Abstract 2641: Microenvironment-dependent intratumoral heterogeneity in the self-renewal and tumorigenic differentiation of ovarian cancer.

Proceedings: AACR 104th Annual Meeting 2013; Apr 6-10, 2013; Washington, DC Solid tumor complexity emanates from the requirement of a supportive microenvironment that provides a compatible network of interactions between heterogeneous cancer cells and various tumor supporting cells. In previous studies we have established a model for studying tumorigenic processes where cancer cells can directly interact with a human microenvironment based on the potential of human embryonic stem cells (hESC) to generate in vivo teratoma tissue. We utilized the hESC - derived experimental platform to advantage as a supportive tumor microenvironment to demonstrate that the balance between self-renewal and tumorigenic differentiation differs strikingly among cancer cell subpopulations (CCSPs), and importantly is dynamically dependent on the tumor microenvironment as a crucial determinant of tumor growth properties. Six clonally expanded CCSPs derived from the ovarian clear cell carcinoma of a single tumor were used to demonstrate striking intratumoral heterogeneity that is also affected by the tumor microenvironment. While only four out of the six CCSPs developed into tumors in a conventional xenograft model, all of the CCSPs robustly generated tumors in the hESC-derived cellular microenvironment, highlighting the potential experimental utility of the hESC-based model in supporting tumor promotion. Moreover, each of the six CCSPs displays a different level of morphologic and tumorigenic differentiation, wherein growth in the hESC-derived microenvironment favors growth of CD44+/ALDH+ pockets of self-renewing cells that sustain tumor growth through a process of tumorigenic differentiation into CD44-/ALDH- derivatives. These derivative cells display microenvironment-dependent plasticity with the capacity to restore self-renewal and CD44 expression. Gene expression profiles of two specific CCSPs grown in vitro and then injected either as intramuscular or as intrateratoma tumors were examined. This gene expression array analysis revealed that the hESC-based model supports the capacity of distinct CCSPs to generate tumors, and maintains CSC properties, in contrast to the conventional direct tumor xenograft platform. Significant gene ontologies correlates for each group of tumors showed greater complexity in the interaction between the tumor cells and the hESC-derived cellular microenvironment as opposed to the xenotransplantation model. In addition, these results demonstrated that the murine microenvironment is incapable to discriminate between different cancer cell populations of a single tumor and therefore excessively simplify tumor progression events. Taken together, the hESC-based in vivo model renders intratumoral heterogeneity in the self-renewal and tumorigenic differentiation amenable to biological analysis as well as anticancer therapy testing. Citation Format: Sagi Abelson, Yeela Shamai, Liron Berger, Irena Reiter, Roni Shouval, Karl Skorecki, Maty Tzukerman. Microenvironment-dependent intratumoral heterogeneity in the self-renewal and tumorigenic differentiation of ovarian cancer. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 2641. doi:10.1158/1538-7445.AM2013-2641