Orthotopic Transplantation of Breast Tumors as Preclinical Models for Breast Cancer

Summary

Patient-derived xenograft (PDX) models and transplantable genetically engineered mouse models faithfully recapitulate human disease and are preferred models for basic and translational breast cancer research. Here, a method is described to orthotopically transplant breast tumor fragments into the mammary fat pad to study tumor biology and evaluate drug response.

Abstract

Preclinical models that faithfully recapitulate tumor heterogeneity and therapeutic response are critical for translational breast cancer research. Immortalized cell lines are easy to grow and genetically modify to study molecular mechanisms, yet the selective pressure from cell culture often leads to genetic and epigenetic alterations over time. Patient-derived xenograft (PDX) models faithfully recapitulate the heterogeneity and drug response of human breast tumors. PDX models exhibit a relatively short latency after orthotopic transplantation that facilitates the investigation of breast tumor biology and drug response. The transplantable genetically engineered mouse models allow the study of breast tumor immunity. The current protocol describes the method to orthotopically transplant breast tumor fragments into the mammary fat pad followed by drug treatments. These preclinical models provide valuable approaches to investigate breast tumor biology, drug response, biomarker discovery and mechanisms of drug resistance.

Introduction

Most breast cancer deaths can be ascribed to recurrent disease that is resistant to conventional therapies^1,2. The inter- and intra-tumor heterogeneity of breast cancers contribute to therapy resistance. Moreover, tumor heterogeneity can impinge on accurate prognosis and challenge disease management^3,4. Identification of predictive biomarkers of response will significantly improve clinical outcomes of patients with breast cancer. Even though most breast cancer types are immunologically 'cold' tumors that are likely unresponsive to immunotherapy....

Protocol

All protocols using animals have been reviewed and approved by the Institutional Animal Care and Use Committee (IACUC). The tumor fragments, around 1−2 mm³ in size, are from viably frozen stock obtained from the Patient-Derived Xenograft and Advanced In Vivo Models Core at Baylor College of Medicine.

1. Preparation of cryopreserved mammary tumor fragments for transplantation

1. Transfer the cryovial with tumor fragments from liquid nitrogen to a 37 °C water bath.
2. Agitate the cryovial with an occasional gentle flick during thawing.
3. After the tissue is thawed, take the cryovial out of water b....

Results

Figure 1 shows the equipment (Figure 1A) and key procedures (Figure 1B) of orthotopic transplantation. Figure 2 shows characterization of a transplanted PDX tumor (MC1). Tumor fragments (1 mm³) of MC1 model were transplanted into the #4 fat pad of SCID/Beige mice. One month later, the average tumor size reached around 350 mm

Discussion

To reduce variations in tumor growth across animals, it is critical to cut the tumor tissue into 1 mm³ fragments for transplantation. Models that grow soft tissue are harder to work with and the tumor fragments need to be cut slightly larger (1−2 mm³). When placing the tissue into the mammary fat pad pocket take care not to split the tissue into multiple pieces as this will result in multiple small tumors or oddly shaped tumors.

In addition, use fresh tumor for tran.......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
1 mg/mL Buprenorphine-SR	ZooPharm (via BCM veterinarians)		Sterile
26G syringe	BD	148232E	Sterile
Betadine Scrub	Fisher	19-027132
Cotton Swabs	VWR International Laboratory	89031-272	Sterile
DMEM	Fisher	MT 10-013-CM	Sterile
Electric shaver	Oster	78005-050
Glass beads sterilizer (Germinator)	Roboz Surgical Store	DS-401
Lubricant ophthalmic ointment	Akorn Animal Health	17478-062-35
Micro Dissecting Forceps; Serrated, Angular (regular forceps)	Roboz Surgical Store	RS-5139	Sterile
Micro Dissecting Spring Scissors (fat pad cutter)	Roboz Surgical Store	RS-5658BT	Sterile
Micro Forceps (tissue placing forceps)	Roboz Surgical Store	RS-5069	Sterile
Petri Dish	Fisher	08-757- 100D	Sterile
Sterile drape	Sai Infusion Technology	PSS-SD1	Sterile
Surgery scissors	Roboz Surgical Store	RS-5960	Sterile
Tissue Forceps (claw forceps)	Roboz Surgical Store	RS-5158	Sterile
Wound clip applier	BD Autoclip Wound System	01-804	Sterile
Wound clip remover	BD Autoclip Wound System	01-804-15	Sterile
Wound clips	BD Autoclip Wound System	01-804-5	Sterile