Isolation and Culture Expansion of Tumor-specific Endothelial Cells

Summary

We report a reliable method to isolate and culture primary tumor-specific endothelial cells from genetically engineered mouse models.

Abstract

Freshly isolated tumor-specific endothelial cells (TEC) can be used to explore molecular mechanisms of tumor angiogenesis and serve as an in vitro model for developing new angiogenesis inhibitors for cancer. However, long-term in vitro expansion of murine endothelial cells (EC) is challenging due to phenotypic drift in culture (endothelial-to-mesenchymal transition) and contamination with non-EC. This is especially true for TEC which are readily outcompeted by co-purified fibroblasts or tumor cells in culture. Here, a high fidelity isolation method that takes advantage of immunomagnetic enrichment coupled with colony selection and in vitro expansion is described. This approach generates pure EC fractions that are entirely free of contaminating stromal or tumor cells. It is also shown that lineage-traced Cdh5^cre:ZsGreen^l/s/l reporter mice, used with the protocol described herein, are a valuable tool to verify cell purity as the isolated EC colonies from these mice show durable and brilliant ZsGreen fluorescence in culture.

Introduction

Endothelial cells (EC) are essential during the development of solid tumors. From initiation of the angiogenic switch in dormant tumors to dissemination and seeding of metastases at distant sites, EC form the conduits that provide blood, oxygen, and nutrients to sustain tumor growth ¹. As recently suggested, EC also have perfusion-independent functions and form a niche that supports the growth of cancer stem cells and other tumor stromal cells ^2-5. Thus, highly purified tumor-specific EC (TEC) for in vitro culture allows for routine functional studies that will shed light on novel molecular mechanisms mediating tumor angiogenesis and cro....

Protocol

The following protocol is carried out according to guidelines established by the Department of Laboratory Animal Medicine at the University of North Carolina at Chapel Hill.

1. Prepare the Following Material and Reagents Before Starting

1. Prepare EC media by supplementing 400 ml low glucose (1 g/L D-glucose or LG) Dulbecco's Modified Eagle's medium (DMEM) with 50 ml heat-inactivated fetal bovine serum, 50 ml Nu-Serum IV, 5 ml antibiotic-antimycotic, and the hFGF, VEGF, hEGF, R3-IGF-1, and heparin components from the commercial kit.
2. Prepare 500 ml FACS buffer (0.5% BSA and 2 mM EDTA in PBS); filter through a ....

Results

EC represent only minor a fraction of the total cell population in most adult tissues ¹¹. It is therefore important to fully digest the harvested tissue into a single-cell suspension that ensures the maximal release of EC from extracellular matrix (ECM) and connective tissues. In our experience, CD31-mediated immunomagnetic selection only provides enriched but not pure EC fractions; therefore, another crucial step is the physical removal of co-purified non-EC and selection/expansion of EC colonies using clonin.......

Discussion

Due to the difficulties in obtaining pure primary TEC cultures, many in vitro studies substitute TEC with commercially available EC lines or primary EC such as human umbilical vein EC (HUVEC) ¹³. However, these EC populations from normal tissues may only serve as a proxy for TEC which differ markedly from their normal counterparts. For example, TEC are phenotypically and functionally abnormal in vivo and some of these abnormalities may be transmittable in vitro ^14-18. TEC .......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
Antibiotic-Antimycotic	Sigma-Aldrich	A5955
Dulbecco's Modified Eagle's medium (1 g/L D-glucose) (LG-DMEM)	Gibco	11885-084
EGM-2 Bullet Kit	Lonza	CC4176	Not all components used
Fetal bovine serum (Hyclone)	Thermo Scientific	SH30071.03	Heat inactivated at 56 °C for 30 min
Nu-Serum IV	Corning	CB-51004
Hank's Balanced Salt Solution (HBBS)	Gibco	14175-095
Phosphate-buffered saline (PBS)	Gibco	14190-144
FACS buffer			0.5 % BSA and 2 mM EDTA in PBS, filtered through a 0.22 μm filter
75% v/v ethanol for disinfection
Anti-PE microbeads	Miltenyi Biotech	130-048-801
Bovine serum albumin (BSA) fraction V, 7.5%	Gibco	15260-37
Cell freezing media (Bambanker)	Wako Chemicals	302-14681
Collagenase type II	Worthington Biochemical	LS004176	Make stock concentration 2 mg/ml in HBSS
Deoxyribonuclease I (DNase)	Worthington Biochemical	LS002004	Make stock concentration 1 mg/ml in PBS
Dil-Ac-LDL	Biomedical Technologies	BT-902
EDTA, 0.5M, pH 8.0	Cellgro	46-034-CL
Enzymatic cell detachment solution (Accutase)	Sigma-Aldrich	A6964-100ML
Gelatin, 2% in water, tissue culture grade	Sigma-Aldrich	G1393-100ML	Dilute in PBS to make 0.5% gelatin solution
Mouse FcR Blocking Reagent	Miltenyi Biotech	130-092-575
Neutral protease (Dispase)	Worthington Biochemical	LS02104	Make stock concentration 2.5 U/ml in HBSS
PE-rat anti-mouse CD31 antibody	BD Pharmingen	553373
RBC lysis buffer (BD Pharm Lyse)	BD Pharmingen	555899
Sterile water
Trypan blue, 0.4 %	Life Technologies	15250-061
10 mm tissue culture dishes	Corning
15 ml conical tubes (sterile)	Corning
50 ml conical tubes (sterile)	Corning
6-well tissue culture plates	Corning
Tissue-dissociator tubes (gentleMACS) C tubes)	Miltenyi Biotech	130-093-237
Cell Separator  (MidiMACS)	Miltenyi Biotech	130-042-302
Cell strainer 100 μm	Corning	352360
Cloning rings (assorted sizes)	Bel-Art Products	378470000
Cryotubes	Thermo Scientific
Dissecting board			Sterilize or disinfect with 75% v/v ethanol before use
Dissecting forceps and scissors			Sterilize before use
Dissecting pins 2"			Sterilize before use
FACS tubes with 35 μm filter cap	Corning	352235
Filter cup (Stericup, 0.22 μm)	Millipore	SCGPU05RE
Fine-tip marker
Hemocytometer
LS Columns	Miltenyi Biotech	130-042-401
Magnetic Multistand	Miltenyi Biotech	130-042-303
Tissue adhesive (Vetbond)	3M	1469SB
Centrifuge	Eppendorf	5810R	Or a centrifuge with similar capacity for 15 ml and 50 ml conical tube centrifugation
Tissue culture hood
Tissue dissociator (gentleMACS)	Miltenyi Biotech	130-093-235	Preset program "m_impTumor_01" used for tissue dissociation
Liquid nitrogen freezer
Microplate or rotary shaker
Phase contrast light microscope