Generation of Prostate Cancer Patient Derived Xenograft Models from Circulating Tumor Cells

Summary

This manuscript details a method used to generate prostate cancer patient derived xenografts (PDXs) from circulating tumor cells (CTCs). The generation of PDX models from CTCs provides an alternative experimental model to study prostate cancer; the most commonly diagnosed tumor and a frequent cause of death from cancer in men.

Abstract

Patient derived xenograft (PDX) models are gaining popularity in cancer research and are used for preclinical drug evaluation, biomarker identification, biologic studies, and personalized medicine strategies. Circulating tumor cells (CTC) play a critical role in tumor metastasis and have been isolated from patients with several tumor types. Recently, CTCs have been used to generate PDX experimental models of breast and prostate cancer. This manuscript details the method for the generation of prostate cancer PDX models from CTCs developed by our group. Advantages of this method over conventional PDX models include independence from surgical sample collection and generating experimental models at various disease stages. Density gradient centrifugation followed by red blood cell lysis and flow cytometry depletion of CD45 positive mononuclear cells is used to enrich CTCs from peripheral blood samples collected from patients with metastatic disease. The CTCs are then injected into immunocompromised mice; subsequently generated xenografts can be used for functional studies or harvested for molecular characterization. The primary limitation of this method is the negative selection method used for CTC enrichment. Despite this limitation, the generation of PDX models from CTCs provides a novel experimental model to be applied to prostate cancer research.

Introduction

Patient derived xenografts are increasingly popular experimental models used for cancer research. They can be used for characterization of biomarkers and biological pathways, pre-clinical evaluation of drug efficacy, and creation of avatars for personalized cancer therapies ^1,2. Previously, other research groups have developed PDX models either by implanting or injecting single tumor cell suspensions or whole tumor explants into immunocompromised mice ¹. These PDX models require surgical collection of fresh solid tumor, malignant ascites or pleural effusions from a patient undergoing a surgical procedure which is both costly and ....

Protocol

This protocol has been conducted at our institution with approval from the institutional research ethics board and is in compliance with all institutional, national, and international guidelines for human welfare.

1. Collection of Peripheral Blood from Patients with Advanced Prostate Cancer

Note: Select patients with metastatic prostate cancer. Obtain written patient consent and record clinical characteristics of patients, including age at isolation and previous chemotherapy and hormonal treatments. Patients with metastatic disease will potentially have highest concentration of CTCs in peripheral blood.

Results

This protocol will lead to the generation of PDX models from isolated CD45 negative prostate cancer CTCs. Based on the negative selection method used in our protocol it is necessary to exclude dead cells using DAPI stain. The percentage of CD45 negative cells detected by flow cytometry is variable and depends on the tumor burden of the patient (Figure 1A). Immunofluorescent staining of unsorted cells using CD45 and DAPI (to identify cell nuclei) reveals CD45 negative cells, as indicated by the white arro.......

Discussion

This manuscript describes a method for the generation of prostate cancer PDX models from CTCs. The use of CTCs for the generation of PDX models has several potential important advantages when compared to existing methods. First, accessible collection of CTCs from peripheral blood enables the generation of experimental models from the same patient at different disease stages. Second, blood collection represents a safer and inexpensive method to isolate tumor cells when compared to existing methodologies t.......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
Roswell Park Memorial Institute (RPMI) 1640	Gibco Life Technologies	11875-093
Fetal Bovine Serum (FBS)	Gibco Life Technologies	10437-028
Penicillin Streptomycin	Gibco Life Technologies	15140-122
Phosphate Buffered Saline (PBS)	Corning Cell Gro	21-031-CM
35 µm Cell Strainer	BD Falcon	352340
50 ml polystyrene conical tube	Crystalgen	23-2263
Red blood cell lysing buffer	Sigma	R7757
DAPI	Invitrogen	d3571
Ficoll-Paque Plus	GE Healthcare	17-1440
12 mm x 75 mm Polystyrene tubes with cell strainer cap	BD Falcon	352235
BD Vacutainer Lavender Blood Collection Tubes with EDTA
BD Winged Blood Collection Set with Push Button Retract Needle 23 gauge
BD Vacutainer One Use Needle Holder
Disposable Latex Tourniquet
Latex or non-latex gloves
alcohol swabs
2 x 2 cotton gauze pads
Adhesive bandage
25 G needle
1 ml syringe