Carbonic Anhydrase IX: From Biology to Therapy

Quinazolinones as Competitive Inhibitors of Carbonic Anhydrase-II (Human and Bovine): Synthesis, in-vitro, in-silico, Selectivity, and Kinetics Studies

Carbonic anhydrase-II (CA-II) is associated with glaucoma, malignant brain tumors, and renal, gastric, and pancreatic carcinomas and is mainly involved in the regulation of the bicarbonate concentration in the eyes. CA-II inhibitors can be used to reduce the intraocular pressure usually associated with glaucoma. In search of potent CA-II inhibitors, a series of quinazolinones derivatives (4a-p) were synthesized and characterized by IR and NMR spectroscopy. The inhibitory potential of all the compounds was evaluated against bovine carbonic anhydrase-II (bCA-II) and human carbonic anhydrase-II (hCA-II), and compounds displayed moderate to significant inhibition with IC50 values of 8.9-67.3 and 14.0-59.6 μM, respectively. A preliminary structure-activity relationship suggested that the presence of a nitro group on the phenyl ring at R position contributes significantly to the overall activity. Kinetics studies of the most active inhibitor, 4d, against both bCA-II and hCA-II were performed to investigate the mode of inhibition and to determine the inhibition constants (Ki). According to the kinetics results, 4d is a competitive inhibitor of bCA-II and hCA-II with Ki values of 13.0 ± 0.013 and 14.25 ± 0.017 μM, respectively. However, the selectivity index reflects that the compounds 4g and 4o are more selective for hCA-II. The binding mode of these compounds within the active sites of bCA-II and hCA-II was investigated by structure-based molecular docking. The docking results are in complete agreement with the experimental findings.

An Activatable NIR Fluorescent Rosol for Selectively Imaging Nitroreductase Activity

Hypoxia (pO₂ ≤ ~1.5%) is an important characteristic of tumor microenvironments that directly correlates with resistance against first-line therapies and tumor proliferation/infiltration. The ability to accurately identify hypoxic tumor cells/tissue could afford tailored therapeutic regimens for personalized treatment, development of more-effective therapies, and discerning the mechanisms underlying disease progression. Fluorogenic constructs identifying aforesaid cells/tissue operate by targeting the bioreductive activity of primarily nitroreductases (NTRs), but collectively present photophysical and/or physicochemical shortcomings that could limit effectiveness. To overcome these limitations, we present the rational design, development, and evaluation of the first activatable ultracompact xanthene core-based molecular probe (NO ₂ -Rosol) for selectively imaging NTR activity that affords an "OFF-ON" near-infrared (NIR) fluorescence response (> 700 nm) alongside a remarkable Stokes shift (> 150 nm) via NTR activity-facilitated modulation to its energetics whose resultant interplay discontinues an intramolecular d-PET fluorescence-quenching mechanism transpiring between directly-linked electronically-uncoupled π-systems comprising its components. DFT calculations guided selection of a suitable fluorogenic scaffold and nitroaromatic moiety candidate that when adjoined could (i) afford such photophysical response upon bioreduction by upregulated NTR activity in hypoxic tumor cells/tissue and (ii) employ a retention mechanism strategy that capitalizes on an inherent physical property of the NIR fluorogenic scaffold for achieving signal amplification. NO ₂ -Rosol demonstrated 705 nm NIR fluorescence emission and 157 nm Stokes shift, selectivity for NTR over relevant bioanalytes, and a 28-/12-fold fluorescence enhancement in solution and between cells cultured under different oxic conditions, respectively. In establishing feasibility for NO ₂ -Rosol to provide favorable contrast levels in solutio/vitro, we anticipate NO ₂ -Rosol doing so in preclinical studies.

Carbonic anhydrase IX inhibitors in cancer therapy: an update

Carbonic anhydrases (CAs; EC 4.2.1.1) are well known zinc metalloproteins involved in the catalysis of a very simple but essential physiological reaction: carbon dioxide hydration to bicarbonate and proton. These enzymes are of clinical relevance in cancer therapy as among the 15 isoforms known in humans, two cell surface CA isoforms, namely CA IX (almost exclusively associated with tumors) and CA XII (overexpressed in some tumor types) are involved in tumorigenesis. Targeting the tumor associated isoforms IX is now considered as a pertinent approach for the development of new cancer therapeutics against hypoxic tumors. Different approaches and new family of pharmacological agents were described in the last 5 years for obtaining compounds that specifically target CA IX over the ubiquitous cytosolic off-target isoforms CA I and CA II. The aim of this review is to give a comprehensive update on the reported discoveries in the field of CA IX inhibitors with an emphasis on the new families of compounds which reach in vivo/preclinical studies for their potential in cancer therapy.

Designing carbonic anhydrase inhibitors for the treatment of breast cancer

INTRODUCTION

Carbonic anhydrase (CA) IX is one of the proteins that are involved in cancerogenesis in hypoxic breast tumors. Indeed, it is present in high amounts in hypoxic tumor cells, where it plays a crucial role in metabolic reprogramming due to the scarcity of oxygen, triggered by the hypoxia inducible factor 1 transcription factor. In such tumors, CA IX is involved, along with other proteins, in tumor pH regulation and its survival in a harsh environment (including hypoxia and acidity). CA IX is also validated as an imaging and treatment target for hypoxic tumors and metastasis.

AREAS COVERED

In this review, the authors highlight the wealth of CA IX inhibitors currently in the literature. This includes the two most investigated classes of compounds being the sulfonamides and the coumarins, including their isosteres.

EXPERT OPINION

The most advanced CA IX inhibitors candidates, which demonstrate antimetastatic activity in breast cancer, are the sulfonamides, with one compound (SLC-0111) currently in Phase I clinical development. The fact that this first inhibitor has progressed could increase interest in the development of conceptually novel antitumor/antimetastic drugs belonging to the CA inhibitors class.