Akt-activated endothelium constitutes the niche for residual disease and resistance to bevacizumab in ovarian cancer

Ovarian cancer is the second leading cause of cancer-related death in women worldwide. Despite optimal cytoreduction and adequate adjuvant therapies, initial tumor response is often followed by relapse suggesting the existence of a tumor niche. Targeted therapies have been evaluated in ovarian cancer to overcome resistant disease. Among them, antiangiogenic therapies inhibit new blood vessel growth, induce endothelial cell apoptosis, and block the incorporation of hematopoietic and endothelial progenitor cells into new blood vessels. Despite in vitro and in vivo successes, antivascular therapy with bevacizumab targeting VEGF-A has limited efficacy in ovarian cancer. The precise molecular mechanisms underlying clinical resistance to anti-VEGF therapies are not yet well understood. Among them, tumor and stromal heterogeneity might determine the treatment outcomes. The present study investigates whether abnormalities in the tumor endothelium may contribute to treatment resistance to bevacizumab and promote a residual microscopic disease. Here, we showed that ovarian cancer cells activate Akt phosphorylation in endothelial cells inducing resistance to bevacizumab leading to an autocrine loop based on FGF2 secretion. Altogether, our results point out the role of an activated endothelium in the resistance to bevacizumab and in the constitution of a niche for a residual disease.

Abstract B69: Preferential transfer of mitochondria from endothelial to cancer cells through tunneling nanotubes modulates chemoresistance

Our vision of cancer has changed during the past decades. Indeed tumors are now perceived as complex entities where tumoral and stromal components interact closely. Among the different elements of tumor stroma the cellular component play a primordial role. Bone Marrow derived mesenchymal cells (MSCs) are attracted to tumor sites and support tumor growth. Endothelial cells (ECs) play a major role in angiogenesis. While the literature documents many aspects of the cross talk between stromal and cancer cells, the role of direct hetero-cellular contact is not clearly established.

Recently, Tunneling nanotubes (TnTs) have been shown to support cell-to-cell transfers of plasma membrane components, cytosolic molecules and organelles within cell lines. Herein, we have investigated the formation of heterocellular TnTs between stromal (MSCs and ECs) and cancer cells. We demonstrate that TnTs occur between different cancer cells, stromal cells and cancer-stromal cell lines. We showed that TnTs-like structure occurred in 3D anchorage independent spheroids and also in tumor explant cultures. In our culture condition, TnTs formation occurred after large membrane adhesion. We showed that intercellular transfers of cytoplasmic content occurred similarly between cancer cells and MSCs or ECs, but we highlighted that the exchange of mitochondria occurred preferentially between endothelial cells and cancer cells. We illustrated that the cancer cells acquiring mitochondria displayed chemoresistance.

Our results illustrate the perfusion-independent role of the endothelium by showing a direct endothelial to cancer cell mitochondrial exchange associated to phenotypic modulation. This supports another role of the endothelium in the constitution of the metastatic niche.

Citation Format: Jennifer Pasquier, Bella s. Guerrouahen, Hamda Al. Thawadi, Nadine Abu Kaoud, Mahtab Maleki, Frank Le Foll, Arash Rafii. Preferential transfer of mitochondria from endothelial to cancer cells through tunneling nanotubes modulates chemoresistance. [abstract]. In: Proceedings of the AACR Special Conference on Advances in Ovarian Cancer Research: From Concept to Clinic; Sep 18-21, 2013; Miami, FL. Philadelphia (PA): AACR; Clin Cancer Res 2013;19(19 Suppl):Abstract nr B69.

Abstract B70: Akt-activated endothelium constitute a niche for residual disease and resistance to bevacizumab in ovarian cancer

Background. Ovarian cancer is the second leading cause of cancer-related death in women worldwide. Despite optimal cytoreduction and adequate adjuvant therapy, initial tumor response is often followed by relapse. Targeted therapies have been evaluated in ovarian cancer to overcome resistant disease. Among them anti-angiogenic therapies inhibit new blood vessel growth, induce endothelial cell apoptosis, and block the incorporation of haematopoietic and endothelial progenitor cells into new blood vessels. Despite in-vitro and in vivo successes anti-vascular therapy with bevacizumab targeting VEGF has limited efficacy in ovarian cancer. Anti-angiogenic treatment increases hypoxia, and might lead to tumor rebound and drug resistance. The precise molecular mechanisms underlying clinical resistance to anti-VEGF therapies are not well understood.

Hypothesis. We hypothesized that abnormalities in the tumor endothelium may contribute to treatment resistance and produce and promote a residual microscopic disease and resistance to bevacizumab.

Methods. We showed that Akt pathway is activated in vitro and in vivo in ovarian cancer endothelium. We used Akt-activated endothelial cells (EC) that replicate tumor endothelium biology, and their control, HUVEC to investigate the anti-angiogenic activity of bevacizumab by angiogenesis and migration assays. We conducted XTT assay to examine the effect of bevacizumab on proliferation of VEGF producing human ovarian cancer cell lines. Expression of FGF-2, phospho-AKT was assessed by western blotting and flow cytometry. Finally, using a feeder-free matrigel and spheroid models of ovarian cancer we examined the effect of bevacizumab on residual disease.

Results. We demonstrated that ovarian cancer cells (OCC) activate the endothelium, which displays resistance to bevacizumab. Bevacizumab had no effect on the proliferation of Akt-activated EC, but significantly inhibited angiogenesis and delayed wound healing in HUVEC. We showed the existence of an autocrine loop based on FGF-2 secretion. We demonstrate the role of Akt-activated EC in supporting expansion and self-renewal of OCC in a residual disease context.

Conclusion. Our data point out the role of an activated endothelium in the constitution of the residual disease and resistance to bevacizumab.

Citation Format: Bella S. Guerrouahen, Jennifer Pasquier, Nadine Abu Kaoud, Marie-Claude Beauchamp, Pegah Ghiabi, Mahtab Maleki, Raphael Lis, Ahmed Saleh, Walter H. Gotlieb, Shahin Rafii, Arash Rafii. Akt-activated endothelium constitute a niche for residual disease and resistance to bevacizumab in ovarian cancer. [abstract]. In: Proceedings of the AACR Special Conference on Advances in Ovarian Cancer Research: From Concept to Clinic; Sep 18-21, 2013; Miami, FL. Philadelphia (PA): AACR; Clin Cancer Res 2013;19(19 Suppl):Abstract nr B70.

Abstract A74: Microparticles mediate cross-talk between tumoral and endothelial cells and promote the constitution of an angiocrine pro-metastatic niche through Arf6 up regulation

During the past few years, evidences in the literature point out the crucial role of the microenvironment in tumor growth, resistance to therapy and occurrence of metastatic phenotype. Tumor vessels have been considered for a long time as passive conducts for nutriments but more recently several studies have also demonstrated secretion of pro-tumoral factors by endothelial cells. It seems therefore mandatory to clearly identify the mechanisms mediating cross-talk between tumor cells and endothelial cells.

Here, we hypothetize that tumor cell and endothelium secrete bio-active microparticles (MPs) that are actively uptaken by the other cell type and that are participating to a functional cross-talk. We characterized the cancer cells MPs, using 2 cells lines from breast cancer (MCF7, MDA-MB231) and 2 from ovarian cancer (SKOV3, OVCAR3) and the endothelium secreted MPs using E4orf1-activated endothelium.

Our data show that MPs from mesenchymal-like metastatic cell lines (MDA-MB231 and SKOV3) were able to promote an angiocrine switch of endothelial cells (activation of akt signaling) compared to MPs from epithelial-like cell lines (OVCAR3 and MCF7). The angiocrine switch increased Arf6 expression and functionalized an MP dependent vascular niche enhancing tumor cells pro-metastatic proprieties. We also show that angiocrine endothelial MPs enhanced tumor cells pro-metastatic proprieties and cancer stemness.

All together we demonstrated that cancer cell derived MPs induced or sustain both an angiogenic but also an angiocrine switch of the endothelium. This has great implication in terms of tumor biology as indeed while the emphasis has mainly been on the angiogenic properties, the angiocrine pro-tumoral effect might be the cause for therapeutic resistance as well as residual and recurrent disease.

Citation Format: Jennifer Pasquier, Hamda Al. Thawadi, Nadine Abu Kaoud, Pegah Ghiabi, Mahtab Maleki, Bella S. Guerrouahen, Arash Rafii. Microparticles mediate cross-talk between tumoral and endothelial cells and promote the constitution of an angiocrine pro-metastatic niche through Arf6 up regulation. [abstract]. In: Proceedings of the AACR Special Conference on Advances in Ovarian Cancer Research: From Concept to Clinic; Sep 18-21, 2013; Miami, FL. Philadelphia (PA): AACR; Clin Cancer Res 2013;19(19 Suppl):Abstract nr A74.