Abstract
About 95% of Glioblastoma (GBM) patients experience tumor relapse as a consequence of resistance to the first-line standard chemotherapy using temozolomide (TMZ). Recent studies reported consistently elevated expression levels of carbonic anhydrase CA2 in recurrent glioblastoma and temozolomide-resistant glioblastoma stem-like cells (GSCs). Here we show that CA2 is preferentially expressed in GSCs and upregulated by TMZ treatment. When expressed in GBM cell lines, CA2 exerts significant metabolic changes reflected by enhanced oxygen consumption and increased extracellular acidification causing higher rates of cell invasion. Notably, GBM cells expressing CA2 respond to combined treatment with TMZ and brinzolamide (BRZ), a non-toxic and potent CA2 inhibitor. Interestingly, brinzolamide was more effective than the pan-CA inhibitor Acetazolamide (ACZ) to sensitize naïve GSCs and TMZ-resistant GSCs to TMZ induced cell death. Mechanistically, we demonstrated that the combined treatment of GBM stem cells with TMZ and BRZ caused autophagy of GBM cell lines and GSCs, reflected by enhanced LC3 cleavage (LC3-II) and p62 reduction. Our findings illustrate the potential of CA2 as a chemo-sensitizing drug target in recurrent GBM and propose a combined treatment of TMZ with CA2 inhibitor to tackle GBM chemoresistance and recurrence.
Highlights
Glioblastoma (GBM) is the most common and lethal brain tumor with a median survival of around 15 months after diagnosis [1,2]
GBM is composed of various brain resident, as well as transformed cell types: there are rapidly multiplying tumor cells that make up the bulk of the tumor mass and, on the other hand, there are self-renewing cell types, often termed Glioblastoma stem-like cells (GSCs) [6,7,8]
To characterize the Carbonic Anhydrase 2 (CA2) producing cells in recurrent glioblastoma, the localization of CA2 was determined by immunofluorescence in paraffin slides of rGBM patients (Figure 1D)
Summary
Glioblastoma (GBM) is the most common and lethal brain tumor with a median survival of around 15 months after diagnosis [1,2]. Whereas differentiated GBM cells are responsive to chemotherapy due to their high proliferation rate, GSCs are thought to exert increased resistance to adjuvant therapy and tumor-initiating capacity as a source of glioma recurrence [3,5,9]. There are several proposed resistance mechanisms, such as metabolic inactivation of drugs, inhibition of conversion from prodrug to bioactive drug, increased drug efflux, and increased DNA repair [10,11]. In this regard, by analyzing GSCs resistant to TMZ treatment, we and others have shown previously that a major factor of TMZ resistance in GBM stem cells and recurrent tumor tissue is Carbonic Anhydrase 2
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