Title: “Toward a quantitative understanding of cancer cell signaling: mathematical models, computational tools, applications, and beyond”
Muhammad H. Zaman, PhD – BU BME (Advisor)
Mary Dunlop, PhD – BU BME (Chair)
James Galagan, PhD – BU BME
Ahmad S. Khalil, PhD – BU BME
Roger D. Kamm, PhD – MIT Biological and Mechanical Engineering
Tumor development and progression are dictated by more than the activities of cancer cells alone and are in large part determined by interactions with the immune system and the surrounding stroma. Therefore, a robust understanding of cancer in the context of this dynamic interplay is required to truly understand the progression toward and past malignancy. The work included herein attempts to develop such an understanding of three particular facets of cancer biology at a quantitative level. The ﬁrst facet of this work modeled the eﬀects of the mechanical properties and cytokine composition of the tumor microenvironment on tumor-associated macrophage migration. Using an integrated in silico and 3D in vitro approach, studied how IF, in concert with other environmental factors, aﬀects macrophage migration and its potential contribution to cancer invasion. The model suggested interleukin-8 (IL-8), chemokine (C-C motif) ligand 2 (CCL2) and β-integrin as key pathways that commonly regulate various Rho GTPases, and, in agreement with the model, in vitro macrophage migration remained elevated when exposed to a saturating concentration of recombinant IL-8 or CCL2, or to the co-addition of a sub-optimal concentration of both cytokines. Next, we sought to quantitatively analyze the eﬀect of tumor-localized macrophage cytokine signaling on the migration behaviors of cancer cells. Using an integrated experimental and computational approach, we analyzed the signaling networks associated with two cytokines secreted by tumor-associated macrophages (TAMs), transforming growth factor beta 1 (TGF-β1) and tumor necrosis factor alpha (TNFα), with the results suggesting that migratory behavior is driven by a nonlinear signaling network characterized by extensive crosstalk between the downstream intracellular signaling pathways activated by these cytokines, where migration persistence is controlled by the synergistic integration of TGF-β1 and TNFα signals and migration speed is more directly regulated by TGF-β1 signals alone. Furthermore, computational analysis of this network suggested that TAK1 and Smad7 are key nodes in the signaling network structure underlying this synergistic signal integration. Finally, we developed a quantitative model of TGF-β signaling and associated gene expression in cancer to analyze the eﬀects of the mechanical properties and cytokine composition of the tumor microenvironment on TGF-β signaling, which can switch between acting as a tumor promoter and tumor suppressor through unclear mechanisms. Sensitivity analyses of the model suggested that signals originating in the mechanical tumor microenvironment, including ECM-induced signaling and cell-cell adhesion, move TGF-β signaling toward a tumor-promoting expression proﬁle, and furthermore that the most inﬂuential reactions on this expression regulation occur at or near the transcriptional level. We then used the model to conduct a simulated drug screen to demonstrate potential applications for models of this type in the development of therapeutic tools targeting mechanically induced TGF-β signaling in cancer. Taken together, the results of these eﬀorts all support the hypothesis that environmental cues not only bear inﬂuence on the outcomes of the processes regulated by these dynamic systems, but can, depending on the nature of the integration of these environmental signals at the intracellular level, be responsible for the biological decision-making between fundamentally diﬀerent behaviors and outcomes.