Can sparsely and heterogeneously expressed proteins be detected using tissue microarrays? A simulation study of the hypoxia marker carbonic anhydrase IX (CA IX) in human soft tissue sarcoma

Carbonic anhydrase IX enhances tumor cell proliferation and tumor progression in osteosarcoma

Purpose

We investigated the effect of carbonic anhydrase IX (CA IX) inhibitor under hypoxia and normoxia in SaOS2 human osteosarcoma cell line. We also evaluated the expression of CA IX in 27 patients diagnosed with osteosarcoma.

Materials and methods

CA IX expression in SaOS2 cells cultured under different oxygen tensions was analyzed by Western blotting. To evaluate the effect of CA IX inhibitor, MTS cell viability assay was performed after cells were treated with various concentrations of doxorubicin with or without a CA IX inhibitor. Finally, CA IX expression in patient-derived osteosarcoma samples was evaluated by immunohistochemistry.

Results

Treatment with CA IX inhibitor significantly suppressed cell proliferation and migration under hypoxic conditions. CA IX expression was observed in 81% of 27 patients. The 5-year survival rates in patients with high and low stain scores were 43.8% and 81.8%, respectively.

Conclusion

CA IX inhibitors have the potential to suppress cell proliferation, migration, and chemoresistance.

The hypoxia marker CAIX is prognostic in the UK phase III VorteX-Biobank cohort: an important resource for translational research in soft tissue sarcoma

BACKGROUND

Despite high metastasis rates, adjuvant/neoadjuvant systemic therapy for localised soft tissue sarcoma (STS) is not used routinely. Progress requires tailoring therapy to features of tumour biology, which need exploration in well-documented cohorts. Hypoxia has been linked to metastasis in STS and is targetable. This study evaluated hypoxia prognostic markers in the phase III adjuvant radiotherapy VorteX trial.

METHODS

Formalin-fixed paraffin-embedded tumour biopsies, fresh tumour/normal tissue and blood were collected before radiotherapy. Immunohistochemistry for HIF-1α, CAIX and GLUT1 was performed on tissue microarrays and assessed by two scorers (one pathologist). Prognostic analysis of disease-free survival (DFS) used Kaplan-Meier and Cox regression.

RESULTS

Biobank and outcome data were available for 203 out of 216 randomised patients. High CAIX expression was associated with worse DFS (hazard ratio 2.28, 95% confidence interval: 1.44-3.59, P<0.001). Hypoxia-inducible factor-1α and GLUT1 were not prognostic. Carbonic anhydrase IX remained prognostic in multivariable analysis.

CONCLUSIONS

The VorteX-Biobank contains tissue with linked outcome data and is an important resource for research. This study confirms hypoxia is linked to poor prognosis in STS and suggests that CAIX may be the best known marker. However, overlap between single marker positivity was poor and future work will develop an STS hypoxia gene signature to account for tumour heterogeneity.

Analysis of the intra- and intertumoral heterogeneity of hypoxia in pancreatic cancer patients receiving the nitroimidazole tracer pimonidazole

Background:

Hypoxia is thought to be an adverse feature of pancreatic cancer, but direct measurement in patients is technically challenging. To address this, we characterised the intra/interpatient heterogeneity of hypoxia in surgical specimens from patients who received the 2-nitroimidazole tracer pimonidazole pre-operatively.

Methods:

Pimondazole was given intravenously 16–20 h before pancreatectomy, and the extent and intratumoral heterogeneity of hypoxia determined by image analysis applied to multiple tissue blocks stained by immunohistochemistry. Intra/interpatient heterogeneity was estimated by variance component analysis.

Results:

Pimonidazole staining was analysed in 10 tumours. The extent of labelling varied amongst patients (0–26%), with a broader range of hypoxia in the epithelial (1–39%) compared with the stromal (1–13%) compartments. Variance component analysis demonstrated greater inter- than intrapatient variability of hypoxia, and that multiple (4–5) tumour sections are required to provide a consistent evaluation of its extent in individual tumours.

Conclusions:

There is significant intra- and intertumoral heterogeneity of hypoxia in pancreatic cancers, and these do not appear to be generally more hypoxic than other cancer types. This study establishes the feasibility to assess hypoxia in pancreatic cancer patients using pimonidazole, but questions the reliability of measurements made using a single tissue section.

Additive Influence of Extracellular pH, Oxygen Tension, and Pressure on Invasiveness and Survival of Human Osteosarcoma Cells

BACKGROUND/PURPOSE

The effects of chemical and physical interactions in the microenvironment of solid tumors have not been fully elucidated. We hypothesized that acidosis, hypoxia, and elevated interstitial fluid pressure (eIFP) have additive effects on tumor cell biology and lead to more aggressive behavior during tumor progression. We investigated this phenomenon using three human osteosarcoma (OS) cell lines and a novel in vitro cell culture apparatus.

MATERIALS AND METHODS

U2OS, SaOS, and MG63 cell lines were cultured in media adjusted to various pH levels, oxygen tension (hypoxia 2% O2, normoxia 20% O2), and hydrostatic gage pressure (0 or 50 mmHg). Growth rate, apoptosis, cell cycle parameters, and expression of mRNA for proteins associated with invasiveness and tumor microenvironment (CA IX, VEGF-A, HIF-1A, MMP-9, and TIMP-2) were analyzed. Levels of CA IX, HIF-1α, and MMP-9 were measured using immunofluorescence. The effect of pH on invasiveness was evaluated in a Matrigel chamber assay.

RESULTS

Within the acidic-hypoxic-pressurized conditions that simulate the microenvironment at a tumor's center, invasive genes were upregulated, but the cell cycle was downregulated. The combined influence of acidosis, hypoxia, and IFP promoted invasiveness and angiogenesis to a greater extent than did pH, pO2, or eIFP individually. Significant cell death after brief exposure to acidic conditions occurred in each cell line during acclimation to acidic media, while prolonged exposure to acidic media resulted in reduced cell death. Furthermore, 48-h exposure to acidic conditions promoted tumor invasiveness in the Matrigel assay.

CONCLUSION

Our findings demonstrate that tumor microenvironmental parameters - particularly pH, pO2, and eIFP - additively influence tumor proliferation, invasion, metabolism, and viability to enhance cell survival and must be controlled in OS research.

Tissue microarrays: one size does not fit all

BACKGROUND

Although tissue microarrays (TMAs) are commonly employed in clinical and basic-science research, there are no guidelines for evaluating the appropriateness of a TMA for a given biomarker and tumor type. Furthermore, TMA performance across multiple biomarkers has not been systematically explored.

METHODS

A simulated TMA with between 1 and 10 cores was designed to study tumor expression of 6 biomarkers with varied expression patterns (B7-H1, B7-H3, survivin, Ki-67, CAIX, and IMP3) using 100 patients with clear cell renal cell carcinoma (RCC). We evaluated agreement between whole tissue section and TMA immunohistochemical biomarker quantification to assess how many TMA cores are necessary to adequately represent RCC whole tissue section expression. Additionally, we evaluated associations of whole tissue section and TMA expression with RCC-specific death.

RESULTS

The number of simulated TMA cores necessary to adequately represent whole tissue section quantification is biomarker specific. Although 2-3 cores appeared adequate for B7-H3, Ki-67, CAIX, and IMP3, even as many as 10 cores resulted in poor agreement for B7-H1 and survivin compared to RCC whole tissue sections. While whole tissue section B7-H1 was significantly associated with RCC-specific death, no significant associations were detected using as many as 10 TMA cores, suggesting that TMAs can result in false-negative findings if the TMA is not optimally designed.

CONCLUSIONS

Prior to TMA analysis, the number of TMA cores necessary to accurately represent biomarker expression on whole tissue sections should be established as there is not a one-size-fits-all TMA. We illustrate the use of a simulated TMA as a cost-effective tool for this purpose.

Effect of distributional heterogeneity on the analysis of tumor hypoxia based on carbonic anhydrase IX

Immunohistochemistry (IHC) is used extensively to assess markers for prognosis and sensitivity to novel anticancer agents, as well as in the routine clinical assessment of cancers. Yet, although it is well known that tumors are highly heterogeneous, the resulting sampling error in the measurement of histological markers is often ignored, particularly in basic scientific studies. In this paper, we tested the hypothesis that the optimization of tissue sampling to compensate for heterogeneity improves the correlation between histological measurements of the intrinsic hypoxia marker carbonic anhydrase IX (CAIX) and global tumor oxygenation status. The study was based on a group of 24 patients with invasive cervical carcinoma from whom multiple biopsies were obtained at the time of direct pO2 assessment within the tumor, done as part of a research study. Measurements were made by image analysis of multiple deep sections cut through these biopsies, labeled for CAIX using both immunofluorescence and immunohistochemical techniques, and included tissue microarray (TMA) simulations. Variance and correlation analysis showed that the size of the tissue sample (biopsy or TMA core) was the major factor affecting accuracy of measurement in the sample. Sampling of multiple biopsies/cores also improved the global tumor assessment, provided that these were sufficiently separated in space. Optimization of sampling resulted in an improved correlation of CAIX staining with tumor pO2 measurements, consistent with the hypothesis. However, CAIX was inferior to pO2 measurements as a tool for patient stratification. Improved analytical methods to account for intratumoral heterogeneity are needed to provide reliable measurements of molecular markers.