Discovery of 4-Hydroxy-3-(3-(phenylureido)benzenesulfonamides as SLC-0111 Analogues for the Treatment of Hypoxic Tumors Overexpressing Carbonic Anhydrase IX

4-Hydroxy-3-nitro-5-ureido-benzenesulfonamides Selectively Target the Tumor-Associated Carbonic Anhydrase Isoforms IX and XII Showing Hypoxia-Enhanced Antiproliferative Profiles

Human carbonic anhydrases (CA, EC, 4.2.1.1) IX and XII are overexpressed in cancer cells as adaptive response to hypoxia and acidic conditions characteristic of many tumors. In addition, hypoxia facilitates the activity of specific oxido-reductases that may be exploited to selectively activate bioreductive prodrugs. Here, new selective CA IX/XII inhibitors, as analogues of the antitumor phase II drug SLC-0111 are described, namely ureido-substituted benzenesulfonamides appended with a nitro-aromatic moiety to yield an antiproliferative action increased by hypoxia. These compounds were screened for the inhibition of the ubiquitous hCA I/II and the target hCA IX/XII. Six X-ray crystallographies with CA II and IX/mimic allowed for the rationalization of the compounds inhibitory activity. The effects of some such compounds on the viability of HT-29, MDA-MB-231, and PC-3 human cancer cell lines in both normoxic and hypoxic conditions were examined, providing the initiation toward the development of hypoxia-activated antitumor CAIs.

Carbonic anhydrase inhibitors as emerging agents for the treatment and imaging of hypoxic tumors

INTRODUCTION

Hypoxic tumors overexpress two carbonic anhydrases (CA, EC 4.2.1.1), CA IX and XII, involved in complex processes connected to tumorigenesis (pH regulation, metabolism, invasion, and dissemination of the tumor). The biochemical rationale behind these processes is orchestrated by the transcription factor hypoxia inducible factor 1 (HIF-1).

AREAS COVERED

CA IX and XII have been validated as antitumor/antimetastatic drug targets and may be used for imaging hypoxic tumors. Many CA inhibitors (CAIs) belonging to the sulfonamide, coumarin and sulfocoumarin classes selectively inhibit these two isoforms. CA IX/XII inhibitors inhibit the growth of primary tumors and the formation of metastases and deplete the cancer stem cell population, alone or in combination with other agents. These are three beneficial antitumor mechanisms that make them unique among anticancer drugs available.

EXPERT OPINION

Indisulam entered clinical trials as an antitumor sulfonamide; it progressed to Phase II trials but was terminated in 2016. However, SLC-0111, a sulfonamide CA IX/XII inhibitor 1, recently completed a successful Phase I clinical trial for the treatment of advanced, metastatic solid tumors. This compound is now in Phase Ib/II clinical trials and is being assessed as a monotherapy or in combination with other agents such as gemcitabine. CA IX/XII inhibitors are synergistic with other anticancer agents (cisplatin, proton pump inhibitors, doxorubicin, temozolamide) and are a versatile, emerging class of antitumor drugs.

SLC-0111 enaminone analogs, 3/4-(3-aryl-3-oxopropenyl) aminobenzenesulfonamides, as novel selective subnanomolar inhibitors of the tumor-associated carbonic anhydrase isoform IX

SLC-0111, an ureido substituted benzenesulfonamide, is a selective carbonic anhydrase (CA, EC 4.2.1.1) IX inhibitor that is currently in Phase I/II clinical trials for the treatment of advanced hypoxic tumors complicated with metastases. Herein we report the synthesis of two series of 3/4-(3-aryl-3-oxopropenyl) aminobenzenesulfonamides 5a-i and 6a-j as SLC-0111 enaminone congeners. The prepared enaminones were in vitro investigated as inhibitors of the metalloenzyme carbonic anhydrase (CA, EC 4.2.1.1) isoforms hCA I, II, IV and IX, using a stopped-flow CO₂ hydrase assay. All these isoforms were inhibited by the enaminones reported here in variable degrees. The target tumor-associated isoform hCA IX was undeniably the most affected one (K_Is: 0.21-7.1 nM), with 6- to 21-fold enhanced activity than SLC-0111 (K_I = 45 nM). All the prepared enaminones displayed interesting selectivity towards hCA IX over hCA I (SI: 32 - >35714), hCA II (SI: 2 - 1689) and hCA IV (SI: 11 - >45454). Of particular interest, bioisosteric replacement of phenyl tail with the bulkier 2-naphthyl tail, sulfonamide 6h, achieved the higher II/IX selectivity herein reported with SI of 1689.