Tumor microenvironments can promote stem cell maintenance, tumor growth, and therapeutic resistance, findings linked by the tumor-initiating cell hypothesis. Standard of care for glioblastoma (GBM) includes temozolomide chemotherapy, which is not curative, due, in part, to residual therapy-resistant brain tumor-initiating cells (BTICs). Temozolomide efficacy may be increased by targeting carbonic anhydrase 9 (CA9), a hypoxia-responsive gene important for maintaining the altered pH gradient of tumor cells. Using patient-derived GBM xenograft cells, we explored whether CA9 and CA12 inhibitor SLC-0111 could decrease GBM growth in combination with temozolomide or influence percentages of BTICs after chemotherapy. In multiple GBMs, SLC-0111 used concurrently with temozolomide reduced cell growth and induced cell cycle arrest via DNA damage in vitro. In addition, this treatment shifted tumor metabolism to a suppressed bioenergetic state in vivo. SLC-0111 also inhibited the enrichment of BTICs after temozolomide treatment determined via CD133 expression and neurosphere formation capacity. GBM xenografts treated with SLC-0111 in combination with temozolomide regressed significantly, and this effect was greater than that of temozolomide or SLC-0111 alone. We determined that SLC-0111 improves the efficacy of temozolomide to extend survival of GBM-bearing mice and should be explored as a treatment strategy in combination with current standard of care.


Nathaniel H. Boyd, Kiera Walker, Joshua Fried, James R. Hackney, Paul C. McDonald, Gloria A. Benavides, Raffaella Spina, Alessandra Audia, Sarah E. Scott, Catherine J. Libby, Anh Nhat Tran, Mark O. Bevensee, Corinne Griguer, Susan Nozell, G. Yancey Gillespie, Burt Nabors, Krishna P. Bhat, Eli E. Bar, Victor Darley-Usmar, Bo Xu, Emily Gordon, Sara J. Cooper, Shoukat Dedhar, Anita B. Hjelmeland


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