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A7092 - Administration of Vesicle-Encapsulated Suppressor of Cytokine Signaling 3 Inhibits Lung Epithelial Cell Transformation and Tumor Cell Function
Author Block: J. Speth1, L. Penke1, J. Bazzill2, D. A. Arenberg1, J. J. Moon2, V. G. Keshamouni1, V. N. Lama1, M. Peters-Golden1; 1Internal Medicine- Pulmonary and Critical Care, University of Michigan, Ann Arbor, MI, United States, 2Department of Pharmaceutical Sciences, University of Michigan, Ann Arbor, MI, United States.
Rationale: Inadequate endogenous expression of suppressor of cytokine signaling 3 (SOCS3) with subsequent activation of its target, the transcription factor STAT3, has been implicated in tumorigenesis and cancer progression in the lung and other organs. We have observed that a “backup” source of SOCS3 in the lung, namely that secreted in microvesicles (MVs) by alveolar macrophages (AMs), is reduced in the bronchoalveolar lavage fluid (BALF) of KRAS mutant mice harboring lung tumors. Here we sought to evaluate levels of SOCS3 in BALF of a cohort of non-small cell lung cancer (NSCLC) patients and to test the effects of vesicular SOCS3 administration on tumor cell transformation and function.
Methods: BALF samples were obtained from healthy volunteers as well as patients undergoing diagnostic bronchoscopies for suspected lung cancer. SOCS3 levels in the BALF were determined by ELISA after brief sonication to disrupt vesicles. In vitro experiments utilized human adenocarcinoma cells (A549) or mutant KRAS- expressing rat lung epithelial cells (RLE-G12V). Proliferation, Fas ligand (FasL)-induced apoptosis, and chemical transformation with N-Methyl-N′-nitro-N-nitrosoguanidine (MNNG) were assessed by CyQuant assay, annexin V staining, and soft agar assay, respectively. For SOCS3 rescue, epithelial cells were treated with natural AM-derived MVs (isolated via ultracentrifugation) or synthetic liposomes containing recombinant SOCS3 for at least 1 h prior to assay.
Results: SOCS3 levels were significantly reduced in BALF samples of patients determined to have NSCLC as compared to healthy volunteers (186.6±26.74 vs. 395.6±74.31 pg/mL, p=0.015, n=11). Addition of exogenous SOCS3-containing liposomes had the capacity to significantly inhibit MNNG-induced transformation and colony formation in soft agar. Exogenous SOCS3 provided in liposomes or in natural MVs significantly induced apoptosis (both in the presence and absence of FasL) and inhibited basal proliferation of A549 cells.
Conclusion: These data identified a novel dysregulation of immune surveillance in the form of decreased SOCS3 secretion in the tumor-bearing lung that may contribute to tumorigenesis via sustained STAT3 activation. Future studies will focus on the mechanism underlying this defect and whether rescuing SOCS3 secretion can inhibit cancer progression in vivo.