Intraductal Delivery to the Rabbit Mammary Gland

Summary

Here, we describe a technique for the localized delivery of reagents to the rabbit mammary gland via an intraductal injection. In addition, we describe a protocol for visualization and the confirmation of delivery by high-resolution ultrasound imaging of contrast agents.

Abstract

Localized intraductal treatments for breast cancer offer potential advantages, including efficient delivery to the tumor and reduced systemic toxicity and adverse effects^{1,2,3,4,5,6,7}. However, several challenges remain before these treatments can be applied more widely. The development and validation of intraductal therapeutics in an appropriate animal model facilitate the development of intraductal therapeutic strategies for patients. While the mouse mammary gland has been widely used as a model system of mammary development and tumorigenesis, the anatomy is distinct from the human gland. A larger animal model, such as the rabbit, may serve as a better model for mammary gland structure and intraductal therapeutic development. In contrast to mice, in which ten ductal trees are spatially distributed along the body axis, each terminating in a separate teat, the rabbit mammary gland more closely resembles the human gland, with multiple overlapping ductal systems that exit through separate openings in one teat. Here, we present minimally invasive methods for the delivery of reagents directly into the rabbit mammary duct and for visualization of the delivery itself with high-resolution ultrasound imaging.

Introduction

The intraductal delivery of therapeutic agents has been studied in rodent models and in early stage human trials^{3,4,5,6,11,12}. A recent Phase I study demonstrated the safety and feasibility of intraductal carboplatin or intraductal pegylated liposomal doxorubicin in women awaiting mastectomy for the treatment of invasive cancer².

Previous protocols for intraductal delivery have been developed for mouse and rat mammary gla....

Protocol

Procedures using animal subjects have been approved by the Institutional Animal Care and Use Committee of the University of Texas at Austin.

1. Preoperative Preparation

1. Record the body weight of each rabbit. As with all preclinical studies, monitor animal weights regularly to assess potential toxicity.
2. Prior to anesthetizing the rabbit, fill a 50 mL conical tube with commercially available ultrasound gel and spin at 500 x g for 30 s; there should be no visible bubbles in the gel upon completion of the centrifugation.
3. Administer glycopyrrolate subcutaneously at a dose of 0.1 mg/kg and acepromazine intramuscula....

Results

Here, we show that the intraductal delivery of contrast reagents to the mammary ducts of a rabbit can be achieved without trauma to the tissue (Figure 2). In rabbits, four separate ductal systems converge at one teat and thus may be accessed and imaged individually using this method. Individual ductal openings are easily visualized; note the arrowhead marking a second ductal opening adjacent to the cannulated duct in Figure 2B.

Discussion

This method of intraductal delivery to the rabbit mammary gland may be used for ultrasound contrast reagents and many other aqueous solutions, including vital dyes and therapeutics. Previous studies have demonstrated the intraductal delivery of hormones^17,18,19. In rodent models, the intraductal delivery of nucleic acids⁸, chemotherapeutics^6,7, an.......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
MicroMarker non-targeted contrast reagent	VisualSonics	VS-11694
Luer Lock 1 mL Syringes	BD	309628
Glycopyrrolate 0.2 mg/mL	Wedgewood Compounding Pharmacy	GLYCOP-INJ013VC	6 month shelf life, supply may be limited.
Atropine Sulfate 0.5 mg/mL	Animal Health International	15320764	If glycopyrrolate is unavailable. Not to be combined with glycopyrrolate.
Ketamine HCL 100 mg/mL	Animal Health International	21250699	http://www.animalhealthinternational.com/
Acepromazine 10 mg/mL	Animal Health International	17640541
Xylazine 20 mg/mL	Animal Health International	20101547
Yohimbine 0.2 mg/mL	Animal Health International	14588965
Hair Removing Cream	Veet		Sensitive skin solution. Available through local retailers.
Blunt tip infusion needles	Sai Infusion Technology	B14-50	http://www.sai-infusion.com/collections/blunt-needles
Veterinary Pulse Oximeter	EdanUSA	VE-H100B	http://www.edanusa.com/Product/VE-H100B-Veterinary-Pulse-Oximeter.html
Warm Water Pump	Gaymar	TP700
Warm Water Blanket	Animal Health International	21232696	Maxi-Therm Lite Warming Pads
Ultrasound system	VisualSonics	Vevo 2100