EPIDERMAL GROWTH FACTOR RECEPTOR EGFR INHIBITORS

1. EPIDERMAL GROWTH FACTOR RECEPTOR (EGFR)INHIBITORS

2. The HER Family HER1 is also known as EGFR, or erb-b1, and is a member of a family of membrane receptor tyrosine kinases known as the HER family, which also includes HER2, HER3, and HER4. These receptors have different ligand binding affinities, as shown in this slide. Epidermal growth factor and transforming growth factor-alpha are the 2 most important ligands of HER1. The neuregulins are important ligands for HER3 and HER4. In normal cells, HER2 is intrinsically devoid of any ligand-binding activity. It is an important signaling partner of HER1 and HER3 and functions as a coreceptor. Ligand binding leads to receptor homo- or heterodimerization, and the resulting stearic change activates the intrinsic kinase activity of these HER family receptor tyrosine kinases. The activated kinase phosphorylates itself and its dimeric partner on conserved tyrosine residues and initiates a signal transduction cascade, which eventually activates key regulators like MAPK and Akt. All HER family proteins, with the exception of HER3, have intrinsic kinase activity.HER1 is also known as EGFR, or erb-b1, and is a member of a family of membrane receptor tyrosine kinases known as the HER family, which also includes HER2, HER3, and HER4. These receptors have different ligand binding affinities, as shown in this slide. Epidermal growth factor and transforming growth factor-alpha are the 2 most important ligands of HER1. The neuregulins are important ligands for HER3 and HER4. In normal cells, HER2 is intrinsically devoid of any ligand-binding activity. It is an important signaling partner of HER1 and HER3 and functions as a coreceptor. Ligand binding leads to receptor homo- or heterodimerization, and the resulting stearic change activates the intrinsic kinase activity of these HER family receptor tyrosine kinases. The activated kinase phosphorylates itself and its dimeric partner on conserved tyrosine residues and initiates a signal transduction cascade, which eventually activates key regulators like MAPK and Akt. All HER family proteins, with the exception of HER3, have intrinsic kinase activity.

3. Effects of HER1/EGFR activation HER1/EGFR activation can produce a range of effects in tumor cells. These are dependent on the signal-transduction pathways that are activated following ligand binding. These effects include increased cellular proliferation, angiogenesis, metastasis, and inhibition of apoptosis.HER1/EGFR activation can produce a range of effects in tumor cells. These are dependent on the signal-transduction pathways that are activated following ligand binding. These effects include increased cellular proliferation, angiogenesis, metastasis, and inhibition of apoptosis.

4. Human tumors withhigh HER1/EGFR expression These data show the proportion of HER1/EGFR expression across a range of solid tumors. The percentages shown for each tumor type vary considerably. This may be because of the difficulties in quantifying HER1/EGFR expression and the inherent heterogeneity of human tumors. HER1 dysregulation is associated with several human cancers. Dysregulation manifests itself in: (i) Overexpression of wild-type protein. (ii) HER1 mutations and overexpression of mutant proteins. (iii) Increased expression of their ligand. However, the clinical relevance of cell membrane HER1 concentrations has not been determined. No approved, validated methods to detect HER1 expression No clear definition of overexpression No clear correlation between levels of HER1 and tumor response to HER1 inhibition (multiple conflicting studies) These data show the proportion of HER1/EGFR expression across a range of solid tumors. The percentages shown for each tumor type vary considerably. This may be because of the difficulties in quantifying HER1/EGFR expression and the inherent heterogeneity of human tumors. HER1 dysregulation is associated with several human cancers. Dysregulation manifests itself in: (i) Overexpression of wild-type protein. (ii) HER1 mutations and overexpression of mutant proteins. (iii) Increased expression of their ligand. However, the clinical relevance of cell membrane HER1 concentrations has not been determined. No approved, validated methods to detect HER1 expression No clear definition of overexpression No clear correlation between levels of HER1 and tumor response to HER1 inhibition (multiple conflicting studies)

5. Clinical consequences of HER1/EGFR dysregulation in cancer patients Metastasis due to increased tumor-cell motility and adhesion Chemotherapy and radiotherapy resistance Resistance to hormonal therapy Poor prognosis Reduced survival HER1/EGFR dysregulation is associated with a number of clinical parameters in cancer patients. The range of consequences may be due to the multiple tumorigenic effects that result from HER1/EGFR activation.HER1/EGFR dysregulation is associated with a number of clinical parameters in cancer patients. The range of consequences may be due to the multiple tumorigenic effects that result from HER1/EGFR activation.

6. HER1/EGFR-Targeted Approaches There are a number of approaches to target HER1 dysregulation. Antibodies against ligand block ligand binding. However, neither approach will work if there is constitutive tyrosine kinase activity such as that found in some mutations of HER1 (eg, EGFR vIII). Using a small molecule that specifically targets and either reversibly or irreversibly inhibits the tyrosine kinase activity is an approach that can block signaling by all active HER1 forms, including those receptors with mutated or deleted extracellular domains. Conjugates of a ligand and a cytotoxic agent or an antibody and a cytotoxic agent is another approach that can have the advantage of killing the cell after internalization, in addition to inhibiting tyrosine kinase activity. There are a number of approaches to target HER1 dysregulation. Antibodies against ligand block ligand binding. However, neither approach will work if there is constitutive tyrosine kinase activity such as that found in some mutations of HER1 (eg, EGFR vIII). Using a small molecule that specifically targets and either reversibly or irreversibly inhibits the tyrosine kinase activity is an approach that can block signaling by all active HER1 forms, including those receptors with mutated or deleted extracellular domains. Conjugates of a ligand and a cytotoxic agent or an antibody and a cytotoxic agent is another approach that can have the advantage of killing the cell after internalization, in addition to inhibiting tyrosine kinase activity.

7. Selected HER1/EGFR-TargetedMonoclonal Antibodies All anti-EGFR MAbs have been developed against different immunogenic epitopes in or around the ligand-binding extracellular domain of EGFR. MAbs exert their biologic activity by binding to the receptor (EGFR) with a higher affinity than the ligand. In the competition that ensues between the ligand and the MAb for epitopes on the receptor, the latter wins due to its higher affinity and its ability to stearically block the access of the ligand to its receptorAll anti-EGFR MAbs have been developed against different immunogenic epitopes in or around the ligand-binding extracellular domain of EGFR. MAbs exert their biologic activity by binding to the receptor (EGFR) with a higher affinity than the ligand. In the competition that ensues between the ligand and the MAb for epitopes on the receptor, the latter wins due to its higher affinity and its ability to stearically block the access of the ligand to its receptor

8. Selected HER Tyrosine Kinase Inhibitors HER1-TKIs are small molecules that bind to the tyrosine kinase domain of HER1 and abrogate its kinase activity. As a consequence of this inhibition in HER1 tyrosine kinase activity, downstream signaling is downregulated. This includes: HER1-dependent mitogenic cascades like MAPK Transcription cascades via Akt Antiapoptotic cascades via Bcl-XL and Bcl-2 Taken together, inhibition of the above pathways results in increased tumor cell death. The binding of HER1-TKI to HER1 tyrosine kinase can either be: Reversible (eg, gefitinib, erlotinib, GW572016, and PKI-166), implying that at steady state there is a constant and fixed rate of the TKI being bound to and removed from the tyrosine kinase domain of HER1. Irreversible (eg, EKB-569 and CI-1033), suggesting that these TKIs stay bound to the tyrosine kinase domain and result in a more permanent shut-down of kinase activity. Based on their mode of action, it is possible to speculate that the reversible inhibitors would require higher doses and more frequent administration to maintain a high, consistent level in the body, while irreversible inhibitors would require lower doses and less frequent administration, given that they could elicit their effect for a longer time. However, since no head-to-head comparison has been performed for the pharmacokinetic-pharmacodynamic parameters for reversible and irreversible TKIs, this assumption is speculative and based solely on their putative mode of action. HER1-TKIs are small molecules that bind to the tyrosine kinase domain of HER1 and abrogate its kinase activity. As a consequence of this inhibition in HER1 tyrosine kinase activity, downstream signaling is downregulated. This includes: HER1-dependent mitogenic cascades like MAPK Transcription cascades via Akt Antiapoptotic cascades via Bcl-XL and Bcl-2 Taken together, inhibition of the above pathways results in increased tumor cell death. The binding of HER1-TKI to HER1 tyrosine kinase can either be: Reversible (eg, gefitinib, erlotinib, GW572016, and PKI-166), implying that at steady state there is a constant and fixed rate of the TKI being bound to and removed from the tyrosine kinase domain of HER1. Irreversible (eg, EKB-569 and CI-1033), suggesting that these TKIs stay bound to the tyrosine kinase domain and result in a more permanent shut-down of kinase activity. Based on their mode of action, it is possible to speculate that the reversible inhibitors would require higher doses and more frequent administration to maintain a high, consistent level in the body, while irreversible inhibitors would require lower doses and less frequent administration, given that they could elicit their effect for a longer time. However, since no head-to-head comparison has been performed for the pharmacokinetic-pharmacodynamic parameters for reversible and irreversible TKIs, this assumption is speculative and based solely on their putative mode of action.

9. Small molecule inhibitors of the tyrosine-kinase activity (TKI): mode of antitumor activity

10. Erlotinib (erlotinib HCl) properties Small-molecule inhibitor of HER1/EGFR TK Chemical class: quinazoline Orally available

11. Erlotinib: mode of antitumor activity

12. Preclinical Data

13. Inhibition of purifiedHER1/EGFR TK by Erlotinib

14. Antitumor activity of Erlotinib in a head and neck cancer xenograft model (HN5)

15. Antitumor activity of Erlotinib in a NSCLC xenograft model (A549)

16. Inhibition of mutant EGFRvIII by Erlotinib

17. Erlotinib in combination with chemotherapeutic agents Significant tumor-growth inhibition in xenograft models with Tarceva� plus cisplatin1,2 doxorubicin3 paclitaxel3 gemcitabine2,3 capecitabine4 no interaction with 5-fluorouracil and vinorelbine tartrate (head and neck model)3 No increase in toxicity

18. Erlotinib: additive antitumor response in combination with cisplatin

19. Enhanced radiation responsewith Erlotinib

20. Phase I monotherapy studies in cancer patients

21. Erlotinib phase I monotherapy studies: PK Dose-proportional Cmax and AUC Repeated daily dosing does not result in drug accumulation High plasma exposure at 150mg/day p.o.

22. Erlotinib phase I monotherapy studies: antitumor activity and tolerability Antitumor activity Daily dosing regimen (n=40) eight patients with SD for >5 months Weekly dosing regimen (n=27) four patients with SD for >6 months Tolerability Acneiform rash (grade 1/2) localized above the waist and diarrhea both dose related diarrhea dose limiting at 200mg/day (daily dosing) MTD not reached in weekly dosing study (>1,600mg) Other less common side effects headache, nausea, and vomiting The MTD, 150mg/day continuous dosing, was selected for phase II studies