The pH of the tumor microenvironment drives the metastatic phenotype and chemotherapeutic resistance of tumors. Understanding the mechanisms underlying this pH-dependent phenomenon will lead to improved drug delivery and allow the identification of new therapeutic targets. This includes an understanding of the role pH plays in primary tumor cells, and the regulatory factors that permit cancer cells to thrive. Over the last decade, carbonic anhydrases (CAs) have been shown to be important mediators of tumor cell pH by modulating the bicarbonate and proton concentrations for cell survival and proliferation. This has prompted an effort to inhibit specific CA isoforms, as an anti-cancer therapeutic strategy. Of the 12 active CA isoforms, two, CA IX and XII, have been considered anti-cancer targets. However, other CA isoforms also show similar activity and tissue distribution in cancers and have not been considered as therapeutic targets for cancer treatment. In this review, we consider all the CA isoforms and their possible role in tumors and their potential as targets for cancer therapy.

The importance of the phospholipase A ₂ domain located within the unique N terminus of the capsid viral protein VP1 (VP1u) in parvovirus infection has been reported. This study used computational methods to characterize the VP1 sequence for adeno-associated virus (AAV) serotypes 1 to 12 and circular dichroism and electron microscopy to monitor conformational changes in the AAV1 capsid induced by temperature and the pHs encountered during trafficking through the endocytic pathway. Circular dichroism was also used to monitor conformational changes in AAV6 capsids assembled from VP2 and VP3 or VP1, VP2, and VP3 at pH 7.5. VP1u was predicted (computationally) and confirmed (in solution) to be structurally ordered. This VP domain was observed to undergo a reversible pH-induced unfolding/refolding process, a loss/gain of α-helical structure, which did not disrupt the capsid integrity and is likely facilitated by its difference in isoelectric point compared to the other VP sequences assembling the capsid. This study is the first to physically document conformational changes in the VP1u region that likely facilitate its externalization from the capsid interior during infection and establishes the order of events in the escape of the AAV capsid from the endosome en route to the nucleus.

The visualization at near atomic resolution of transient substrates in the active site of enzymes is fundamental to fully understanding their mechanism of action. Here we show the application of using CO₂-pressurized, cryo-cooled crystals to capture the first step of CO₂ hydration catalyzed by the zinc-metalloenzyme human carbonic anhydrase II, the binding of substrate CO₂, for both the holo and the apo (without zinc) enzyme to 1.1Å resolution. Until now, the feasibility of such a study was thought to be technically too challenging because of the low solubility of CO₂ and the fast turnover to bicarbonate by the enzyme (Liang, J. Y., and Lipscomb, W. N. (1990) Proc. Natl. Acad. Sci. U. S. A. 87, 3675–3679). These structures provide insight into the long hypothesized binding of CO₂ in a hydrophobic pocket at the active site and demonstrate that the zinc does not play a critical role in the binding or orientation of CO₂. This method may also have a much broader implication for the study of other enzymes for which CO₂ is a substrate or product and for the capturing of transient substrates and revealing hydrophobic pockets in proteins.

4-Substituted-ureido benzenesulfonamides showing inhibitory activity against carbonic anhydrase (CA, EC 4.2.1.1) II between 3.3–226 nM were crystallized in complex with the enzyme. Hydrophobic interactions between the scaffold of the inhibitors in different hydrophobic pockets of the enzyme were observed, explaining the diverse inhibitory range of these derivatives.

(2013). Anticonvulsant/antiepileptic carbonic anhydrase inhibitors: a patent review. Expert Opinion on Therapeutic Patents: Vol. 23, No. 6, pp. 717-724.