Lerociclib diminishes stemness in pediatric sarcoma cell lines.

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e22010 Background: The outcomes for children with osteosarcoma and synovial sarcoma remain poor and are even worse for metastatic or relapsed disease. Those who do survive frequently suffer from long-term toxicities from current standard-of-care therapies. It is evident novel therapeutics are warranted to improve the outcomes for patients with these difficult tumors. Stem cell-like cancer cells (SCLCCs) are a subpopulation of tumor cells thought to be responsible for treatment resistance, development of metastases and tumor recurrence, making the targeting of this cell population critical. We sought to evaluate the effect of lerociclib, a CDK4/6 inhibitor, on pediatric sarcoma cell stemness. Methods: We investigated two established human osteosarcoma cells lines (U2-OS and MG-63), two metastatic synovial sarcoma patient-derived xenografts (PDXs) (COA-30 and COA-79) and a metastatic epithelioid sarcoma PDX (COA-171). Cells were treated with the CDK4/6 inhibitor, lerociclib, at concentrations below the known LD50. Synovial sarcoma stemness markers Octamer-binding transcription factor 4 (Oct4), homeobox protein Nanog, SOX 2 and nestin were evaluated by qPCR. CD117, a marker of stemness in osteosarcoma cells, was examined by flow cytometry. Finally, long-term passaged U2-OS and MG-63 cells were placed in low attachment serum-free conditions, and tumorsphere formation was evaluated using extreme limiting dilution assay (ELDA) in all cell lines. Results: Lerociclib treatment significantly decreased abundance of Oct4 (by 54%), Nanog (by 29%), SOX 2 (by 60%) and nestin (by 63%) mRNA in COA-30 synovial sarcoma cells. Cell surface expression of CD117 decreased from 17% to 11% in MG-63 cells when treated with lerociclib 2μM. Treatment of all cell types with lerociclib led to significantly decreased tumorsphere formation (Table). Conclusions: Treatment with lerociclib led to a decrease in mRNA abundance in known synovial sarcoma stem cell markers, a decrease in CD117 cell surface expression in osteosarcoma cells and decreased the ability of cells to form tumorspheres. These findings indicate lerociclib leads to decreased sarcoma cell stemness, which plays a key role in tumor progression and recurrence and should be further investigated for potential translation to the clinical setting.[Table: see text]