Abstract 3428: Astrocytes upregulate survival genes in tumor cells and induce protection from chemotherapy

Abstract

Abstract Background. In the USA, more than 40% of cancer patients develop brain metastasis. The median survival of untreated patients is 1-2 months which may be extended to 6 months with conventional therapy. The resistance of tumor cells growing in the brain to chemotherapy has been attributed to the blood-brain barrier (BBB). Recent data, however, reveal that tumor cells growing in the brain release VEGF that leads to vascular permeability, ruling out that the BBB is a sole mechanism of drug resistance. Brain metastases are surrounded and infiltrated by activated astrocytes whose role in physiology is to protect neurons from toxicity. We became intrigued by the possibility that tumor cells exploit astrocytes for protection from apoptosis induced by chemotherapeutic drugs. Material and Methods. Human breast cancer cells (MDA231) and human lung cancer cells (PC14Br4) were co-cultured with GFP-labeled murine astrocytes or NIH3T3 fibroblasts. Chemosensitivity assays against P-glycoprotein (P-gp)-1-associated chemotherapeutic agents, such as paclitaxel, adriamycin, vinblastine, and vincristine, or P-gp-1-dissociated agents such as 5-FU and cisplatinum, were performed by propidium iodide staining and FACS analysis. The development of tumor cell resistance from chemotherapeutic agents was correlated with gap junction communication and expression of survival genes. Identified genes were knocked-down by SiRNA and chemosensitivity was repeated for functional validation. Lastly, to confirm the influence of the microenvironment, tumor cells were first co-cultured with murine astrocytes or fibroblasts and then cultured with either murine astrocytes or fibroblasts. Chemosensitivity assays and gene arrays were performed. Results. Direct cultures of murine astrocytes (but not fibroblasts) with human breast cancer cells or lung cancer cells protected the tumor cells against all tested chemotherapeutic agents, correlating with upregulation of survival genes including GSTA5, BCL2L1, and TWIST1, and activation of Akt and MAPK pathways in the tumor cells. The upregulation of the survival genes and consequent drug resistance were dependent on direct contact between the astrocytes and tumor cells through gap junctions. Knocking down the genes in the tumor cells using specific SiRNA rendered the tumor cells sensitive to the chemotherapeutic agents. The gene expression profiles and chemoresistance were transient, i.e., loss of direct contact of tumor cells with murine astrocytes resulted in loss of resistance and downregulation of the survival genes. Conclusion. Our data clearly demonstrate that host cells, e.g., astrocytes, influence the biological behavior of tumor cells and reinforces the contention that successful therapy of brain metastasis requires targeting both tumor cells and the organ microenvironment. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 3428.