|Ph.D Student||Timaner Michael|
|Subject||Protumorigenic Effects of Tumor Microenvironment on Cancer|
Progression, Resistance and Metastasis: Role of
Macrophages and Mesenchymal Stem Cells
|Department||Department of Medicine||Supervisor||PROF. Yuval Shaked|
One of the major obstacles in clinical oncology is that while treatment usually beneficial in the first phase of therapy, in later stages, tumors sometimes re-grow and spread. Recent studies from our lab and others have demonstrated that therapy resistance and spread is related to therapy-induced host effects. Such host pro-tumorigenic and pro-metastatic effects alter the tumor microenvironment to the tumor advantage. To study these effects, we have first developed an optimal method to characterize cells isolated from the tumor mass. Following mechanical and enzymatic dissociation of the tumor and subsequent flow cytometry analysis, we have demonstrated that we are able to analyze in high yield various cell populations in the tumor microenvironment including macrophages, mesenchymal stem cells (MSCs) and bone marrow-derived immune cells. To study the specific effects of host cells on tumor progression, we next focused on cells which reside in the tumor especially after therapy. In particular, we analyzed the host response effects generated after radiotherapy and chemotherapy with the focus on macrophages and MSCs, respectively. Our results show that plasma from locally irradiated mice increased the migratory and invasive properties of colon carcinoma cells, an effect which was shown to contribute to increased mortality rate in mice that were exposed to radiation and subsequently injected with CT26 cells. Furthermore, the irradiated tumors exhibited an increase in macrophage number colonized the tumor compared to their respective controls. The depletion of macrophages in irradiated tumors reduced the number of metastatic lesions, suggesting that macrophages play a significant role in tumor cell aggressiveness in response to radiotherapy. Finally, the anti-tumor agent, Dequalinium-14, reduced macrophage motility, and therefore inhibited the infiltration of macrophages to the irradiated tumors and reduces the extent of metastasis.
When focusing on MSCs, we investigated their role in mice treated with chemotherapy, as MSCs were shown to induce chemoresistance. Moreover, as tumor initiating cells (TICs), a subset of stem cell-like tumor cells, are known to acquire resistance to many different anti-cancer therapies, we studied the link between chemotherapy-activated MSCs and TICs. Our results showed that following gemcitabine chemotherapy, MSCs home to pancreatic adenocarcinoma tumors, and reside in close proximity to TICs. Furthermore, MSCs exposed to gemcitabine promote pancreatic TIC enrichment in vitro, and enhance tumor growth, when co-?implanted in mice with pancreatic cancer cells. Cytokine screening revealed that gemcitabine-?activated MSCs highly secrete CXCL10 and induce STAT3 phosphorylation in TICs; blocking CXCL10 or its receptor CXCR3 resulted in a decreased enrichment of TICs and attenuated tumor growth. Lastly, using MSC-derived Nano-Ghosts (NG) loaded with CXCR3 antagonist along with gemcitabine, we enhanced the anti-tumor activity of chemotherapy and inhibited tumor re-growth by specifically eliminating TICs in the tumor microenvironment.
Collectively, these studies demonstrate the adverse effects of local radiation and chemotherapy on different host cells, inducing their pro-tumorigenic and pro-metastatic activity. These studies provide another mechanism to explain tumor resistance and spread in response to anti-cancer drug therapy. This research widens our understanding of the changes occurred in the tumor microenvironment following therapy and their outcome.