Methylation of the CA9 promoter can modulate expression of the tumor-associated carbonic anhydrase IX in dense carcinoma cell lines.

CA IX is a tumor-associated transmembrane isoform of the carbonic anhydrase with a high enzyme activity and a functional involvement in the pH regulation and cell adhesion. Expression of CA9 gene in tumor cells is principally regulated by the high cell density and the hypoxia-related VHL-HIF pathway. In renal cell carcinomas with VHL inactivation, CA9 transcription is further controlled by site-specific promoter methylation. Here we explored a possible role of methylation in the non-RCC cell lines represented mainly by HeLa cervical carcinoma cells. Using metabisulfite sequencing and treatment with the methylation inhibitor 5-aza-2'-deoxycytidine we showed that the methylation of a single CpG site at -74 position with respect to the transcription start can down-modulate the expression of CA9 in cells cultivated at high density, but not in cells grown in sparse culture nor in cells exposed to hypoxia. Methylation appears to act in tumor cells expressing intermediate levels of CA IX protein, but not in cell lines expressing high CA IX levels. Our results indicate that promoter methylation is not crucial for the control of CA9 gene expression in the non-RCC cell lines but could represent an accessory mechanism restricting its expression in highly dense carcinoma cell cultures.

Carbonic anhydrase inhibitors: synthesis and inhibition of cytosolic/tumor-associated carbonic anhydrase isozymes I, II, and IX with bis-sulfamates.

A series of bis-sulfamates incorporating aliphatic, aromatic, or betulinyl moieties in their molecules was obtained by reaction of the corresponding diols/diphenols with sulfamoyl chloride. The library of bis-sulfamates thus obtained was tested for the inhibition of three physiologically relevant human carbonic anhydrase (hCA, EC 4.2.1.1) isozymes, the cytosolic hCA I and II, and the transmembrane, tumor-associated hCA IX. The new compounds reported here inhibited hCA I with K(I) s in the range of 79 nM-16.45 microM, hCA II with K(I) s in the range of 6-643 nM, and hCA IX with K(I) s in the range of 4-5400 nM. Several low nanomolar hCA IX inhibitors were detected, such as 1,8-octylene-bis-sulfamate or 1,10-decylene-bis-sulfamate (K(I) s in the range of 4-7 nM), which showed good selectivity ratios (in the range of 3.50-3.85) for hCA IX over hCA II inhibition. The most selective hCA IX inhibitor was phenyl-1,4-dimethylene-bis-sulfamate (K(I) of 61.6 nM), which was a 10.43 times better hCA IX than hCA II inhibitor. These derivatives are interesting candidates for the development of novel antitumor therapies targeting hypoxic tumors, since hCA IX is highly overexpressed in such tissues, and its presence is correlated with bad prognosis and unfavorable clinical outcome.

Monoclonal antibodies generated in carbonic anhydrase IX-deficient mice recognize different domains of tumour-associated hypoxia-induced carbonic anhydrase IX.

Transmembrane carbonic anhydrase IX (CA IX) is frequently expressed in human tumours in response to hypoxia and may serve as a tumour marker and therapeutic target. So far, only a single monoclonal antibody (MAb) M75 with an epitope in the N-terminal proteoglycan (PG)-like region has been available for detection purposes. Attempts to produce MAbs against other parts of CA IX were unsuccessful due to the immunodominance of the PG region that significantly differs between human and mouse homologues. To overcome this problem, we used various forms of human CA IX antigen to immunize CA IX-deficient mice recently produced by targeted disruption of Car9 gene. Here, we describe new MAbs that react with human, but not mouse CA IX in different immunodetection settings, and show no cross-reactivity with CA I, II and XII. MAb IV/18 is directed to the PG region, while the other six antibodies bind to the CA domain, as determined by CA IX deletion variants. IV/18 recognizes a linear epitope, while anti-CA MAbs V/10, V/12, VII/20, VII/28, VII/32 and VII/38 react with conformational epitopes clustered into three antigenic sites. The new antibodies represent important tools for improving our knowledge of structure-function relationships in the CA IX molecule and a better understanding of the role of CA IX in cancer development. Moreover, the availability of the MAbs specific for distinct antigenic regions on two separate extracellular domains offers an opportunity to elaborate a sensitive assay that could be particularly important for CA IX detection in body fluids of cancer patients.