An In Vitro System to Study Tumor Dormancy and the Switch to Metastatic Growth
Summary
A modified 3-D in vitro system is presented in which growth characteristics of several tumor cell lines in reconstituted basement membrane correlate with the dormant or proliferative behavior of the tumor cells at a metastatic secondary site in vivo.
Abstract
Recurrence of breast cancer often follows a long latent period in which there are no signs of cancer, and metastases may not become clinically apparent until many years after removal of the primary tumor and adjuvant therapy. A likely explanation of this phenomenon is that tumor cells have seeded metastatic sites, are resistant to conventional therapies, and remain dormant for long periods of time 1-4.
The existence of dormant cancer cells at secondary sites has been described previously as quiescent solitary cells that neither proliferate nor undergo apoptosis 5-7. Moreover, these solitary cells has been shown to disseminate from the primary tumor at an early stage of disease progression 8-10 and reside growth-arrested in the patients’ bone marrow, blood and lymph nodes 1,4,11. Therefore, understanding mechanisms that regulate dormancy or the switch to a proliferative state is critical for discovering novel targets and interventions to prevent disease recurrence. However, unraveling the mechanisms regulating the switch from tumor dormancy to metastatic growth has been hampered by the lack of available model systems.
in vivo and ex vivo model systems to study metastatic progression of tumor cells have been described previously 1,12-14. However these model systems have not provided in real time and in a high throughput manner mechanistic insights into what triggers the emergence of solitary dormant tumor cells to proliferate as metastatic disease. We have recently developed a 3D in vitro system to model the in vivo growth characteristics of cells that exhibit either dormant (D2.OR, MCF7, K7M2-AS.46) or proliferative (D2A1, MDA-MB-231, K7M2) metastatic behavior in vivo . We demonstrated that tumor cells that exhibit dormancy in vivo at a metastatic site remain quiescent when cultured in a 3-dimension (3D) basement membrane extract (BME), whereas cells highly metastatic in vivo readily proliferate in 3D culture after variable, but relatively short periods of quiescence. Importantly by utilizing the 3D in vitro model system we demonstrated for the first time that the ECM composition plays an important role in regulating whether dormant tumor cells will switch to a proliferative state and have confirmed this in in vivo studies15-17. Hence, the model system described in this report provides an in vitro method to model tumor dormancy and study the transition to proliferative growth induced by the microenvironment.
Protocol
Discussion
The underlying mechanisms that maintain disseminated tumor cells in a dormant state or result in their transition to metastatic growth remain largely unknown. This phenomenon has been extremely difficult to study in human patients 4,12 and few preclinical models have been developed to address this issue. Nevertheless, some in vivo and ex-vivo model systems for tumor dormancy have been characterized (reviewed in 1,12). However, the in vivo models for tumor dormancy can p…
Disclosures
The authors have nothing to disclose.
Acknowledgements
This research was supported in part by the Intramural Research Program of the National Cancer Institute.
Materials
| Name of the reagent | Company | Catalogue number | Comments |
|---|---|---|---|
| DMEM high glucose | Invitrogen | 11965-118 | |
| DMEM low glucose | Invitrogen | 11885-092 | |
| Fetal bovine serum (FBS) | Invitrogen | 10091-148 | |
| Growth factor-reduced 3-D Cultrex Basement Membrane Extract | Trevigen Inc. | Protein concentration between 14-15mg/ml | |
| D2.0R and D2A1 cell lines | 5,19 | ||
| K7M2 and K7M2AS1.46 cells | 20 | ||
| MCF-7 and MDA-MB-231 breast cancer cells | ATCC | ||
| An 8 chamber glass slide system | (Lab -TEK, Thermo scientific) | 177402 | |
| Cell Titer 96 AQueous One Solution cell proliferation assay kit | Promega | G3580 | |
| VECTASHIELD mounting medium with DAPI | Vector Laboratories Inc. | H-1200 | |
| Normal donkey serum | Jackson ImmunoResearch | 017-000-121 | |
| Elisa Plate Reader | Bio-Tec | Record 490nm | |
| Confocal microscope | Zeiss-LSM-510 | Magnification x63 |
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