiting EGFR stimulated cell growth and had no inhibitory effect on tumour cell growth in mice. It is therefore considered unlikely that it contributes to the clinical activity of gefitinib.
The production of O-desmethyl gefitinib has been shown, in vitro, to be via CYP2D6. The role of CYP2D6 in the metabolic clearance of gefitinib has been evaluated in a clinical trial in healthy volunteers genotyped for CYP2D6 status. In poor metabolisers, no measurable levels of O-desmethyl gefitinib were produced. The range of gefitinib exposures achieved in both the extensive and the poor metaboliser groups were wide and overlapping but the mean exposure to gefitinib was 2-fold higher in the poor metaboliser group. The higher average exposures that could be achieved by individuals with no active CYP2D6 may be clinically relevant since adverse experiences are related to dose and exposure.
Elimination: Gefitinib total plasma clearance is approximately 500 mL/min. Excretion is predominantly via the faeces with renal elimination of drug and metabolites accounting for less than 4% of the administered dose.
Special populations: In population based data analyses in cancer patients, no relationships were identified between predicted steady state trough concentration and patient age, body weight, gender, ethnicity or creatinine clearance.
In a phase I open-label study of single dose gefitinib 250mg in patients with mild, moderate or severe hepatic impairment due to cirrhosis (according to Child-Pugh classification), there was an increase in exposure in all groups compared with healthy controls. An average 3.1-fold increase in exposure to gefitinib in patients with moderate and severe hepatic impairment was observed. None of the patients had cancer, all had cirrhosis and some had hepatitis. This increase in exposure may be of clinical relevance since adverse experiences are related to dose and exposure to gefitinib.
Gefitinib has been evaluated in a clinical trial conducted in 41 patients with solid tumours and normal hepatic function or, moderate or severe hepatic dysfunction due to liver metastases. It was shown that following daily dosing of 250 mg IRESSA, time to steady state, total plasma clearance and steady state exposure (CmaxSS, AUC24SS) were similar for the groups with normal and moderately impaired hepatic function. Data from 4 patients with severe hepatic dysfunction due to liver metastases suggested that steady state exposures in these patients are also similar to those in patients with normal hepatic function.
Toxicology: Pre-clinical Safety Data Relevant to the Prescriber: Gefitinib showed no genotoxic potential.
There was, as expected from the pharmacological activity of gefitinib, a reduction in female fertility in the rat at a dose of 20 mg/kg/day. When administered during organogenesis, there were no effects on rat embryofetal development at the highest dose (30 mg/kg/day), however in the rabbit, there were reduced foetal weights at 20 mg/kg/day and above. There were no compound induced malformations in either species. When dosed to the rat throughout gestation and parturition, there was a reduction in pup survival at a dose of 20 mg/kg/day (see Use in Pregnancy & Lactation).
Following oral administration of carbon-14 labelled gefitinib to rats 14 days post partum, concentrations of radioactivity in milk were higher than in blood (see Use in Pregnancy & Lactation).
Data from nonclinical (in vitro) studies indicate that gefitinib has the potential to inhibit the cardiac action potential repolarization process (e.g. QT interval). Clinical experience has not shown a causal association between QT prolongation and gefitinib.
A 2-year carcinogenicity study in rats resulted in a small but statistically significant increased incidence of hepatocellular adenomas in both male and female rats and mesenteric lymph node haemangiosarcomas in female rats at the highest dose (10 mg/kg/day) only. The hepatocellular adenomas were also seen in a 2-year carcinogenicity study in mice, which demonstrated a small increased incidence of this finding in male mice dosed at 50 mg/kg/day, and in both male and female mice at the highest dose of 90 mg/kg/day (reduced from 125 mg/kg/day from week 22). The effects reached statistical significance for the female mice, but not for the males. The clinical relevance of these findings is unknown.
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