Cyclin-dependent kinase 9 (CDK9) is a novel prognostic marker and therapeutic target in osteosarcoma

Abstract

Background Cyclin-dependent protein kinase 9 (CDK9) has been shown to play an important role in the pathogenesis of malignant tumors. However, the expression and function of CDK9 remain unknown in osteosarcomas. The purpose of this study is to assess the expression, function and clinical prognostic relationship of CDK9 in osteosarcomas. Methods A tissue microarray of 70 patient specimens was analyzed by immunohistochemistry to measure CDK9 expression, which was further investigated for correlation with patient clinical characteristics. CDK9 expression in osteosarcoma cell lines and patient tissues was also evaluated by Western blotting. CDK9-specific siRNA and the CDK9 inhibitor were applied to determine the effect of CDK9 inhibition on osteosarcoma cell proliferation and anti-apoptotic activity. The clonogenicity and migration activity were also examined using clonogenic and wound healing assays. A 3D cell culture model was performed to mimic the in vivo osteosarcoma environment to further validate the effect of CDK9 inhibition on osteosarcoma cells. Findings We demonstrated that higher CDK9-expression is associated with significantly shortened patient survival by immunohistochemistry. Expression of CDK9 is inversely correlated to the percent of tumor necrosis post-neoadjuvant chemotherapy, which is the most important predictive factor of disease outcome for osteosarcoma patients. Knockdown of CDK9 with siRNA and inhibition of CDK9 activity with inhibitor decreased cell proliferation and induced apoptosis in osteosarcoma. Interpretation High expression of CDK9 is an independent predictor of poor prognosis in osteosarcoma patients. Our results suggest that CDK9 is a novel prognostic marker and a promising therapeutic target for osteosarcomas.

CDKs in Sarcoma: Mediators of Disease and Emerging Therapeutic Targets

“…In agreement with those results, knockdown or pharmacological inhibition of CDK9 in SS cells caused cell death, growth arrest, and reduced motility [141]. Likewise, increased expression of CDK9 was observed in osteosarcoma cells lines compared to normal osteoblasts and~67% of osteosarcoma patient tumors (from a TMA containing 70 OS) had elevated CDK9 [142]. High expression of CDK9 again correlated with worse overall survival.…”

Inhibition of ATR-Chk1 signaling blocks DNA double-strand-break repair and induces cytoplasmic vacuolization in metastatic osteosarcoma

“…The formalin-fixed, paraffin-embedded osteosarcoma tissue microarray (TMAs) were constructed with 70 patient specimens as previously described. 13 , 14 The study was approved by the Partners Human Research Committee (#: 2007P-002464) and all patients signed a consent form for their clinical information to be used for this research. ATR and phospho-ATR (pATR) expressions were first analyzed by immunohistochemistry (IHC), with follow-up correlation with patient clinical features.…”

P-TEFb as A Promising Therapeutic Target

“…In particular, mutations in LARP7 observed in various breast cancer patients cause a disruption of 7SK snRNP and subsequent constitutive activation of P-TEFb-dependent transcription [198,200]. In some types of cancer including ovarian cancer, pancreatic cancer, breast cancer, and osteosarcoma, on the other hand, P-TEFb expression (CDK9 and/or CycT1) is aberrantly upregulated [201][202][203][204][205], resulting in global stimulation of P-TEFb-dependent transcription. Although P-TEFb protein level is closely correlated with cells' proliferative state [14,15,206] as described above, it is still unclear whether the upregulation of P-TEFb expression in these cancer cells is a cause or a consequence of high rates of cell proliferation.…”