Increased stiffness in the extracellular matrix (ECM) contributes to tumor progression and metastasis. Therefore, stromal modulating therapies and accompanying biomarkers are being developed to target ECM stiffness. Magnetic resonance (MR) elastography can noninvasively and quantitatively map the viscoelastic properties of tumors in vivo and thus has clear clinical applications. Herein, we used MR elastography, coupled with computational histopathology, to interrogate the contribution of collagen to the tumor biomechanical phenotype and to evaluate its sensitivity to collagenase-induced stromal modulation. Elasticity (G d) and viscosity (G l) were significantly greater for orthotopic BT-474 (G d ¼ 5.9 AE 0.2 kPa, G l ¼ 4.7 AE 0.2 kPa, n ¼ 7) and luc-MDA-MB-231-LM2-4 (G d ¼ 7.9 AE 0.4 kPa, G l ¼ 6.0 AE 0.2 kPa, n ¼ 6) breast cancer xenografts, and luc-PANC1 (G d ¼ 6.9 AE 0.3 kPa, G l ¼ 6.2 AE 0.2 kPa, n ¼ 7) pancreatic cancer xenografts, compared with tumors associated with the nervous system, including GTML/Trp53 KI/KI medulloblastoma (G d ¼ 3.5 AE 0.2 kPa, G l ¼ 2.3 AE 0.2 kPa, n ¼ 7), orthotopic luc-D-212-MG (G d ¼ 3.5 AE 0.2 kPa, G l ¼ 2.3 AE 0.2 kPa, n ¼ 7), luc-RG2 (G d ¼ 3.5 AE 0.2 kPa, G l ¼ 2.3 AE 0.2 kPa, n ¼ 5), and luc-U-87-MG (G d ¼ 3.5 AE 0.2 kPa, G l ¼ 2.3 AE 0.2 kPa, n ¼ 8) glioblastoma xenografts, intracranially propagated luc-MDA-MB-231-LM2-4 (G d ¼ 3.7 AE 0.2 kPa, G l ¼ 2.2 AE 0.1 kPa, n ¼ 7) breast cancer xenografts, and Th-MYCN neuroblastomas (G d ¼ 3.5 AE 0.2 kPa, G l ¼ 2.3 AE 0.2 kPa, n ¼ 5). Positive correlations between both elasticity (r ¼ 0.72, P < 0.0001) and viscosity (r ¼ 0.78, P < 0.0001) were determined with collagen fraction, but not with cellular or vascular density. Treatment with collagenase significantly reduced G d (P ¼ 0.002) and G l (P ¼ 0.0006) in orthotopic breast tumors. Texture analysis of extracted images of picrosirius red staining revealed significant negative correlations of entropy with G d (r ¼ À0.69, P < 0.0001) and G l (r ¼ À0.76, P < 0.0001), and positive correlations of fractal dimension with G d (r ¼ 0.75, P < 0.0001) and G l (r ¼ 0.78, P < 0.0001). MR elastography can thus provide sensitive imaging biomarkers of tumor collagen deposition and its therapeutic modulation. Significance: MR elastography enables noninvasive detection of tumor stiffness and will aid in the development of ECM-targeting therapies.

Hyaluronan (HA) is a key component of the dense extracellular matrix in breast cancer, and its accumulation is associated with poor prognosis and metastasis. Pegvorhyaluronidase alfa (PEGPH20) enzymatically degrades HA and can enhance drug delivery and treatment response in preclinical tumour models. Clinical development of stromal‐targeted therapies would be accelerated by imaging biomarkers that inform on therapeutic efficacy in vivo. Here, PEGPH20 response was assessed by multiparametric magnetic resonance imaging (MRI) in three orthotopic breast tumour models. Treatment of 4T1/HAS3 tumours, the model with the highest HA accumulation, reduced T1 and T2 relaxation times and the apparent diffusion coefficient (ADC), and increased the magnetisation transfer ratio, consistent with lower tissue water content and collapse of the extracellular space. The transverse relaxation rate R2* increased, consistent with greater erythrocyte accessibility following vascular decompression. Treatment of MDA‐MB‐231 LM2‐4 tumours reduced ADC and dramatically increased tumour viscoelasticity measured by MR elastography. Correlation matrix analyses of data from all models identified ADC as having the strongest correlation with HA accumulation, suggesting that ADC is the most sensitive imaging biomarker of tumour response to PEGPH20.

The impact of HA on tumour characteristics measured by MRI/E is not fully understood. We evaluated relationships between MRI biomarkers and histology in saline (HA present) and PEGPH20 treated (HA absent) breast tumours. ADC had the strongest association with HA, reaffirming that ADC is the most sensitive biomarker of tumour response to PEGPH20. MTR negatively correlated with HA, likely due to a HA-mediated dilution of MT-inducing components including collagen. MRE-derived elasticity (Gd) did not directly correlate with HA, however, HA degradation reduced the contribution of collagen to tumour viscoelasticity and may shift the sensitivity of Gd to the cellular compartment.

<div>Abstract<p>Increased stiffness in the extracellular matrix (ECM) contributes to tumor progression and metastasis. Therefore, stromal modulating therapies and accompanying biomarkers are being developed to target ECM stiffness. Magnetic resonance (MR) elastography can noninvasively and quantitatively map the viscoelastic properties of tumors <i>in vivo</i> and thus has clear clinical applications. Herein, we used MR elastography, coupled with computational histopathology, to interrogate the contribution of collagen to the tumor biomechanical phenotype and to evaluate its sensitivity to collagenase-induced stromal modulation. Elasticity (<i>G</i>_d) and viscosity (<i>G</i>_l) were significantly greater for orthotopic BT-474 (<i>G</i>_d = 5.9 ± 0.2 kPa, <i>G</i>_l = 4.7 ± 0.2 kPa, <i>n</i> = 7) and luc-MDA-MB-231-LM2-4 (<i>G</i>_d = 7.9 ± 0.4 kPa, <i>G</i>_l = 6.0 ± 0.2 kPa, <i>n</i> = 6) breast cancer xenografts, and luc-PANC1 (<i>G</i>_d = 6.9 ± 0.3 kPa, <i>G</i>_l = 6.2 ± 0.2 kPa, <i>n</i> = 7) pancreatic cancer xenografts, compared with tumors associated with the nervous system, including GTML/<i>Trp53^KI/KI</i> medulloblastoma (<i>G</i>_d = 3.5 ± 0.2 kPa, <i>G</i>_l = 2.3 ± 0.2 kPa, <i>n</i> = 7), orthotopic luc-D-212-MG (<i>G</i>_d = 3.5 ± 0.2 kPa, <i>G</i>_l = 2.3 ± 0.2 kPa, <i>n</i> = 7), luc-RG2 (<i>G</i>_d = 3.5 ± 0.2 kPa, <i>G</i>_l = 2.3 ± 0.2 kPa, <i>n</i> = 5), and luc-U-87-MG (<i>G</i>_d = 3.5 ± 0.2 kPa, <i>G</i>_l = 2.3 ± 0.2 kPa, <i>n</i> = 8) glioblastoma xenografts, intracranially propagated luc-MDA-MB-231-LM2-4 (<i>G</i>_d = 3.7 ± 0.2 kPa, <i>G</i>_l = 2.2 ± 0.1 kPa, <i>n</i> = 7) breast cancer xenografts, and Th-<i>MYCN</i> neuroblastomas (<i>G</i>_d = 3.5 ± 0.2 kPa, <i>G</i>_l = 2.3 ± 0.2 kPa, <i>n</i> = 5). Positive correlations between both elasticity (<i>r</i> = 0.72, <i>P</i> < 0.0001) and viscosity (<i>r</i> = 0.78, <i>P</i> < 0.0001) were determined with collagen fraction, but not with cellular or vascular density. Treatment with collagenase significantly reduced <i>G</i>_d (<i>P</i> = 0.002) and <i>G</i>_l (<i>P</i> = 0.0006) in orthotopic breast tumors. Texture analysis of extracted images of picrosirius red staining revealed significant negative correlations of entropy with <i>G</i>_d (<i>r</i> = −0.69, <i>P</i> < 0.0001) and <i>G</i>_l (<i>r</i> = −0.76, <i>P</i> < 0.0001), and positive correlations of fractal dimension with <i>G</i>_d (<i>r</i> = 0.75, <i>P</i> < 0.0001) and <i>G</i>_l (<i>r</i> = 0.78, <i>P</i> < 0.0001). MR elastography can thus provide sensitive imaging biomarkers of tumor collagen deposition and its therapeutic modulation.</p>Significance:<p>MR elastography enables noninvasive detection of tumor stiffness and will aid in the development of ECM-targeting therapies.</p></div>

Radiotherapy is widely used to treat cancer. In this study, we used MR elastography to evaluate early tumour response to radiation therapy. A significant increase in stiffness |G*| and elasticity Gd were determined 3 days after orthotopic 4T1 breast tumours were irradiated with a single 8Gy dose, compared to untreated control tumour-bearing mice. The increase in tumour stiffness was associated with an increased macromolecule pool measured by magnetisation transfer, and increased collagen deposition observed histologically.