Stem Cell Factor-Based Identification and Functional Properties of In Vitro-Selected Subpopulations of Malignant Mesothelioma Cells

Summary: Malignant mesothelioma (MM) is an aggressive neoplasm characterized by a poor patient survival rate, because of rapid tumor recurrence following first-line therapy. Cancer stem cells (CSCs) are assumed to be responsible for initiating tumorigenesis and driving relapse after therapeutic interventions. CSC-enriched MM cell subpopulations were identified by an OCT4/SOX2 reporter approach and were characterized by (1) increased resistance to cisplatin, (2) increased sensitivity toward the FAK inhibitor VS-6063 in vitro, and (3) a higher tumor-initiating capacity in vivo in orthotopic xenograft and allograft mouse models. Overexpression of NF2 (neurofibromatosis 2, merlin), a tumor suppressor often mutated or lost in MM, did not affect proliferation and viability of CSC-enriched MM populations but robustly decreased the viability of reporter-negative cells. In contrast, downregulation of calretinin strongly decreased proliferation and viability of both populations. In summary, we have enriched and characterized a small MM cell subpopulation that bears the expected CSC characteristics. : A cancer stem cell (CSC)-enriched malignant mesothelioma (MM) cell subpopulation was identified by an OCT4/SOX2 reporter approach. These EGFP-expressing cells showed an altered sensitivity toward chemotherapeutic drugs and a higher tumor-initiating capacity in vivo in orthotopic xenograft and allograft mouse models. While NF2 overexpression had no effect on proliferation/viability of CSC-enriched MM populations, they were susceptible to downregulation of calretinin. Keywords: mesothelioma, cancer stem cells, SOX2, OCT4, NF2, merlin, calretinin, defactini