A series of sulfamates or bis-sulfamates incorporating aliphatic, aromatic, polycyclic (steroidal), and
sugar moieties in their molecules has been synthesized and assayed as inhibitors of the
zinc enzyme carbonic anhydrase (CA), and more precisely of the cytosolic
isozymes CA I andII, and the transmembrane,
tumor-associated
isozymes CA IX. Some of these compounds were previously reported to act as inhibitors of
steroid sulfatases, among which
estrone sulfatase (ES) and
dehydroepiandrosterone sulfatase (DHEAS) are the key therapeutic targets for
estrogen-dependent
tumors. Very potent (nanomolar) inhibitors were detected against the three investigated CA
isozymes. Best CA I inhibitors were phenylsulfamate and some of its 4-halogeno derivatives, as well as the aliphatic compound n-octyl
sulfamate. Against CA II, low nanomolar inhibitors (1.1-5 nM) were phenylsulfamate and some of its 4-halogeno/nitro derivatives, n-octyl
sulfamate, and
estradiol 3,17beta-disulfamate among others. All the investigated sulfamates showed efficient CA IX inhibitory properties, with inhibition constants in the range of 18-63 nM. The best CA IX inhibitor detected so far was 4-chlorophenylsulfamate. These data are critical for the design of novel antitumor properties, mainly for hypoxic
tumors that overexpress CA IX, which are nonresponsive to radiation or
chemotherapy. The antitumor properties of the ES/DHEAS inhibitors in clinical trials may on the other hand also be due to their potent inhibitory properties of CA
isozymes involved in tumorigenicity, such as CA II and CA IX.