Despite the promise, and hope, that molecular therapies could bring durable remissions to cancer patients, most targeted drugs did not live up to this expectation, providing only limited, and, in most cases, short-lived benefit due to the emergence of metastatic disease. Although much effort has focused on mechanisms of drug resistance, the possibility that molecular therapies may actually reprogram tumors, and select new cancer phenotypes important for disease progression, or tumor plasticity, has not been widely considered. We tested this concept by examining the response of tumors to targeted inhibition of the phosphatidylinositol-3 kinase (PI3K) network, a disease driver in virtually every human cancer and important therapeutic target. Our preliminary data show that small molecule inhibitors of PI3K induce a global transcriptional and metabolic reprogramming in tumors. This adaptive response imparts a new cancer phenotype that combines paradoxical traits of protracted proliferative and bioenergetics quiescence, appearance of senescence, heightened cell survival and increased tumor cell invasion. These are pivotal hallmarks of dormancy, an elusive process in which tumor cells disseminate early from a primary lesion, resist apoptosis, seed metastatic sites, and remain quiescent for long periods of time only to re-awaken as recurrent (and incurable) disease. Mechanistically, tumor plasticity induced by PI3K inhibition involves reactivation of Akt in cytosol and mitochondria, and Akt- dependent phosphorylation of cyclophilin D (CypD), a multifunctional regulator of mitochondrial bioenergetics and apoptosis. Conversely, when combined with a small molecule antagonist of mitochondrial integrity, Gamitrinib, PI3K inhibitors no longer trigger adaptive tumor reprogramming, suppress invasion and exert considerably enhanced anticancer activity. Therefore, the hypothesis that tumor dormancy can be induced as an adaptive response to molecular therapy and coordinated by mitochondrial reprogramming can be formulated, and will constitute the focus of the present application. Experiments in the first specific aim will recapitulate the phenotype of PI3K inhibitin in established dormancy models, and dissect the mechanistic requirements of this pathway with respect to cell cycle quiescence, senescence, and kinase cascade(s) of cell invasion. In the second specific aim, we will define the mechanism(s) of Akt reactivation in dormancy, characterize a CypD-Akt complex in mitochondria, and dissect the role of Akt phosphorylation of CypD in repurposing of mitochondrial functions in apoptosis, bioenergetics, and autophagy. The third specific aim will examine the rational combination of PI3K inhibitors plus an antagonist of mitochondrial quality control, Gamitrinib, in tumor cell killing, reversal of the adaptive phenotyp, and preclinical activity in models of angiogenesis, metastasis, and tumor dormancy, in vivo. Overall, the experimental plan will characterize a new mechanism of tumor dormancy as an adaptive response to molecular therapy. The results will credential novel therapeutic strategies to obliterate dormancy and eradicate metastatic competency of tumors.
Metastasis, or the dissemination of tumor cells to distant organs, is the primary cause of morbidity and mortality in cancer patients, but therapeutic strategies to limit this process do not currently exist. In some cases, metastatic foci manage to remain dormant for long periods of time after initial treatment, only to reawaken as relapsed and incurable disease. Our findings that dormancy traits can be acquired as part of an adaptive response to molecular therapies, and through reprogramming of mitochondrial functions, now opens concrete prospects for the introduction of novel anti-metastatic therapies in humans.
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