A Possible Development Pathway for Biotech Companies with PanHER Inhibitors?
Many Breast Cancer Patients Not Helped by Herceptin
For more than ten years oncologists have been aware of the role that Herceptin (trastuzumab, Roche/Genentech) has played in extending the lives of women with HER2 overexpressed breast cancer. Herceptin works by blocking the HER2 receptor from receiving activating stimuli from outside of the cell. In addition there is a second agent, Tykerb (lapatinib, GSK) which is able to block signaling from the tyrosine kinase domain of the receptor, inside the cell. Still, there are many patients who are not helped by these agents. These targeted therapies work when the receptor is overexpressed, but may not work when the receptors are mutated.
Somatic Breast Cancer Mutations Identified
At December’s San Antonio Breast Cancer Symposium, there was a talk given by Ron Bose from Washington University, about other perturbances of the HER2 receptor. Over the last year, the Cancer Genome Atlas Breast Cancer has conducted genome sequencing of breast cancers. This endeavor has identified several somatic mutations that appear on the HER2 receptors in some breast cancers. A majority of the mutations were found in the kinase domain of the receptor. Most of the lesions analyzed were considered HER2 negative as they did not achieve the 3+ score in IHC testing.
Ph II Trial of Neratinib in Breast Cancer Patients
Because the mutations cause constitutive activation of the receptor (it is always turned on), Herceptin cannot block its signaling from outside of the cell. The mutations are rare, and it is estimated that only about 5000 women in the US with breast cancer would have them. In cell line studies, Tykerb has some effect on cells with these mutations, but the agent that appears to have the most activity is neratinib (Puma), a “pan-HER” inhibitor. To that end, there will be a fairly large Ph II trial of neratinib in breast cancer patients who test negative for HER2 amplification but positive for these somatic mutations.
Breast Cancer Drug Development - Targeting Somatic Cancer Mutations
There is precedent for targeting somatic mutations in malignant lesions. Even in the same family of receptors, there are three agents with activity against EGFR: Iressa (gefitinib, AstraZeneca), Tarceva (erlotinib, Roche/Genentech) and afatinib (Boheringer Ingleheim). This has implications for the larger world of breast cancer biotech drug development targeted at the EGFR family of receptors as there are many “pan-HER” inhibitors in development that could potentially be used to treat tumors with these mutations.
Barriers to Breast Cancer Drug Development
The biggest barriers for development would be working up accurate testing systems to detect the mutations as predictive biomarkers of drug efficacy, and then getting these tests included in the battery of diagnostics used to analyze both primary breast tumors and recurrent disease.
 Bose, R Activating HER2 mutations in HER2 gene amplification negative breast cancers, SABCS December 2012, S5-6