Abstract B006: The role of tumor specific IGFBP-3 in the onset and progression of skeletal muscle wasting in a murine model of pancreatic cancer
Authors: Sechrist Zachary R , Cole Calvin L 
Published: September 2024

Abstract
Background: Pancreatic ductal adenocarcinoma (PDAC) is the fourth leading cause of cancer- related death and is highly associated with skeletal muscle wasting (SMW) that leads to treatment intolerance and reduced survival. Research substantiates the role of increased levels of Insulin-like Growth Factor Binding Protein-3 (IGFBP-3) in PDAC-related SMW. Canonically, supraphysiological levels of IGFBP-3 block insulin-like growth factor-1 (IGF-1) binding, thus downregulating the activation of its downstream targets Akt and mTOR. Non-canonical signaling via TGF-βRI results in aberrant FoxO1 signaling, which upregulates the ubiquitin proteasome pathway (UPP) and induces autophagy. Dysregulated UPP and autophagy activation have been shown to promote muscle degradation. Recent findings from our lab implicate canonical and non-canonical signaling of tumor associated IGFBP-3 in increased protein catabolism and decreased anabolism, resulting in SMW in a syngeneic murine model of PDAC. We tested the hypothesis that genetic ablation of IGFBP-3 in PDAC tumor cells attenuates SMW via regulation of Akt and FoxO1, leading to decreases in UPP and autophagy in skeletal muscle.Methods: C57BL/6J female mice (6-8 weeks) were randomized to one of three groups: 1) no tumor control (NTC) (n=10), 2) KCKO-Luc parental cells (PDAC) (n=14), or 3) IGFBP-3-/- KCKO-Luc (n=14). Tumor cells were injected orthotopically. Tumor and lean mass were assessed longitudinally via dual energy x-ray absorptiometry (DEXA). At sacrifice, quadriceps muscles were collected for protein and transcriptional analysis, Tibialis Anterior (TA) muscles for histology and serum for ELISA. TA frozen sections were stained with Oil Red O (ORO) to highlight intramuscular adipogenesis.Results: PDAC mice experience significantly reduced survival (T1/2=56 days) compared to IGFBP-3-/- mice that maintained 100% survival at day 100 (p&lt;0.0001). IGFBP-3-/- mice lost significantly less lean mass from baseline to day 56 compared to PDAC mice (p&lt;0.0001). PDAC mice exhibited 3-fold elevated serum levels of IGFBP-3 compared to NTC and IGFBP-3-/- mice (p&lt;0.01). Transcriptionally, PDAC mice displayed increased expression of igfbp3, tgfbr1, and UPP associated genes fbxo32, and trim63 compared to NTC and IGFBP-3-/- mice. Further, the ratio of pAkt (Ser473), pS6 (Ser235/236), and pFoxO1 (Ser253) to total protein levels were significantly reduced in PDAC mice (p&lt;0.05 vs NTC and IGFBP-3-/-). Additionally, protein levels of ULK1 and the ratio of LC3bII over LC3bI, markers of autophagy, are elevated in PDAC mice compared to NTC and IGFBP-3-/- mice (p&lt;0.05). Lastly, there is a significant increase in ORO positive staining in PDAC mice compared to NTC and IGFBP-3-/- mice (p&lt;0.0001).Conclusion: These findings suggest that PDAC-related SMW is driven by tumor derived IGFBP-3, which acts as an endocrine factor on skeletal muscle cells to inhibit protein synthesis and activate FoxO1 signaling to upregulate the UPP and autophagy. Lastly, we identify skeletal muscle adipogenesis as a biomarker for autophagy upregulation and SMW.
Citation Format: Zachary R Sechrist, Calvin L Cole. The role of tumor specific IGFBP-3 in the onset and progression of skeletal muscle wasting in a murine model of pancreatic cancer [abstract]. In: Proceedings of the AACR Special Conference in Cancer Research: Advances in Pancreatic Cancer Research; 2024 Sep 15-18; Boston, MA. Philadelphia (PA): AACR; Cancer Res 2024;84(17 Suppl_2):Abstract nr B006.