Cancer sticking to bone: Analyzing the adhesion between mesenchymal stem cells and multiple myeloma both on microscopic and molecular scale

Introduction:

Multiple myeloma is the cancerous form of plasma cells that, like breast- or prostate cancer, are highly malignant and spread towards different locations within the skeleton. There, they take control of the bone microenvironment according to their needs, perturbing bone function, causing lytic lesions. However, since myeloma originate from bone, their interaction with the bone marrow, especially with mesenchymal stem cells (MSCs), remains unique.

Materials and methods:

We are working with the IL-6 dependent myeloma cell line INA-6 that adheres to human-derived mesenchymal stem cells, when co-cultured in vitro. This is tested using physical or chemical washing assays (Trypsin or EDTA). Time-lapse digital holography microscopy resolves the membrane structures of the binding interface and identifies morphologies characteristic for apoptosis. Further insight is gained by Bioluminescent Viability/Apoptosis assays based on ATP/Caspase3,7.

Results:

The interaction between myeloma and MSCs is dynamic and has many facetts. This includes short-term interactions with extensive filopodia-like structures, but also irreversible interactions that can only be severed chemically. Interestingly, myeloma cells surrounded by apparently apoptotic bodies adhere to MSCs, which is independent of co-culturing conditions.

Discussion:

This study shows that the adhesion of Myeloma to the bone marrow has many facetts. We use advanced microscopy methods (DHM) coupled with washing experiments, showing dependecies on both time and adhesion strength. Further analysis on molecular scale is needed. For this purpose, single cell picking using fluid atomic force microscopy and single cell RNA-seq is planned. This will identify individual pre-disposing factors, which is necessary due to the heterogenous nature of in vitro isolated MSCs.

Key words:

Cancer, Myeloma, Cell-Cell Adhesion, Digital Holography Microscopy