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

Abstract

Carbonic anhydrase (CA) IX has emerged as a promising target for cancer therapy. It is highly upregulated in hypoxic regions and mediates pH regulation critical for tumor cell survival as well as extracellular acidification of the tumor microenvironment, which promotes tumor aggressiveness via various mechanisms, such as augmenting metastatic potential. Therefore, the aim of this study was to analyze the complex interdependency between CA IX and the tumor microenvironment in prostate tumor cells with regard to potential therapeutic implications. CA IX was upregulated by hypoxia as well as acidosis in prostate cancer cells. This induction did not modulate intracellular pH but led to extracellular acidification. Pharmacological inhibition of CA IX activity by U104 (SLC-0111) resulted in a reduction in tumor cell growth and an increase in apoptotic cell death. Intracellular pH was reduced under normoxic and even more so under hypoxic conditions when CA IX level was high. However, although intracellular pH regulation was disturbed, targeting CA IX in combination with daunorubicin or cisplatin did not intensify apoptotic tumor cell death. Hence, targeting CA IX in prostate cancer cells can lead to intracellular pH dysregulation and, consequently, can reduce cellular growth and elevate apoptotic cell death. Attenuation of extracellular acidification by blocking CA IX might additionally impede tumor progression and metastasis. However, no beneficial effect was seen when targeting CA IX in combination with chemotherapeutic drugs.

Cellular and radiobiological effects of carbonic anhydrase IX in human breast cancer cells

“…The decreased pHi may be responsible for the decreased proliferation and increased apoptosis rate (16,28). This study of rat prostate cancer cells confirmed the intracellular acidification, anti-proliferative and pro-apoptotic effects of CAIX inhibition with CAI U104 (29). In addition, recently, our previous results confirmed CAI-induced apoptosis for betulinyl sulfamates in MDA-MB-231 and MCF7 cells using different methods (21,40).…”

“…1). Recently, we detected similar effects in AT1 prostate cancer cells (29). In contrast to our investigations, Tang et al observed a decrease in CA9 mRNA level in MCF-7 cells after incubation with lactic acid under hypoxic conditions (30).…”

Plasmatic exosomes from prostate cancer patients show increased carbonic anhydrase IX expression and activity and low pH

“…However, to prevent intracellular H þ accumulation cancer cells upregulates proton exchangers that extrude protons in excess contributing to acidify extracellular tumour microenvironment 9,11,12 . Among these proton exchangers, a primary role is played by CA IX, an enzyme overexpressed in many types of cancers, including prostate cancer, with the potential to represent both a promising tumour biomarker and a specific target for future cancer therapies 13,[30][31][32][33][37][38][39][40][41]44 . Under the pressure of the acidic microenvironment, CA IX expression and activity are upregulated in both tumour cells 30,44 and the exosomes released extracellularly 30 .…”

“…CA IX is overexpressed in a large number of solid tumours, whereas its expression in normal tissues is quite limited, suggesting its role as valuable tumour biomarker. Furthermore, CA IX has been validated as a target of new therapies against hypoxic tumours with one sulphonamide inhibitor (SLC-0111) in Phase Ib/II clinical trials 13,30,37-39(p20), [40][41][42] . Indeed CA IX is the most widely expressed gene in response to hypoxia, playing a pivotal role in tumour pH regulation 13,30,37,41 ; thus conferring to cancer cells a survival advantage in hypoxic and acidic microenvironments 43 .…”

“…Furthermore, CA IX has been validated as a target of new therapies against hypoxic tumours with one sulphonamide inhibitor (SLC-0111) in Phase Ib/II clinical trials 13,30,37-39(p20), [40][41][42] . Indeed CA IX is the most widely expressed gene in response to hypoxia, playing a pivotal role in tumour pH regulation 13,30,37,41 ; thus conferring to cancer cells a survival advantage in hypoxic and acidic microenvironments 43 . Thus, it is clear that the acidic microenvironment induces the up-regulation of the CA IX expression and activity in both tumour cells 30,44 and tumour released exosomes 30 .…”