Carbonic anhydrase IX (CAIX) is a hypoxia and HIF-1-inducible protein that regulates intra-and extracellular pH under hypoxic conditions and promotes tumor cell survival and invasion in hypoxic microenvironments. Interrogation of 3,630 human breast cancers provided definitive evidence of CAIX as an independent poor prognostic biomarker for distant metastases and survival. shRNA-mediated depletion of CAIX expression in 4T1 mouse metastatic breast cancer cells capable of inducing CAIX in hypoxia resulted in regression of orthotopic mammary tumors and inhibition of spontaneous lung metastasis formation. Stable depletion of CAIX in MDA-MB-231 human breast cancer xenografts also resulted in attenuation of primary tumor growth. CAIX depletion in the 4T1 cells led to caspase-independent cell death and reversal of extracellular acidosis under hypoxic conditions in vitro. Treatment of mice harboring CAIX-positive 4T1 mammary tumors with novel CAIX-specific small molecule inhibitors that mimicked the effects of CAIX depletion in vitro resulted in significant inhibition of tumor growth and metastasis formation in both spontaneous and experimental models of metastasis, without inhibitory effects on CAIX-negative tumors. Similar inhibitory effects on primary tumor growth were observed in mice harboring orthotopic tumors comprised of lung metatstatic MDA-MB-231 LM2-4Lucþ cells. Our findings show that CAIX is vital for growth and metastasis of hypoxic breast tumors and is a specific, targetable biomarker for breast cancer metastasis. Cancer Res; 71(9); 3364-76. Ó2011 AACR.

ACKNOWLEDGMENT Thanks are given to Prof. R. McKenna and M. Aggarwal for the generation of Figure 1 from the PDB files of the CA II-inhibitor adducts.

Integrin-linked kinase (ILK) is a multifunctional intracellular effector of cell-matrix interactions and regulates many cellular processes, including growth, proliferation, survival, differentiation, migration, invasion and angiogenesis. The use of recently developed Cre-lox-driven recombination and RNAinterference technologies has enabled the evaluation of the physiological roles of ILK in several major organ systems. Significant developmental and tissue-homeostasis defects occur when the gene that encodes ILK is deleted, whereas the expression of ILK is often elevated in human malignancies. Although the cause(s) of ILK overexpression remain to be fully elucidated, accumulating evidence suggests that its oncogenic capacity derives from its regulation of several downstream targets that provide cells with signals that promote proliferation, survival and migration, supporting the concept that ILK is a relevant therapeutic target in human cancer. Furthermore, a global analysis of the ILK 'interactome' has yielded several novel interactions, and has revealed exciting and unexpected cellular functions of ILK that might have important implications for the development of effective therapeutic agents.

Carbonic anhydrase IX (CAIX) is a hypoxia-inducible enzyme that is overexpressed by cancer cells from many tumor types, and is a component of the pH regulatory system invoked by these cells to combat the deleterious effects of a high rate of glycolytic metabolism. CAIX functions to help produce and maintain an intracellular pH (pHi) favorable for tumor cell growth and survival, while at the same time participating in the generation of an increasingly acidic extracellular space, facilitating tumor cell invasiveness. Pharmacologic interference of CAIX catalytic activity using monoclonal antibodies or CAIX-specific small molecule inhibitors, consequently disrupting pH regulation by cancer cells, has been shown recently to impair primary tumor growth and metastasis. Many of these agents are in preclinical or clinical development and constitute a novel, targeted strategy for cancer therapy.

The sub-population of tumor cells termed 'cancer stem cells' (CSCs) possess the capability to generate tumors, undergo epithelialmesenchymal transition (EMT) and are implicated in metastasis, making treatments to specifically target CSCs an attractive therapeutic strategy. Tumor hypoxia plays a key role in regulating EMT and cancer stem cell function. Carbonic anhydrase IX (CAIX) is a hypoxia-inducible protein that regulates cellular pH to promote cancer cell survival and invasion in hypoxic microenvironments and is a biomarker of poor prognosis for breast cancer metastasis and survival. Here, we demonstrate that inhibition of CAIX expression or activity with novel small-molecule inhibitors in breast cancer cell lines, or in primary metastatic breast cancer cells, results in the inhibition of breast CSC expansion in hypoxia. We identify the mTORC1 axis as a critical pathway downstream of CAIX in the regulation of cancer stem cell function. CAIX is also required for expression of EMT markers and regulators, as well as drivers of 'stemness', such as Notch1 and Jagged1 in isolated CSCs. In addition, treatment of mice bearing orthotopic breast tumors with CAIX-specific small-molecule inhibitors results in significant depletion of CSCs within these tumors. Furthermore, combination treatment with paclitaxel results in enhanced tumor growth delay and eradication of lung metastases. These data demonstrate that CAIX is a critical mediator of the expansion of breast CSCs in hypoxic niches by sustaining the mesenchymal and 'stemness' phenotypes of these cells, making CAIX an important therapeutic target for selectively depleting breast CSCs.

An unbiased proteomic screen to identify integrin-linked kinase (ILK) interactors revealed rictor as an ILK-binding protein. This finding was interesting because rictor, originally identified as a regulator of cytoskeletal dynamics, is also a component of mammalian target of rapamycin complex 2 (mTORC2), a complex implicated in Akt phosphorylation. These functions overlap with known ILK functions. Coimmunoprecipitation analyses confirmed this interaction, and ILK and rictor colocalized in membrane ruffles and leading edges of cancer cells. Yeast two-hybrid assays showed a direct interaction between the NH 2 -and COOH-terminal domains of rictor and the ILK kinase domain. Depletion of ILK and rictor in breast and prostate cancer cell lines resulted in inhibition of Akt Ser 473 phosphorylation and induction of apoptosis, whereas, in several cell lines, depletion of mTOR increased Akt phosphorylation. Akt and Ser 473 P-Akt were detected in ILK immunoprecipitates and small interfering RNA-mediated depletion of rictor, but not mTOR, inhibited the amount of Ser 473 P-Akt in the ILK complex. Expression of the NH 2 -terminal (1-398 amino acids) rictor domain also resulted in the inhibition of ILK-associated Akt Ser 473 phosphorylation. These data show that rictor regulates the ability of ILK to promote Akt phosphorylation and cancer cell survival. [Cancer Res 2008;68(6):1618-24]

A series of 7-substituted coumarins incorporating various glycosyl moieties were synthesized and investigated for the inhibition of the zinc enzyme carbonic anhydrase (CA, EC 4.2.1.1). These coumarins were very weak or ineffective as inhibitors of the housekeeping, offtarget isoforms CA I and II, but some of them inhibited tumor-associated CA IX and XII in the low nanomolar range. They also significantly inhibited the growth of primary tumors by the highly aggressive 4T1 syngeneic mouse mammary tumor cells at 30 mg/kg, constituting interesting candidates for the development of conceptually novel anticancer drugs. Because CA IX is overexpressed in hypoxic tumors and exhibits very limited expression in normal tissues, such compounds may be useful for treating cancers not responsive to classic chemo-and radiotherapy.

One of the hallmarks of cancers is the silencing of tumour suppressor genes and pathways. The Hippo tumour suppressor pathway is inactivated in many types of cancers, leading to tumour progression and metastasis. However, the mechanisms of pathway inactivation in tumours remain unclear. Here we demonstrate that integrin-linked kinase (ILK) plays a critical role in the suppression of the Hippo pathway via phospho-inhibition of MYPT1-PP1, leading to inactivation of Merlin. Inhibition of ILK in breast, prostate and colon tumour cells results in the activation of the Hippo pathway components MST1 and LATS1 with concomitant inactivation of YAP/TAZ (Yes-associated protein/transcriptional co-activator with PDZ-binding motif) transcriptional co-activators and TEAD-mediated transcription. Genetic deletion of ILK suppresses ErbB2-driven YAP/TAZ activation in mammary tumours, and its pharmacological inhibition suppresses YAP activation and tumour growth in vivo. Our data demonstrate a role for ILK as a multiple receptor proximal regulator of Hippo tumour suppressor pathway and as a cancer therapeutic target.