Abstract 3901: Polymeric mechanical amplifiers of tumor cell receptor-mediated apoptosis
Authors: Mitchell Michael J. , Langer Robert 
Published: July 2016

Abstract
Introduction: It has become evident that tumor cells are responsive to mechanical forces in vivo, and prove critical to tumor cell proliferation and death. Recent work has shown that tumor cells exposed to fluid shear forces increase receptor-mediated signaling. We hypothesized that biocompatible, polymeric particles conjugated to the tumor cell surface act as mechanical amplifiers in presence of fluid shear forces to increase mechanotransduction, and can be exploited to increase the efficacy of therapeutic ligands.
Methods: Polymeric particles (size:100 nm-1 μm) were conjugated to free amines on tumor cells via NHS cross linker chemistry. Particles bound to tumor cells were assessed using flow cytometry, brightfield, and confocal fluorescence microscopy. A cone-and-plate viscometer was used to apply a fluid shear force (2.0 dyn/cm⁁2) to tumor cell suspensions and to amplify the force exerted by polymeric particles on tumor cells. Tumor cells (COLO 205, PC-3) were treated with 0.1 μg/mL of a TNF-related apoptosis-inducing ligand (TRAIL) to assess amplified mechanotransduction and receptor-mediated apoptosis in the presence of polymeric particles. An annexin-V apoptosis assay was used to characterize the mode of cell death. Caspase colorimetric assays and inhibitors (Z-VAD-FMK) were utilized to assess caspase-dependence in the mechanotransduction response. Tumor cells were injected into C57/BL6 via tail vein to assess amplification of TRAIL apoptosis in vivo.
Results and Discussion: NHS crosslinker chemistry was successfully used to conjugate polymeric particles to the tumor cell surface. In the presence of fluid shear forces, it was found that polymeric particles act to mechanical amplify tumor cell mechanotransduction, as evidenced by increased receptor-mediated apoptosis and decreased tumor cell viability in the presence of the therapeutic ligand TRAIL. Additionally, amplification of TRAIL-mediated apoptosis was increased with particles of increasing size, demonstrating that increasing the force exerted on the cell surface with larger particles amplified the therapeutic response. Annexin-V apoptosis assays showed the addition of conjugated polymeric particles to the cell surfaces nearly doubled tumor cell apoptosis in the presence of TRAIL under shear forces, and inhibition assays revealed the response to be caspase-dependent apoptosis. Polymeric particles amplified
TRAIL-mediated tumor cell killing in mice, and reduced both circulating tumor cells in blood and overall tumor cell burden in vivo by over 90%.
Conclusions: These data demonstrate that polymeric particles, both degradable and non-degradable, act as mechanical amplifiers of tumor mechanotransduction in the presence of shear forces in vitro and in vivo, and are exploited to increase therapeutic efficacy. Clinically, this approach shows that increased mechanical force applied to target tumor cells can increase sensitivity to therapeutic ligands.
Citation Format: Michael J. Mitchell, Robert Langer. Polymeric mechanical amplifiers of tumor cell receptor-mediated apoptosis. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 3901.