Stretching inhibits tumor growth in MMTV-PYMT via a direct mechanical effect

Background: Tumor-associated architecture and emerging mechanical properties (forces, pressure, tension, stiffness) affect the growth and invasiveness of cancer cells. Collagen fibers aligned perpendicular to the boundaries of tumors promote local tumor invasiveness in mouse mammary tumor models and are associated with a poor prognosis in human breast cancer. Our previous study revealed that daily gentle stretching (~25% strain) for 10 min reduced the growth of P53/PTEN-/- orthotopic mouse mammary tumors by 50%.

Results: In this study, we further investigated the mechanism of stretching in a more aggressive MMTV-PYMT (mammary tumor virus-polyomavirus middle T antigen) tumor model in vivo and in vitro and analyzed its impact on collagen reorganization at both the tumor-stromal interface and the tumor microenvironment composition at single cell level. Stretching reduced the average tumor size by 30–50% in orthotopic (Active and Passive Stretch) and transgenic (Passive Stretch) models. In the orthotopic model, the ratio of parallel vs. perpendicular collagen fibers relative to the tumor boundary, was greater in the Stretch group compared with the No Stretch group. Finally, stretching reduced the cell migration of collagen-embedded tumor spheroids in vitro.

Conclusions: These results show that short-duration, moderate-amplitude stretching reduces tumor growth in several different animal models.  We also provide evidence that this beneficial effect may be a direct mechanical effect on local matrix properties and tumor cell invasiveness.

Methods
Berrueta et al tumors collagen signature Data  092624: data was collected from images taken by confocal second harmonic generation microscopy and analyzed using the CurveAlign sofware

Berrueta et al Orthotopic active stretch Master file  72623: data was collected by weekly measurements of the tumor using caliper and 3D ultrasound and procceced with the VevoLab sofware  

Berrueta et al Orthotopic model Passive stretch master file 61223: data was collected by weekly measurements of the tumor using caliper and 3D ultrasound and procceced with the VevoLab sofware 

Berrueta et al  qPCR data from Orthotopic active stretch Master file _Batch 16-18   062323: data was collected by homogenizing the tumors after euthanasia, then extracting RNA and running qPCR for gene expression 

Berrueta et al  qPCR Orthotopic passive stretch Master file Batch   071823: data was collected by homogenizing the tumors after euthanasia, then extracting RNA and running qPCR for gene expression 

Berrueta et al  Transgenics passive stretch Master file: data was collected weekly using 3D ultrasound and analyzed with the VevoLab software 

Berrueta et al  Transgenics active stretch Master file: data was collected weekly using 3D ultrasound and analyzed with the VevoLab software 

Berrueta et al _Spheroids Crown area at day 3: data was obtained measuring the area of cell migration surrounding each spheroid using the ImageJ software, creating a binary image by applying thresholding through: Image/Adjust/Threshold

Berrueta et al, Spheroids distance Travelled at day 3_all data: Data was obtained from photograph taken from the spheroids and then measuring the distance between the spheroid boundery and the location of the cell using ImajeJ software The calculation of the maximum distance traveled by migratory cells involved measuring the distance from the edge of the spheroid to the furthest point reached by the migratory cells (the sixteen cells that were at the furthest distance from the edge of the spheroid were measured in all spheroids)

Berrueta et el,  Spheroids single cell migration at day 3 This data was obtained by counting the total number of individual cells that migrated away from the spheroid