Abstract A18: Autophagy as a mechanism implicated in osteosarcoma resistance to gemcitabine.

Abstract

Abstract The purpose of this study is to demonstrate the role of autophagy in osteosarcoma (OS) lung metastases resistance to aerosol Gemcitabine (GCB). Despite many advances in chemotherapy and successful control of the primary tumor, osteosarcoma overall survival has remained the same in the last 15 years. Pulmonary metastases remain the main cause of death in patients with OS underscoring the need for new therapeutic strategies. Using a human OS mouse model, we had previously demonstrated that aerosol Gemcitabine (GCB) has a significant therapeutic effect in OS lung metastases. Nevertheless, a subset of cells failss to respond to GCB treatment and persist as small isolated lung metastases in vivo. Resistance to GCB is also evidenced by survival of OS cells after treatment in vitro. Therefore, understanding the underlying mechanism of OS resistance to GCB will allow the implementation of new therapeutic strategies. Autophagy has been suggested as a mechanism induced by a variety tumor cells after chemotherapy treatment. It is a process involved in the degradation of organelles and damaged proteins, providing the cells amino acids to sustain survival under stressful conditions. Recently, it has also been associated with tumor cells resistance to chemotherapy. GCB-induced autophagy in OS primary and metastatic disease has not been studied. Therefore, we characterized the role of autophagy in OS cells after treatment with GCB. We first demonstrated GCB-induced autophagy in LM7 OS cells as indicated by an increase in autophagy markers: microtubule-associated light chain 3 (LC3I/LC3II) conversion, Beclin 1 (BECN1) expression and development of acidic vesicular organelles. GCB also caused a decrease in p62/SQSTM1 and Blc-2 expression, further indicating autophagy induction. Blockage of autophagy with the pharmacologic inhibitor Hydroxychroloquine (HCQ) coupled with GCB treatment decreased cell viability of LM7 OS cells. Furthermore, knockdown of BECN1 in LM7 cells coupled with GCB treatment also decreased cell viability of LM7 OS cells, indicating that autophagy plays an important role in OS cells resistance to GCB treatment. In conclusion, we demonstrated that autophagy is one of the mechanisms implicated in the resistance of OS cells to GCB. Autophagy modulation may shed new light towards metastatic OS therapy, possibly by implementing the use of combination therapy HCQ-aerosol GCB in the adjuvant setting. Current studies are underway to test our hypothesis in vivo and to address these results using other OS cells in vitro. Citation Information: Mol Cancer Ther 2013;12(11 Suppl):A18. Citation Format: Janice M. Santiago-O'Farrill, Mario G. Hollomon, Eugenie S. Kleinerman, Nancy Gordon. Autophagy as a mechanism implicated in osteosarcoma resistance to gemcitabine. [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2013 Oct 19-23; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2013;12(11 Suppl):Abstract nr A18.