Carbonic anhydrase IX as an imaging and therapeutic target for tumors and metastases

Abstract

Carbonic anhydrase IX (CAIX) which is a zinc containing metalloprotein, efficiently catalyzes the reversible hydration of carbon dioxide. It is constitutively up-regulated in several cancer types and has an important role in tumor progression, acidification and metastasis. High expression of CAIX generally correlates with poor prognosis and is related to a decrease in the disease-free interval following successful therapy. Therefore, it is considered as a prognostic indicator in oncology.In this review, we describe CAIX regulation and its role in tumor hypoxia, acidification and metastasis. In addition, the molecular imaging of CAIX and its potential for use in cancer detection, diagnosis, staging, and for use in following therapy response is discussed. Both antibodies and small molecular weight compounds have been used for targeted imaging of CAIX expression. The use of CAIX expression as an attractive and promising candidate marker for systemic anticancer therapy is also discussed.

Figure 1

Proposed model showing the structural arrangement of the CAXII and CAIX dimer on the cellular membrane (23, 24). PG= proteoglycan-like domain, CA= catalytic domain, TM= transmembrane segment, IC= intracellular, cytosolic tail.

Figure 2

Hypoxia-induced gene expression mediated by the HIF1 transcription factor heterodimer. HIF-1α is degraded in normoxia by the ubiquitin-proteasomal pathway. In hypoxia, it is phosphorylated by MAPK and bound by CBP/p300, inducing heterodimirezation with HIF-1β and transcription of variety of genes.

Figure 3

Immunohistochemical staining of CAIX is an important tool to investigate 2-D localization of expression. A) Dark brown CAIX overexpression at the edge of the tumor (white arrow) contrasts not only with the adjacent microenvironment in blue (black arrow), but also with the decreased expression of the tumor >200microns from the edge (yellow arrow). B) A mask depicts regions selected by computer learning which segment and classify the tumor (red) and non-tumor (blue) regions. C) Single cell segmentation and classification of the tumor cells demonstrates the location of strong (red), moderate (orange), weak (yellow) and negative (white) expressing cells. These classifications allow investigators to quantify metrics of the IHC stain localization. Scale = 150 microns.

Figure 4

Bubble plot of pathologist scores for CAIX and CAXII IHC staining A) for samples from all breast cancer patients on the tissue microarray (TMA), n = 180; or B) for 47 normal breast tissues, 42 ductal carcinoma in situ, 43 invasive ductal carcinomas without metastasis, 46 invasive ductal carcinomas with metastasis and 49 lymph node macrometastases of breast cancer on the TMA.

Figure 5

In vivo bioluminescence and fluorescence images of a mouse following spontaneous metastasis to the axillary lymph node from a primary mammary fat pad (MFP) xenograft tumor. MDA-mb-231 cells were used that were engineered to overexpress luciferase and constitutively express CAIX. The fluorescence image was acquired 24 h after MFP injection of CA9Ab-680 probe.

Figure 6

A) CAIX and CAXII IHC staining in a region of a representative MCF-7 tumor xenograft adjacent to necrosis. B) Quantified staining intensity by distance from necrosis with pixels 0–100 being adjacent to a necrotic region.