Overexpression or knock down inhibition of TWIST and or miR 33a did not sig nificantly alter cell apoptosis in both Saos 2 and MG 63 cells under normal culture conditions. In Saos 2 cells treated with cisplatin, inhibition of miR 33a by antagomir 33a markedly increased cell apoptosis, which was enhanced by overexpression of TWIST. The apoptosis inducing effect of TWIST overexpression was reversed by overexpression of miR 33a. In MG 63 cells, overexpression of miR 33a significantly decreased cisplatin induced cell apoptosis, which was enhanced by knockdown of TWIST. Antagomir 33a significantly in creased cisplatin induced cell apoptosis, which was re versed by knockdown of TWIST. Discussion Chemoresistance is the major reason for poor survival of OS patients.

Previous studies reported that TWIST could decrease OS cell survival against cisplatin by inhibiting multiple signaling pathways, suggesting that TWIST is a pivotal negative regulator of OS chemoresis tance. miRNAs reportedly are involved in the pathogenesis and chemoresistance selleck chemicals L-Mimosine of various cancers, including OS. In the present study, we profiled miRNAs differentially expressed in chemoresistant OS by microarray analysis, with a focus to identify miRNAs that regulate TWIST ex pression and OS chemoresistance. We provide the first evidence suggesting that miR 33a promotes OS chemore sistance by down regulating TWIST. OS is the most common pediatric bone malignancy in the world. As the inclusion rate for adult OS patients was low, we performed this study only in pediatric OS pa tients.

Patients in the discovery selleck inhibitor cohort were matched on age, sex and tumor stages to reduce the effects of confounders on miRNA profiling between chemoresis tant and control OS samples. Patients in the valid ation cohort were not matched in order to verify the profiling findings in a more generalizable setting. Among the up regulated miRNAs identified in chemoresistant OS samples in this study, miR 140, miR 215 and miR 221 have been reported to induce human OS chemoresistance. Among the down regulated miRNAs identified in chemoresistant OS samples, miR 451 and miR 15b have been reported to increase chemosensitivity of OS. Thus, our findings were in agreement with previous stud ies, indicating good reliability of the data. High expression of TWIST has been detected in sev eral cancers and has been associated with the initial phase of metastatic progression.

One recent study reported that TWIST overexpression correlated with disease progression and a poor clinical outcome in OS patients. On the other hand, it has been reported that in homogeneous cohort of OS patients, the TWIST gene was frequently deleted in the tumors at diagnosis, and its haploinsufficiency was significantly correlated with a poorer patient outcome.