Blood vessel hyperpermeability and pathophysiology in human tumour xenograft models of breast cancer: a comparison of ectopic and orthotopic tumours

Abstract

BackgroundHuman tumour xenografts in immune compromised mice are widely used as cancer models because they are easy to reproduce and simple to use in a variety of pre-clinical assessments. Developments in nanomedicine have led to the use of tumour xenografts in testing nanoscale delivery devices, such as nanoparticles and polymer-drug conjugates, for targeting and efficacy via the enhanced permeability and retention (EPR) effect. For these results to be meaningful, the hyperpermeable vasculature and reduced lymphatic drainage associated with tumour pathophysiology must be replicated in the model. In pre-clinical breast cancer xenograft models, cells are commonly introduced via injection either orthotopically (mammary fat pad, MFP) or ectopically (subcutaneous, SC), and the organ environment experienced by the tumour cells has been shown to influence their behaviour.MethodsTo evaluate xenograft models of breast cancer in the context of EPR, both orthotopic MFP and ectopic SC injections of MDA-MB-231-H2N cells were given to NOD scid gamma (NSG) mice. Animals with matched tumours in two size categories were tested by injection of a high molecular weight dextran as a model nanocarrier. Tumours were collected and sectioned to assess dextran accumulation compared to liver tissue as a positive control. To understand the cellular basis of these observations, tumour sections were also immunostained for endothelial cells, basement membranes, pericytes, and lymphatic vessels.ResultsSC tumours required longer development times to become size matched to MFP tumours, and also presented wide size variability and ulcerated skin lesions 6 weeks after cell injection. The 3 week MFP tumour model demonstrated greater dextran accumulation than the size matched 5 week SC tumour model (for P < 0.10). Immunostaining revealed greater vascular density and thinner basement membranes in the MFP tumour model 3 weeks after cell injection. Both the MFP and SC tumours showed evidence of insufficient lymphatic drainage, as many fluid-filled and collagen IV-lined spaces were observed, which likely contain excess interstitial fluid.ConclusionsDextran accumulation and immunostaining results suggest that small MFP tumours best replicate the vascular permeability required to observe the EPR effect in vivo. A more predictable growth profile and the absence of ulcerated skin lesions further point to the MFP model as a strong choice for long term treatment studies that initiate after a target tumour size has been reached.

Patterns of Vasculature in Mouse Models of Lung Cancer Are Dependent on Location

“…Tumor vascular permeability as well as the lack of functional lymphatic vessels influences angiogenesis, tumor growth and metastasis, and drug delivery [40–42]. Studies from Ho et al demonstrated that tumors grown orthotopically in the mammary fad pad exhibit a higher vascular size and density and thinner basement membranes compared to subcutaneously injected ones [17]. Similarly, prostate tumors have increased vascular density, vessel permeability, oxygenation, and VEGF expression when grown orthotopically as compared to in the subcutis [43].…”

“…Differences in vascular transport have been observed when comparing different tumor models, grown either orthotopically or ectopically. However there remains significant controversy on this topic, and while some studies have observed reduced transvascular transport of large macromolecules when tumors are grown orthotopically in the cranial microenvironment compared to their ectopic subcutis-implanted counterparts [15], higher vascular permeability and higher accumulation of nanocarriers has been observed when tumors were grown orthotopically in the liver and breast compared to their ectopic subcutaneous counterparts [16, 17]. Other discrepancies, such as growth rate, metastatic potential, and efficacy of treatment, have also been demonstrated across different tumor models.…”

The effect of chemotherapeutic agents on tumor vasculature in subcutaneous and orthotopic human tumor xenografts

“…A study by Ho et al . showed higher vascular density in orthotopic breast tumors compared to subcutaneous tumors of similar size [28], but the CD31 endothelial marker was utilized in their study, which makes it difficult to ascertain whether there was a similar difference in functional vasculature. Our study utilizes the perfusion marker DiOC7 in addition to CD31 to evaluate changes in the functional blood vessels, and highlights the importance of quantifying both total and functional vasculature.…”

Efficient intrahepatic tumor generation by cell sheet transplantation to fabricate orthotopic hepatocarcinoma‐bearing model mice for drug testing

“…Although antitumor activity against subcutaneous tumors is simple to evaluate by measuring the volume changes of tumors on the subcutis, subcutaneous and orthotopic tumors exhibit different pharmaceutical response . In addition, recent studies have revealed that ectopic and orthotopic tumors possess considerably different characters (e.g., tumor microenvironment and gene expression) . In particular, tumor microenvironments strongly affect tumor generation and drug responses .…”