The Sulfamate Small Molecule CAIX Inhibitor S4 Modulates Doxorubicin Efficacy

Abstract

Carbonic anhydrase IX (CAIX) is a tumor-specific protein that is upregulated during hypoxic conditions where it is involved in maintaining the pH balance. CAIX causes extracellular acidification, thereby limiting the uptake of weak basic chemotherapeutic agents, such as doxorubicin, and decreasing its efficacy. The aim of this study was to determine if doxorubicin efficacy can be increased when combined with the selective sulfamate CAIX inhibitor S4. The effect of S4 on doxorubicin efficacy was tested in vitro using cell viability assays with MDA-MB-231, FaDu, HT29 –CAIX high and HT29 –CAIX low cell lines. In addition, the efficacy of this combination therapy was investigated in tumor xenografts of the same cell lines. The addition of S4 in vitro increased the efficacy of doxorubicin in the MDA-MB-231 during hypoxic exposure (IC50 is 0.25 versus 0.14 µM, p = 0.0003). Similar results were observed for HT29—CAIX high with S4 during normoxia (IC50 is 0.20 versus 0.08 µM, p<0.0001) and in the HT29 –CAIX low cells (IC50 is 0.09 µM, p<0.0001). In vivo doxorubicin treatment was only effective in the MDA-MB-231 xenografts, but the efficacy of doxorubicin was decreased when combined with S4. In conclusion, the efficacy of doxorubicin treatment can be increased when combined with the selective sulfamate CAIX inhibitor S4 in vitro in certain cell lines. Nevertheless, in xenografts S4 did not enhance doxorubicin efficacy in the FaDu and HT29 tumor models and decreased doxorubicin efficacy in the MDA-MB-231 tumor model. These results stress the importance of better understanding the role of CAIX inhibitors in intratumoral pH regulation before combining them with standard treatment modalities, such as doxorubicin.

Inhibition of Carbonic Anhydrase IX by Ureidosulfonamide Inhibitor U104 Reduces Prostate Cancer Cell Growth, But Does Not Modulate Daunorubicin or Cisplatin Cytotoxicity

“…This decrease in apoptosis was not caused by changes in the activity of active drug transporters because no changes in intracellular daunorubicin levels were observed, because changes were independent of the type of chemotherapeutic agent used, and because they were also seen in the absence of daunorubicin and cisplatin. In line with our results, the group of van Kuijk et al also found no enhanced doxorubicin efficiency in xenografts when CA IX activity was simultaneously blocked 41 . To further complicate matters, some chemotherapeutic agents, including cisplatin, seem to be able to block CA IX activity as well 44 .…”

“…CA IX promotes extracellular acidification and stabilizes pH i in an acidic environment, and therefore the inhibition of CA IX in combination with the use of daunorubicin or cisplatin should increase the efficiency of chemotherapeutic drugs and restore chemosensitivity. Increased efficiency of chemotherapeutics in vitro, when administered together with inhibitors of CA IX, was recently described 41,42 . Furthermore, a cotreatment of HT-29 tumor-bearing mice with doxorubicin (which is a 14-hydroxylated version of daunorubicin) and CA IX inhibitors led to augmented chemosensitization and reduced tumor growth 43 .…”

HIF-1α and HIF-2α Differently Regulate the Radiation Sensitivity of NSCLC Cells

“…The metabolic switch towards increased glycolysis in hypoxic environments also affects the ability of these cells to survive therapy. For instance, the enhanced glycolytic rate increases the intracellular amounts of lactate and CO 2 , which are transported out of the cell, contributing to an extracellular acidic pH [16] and an increased therapy resistance [17]. The substantial increase of lactate production during hypoxia allows the scavenging of reactive oxygen species (ROS) molecules generated after radiation exposure due to the antioxidant properties of lactate [18].…”

Carbonic Anhydrase IX Inhibitors as Candidates for Combination Therapy of Solid Tumors

“…Inspired by the acetazolamide-induced intensification of DOX treatment in CA IX-rich cell lines reported by Gieling et al (vide supra), Kuijk and colleagues performed a followon study by using an isoform-selective CA IX inhibitor S4 [74]. This ureido-substituted sulfamate SLC-0111 analog has been earlier described to exert significant antiproliferative efficacy in vitro in different breast cancer tumor models [75,76].…”