Enhancing TKI Therapy in Ph-Like Leukemia
A cellular enzyme known as mTOR is a master regulator of metabolic adaptation that senses nutrients and growth factors to control different cell functions. Many cancer cells depend on mTOR activity to maintain survival. mTOR hyperactivity is associated with poor prognosis in various tumors, especially leukemias. mTOR activity can be reduced pharmacologically using different classes of inhibitors or by dietary interventions. This proposal aims to test whether a nutritional approach or novel third-generation inhibitors of mTOR could enhance therapeutic efficacy of tyrosine kinase inhibitors (TKI) for B cell acute lymphoblastic leukemia (B-ALL) treatment. B-ALL is the most common childhood cancer but can also occur in older adults. Leukemias in this “high-risk” group include a subtype known as Ph-like B-ALL that is highly prevalent in people of Hispanic ethnicity. TKIs slow the progression of Ph-like B-ALL in mouse models and are being tested in human clinical trials. However, TKI resistance develops in many cancers, emphasizing the need to target additional survival mechanisms. mTOR inhibitors can improve the effect of TKI inhibitors yet have not achieved clinical utility. To overcome the limitations of previous mTOR inhibitor classes, we will test a third-generation inhibitor that has improved selectivity and potency. As a nutritional approach, we will test a model of dietary intervention using low glucose conditions. Periodic fasting reduces mTOR activity and sensitizes a wide range of mouse tumor models to chemotherapy and targeted therapy. Furthermore, recent clinical studies demonstrate that fasting mimicking diet enhances antitumor immunity and delays cancer progression.
For this proposal we will use Ph-like B-ALL cells representing two subtypes known as the ABL/PDGFR class and the CRLF2-r class. Tumors of the ABL/PDGFR class are sensitive to a TKI known as dasatinib, while tumors of the CRLF2-r class are sensitive to a different TKI known as ruxolitinib. We will treat human Ph-like B-ALL cell lines with third generation mTOR inhibitors or with fasting-mimicking media alone, or in combination with TKIs dasatinib or ruxolitinib. We will evaluate cell proliferation and cell death markers to determine if these interventions enhance the anti-leukemic efficacy of TKIs. To determine the mechanism of action, we will measure outputs of the mTOR kinase, specifically phosphorylation of mTOR substrate proteins and total protein synthesis rates. We will also use a mouse model to test the efficacy of single and combined treatments in vivo. Lastly, we will investigate alternative targets in the mTOR network using an approach based on CRISPR technology. This study will generate data for larger extramural grant proposals and may serve as proof-of-concept to test new clinical strategies to improve treatment of children, adolescents and adults with high-risk leukemias.