- Email: [email protected]
429 Reversing Resistance to Targeted Therapies in Breast Cancer
Plenary Session 8
Friday 9 November 2012
Friday 9 November 2012 133
11:00–12:45
PLENARY SESSION 8
Drug Resistance in Targeted Agents 426 INVITED Using Functional Genetics to Optimize the Treatment of Cancer R. Bernards1 . 1 The Netherlands Cancer Institute, Division of Molecular Carcinogenesis, Center for Biomedical Genetic and Cancer Genomics Center, Amsterdam, The Netherlands Unresponsiveness to therapy remains a significant problem in the treatment of cancer, also with the new classes of cancer drugs. In my laboratory, we use functional genetic approaches to identify biomarkers that can predict responsiveness to targeted cancer therapeutics. Nevertheless, it remains poorly explained why a significant number of tumors do not respond to these therapies. We aim to elucidate the molecular pathways that contribute to unresponsiveness to targeted cancer therapeutics using a functional genetic approach. This will yield biomarkers that may be useful to predict how individual patients will respond to these drugs. Furthermore, this work may allow the development of drugs that act in synergy with the established drug to prevent or overcome drug resistance. To identify biomarkers that control tumor cell responsiveness to cancer therapeutics, we use multiple complementary approaches. First, we use genome wide loss-of-function genetic screens (with shRNA interference libraries) in cancer cells that are sensitive to the drug-of-interest to search for genes whose down-regulation confers resistance to the drugof-interest (resistance screens). In addition, we use shRNA screens to screen for genes whose inhibition enhances the toxicity of cancer drugs (sensitizer screens). As a third approach, we use gain of function genetic screens in which we search for genes whose over-expression modulates drug responsiveness. Once we have identified candidate drug response biomarkers in relevant cell line models, we ask if the expression of these genes is correlated with clinical response to the drug-of-interest. For this, we use tumor samples of cancer patients treated with the drug in question and whose response to therapy is documented. In a fourth and distinct approach we perform high throughput sequencing of the “kinome” (some 600 genes) of tumor samples to identify connections between cancer genotype and drug responses. Examples of some of these approaches to identify biomarkers of response to different cancer drugs will be presented. 427 INVITED The mitochondrial basis of resistance to BCL-2 antagonists and conventional chemotherapy A. Letai1 , O. Kutuk1 , T. Vo1 , J. Ryan1 , J. Deng1 , K. Sarosiek1 , T. Ni Chonghaile1 . 1 Dana Farber Cancer Institute, Mayer 430, Boston Massachusetts, USA The mitochondrial pathway of apoptosis is used by many types of anti-cancer agents, both modern targeted therapies and older cytotoxic agents, to kill cancer cells. We have investigated this pathway, assisted by a functional tool called BH3 profiling, which measures response of mitochondria to BH3 peptides. We have found that differential mitochondrial priming, measured via response to BH3 peptides, can explain differences in clinical chemosensitivity to conventional cytotoxic chemotherapy among cancer cells of a given type and between cancer cells and normal cell. We have paid particular attention to acute myelogenous leukemia, where we find that the therapeutic index is set by the difference in mitochondrial priming between myeloblasts and hematopoietic stem cells (HSC). We furthermore show that mitochondria from myeloblasts, even chemoresistant ones, are more sensitive to BCL-2 inhibition than those from HSC. We can use selective BCL-2 antagonists like ABT-737 to prime myeloblast for death and overcome resistance to conventional chemotherapy. We have examined the upstream determinants of mitochondrial priming and found that certain well-known pathways control priming by a novel mechanism of interaction with mitochondrial proteins. 428 Resistance to Targeted Therapies in Lung Cancer
INVITED
T. Bivona1 . 1 University of California San Francisco, Medicine Hematology-Oncology, San Francisco, USA Background: Despite the success of oncogene-targeted therapies, singleagent treatment with an inhibitor of an oncogenic driver results in
heterogeneous, transient, and incomplete responses in patients (with a few notable exceptions) because of both innate and acquired treatment resistance. This challenge provides strong motivation to discover the molecular mechanisms that tumors use to evade driver oncogene inhibition. The identification of these molecular events will allow us to define biomarkers of response to oncogene inhibitor treatment and rational companion therapeutic targets to overcome resistance to oncogene inhibition in patients. Material and Methods: We developed a multidisciplinary approach to conduct bench-to-bedside-and-back research and optimize the personalized treatment of cancer patients with molecularly targeted therapy. Our chemical genetic strategy is to identify rational companion targets through shRNA loss of function genetic screens and pharmacological screens using clinical oncogene inhibitors in patient-derived, oncogene expressing tumor models. We then validate the screening findings in human cancer specimens that harbor the oncogene of interest and are obtained from patients treated with the cognate oncogene inhibitor. Results: Using this approach, we have further defined the molecular basis of EGFR oncogene dependence and of resistance to EGFR oncogene driver inhibition in lung cancer patients (Bivona TG et al, Nature 2011; Zheng Z et al Bivona TG, Nature Genetics 2012). We tested the hypothesis that EGFR inhibitor treatment responses in EGFR-mutant lung cancer patients are heterogeneous and incomplete as a result of genetic modifiers that determine the degree to which tumor cells are dependent on mutant EGFR and, thus, sensitive to EGFR inhibition by the FDA-approved tyrosine kinase inhibitor (TKI) erlotinib. We discovered novel mechanisms of erlotinib resistance in EGFR mutant lung cancer patients including activation of: 1) the NF-kB pathway, and 2) the AXL kinase. Conclusions: Our data provide rationale for clinical trials testing if inhibitors of NF-kB or of AXL overcome erlotinib resistance in EGFR mutant lung cancer patients. We propose that our strategy can bridge the translational gap between laboratory discoveries and clinical testing of rational polytherapies that could improve the survival of, and potentially cure, patients with lung and other cancers. 429 INVITED Reversing Resistance to Targeted Therapies in Breast Cancer F. Andre1 . 1 Institut Gustave Roussy, Pathologie Mammaire Comite 5, Villejuif, France Therapies targeting oncogenic events are being developed in breast cancers. Although these therapies improve outcome in patients with metastatic breast cancers, a resistance occurs in most of the cases. In the present discussion, we will review all the strategies to overcome resistance to targeted therapies. Six different approaches are being used to reverse resistance to targeted agents. Improving the targeting of the receptor has been the most widely investigated approach. Dual targeting has been shown to improve efficacy endpoint in patients with Her2-overexpressing breast cancer resistant to trastuzumab. Targeting co-existing genomic events is another approach under development. For this purpose, there is a wide interest in describing clusterings of genomic events. As illustration, FGFR1 is frequently coamplified with CCND1, leading to a rationale for developing FGFR1inh in combination with CDK4 inh. In the similar way, a few number of triple negative breast cancers present with EGFR-amplifications and PTENdeletion of PIK3CA mutation. The third mechanism of resistance is the development of feedback loops. The most relevant mechanism is the occurrence of activating feedback loops after mTORC1 inhibition by everolimus. This observation has led to the development of combination between mTORC1 inhibitors and either tyrosine kinase or PIK3CA inhibitors. More recently, several additional mechanisms of resistance have been described in preclinical models. The existence of tumor heterogeneity and minor clones could mediate resistance to targeted therapies. Nevertheless, the involvement of clonal selection in the resistance to targeted therapies for breast cancer still remains to be shown. The co-targeting of DNA repair, together with the targeting of immune system complete the panel of mechanisms of resistance and are leading to clinical trials combining therapies directed against oncogenic events together with either DNA repair inhibitors (PARP1 inh) or activators of immune checkpoints (PD1 Ab). Overall, the mechanisms of resistance to targeted therapies in breast cancer are pleiotropic and several approaches are needed to reverse it. Several ongoing programs will be presented, that investigate the involvement of co-mutations and immune system in the resistance to targeted agents.
Friday 9 November 2012
Friday 9 November 2012 133
11:00–12:45
PLENARY SESSION 8
Drug Resistance in Targeted Agents 426 INVITED Using Functional Genetics to Optimize the Treatment of Cancer R. Bernards1 . 1 The Netherlands Cancer Institute, Division of Molecular Carcinogenesis, Center for Biomedical Genetic and Cancer Genomics Center, Amsterdam, The Netherlands Unresponsiveness to therapy remains a significant problem in the treatment of cancer, also with the new classes of cancer drugs. In my laboratory, we use functional genetic approaches to identify biomarkers that can predict responsiveness to targeted cancer therapeutics. Nevertheless, it remains poorly explained why a significant number of tumors do not respond to these therapies. We aim to elucidate the molecular pathways that contribute to unresponsiveness to targeted cancer therapeutics using a functional genetic approach. This will yield biomarkers that may be useful to predict how individual patients will respond to these drugs. Furthermore, this work may allow the development of drugs that act in synergy with the established drug to prevent or overcome drug resistance. To identify biomarkers that control tumor cell responsiveness to cancer therapeutics, we use multiple complementary approaches. First, we use genome wide loss-of-function genetic screens (with shRNA interference libraries) in cancer cells that are sensitive to the drug-of-interest to search for genes whose down-regulation confers resistance to the drugof-interest (resistance screens). In addition, we use shRNA screens to screen for genes whose inhibition enhances the toxicity of cancer drugs (sensitizer screens). As a third approach, we use gain of function genetic screens in which we search for genes whose over-expression modulates drug responsiveness. Once we have identified candidate drug response biomarkers in relevant cell line models, we ask if the expression of these genes is correlated with clinical response to the drug-of-interest. For this, we use tumor samples of cancer patients treated with the drug in question and whose response to therapy is documented. In a fourth and distinct approach we perform high throughput sequencing of the “kinome” (some 600 genes) of tumor samples to identify connections between cancer genotype and drug responses. Examples of some of these approaches to identify biomarkers of response to different cancer drugs will be presented. 427 INVITED The mitochondrial basis of resistance to BCL-2 antagonists and conventional chemotherapy A. Letai1 , O. Kutuk1 , T. Vo1 , J. Ryan1 , J. Deng1 , K. Sarosiek1 , T. Ni Chonghaile1 . 1 Dana Farber Cancer Institute, Mayer 430, Boston Massachusetts, USA The mitochondrial pathway of apoptosis is used by many types of anti-cancer agents, both modern targeted therapies and older cytotoxic agents, to kill cancer cells. We have investigated this pathway, assisted by a functional tool called BH3 profiling, which measures response of mitochondria to BH3 peptides. We have found that differential mitochondrial priming, measured via response to BH3 peptides, can explain differences in clinical chemosensitivity to conventional cytotoxic chemotherapy among cancer cells of a given type and between cancer cells and normal cell. We have paid particular attention to acute myelogenous leukemia, where we find that the therapeutic index is set by the difference in mitochondrial priming between myeloblasts and hematopoietic stem cells (HSC). We furthermore show that mitochondria from myeloblasts, even chemoresistant ones, are more sensitive to BCL-2 inhibition than those from HSC. We can use selective BCL-2 antagonists like ABT-737 to prime myeloblast for death and overcome resistance to conventional chemotherapy. We have examined the upstream determinants of mitochondrial priming and found that certain well-known pathways control priming by a novel mechanism of interaction with mitochondrial proteins. 428 Resistance to Targeted Therapies in Lung Cancer
INVITED
T. Bivona1 . 1 University of California San Francisco, Medicine Hematology-Oncology, San Francisco, USA Background: Despite the success of oncogene-targeted therapies, singleagent treatment with an inhibitor of an oncogenic driver results in
heterogeneous, transient, and incomplete responses in patients (with a few notable exceptions) because of both innate and acquired treatment resistance. This challenge provides strong motivation to discover the molecular mechanisms that tumors use to evade driver oncogene inhibition. The identification of these molecular events will allow us to define biomarkers of response to oncogene inhibitor treatment and rational companion therapeutic targets to overcome resistance to oncogene inhibition in patients. Material and Methods: We developed a multidisciplinary approach to conduct bench-to-bedside-and-back research and optimize the personalized treatment of cancer patients with molecularly targeted therapy. Our chemical genetic strategy is to identify rational companion targets through shRNA loss of function genetic screens and pharmacological screens using clinical oncogene inhibitors in patient-derived, oncogene expressing tumor models. We then validate the screening findings in human cancer specimens that harbor the oncogene of interest and are obtained from patients treated with the cognate oncogene inhibitor. Results: Using this approach, we have further defined the molecular basis of EGFR oncogene dependence and of resistance to EGFR oncogene driver inhibition in lung cancer patients (Bivona TG et al, Nature 2011; Zheng Z et al Bivona TG, Nature Genetics 2012). We tested the hypothesis that EGFR inhibitor treatment responses in EGFR-mutant lung cancer patients are heterogeneous and incomplete as a result of genetic modifiers that determine the degree to which tumor cells are dependent on mutant EGFR and, thus, sensitive to EGFR inhibition by the FDA-approved tyrosine kinase inhibitor (TKI) erlotinib. We discovered novel mechanisms of erlotinib resistance in EGFR mutant lung cancer patients including activation of: 1) the NF-kB pathway, and 2) the AXL kinase. Conclusions: Our data provide rationale for clinical trials testing if inhibitors of NF-kB or of AXL overcome erlotinib resistance in EGFR mutant lung cancer patients. We propose that our strategy can bridge the translational gap between laboratory discoveries and clinical testing of rational polytherapies that could improve the survival of, and potentially cure, patients with lung and other cancers. 429 INVITED Reversing Resistance to Targeted Therapies in Breast Cancer F. Andre1 . 1 Institut Gustave Roussy, Pathologie Mammaire Comite 5, Villejuif, France Therapies targeting oncogenic events are being developed in breast cancers. Although these therapies improve outcome in patients with metastatic breast cancers, a resistance occurs in most of the cases. In the present discussion, we will review all the strategies to overcome resistance to targeted therapies. Six different approaches are being used to reverse resistance to targeted agents. Improving the targeting of the receptor has been the most widely investigated approach. Dual targeting has been shown to improve efficacy endpoint in patients with Her2-overexpressing breast cancer resistant to trastuzumab. Targeting co-existing genomic events is another approach under development. For this purpose, there is a wide interest in describing clusterings of genomic events. As illustration, FGFR1 is frequently coamplified with CCND1, leading to a rationale for developing FGFR1inh in combination with CDK4 inh. In the similar way, a few number of triple negative breast cancers present with EGFR-amplifications and PTENdeletion of PIK3CA mutation. The third mechanism of resistance is the development of feedback loops. The most relevant mechanism is the occurrence of activating feedback loops after mTORC1 inhibition by everolimus. This observation has led to the development of combination between mTORC1 inhibitors and either tyrosine kinase or PIK3CA inhibitors. More recently, several additional mechanisms of resistance have been described in preclinical models. The existence of tumor heterogeneity and minor clones could mediate resistance to targeted therapies. Nevertheless, the involvement of clonal selection in the resistance to targeted therapies for breast cancer still remains to be shown. The co-targeting of DNA repair, together with the targeting of immune system complete the panel of mechanisms of resistance and are leading to clinical trials combining therapies directed against oncogenic events together with either DNA repair inhibitors (PARP1 inh) or activators of immune checkpoints (PD1 Ab). Overall, the mechanisms of resistance to targeted therapies in breast cancer are pleiotropic and several approaches are needed to reverse it. Several ongoing programs will be presented, that investigate the involvement of co-mutations and immune system in the resistance to targeted agents.