Basic Biology IV
In about one quarter of acute leukemias and almost in all cases of chronic myeloid leukemia, the tumor cells are driven by an oncogenic tyrosine kinase. Current efforts of targetred therapy almost entirely focus on the development of new compounds that attenuate oncogenic signaling from these tyrosine kinase molecules. Targeting negative feedback regulators of oncogenic tyrosine kinases for the treatment leukemias seems counter intuitive because it represents effectively the opposite of current efforts to improve existing tyrosine kinase inhibitor (TKI)-therapies. However, our preliminary data using genetic mouse models and a small molecule inhibitor of inhibitory phosphatases demonstrate an unexpected dependence of TKD-tumor cells on negative feedback regulation. The central goal of this proposal is to build a fundamental understanding of how blockade of negative feedback mechanistically leads to cell death in TKD-malignancies (Aims 1-2), and to leverage this mechanistic information towards the development of a new therapy concept based on alternating treatment schedules between TKIs and pharmacological inhibitors of negative feedback (Aim 3).
Statement of Benefit to California:
In 2008, the California Cancer Registry expected 3,655 patients with newly diagnosed leukemia and at total of 2,185 death resulting from fatal leukemia. In addition, ~23,300 Californians lived with leukemia in 2008, which highlights that leukemia remains a frequent and life-threatening disease in the State of California despite substantial clinical progress. Here we propose the development of a fundamentally novel treatment approach that is directed at leukemia stem cells. While current treatment approaches effectively diminish the bulk of proliferating leukemia cells, they fail to eradicate the rare leukemia stem cells (LSC), which give rise to drug-resistance and recurrence of the disease. We propose a sequential targeting approach which combines targeted therapy of the leukemia-causing oncogene and blockade of inhibitory phosphatases. Tyrosine kinase inhibitors (TKI) effectively eliminate transient amplifying progenitors but not quiescent LSC. Here propose that pharmacological blockade of inhibitory phosphatases represents a conceptually novel approach to selectively induce eradication of LSC. To validate this concept, we are proposing three Aims to (1) reconstruct the pathway through which inhibitory phosphatases promote LSC self-renewal, (2) to determine whether LSC depletion results from forced differentiation or cell death and (3) to study pharmacological blockade of inhibitory phosphatases in patient-derived human leukemia samples.
The standard therapy for acute leukemia, such as acute myeloid leukemia (AML), and most chronic leukemias are tyrosine kinase inhibitors that are therapeutic in the primary disease but are not effective in killing leukemic stem cells (LSCs). The goal of this proposal is to test the hypothesis that a class of intracellular signal transducers, named inhibitory phosphatases, represent a critical therapeutic target for LSC elimination and that a blockade of inhibitory phosphatases will be an effective therapeutic approach. The first specific aim is to analyze inhibitory signaling involved in LSC maintenance. The second aim is to investigate mechanisms of LSC loss in response to inhibitory phosphatase signaling. The third specific aim is to validate small molecule blockers of inhibitory phosphatases as potential agents to eradicate LSCs. Significance and Innovation - Although reviewers considered the approach to be highly novel, they expressed strong doubts that blockade of inhibitory phosphatases would deplete LSCs. - Reviewers cautioned that in most diseases, tyrosine kinase inhibitors were not effective for long-term therapy, and this could be a serious issue also for inhibitory phosphatase inhibitors. - Reviewers appreciated the use multiple transgenic mouse models but found the predominant focus on mouse work and the limited use of human cells in proposed experiments to be a significant problem and major weakness. - The project addresses a major unsolved problem with state-of-the art techniques. - Reviewers questioned whether many of the experiments actually addressed LSCs (as opposed to bulk cancer cells), since many proposed experiments do not include prospective isolation of LSCs and confirmation of their identity. Feasibility and Experimental Design - The PI provided strong preliminary data about inhibitory phosphatase inhibition in mouse cells, but adequate data on human LSCs was lacking. - The tyrosine phosphorylation changes may be difficult to assess with the described techniques, and no alternatives were proposed. - There was concern that proposed experiments will not actually study AML disease, because the mice may just develop myeloproliferative disease. - Reviewers found many of the experiments, for example, those using clinical specimen, to be inadequately described and questioned many features of the experimental design. Principal Investigator (PI) and Research Team - The PI is a leader in the LSC field and knowledgeable in the area of hematopoietic malignancies. - The research team and collaborators are excellent and have appropriate experience to carry out the proposed research. Responsiveness to the RFA -The proposal is only marginally responsive to the RFA, since much of the work focuses on mouse LSCs. - Reviewers were uncertain whether many of the proposed experiments actually focused on stem cells (LSCs) rather than bulk tumor cells.