Culture and Imaging of Ex Vivo Organotypic Pseudomyxoma Peritonei Tumor Slices from Resected Human Tumor Specimens

Summary

We describe a protocol for the production, culture, and visualization of human cancers, which have metastasized to the peritoneal surfaces. Resected tumor specimens are cut using a vibratome and cultured on permeable inserts for increased oxygenation and viability, followed by imaging and downstream analyses using confocal microscopy and flow cytometry.

Abstract

Pseudomyxoma peritonei (PMP) is a rare condition that results from the dissemination of a mucinous primary tumor and the resultant accumulation of mucin-secreting tumor cells in the peritoneal cavity. PMP can arise from various types of cancers, including appendiceal, ovarian, and colorectal, though appendiceal neoplasms are by far the most common etiology. PMP is challenging to study due to its (1) rarity, (2) limited murine models, and (3) mucinous, acellular histology. The method presented here allows real-time visualization and interrogation of these tumor types using patient-derived ex vivo organotypic slices in a preparation where the tumor microenvironment (TME) remains intact. In this protocol, we first describe the preparation of tumor slices using a vibratome and subsequent long-term culture. Second, we describe confocal imaging of tumor slices and how to monitor functional readouts of viability, calcium imaging, and local proliferation. In short, slices are loaded with imaging dyes and are placed in an imaging chamber that can be mounted onto a confocal microscope. Time-lapse videos and confocal images are used to assess the initial viability and cellular functionality. This procedure also explores translational cellular movement, and paracrine signaling interactions in the TME. Lastly, we describe a dissociation protocol for tumor slices to be used for flow cytometry analysis. Quantitative flow cytometry analysis can be used for bench-to-bedside therapeutic testing to determine changes occurring within the immune landscape and epithelial cell content.

Introduction

Pseudomyxoma peritonei (PMP) is rare syndrome with an incidence rate of 1 per million people per year¹. Most PMP cases are caused by metastases from appendiceal neoplasms. Given that mice do not have a human-like appendix, modeling this type of cancer remains extremely challenging. While the primary disease is often curable by surgical resection, treatment options for metastatic disease are limited. Therefore, the rationale for developing this novel organotypic slice model is to study the pathobiology of PMP. To date, there are no appendiceal organoid models that can be perpetually cultured; however, a recent model was shown to be useful for th....

Protocol

The deidentification and acquisition of all tissues were performed under an IRB-approved protocol at the University of California, San Diego.

1. Preparation of human PMP tissues for tissue processing and culture

1. Transport of tumor tissues and microdissection
   1. Prepare the transport and culture media: complete 10% (v/v) Dulbecco's Modified Eagle Media (DMEM), 10% FBS, 2 mM L-Glutamine, 1% Penicillin/Streptomycin (Pen Strep).
   2. Upon tissue arrival and according to an institutional IRB-approved protocol, transfer PMP tumor tissues into 35 dishes with a 6 cm diameter containing complete DMEM.<....

Discussion

This manuscript describes a technique that can be used to culture, interrogate, and analyze human pseudomyxoma peritonei (PMP) tumor specimens. We have utilized numerous downstream functional assays to interrogate the tumor immune microenvironment and a platform for bench-to-bedside testing.

While the method is highly efficient in our hands, it will require some practice to cut tumor specimens using a vibratome. Namely, we encountered problems that were due to highly mucinous samples, as well .......

Materials

Name	Company	Catalog Number	Comments
1 M CaCl2 solution	Sigma	21115
1 M HEPES solution	Sigma	H0887
1 M MgCl2 solution	Sigma	M1028
100 micron filter	ThermoFisher	22-363-549
22 x 40 glass coverslips	Daiggerbrand	G15972H
3 M KCl solution	Sigma	60135
5 M NaCl solution	Sigma	S5150
ATPγS	Tocris	4080
Bovine Serum Albumin	Sigma	A2153
Calcein-AM	Invitrogen	L3224
CD11b	Biolegend	101228
CD206	Biolegend	321140
CD3	Biolegend	555333
CD4	Biolegend	357410
CD45	Biolegend	304006
CD8	Biolegend	344721
CellTiter-Glo	Promega	G9681
DMEM	Thermo Fisher	11965084
DPBS	Sigma Aldrich	D8537
FBS, heat inactivated	ThermoFisher	16140071
Fc-block	BD Biosciences	564220
Fluo-4	Thermo Fisher	F14201
Gentle Collagenase/Hyaluronidase	Stem Cell	7912
Imaging Chamber	Warner Instruments	RC-26
Imaging Chamber Platform	Warner Instruments	PH-1
LD-Blue	Biolegend	L23105
L-Glutamine 200 mM	ThermoFisher	25030081
LIVE/DEAD imaging dyes	Thermofisher	R37601
Nikon Ti microscope	Nikon		Includes: A1R hybrid confocal scanner including a high-resolution (4096x4096) scanner, LU4 four-laser AOTF unit with 405, 488, 561, and 647 lasers, Plan Apo 10 (NA 0.8), 20X (NA 0.9) dry objectives.
Peristaltic pump	Isamtec	ISM832C
Propidium Iodide	Invitrogen	L3224
Vacuum silicone grease	Sigma	Z273554-1EA