Yuanmei Lou

Targeting tumor hypoxia: suppression of breast tumor growth and metastasis by novel carbonic anhydrase IX inhibitors.

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 LM2-4(Luc+) 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.

Targeting carbonic anhydrase IX depletes breast cancer stem cells within the hypoxic niche

The sub-population of tumor cells termed ‘cancer stem cells’ (CSCs) possess the capability to generate tumors, undergo epithelial–mesenchymal 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.

Glycosyl coumarin carbonic anhydrase IX and XII inhibitors strongly attenuate the growth of primary breast tumors.

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, off target 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.

Epithelial-mesenchymal transition (EMT) is not sufficient for spontaneous murine breast cancer metastasis.

Epithelial–mesenchymal transition (EMT) has been linked to metastatic propensity. The 4T1 tumor is a clinically relevant model of spontaneous breast cancer metastasis. Here we characterize 4T1‐derived cell lines for EMT, in vitro invasiveness and in vivo metastatic ability. Contrary to expectations, 67NR cells, which form primary tumors but fail to metastasize, express vimentin and N‐cadherin, but not E‐cadherin. 4T1 cells express E‐cadherin and ZO‐1, but are migratory, invasive, and metastasize to multiple sites. 66cl4 cells form lung metastases and display a mixed phenotype, but are not as migratory or invasive as 67NR cells. These findings demonstrate that the metastatic ability of breast cancer cells does not strictly correlate with genotypic and phenotypic properties of EMT per se, and suggest that other processes may govern metastatic capability. Gene expression analysis of primary tumors did not identify differences in EMT markers, but did reveal candidate genes that may influence metastatic ability. Developmental Dynamics 237:2755–2768, 2008.

Novel Matrix Metalloproteinase Inhibitor [18F]Marimastat-Aryltrifluoroborate as a Probe for In vivo Positron Emission Tomography Imaging in Cancer

Matrix metalloproteinases (MMP), strongly associated pathogenic markers of cancer, have undergone extensive drug development programs. Marimastat, a noncovalent MMP inhibitor, was conjugated with FITC to label cellular metalloproteinase cancer targets in MDA-MB-231 cells in vitro. Punctate localization of active transmembrane MMP14 was observed. For molecular-targeted positron emission tomography imaging of syngeneic 67NR murine mammary carcinoma in vivo, marimastat was (18)F-labeled using a shelf-stable arylboronic ester conjugate as a captor for aqueous [(18)F]fluoride in a novel, rapid one-step reaction at ambient temperature. [(18)F]Marimastat-aryltrifluoroborate localized to the tumors, with labeling being blocked in control animals first loaded with >10-fold excess unlabeled marimastat. The labeled drug cleared primarily via the hepatobiliary and gastrointestinal tract, with multiple animals imaged in independent experiments, confirming the ease of this new labeling strategy.

Carbonic Anhydrase IX promotes myeloid-derived suppressor cell mobilization and establishment of a metastatic niche by stimulating G-CSF production

The mobilization of bone marrow-derived cells (BMDC) to distant tissues before the arrival of disseminated tumor cells has been shown preclinically to facilitate metastasis through the establishment of metastatic niches. Primary tumor hypoxia has been demonstrated to play a pivotal role in the production of chemokines and cytokines responsible for the mobilization of these BMDCs, especially in breast cancer. Carbonic anhydrase IX (CAIX, CA9) expression is highly upregulated in hypoxic breast cancer cells through the action of hypoxia-inducible factor-1 (HIF1). Preclinical evidence has demonstrated that CAIX is required for breast tumor growth and metastasis; however, the mechanism by which CAIX exerts its prometastatic function is not well understood. Here, we show that CAIX is indispensable for the production of granulocyte colony-stimulating factor (G-CSF) by hypoxic breast cancer cells and tumors in an orthotopic model. Furthermore, we demonstrate that tumor-expressed CAIX is required for the G-CSF-driven mobilization of granulocytic myeloid-derived suppressor cells (MDSC) to the breast cancer lung metastatic niche. We also determined that CAIX expression is required for the activation of NF-κB in hypoxic breast cancer cells and constitutive activation of the NF-κB pathway in CAIX-depleted cells restored G-CSF secretion. Together, these findings identify a novel hypoxia-induced CAIX-NF-κB-G-CSF cellular signaling axis culminating in the mobilization of granulocytic MDSCs to the breast cancer lung metastatic niche.

Abstract 841: Therapeutic targeting of cancer cells in the hypoxic microenvironment using an orally bioavailable small molecule inhibitor of carbonic anhydrase IX

Proceedings: AACR Annual Meeting 2014; April 5-9, 2014; San Diego, CA Carbonic anhydrase IX (CAIX) is a membrane-bound, hypoxia-inducible enzyme that is highly expressed in many types of solid tumors, is an independent marker of poor prognosis and functions as a critical component of the pH regulatory machinery required by hypoxic cancer cells for survival, invasion and metastasis. These attributes make CAIX an attractive therapeutic target for cancer therapy. The development of pharmacologic inhibitors that selectively target tumor-associated, extracellular carbonic anhydrases (CAs) without “off-target” inhibition of cytosolic isoforms is critical for their use as cancer therapeutics. Here, we characterize an orally bioavailable, highly selective small molecule inhibitor of CAIX and CAXII, SLC-0111, and investigate its efficacy when used as a monotherapy and in combination with conventional chemotherapy in vivo. SLC-0111 exhibited a favorable in vitro ADME profile, including IC50 values of >100 mM against most CYP isoforms, an IC50 for hERG inhibition of >30 mM and absence of mutagenic properties. Incubation of the compound with 67NR cells constitutively expressing human CAIX significantly suppressed, in a dose-dependent fashion, a drop in extracellular pH in a cell-based CAIX activity assay. The active compound was formulated as a self-emulsifying liquid for oral administration in vivo and evaluation of plasma levels showed good oral bioavailability of 40%. Toxicity studies involving repeat dosing by oral gavage for 7 days established maximum-tolerated doses in excess of 1,000 and 750 mg/kg for rats and dogs, respectively. Daily oral administration of SLC-0111 to mice harboring established MDA-MB-231 LM2-4 orthotopic human breast tumors, a model of hypoxic, CAIX-positive triple negative metastatic breast cancer, resulted in a significant, dose-dependent reduction in tumor growth, with 30% inhibition at a dose of 50 mg/kg, no toxicity and a 10-fold therapeutic window. Treatment also reduced viable tumor volume as determined by 18F-deoxyglucose uptake detected by positron emission tomography. Furthermore, treatment of mice with SLC-0111 in combination with paclitaxel resulted in significantly reduced tumor growth compared to either treatment administered alone, with no additional toxicity and plasma levels of SLC-0111 similar to those observed with its use as a monotherapy. Plasma levels of SLC-0111 showed dose proportionality and analysis of tumor levels demonstrated a greater than proportional relationship, with a 4-fold increase in dose (25-100 mg/kg) resulting in more than a 13-fold increase in tumor levels of the compound. Collectively, these data demonstrate the potential utility of SLC-0111 as a safe, target-specific inhibitor of CAIX for the treatment of cancer, particularly in combination with conventional chemotherapy. Citation Format: Paul C. McDonald, Jasbinder Sanghera, Madhu Singh, Yuanmei Lou, Marylou Vallejo, Claudiu T. Supuran, Shoukat Dedhar. Therapeutic targeting of cancer cells in the hypoxic microenvironment using an orally bioavailable small molecule inhibitor of carbonic anhydrase IX. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 841. doi:10.1158/1538-7445.AM2014-841

Abstract 3305: The role of carbonic anhydrase IX in tumor hypoxia, metastasis and the cancer stem cell niche

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. shRNA-mediated depletion of CAIX expression in mouse and human metastatic breast cancer cells, capable of inducing CAIX in hypoxia, resulted in regression of orthotopic mammary tumors and inhibition of spontaneous lung metastasis formation. CAIX depletion led to caspase-independent cell death and reversal of extracellular acidosis under hypoxic conditions in vitro. In addition, the CD44+/CD24-/low “cancer stem cell” compartment, which exhibited hallmarks of EMT (E-cadherin low/SMA high) was significantly enhanced in hypoxia, but was severely depleted in shRNA-CAIX knock-down cells as well as in cells treated with CAIX small molecule inhibitors. CAIX depletion or inhibition of its activity prevented mesenchymal conversion of the stem cells and also resulted in the suppression of expression of several EMT and “stemness” regulator genes. Treatment of mice harboring CAIX-positive 4T1 and MDA-MB-231/LM2 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 any inhibitory effects on CAIX negative tumors, or any adverse toxic effects. This was associated with significant depletion of cells expressing “cancer stem cell” markers. Furthermore, interrogation of 3,630 human breast cancers revealed CAIX to be an independent poor prognostic biomarker for distant metastases and survival. Our findings demonstrate that CAIX is vital for the survival of “cancer stem cells” in hypoxic niches as well as for the growth and metastasis of hypoxic breast tumors. It is a specific, targetable biomarker for breast cancer metastasis. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 3305. doi:1538-7445.AM2012-3305

Abstract 455: Hypoxia induced carbonic anhydrase IX is essential for the growth and metastasis of breast tumors

Metastasis of primary malignancies is a multi-step process and remains the principal cause of cancer deaths. Carbonic anhydrase IX (CAIX) is a hypoxia inducible protein and a poor prognostic marker for several types of cancer, including breast cancer. However, the functional role of CAIX in the metastatic progression of breast cancer is unclear. Here, we have investigated its role in the growth and metastasis of breast tumors. Orthotopic mouse mammary tumors derived from metastatic 4T1 and 66cl4 cells or non-metastatic 67NR cells were examined for levels of proliferation (BrdU), hypoxia, (pimonidazole), perfusion (DiOC 7 ), vasculature (CD31), apoptosis (TUNEL) and lymphangiogenesis (LYVE-1). Metastatic 4T1 and 66cl4 tumors expressed a hypoxia gene signature and were characterized as being poorly vascularized, with high levels of hypoxia. Large numbers of apoptotic cells and well developed intratumoral lymphatic vessels were also evident. Inhibition of expression of CAIX in the metastatic 4T1 cells by stable expression of short hairpin RNA (shRNA) resulted in cell death and reversal of extracellular acidosis in hypoxia in vitro, dramatic regression of tumors in vivo, and inhibition of metastasis. These properties were rescued by constitutive expression of human CAIX. Treatment of mice harboring 4T1 tumors with a novel CAIX-specific inhibitor resulted in significant inhibition of tumor growth. Interrogation by immunohistochemistry of a large (3992 patient samples) primary breast tumor tissue microarray showed that CAIX expression was significantly associated with worse distant relapse free survival (p −16 ) and was most prominent in the basal breast cancers (51%). Our data show that CAIX-mediated function is required for the survival and metastasis of hypoxic breast tumors, and suggest that CAIX is a promising therapeutic target for metastatic breast cancer. This work was supported by the Canadian Breast Cancer Research Alliance, with special funding from the Canadian Breast Cancer Foundation. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 455.