Partner: F. Hoffmann-La Roche
3rd Supervisor: Nuria Gutierrez-Prat
Project:
Oncogene addiction is defined as the unusual dependence of certain cancer cells to the activity of aberrantly activated gene products. These dependencies can be targeted therapeutically and represent the basis of most targeted therapies in oncology. Interestingly, normal cells also exhibit cell-type-specific molecular dependencies driven by lineage-associated genes, and such dependencies remain functional following malignant transformation. One example of this phenomenon that carries significant therapeutic implications is the dependence of prostate epithelial cells on the activity of the androgen receptor, which when targeted pharmacologically, can lead to the death of prostate cancer cells. Another example of this phenomenon is seen in melanoma. Similar to the pigmented melanocytes from which they arise, melanoma cells retain their dependence on the activity of the lineage-defining transcription factor MITF *1. Importantly, mutational activation of BRAF (which occurs in approximately one half of melanoma cases) leads to rewiring of the molecular mechanisms that control MITF function. These changes result in the endowment of the mutant kinase with the ability to regulate MITF activity *2 thus creating a cancer-specific liability where inhibition of BRAF selectively kills melanoma cells through suppression of MITF function. Paradoxically, MITF overexpression can also have growth-inhibitory effects in BRAF-transformed melanocytes, suggesting that, akin to the toxic effects of oncogene overdose *3, excessive MITF signalling outputs can be detrimental to cancer cells.
In hematopoietic and lymphoid tissues, c-Myb is a lineage defining transcription factor whose function is necessary for lineage-specific cell survival. Not surprisingly, the DRIVE project *4 found that cancer cell lines of hematopoietic and lymphoid lineage (including leukemias and lymphomas) showed sensitivity to c-Myb depletion. Similar data can be obtained through analysis of data in The Cancer Dependency Map (DEPMAP). Therefore, c-Myb targeting could represent a lineage–addiction-based therapeutic strategy in haeme malignancies. One obvious limitation to such an approach is the inherent dependence of normal hematopoietic tissue to the activity of c-Myb, and the potential toxicities that could be associated with systemic inhibition of c-Myb. However, we reasoned that if oncogenic signal transduction rewiring in haeme cancers confers specific oncogenes with a neomorphic ability to regulate c-Myb function, it would render these oncogenes attractive therapeutic targets for these diseases.
The PI3K/AKT/mTOR pathway (hereafter simply referred to as “the PI3K pathway”) is one of the most commonly deregulated pathways in human cancer. PI3Ks are heterodimeric lipid kinases that drive the generation of phosphoinositide second messengers that activate a number of effector proteins including the serine/threonine kinase AKT*5. Its pleotropic functions include but are not limited to the regulation of cell proliferation and cell survival, the regulation of cellular metabolism, and the regulation of cell differentiation. Activation of the PI3K/AKT/mTOR pathway in human leukemias and lymphomas is well documented *6, *7 and has prompted a number of clinical trials to interrogate the clinical utility of a variety of PI3K pathway inhibitors. Interestingly, AKT inhibitors have not been assessed very extensively in hematological cancers *8. Our preliminary data, and that of others *9 show that AKT inhibitors can induce significant cytotoxic responses in leukemic cell lines. Interestingly, we find that these effects correlate with an upregulation of c- MYB protein. This increase is also observed when leukemia cells are treated with an inhibitor of PI3Kδ *6, the major source of PI3K activity in hematopoietic cells, but not when treated with the MEK inhibitor trametinib. Altogether, these data suggest a potential link between AKT activation and c-Myb regulation in hematological malignancies. Consistently, it has been previously shown that knockdown of FOXO1, a transcription factor that is negatively regulated by AKT phosphorylation, causes significant downregulation of MYB protein and MYB transcription targets*10, and that ectopic overexpression of c- Myb had a transient growth inhibitory. We therefore hypothesise that, similar to how mutational activation of BRAF in melanoma renders MITF subject to BRAF control, the molecular rewiring caused by PI3K pathway activation in blood cancers renders c-Myb subject to regulatory control by AKT through mechanisms this proposal will investigate.
The proposed PhD project will investigate 1) the mechanism of AKT inhibitor- induced MYB upregulation, 2) whether the cytotoxic response of leukemic cells to AKT inhibition depends on this mechanism, and 3) the molecular nature of the signalling programme driven by MYB overdose and of its toxicity. The data generated by this project will shed new light on the molecular mechanisms that underlie response to AKT inhibitors in blood and lymphocytic cancers, and could generate new rationale to develop novel therapeutic strategies based on pharmacologically phenocopying the relevant growth inhibitory signals downstream of c-Myb overdose. Although normal hematopoieic cells are also c-Myb-dependent, it is the selective nature of the overdose signal that could provide a therapeutic window. Additionally, it is currently believed that the overexpression of c-Myb in blood cancers renders these cells addicted to higher-than-normal levels of c-Myb suggesting that partial c-Myb inhibition might be sufficient to selectively kill cancer cells*11. The project will have the following specific aims:
Aim 1. Characterise the functional relationship between FOXO1, c-Jun, and c-Myb in the response to AKT inhibitors in blood and lymphocytic cancer cell lines.
Aim 2. Characterise the molecular nature of MYB overdose.
The project will involve the use of cell engineering and gene editing technologies including RNAi and CRISPR. The student will acquire important skills in these methodologies as well as in cancer pharmacology and signal transduction. This project is a collaboration between King’s College London (Institute of Pharmaceutical Sciences) and Roche. The student will spend 12 weeks in Basel (Switzerland) learning how to analyse molecular profiling data and beconing familiar with various aspects of the drug development process. In order to disseminate their work, the student will have an opportunity to attend a conference to present their work during their final year. Additionally, interim results will be presented at internal seminar series and other student events at KCL, as well as at Roche during their placement.
This project will suite an individual with an interest in cancer, translational science, omics approaches, drug development, cell engineering etc. This project is co-funded by the MRC and Roche through the iCASE programme. As such, the successful applicant will benefit not only from training in a world class university, but also from carrying out research at the interface of academic and industry science with one of the world’s largest pharmaceutical companies.
References
- Garraway, L.A. & Sellers, W.R. From integrated genomics to tumor lineage dependency. Cancer Res 66, 2506-2508 (2006).
2. Wellbrock, C., Rana, S., Paterson, H., Pickersgill, H., Brummelkamp, T. & Marais, R. Oncogenic BRAF regulates melanoma proliferation through the lineage specific factor MITF. PLoS One 3, e2734 (2008).
3. Amin, A.D., Rajan, S.S., Groysman, M.J., Pongtornpipat, P. & Schatz, J.H. Oncogene Overdose: Too Much of a Bad Thing for Oncogene-Addicted Cancer Cells. Biomark Cancer 7, 25-32 (2015).
4. McDonald, E.R., 3rd, de Weck, A., Schlabach, M.R., Billy, E., Mavrakis, K.J., Hoffman, G.R., Belur, D., Castelletti, D., Frias, E., Gampa, K., Golji, J., Kao, I., Li, L., Megel, P., Perkins, T.A., Ramadan, N., Ruddy, D.A., Silver, S.J., Sovath, S., Stump, M., Weber, O., Widmer, R., Yu, J., Yu, K., Yue, Y., Abramowski, D., Ackley, E., Barrett, R., Berger, J., Bernard, J.L., Billig, R., Brachmann, S.M., Buxton, F., Caothien, R., Caushi, J.X., Chung, F.S., Cortes-Cros, M., deBeaumont, R.S., Delaunay, C., Desplat, A., Duong, W., Dwoske, D.A., Eldridge, R.S., Farsidjani, A., Feng, F., Feng, J., Flemming, D., Forrester, W., Galli, G.G., Gao, Z., Gauter, F., Gibaja, V., Haas, K., Hattenberger, M., Hood, T., Hurov, K.E., Jagani, Z., Jenal, M., Johnson, J.A., Jones, M.D., Kapoor, A., Korn, J., Liu, J., Liu, Q., Liu, S., Liu, Y., Loo, A.T., Macchi, K.J., Martin, T., McAllister, G., Meyer, A., Molle, S., Pagliarini, R.A., Phadke, T., Repko, B., Schouwey, T., Shanahan, F., Shen, Q., Stamm, C., Stephan, C., Stucke, V.M., Tiedt, R., Varadarajan, M., Venkatesan, K., Vitari, A.C., Wallroth, M., Weiler, J., Zhang, J., Mickanin, C., Myer, V.E., Porter, J.A., Lai, A., Bitter, H., Lees, E., Keen, N., Kauffmann, A., Stegmeier, F., Hofmann, F., Schmelzle, T. & Sellers, W.R. Project DRIVE: A Compendium of Cancer Dependencies and Synthetic Lethal Relationships Uncovered by Large-Scale, Deep RNAi Screening. Cell 170, 577-592 e510 (2017).
5. Vivanco, I. & Sawyers, C.L. The phosphatidylinositol 3-Kinase AKT pathway in human cancer. Nat Rev Cancer 2, 489-501 (2002).
6. Blachly, J.S. & Baiocchi, R.A. Targeting PI3-kinase (PI3K), AKT and mTOR axis in lymphoma. Br J Haematol 167, 19-32 (2014).
7. Nepstad, I., Hatfield, K.J., Gronningsaeter, I.S. & Reikvam, H. The PI3K-Akt- mTOR Signaling Pathway in Human Acute Myeloid Leukemia (AML) Cells. Int J Mol Sci 21 (2020).
8. Coleman, N., Moyers, J.T., Harbery, A., Vivanco, I. & Yap, T.A. Clinical Development of AKT Inhibitors and Associated Predictive Biomarkers to Guide Patient Treatment in Cancer Medicine. Pharmgenomics Pers Med 14, 1517-1535 (2021).
9. Lynch, J.T., McEwen, R., Crafter, C., McDermott, U., Garnett, M.J., Barry, S.T. & Davies, B.R. Identification of differential PI3K pathway target dependencies in T-cell acute lymphoblastic leukemia through a large cancer cell panel screen. Oncotarget 7, 22128-22139 (2016).
10. Gehringer, F., Weissinger, S.E., Swier, L.J., Moller, P., Wirth, T. & Ushmorov, A. FOXO1 Confers Maintenance of the Dark Zone Proliferation and Survival Program and Can Be Pharmacologically Targeted in Burkitt Lymphoma. Cancers (Basel) 11 (2019).
11. Uttarkar, S., Dasse, E., Coulibaly, A., Steinmann, S., Jakobs, A., Schomburg, C., Trentmann, A., Jose, J., Schlenke, P., Berdel, W.E., Schmidt, T.J., Muller- Tidow, C., Frampton, J. & Klempnauer, K.H. Targeting acute myeloid leukemia with a small molecule inhibitor of the Myb/p300 interaction. Blood 127, 1173-1182 (2016).