CA9: A Key Molecule Driving Tumor Invasion and Metastasis

The expression of Carbonic Anhydrase IX (CA9) in normal tissues is highly restricted, primarily distributed in the gastrointestinal tract. However, its expression is significantly upregulated in tumor tissues. Numerous studies have confirmed that this protein is highly expressed in a variety of tumor tissues, including breast cancer, renal cancer, lung cancer, pancreatic cancer, colorectal cancer, head and neck oral tumors, cervical cancer, gallbladder cancer, high-grade brain tumors, liver cancer, and gastric epithelial tumors^[1]. Furthermore, the expression level of the CA9 protein is positively correlated with the degree of malignant tumor invasion. Hypoxic environments can significantly upregulate its expression, making CA9 a highly promising target for targeted cancer therapy^[2]. 

CA9: A Key Regulatory Molecule in the Tumor Microenvironment

Carbonic Anhydrases (CAs) are a class of metalloenzymes capable of reversibly catalyzing the hydration reaction of carbon dioxide and water to generate bicarbonate and hydrogen ions. This family is divided into 8 independent subtypes, among which only the α carbonic anhydrases are expressed in the human body. There are a total of 12 α-carbonic anhydrases with catalytic functions in the human body, and only the membrane-bound CA9 and CA12 have been confirmed to be associated with tumorigenesis^[2]. The CA9 protein is composed of an N-terminal proteoglycan-like (PG) domain, a carbonic anhydrase catalytic (CA) domain, a transmembrane segment, and an intracellular fragment. In its native state, CA9 exists as a homodimer, and the dimeric conformation is maintained by an intermolecular disulfide bond formed via cysteines (Cys) between the catalytic domains of the two monomers^[3]. 

Schematic Diagram of CA9 Structure^[3]

In the tumor microenvironment, hypoxia upregulates the expression of glucose transporters, pro-angiogenic factors, and key enzymes of multiple glycolysis pathways via the transcription factor hypoxia-inducible factor 1α (HIF1α)Upon stabilization, the HIF1α protein transcriptionally activates a series of pro-tumorigenic and pro-angiogenic genes, driving cells to form a highly glycolytic phenotype, enabling tumor cells to synthesize adenosine triphosphate (ATP) to maintain energy supply independent of oxygen. 

Enhanced glycolytic metabolism prompts cells to secrete large amounts of lactic acid outward. This process is mediated by monocarboxylate transporter 1 (MCT1) and is accompanied by the co-transport of hydrogen ions, ultimately leading to an acidic extracellular microenvironment, thereby maintaining intracellular pH homeostasis. Meanwhile, CO₂ generated from mitochondrial decarboxylation reactions diffuses extracellularly and undergoes a hydration reaction catalyzed by CA9 (and membrane-bound CA12 in some tumors), further exacerbating the extracellular acidification effect^[2]. 

Continuous extracellular acidification activates and releases various matrix metalloproteinases, which can degrade the extracellular matrix and promote the migration, invasion, and metastasis of tumor cells. Research indicates that in patients with breast cancer, lung cancer, ovarian cancer, and bladder cancer, the abundance of CA9 expression is positively correlated with poor prognosis and tumor invasion^[1]. Conversely, targeted inhibition of the catalytic activity of CA9 can disrupt the acid-base homeostasis of the tumor microenvironment and weaken the survival ability and proliferation rate of tumor cells. 

CA9 Regulates the Tumor Microenvironment^[1]

CA9 Drug Development Progress

Currently, the types of drugs targeting CA9 are primarily focused on radionuclide-drug conjugates (RDCs), monoclonal antibodies, and small molecule inhibitors. Among them, the one progressing fastest in clinical trials is the antibody-radionuclide conjugate Lutetium-177 DOTA girentuximab, developed by Telix Pharmaceuticals. This drug uses girentuximab as the targeting antibody, which specifically recognizes the catalytic domain of CA9. The β-emitting radionuclide Lutetium-177 (¹⁷⁷Lu) is conjugated to the antibody backbone via the chelator DOTA, achieving precise delivery of the radioactive payload to CA9-positive tumor cells. Phase I/II clinical data in metastatic clear cell renal cell carcinoma showed that the drug has good safety, tolerability, and anti-tumor efficacy. At the 2026 American Society of Clinical Oncology (ASCO) Annual Meeting, Telix announced the trial plan for the Phase III LUTEON study, aimed at evaluating the safety and efficacy of 177Lu-girentuximab in a population with advanced, relapsed clear cell renal cell carcinoma^[4]. 

Mechanism of Action of ¹⁷⁷Lu-girentuximab^[5]

A representative monoclonal antibody drug is CA9hu-1, a humanized antibody that recognizes the catalytic domain of CA9. Upon binding, it can be endocytosed by tumor cells, thereby inhibiting the extracellular acidification process and delaying tumor growth. Cellular experiments have confirmed that the CA9hu-1 antibody can significantly weaken the invasive ability of CA9-positive C33-a tumor cells. Currently, this antibody is in Phase I clinical trials. 

CA9hu-1 Inhibits Tumor Cell Invasion^[6]

Partial list of CA9-targeted drugs

KACTUS Supplies High-Quality CA9 Proteins

CA9, highly expressed under the induction of hypoxia, continuously remodels the acidic tumor microenvironment, driving the proliferation and invasion of various cancers. To support the development of CA9 drugs, KACTUS provides high-quality CA9 and CA9 Domain proteins. The products cover different species and different tags. All proteins have validated enzyme activity data and undergo strict quality control, making them suitable for various R&D needs such as immunization, screening, and epitope identification. 

Product Data

Immobilized Human CA9, His Tag at 0.5μg/ml (100μl/well) on the plate. Dose response curve for Anti-CA9 Antibody, hFc Tag with the EC50 of 0.8ng/ml determined by ELISA.

Immobilized Human CA9 CA Domain, His Tag at 0.5μg/ml (100μl/well) on the plate. Dose response curve for Anti-CA9 Antibody, hFc Tag with the EC50 of 0.8ng/ml determined by ELISA.

Measured by its esterase activity. The specific activity is >80 pmol/min/µg.

Product List

References

[1] Ronca R, Supuran CT. Carbonic anhydrase IX: An atypical target for innovative therapies in cancer. Biochim Biophys Acta Rev Cancer. 2024 Jul;1879(4):189120. doi: 10.1016/j.bbcan.2024.189120. Epub 2024 May 25. PMID: 38801961.

[2] Koruza K, Murray AB, Mahon BP, Hopkins JB, Knecht W, McKenna R, Fisher SZ. Biophysical Characterization of Cancer-Related Carbonic Anhydrase IX. Int J Mol Sci. 2020 Jul 25;21(15):5277. doi: 10.3390/ijms21155277. PMID: 32722392; PMCID: PMC7432807.

[3] Koltai, Tomas. (2018). Chapter 6 part I Carbonic anhydrase and the pH paradigm in cancer.

[4] David Cade et al. Phase 3 study to assess the safety and efficacy of 177Lu-girentuximab in advanced, relapsed, or recurrent ccRCC (LUTEON).. J Clin Oncol 44, TPS4631-TPS4631(2026).DOI:10.1200/JCO.2026.44.16_suppl.TPS4631

[5] ASCO 2023: Phase 1b/2 Study of Combination 177Lu Girentuximab + Cabozantinib and Nivolumab in Treatment Naïve Patients with Advanced Clear Cell RCC

[6] Zatovicova M, Kajanova I, Barathova M, et al. Novel humanized monoclonal antibodies for targeting hypoxic human tumors via two distinct extracellular domains of carbonic anhydrase IX. Cancer & Metabolism. 2022 Feb;10(1):3. DOI: 10.1186/s40170-022-00279-8. PMID: 35109923; PMCID: PMC8811981.