Soluble mesothelin related peptides (SMRP) and osteopontin as protein biomarkers for malignant mesothelioma: analytical validation of ELISA based assays and characterization at mRNA and protein levels

Our plain-English summary of Soluble mesothelin related peptides (SMRP) and osteopontin as protein biomarkers for malignant mesothelioma: analytical validation of ELISA based assays and characterization at mRNA and protein levels, by A.J. Rai, R.M. Flores, A. Mathew, et al (Clinical Chemistry and Laboratory Medicine, 2010).

The study

• Authors: A.J. Rai, R.M. Flores, A. Mathew, R. Gonzalez-Espinoza, M. Bott, M. Ladanyi, V. Rusch, M. Fleisher
• Journal: Clinical Chemistry and Laboratory Medicine
• Published: 2010;48(2):271-8
• Cited by: 25 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Background: There is a need to identify reliable markers for malignant mesothelioma. Soluble mesothelin related peptides (SMRP) and osteopontin (OPN) have gained interest in recent years for this purpose.

Methods: SMRP (Fujirebio Diagnostics Inc.) and OPN (R&D Inc.) ELISA methods were evaluated for multiple parameters. Concentrations were measured in blood from patients with mesothelioma, normal healthy volunteers, and patients with other (non-mesothelioma) cancers. In silico analysis was performed using the GeoProfiles database. At the protein level, SMRP and OPN were measured in cell culture supernatants, and values were compared in patients pre- and post-extrapleural pneumonectomy.

Results: The SMRP assay demonstrates intra-assay CVs of 2.3% and 3% (at 4.6 nM and 13.7 nM, respectively), and inter-assay CVs of 3.5% and 3.7% at the same concentrations. The limit of detection (LOD) is 0.182 nM. The OPN assay demonstrates intra-assay CVs of 5.8%, 4.1%, and 5.2% (at 1.9, 5.1, and 11.1 ng/mL, respectively), and inter-assay CVs of 8.5%, 8.4%, and 12.1% at the same concentrations. The LOD is 0.032 ng/mL. Both SMRP and OPN in mesothelioma patients were significantly higher than in patients with other (non-mesothelioma) cancer and in healthy volunteers. The two markers do not appear to correlate with each other and exhibit different tissue expression patterns. Protein concentrations of these markers are highest in different sets of cell lines. Finally, SMRP but not OPN concentrations were decreased in five of seven consecutive patients after extrapleural pneumonectomy, compared to their respective pre-operative values.

Conclusions: These assays provide reliable and reproducible quantitation of SMRP and OPN proteins. Both are increased in mesothelioma patients compared to non-mesothelioma controls. However, the two analytes do not correlate with each other and show distinct expression profiles and protein expression. Concentrations of SMRP but not OPN are decreased in post-surgical samples. Our results further characterize these markers, establish assay performance characteristics, and lay the groundwork for further studies to measure these markers in blood.

In plain English

This laboratory study at Memorial Sloan-Kettering Cancer Center in New York evaluated two commercial blood tests for proteins proposed as markers of malignant mesothelioma: soluble mesothelin related peptides (SMRP) and osteopontin (OPN). The authors reported that both tests gave reliable, reproducible measurements. Levels of both proteins were higher in untreated mesothelioma patients than in 51 healthy volunteers and in 30 patients with prostate, breast or ovarian cancer. For SMRP, the figure reported 3.24 plus or minus 4.27 nM in 139 mesothelioma patients, against 0.72 plus or minus 0.47 nM in healthy volunteers. SMRP separated mesothelioma patients from other groups better than OPN did (area under the curve 0.89, 95% confidence interval 0.83 to 0.92, for SMRP versus 0.68, 0.61 to 0.74, for OPN), and the two markers did not track each other. In seven patients who had extrapleural pneumonectomy, SMRP fell after surgery in five, but this was not statistically significant (p=0.07). OPN showed no consistent change. The study did not look at asbestos exposure. The authors called the surgery result preliminary and noted that their healthy reference group was small.

We wrote this plain-English summary from the full article with the help of AI, and a second AI model checked each sentence against the article. It is not the authors' wording; the abstract and the article are their own account.

What the study did and found

• Design: Laboratory (analytical and clinical) validation study of two ELISA blood tests, with an in silico (database) analysis of mRNA in normal tissues, measurements in cell lines, and a small pilot comparison of blood before and after surgery
• Who was studied: Consecutive clinic patients at Memorial Sloan-Kettering Cancer Center, New York, with mesothelioma and no previous treatment (age 55–70, median 64; 139 tested for SMRP, 205 for OPN; mostly stage 2–3, over 90% with an epithelioid component). Controls were 51 healthy volunteers (age 40–59) and 30 patients with prostate, breast or ovarian cancer (10 each, most late stage). A pilot group of 7 consecutive extrapleural pneumonectomy patients was also studied, along with 8 cell lines.
• Exposure: Not studied: the article does not report participants' asbestos exposure, fiber types or jobs. What was measured was blood levels of SMRP and osteopontin.
• Main results:
  • SMRP test: within-run variation (CV) was 2.3% at 4.6 nM and 3% at 13.7 nM. Between-run variation was 3.5% and 3.7%. The limit of detection was 0.182 nM.
  • OPN test: within-run CVs were 5.8%, 4.1% and 5.2% at 1.9, 5.5 and 11.1 ng/mL. Between-run CVs were 8.5%, 8.4% and 12.5%. The limit of detection was 0.032 ng/mL.
  • SMRP levels were 3.24 plus or minus 4.27 nM in mesothelioma patients (n=139), 0.72 plus or minus 0.47 nM in healthy volunteers (n=51), and 0.63 plus or minus 1.12 nM in patients with other cancers (n=30).
  • OPN levels were 129 plus or minus 115 ng/mL in mesothelioma patients (n=205), 41 plus or minus 19 ng/mL in healthy volunteers (n=51), and 43 plus or minus 35 ng/mL in patients with other cancers (n=30).
  • In the 51 healthy volunteers, SMRP ranged up to 0.82 nM and OPN ranged from 7.5 to 67.5 ng/mL. SMRP reached a maximum of 26 nM in mesothelioma patients. Patients with prostate, breast and ovarian cancer had SMRP values up to 5 nM.
  • For separating mesothelioma patients from healthy volunteers and patients with other cancers, the area under the ROC curve was 0.89 (95% CI 0.83–0.92) for SMRP and 0.68 (95% CI 0.61–0.74) for OPN.
  • SMRP and OPN results agreed poorly with each other in the 135 samples that had both measurements.
  • In the database survey of normal tissues, mesothelin (MSLN) mRNA was highest in fetal lung, lung and trachea, while OPN mRNA was highest in kidney.
  • In cell line fluids, SMRP was highest in the Meso37 (mesothelioma) and HeLa lines. OPN was highest in the A549 and PC9 lung cancer lines.
  • In 7 extrapleural pneumonectomy patients, SMRP decreased after surgery in 5. It was unchanged in one and increased slightly in another.
  • The decrease in SMRP after surgery was not statistically significant (p=0.07).
  • OPN showed no consistent change after surgery in the 7 patients.
• The authors' conclusion: The authors concluded that the two tests measure SMRP and OPN reliably and reproducibly, and that both markers are higher in mesothelioma patients than in controls. They also concluded that the two markers do not correlate with each other. They described the post-surgical drop in SMRP as a preliminary result warranting study in a larger group.
• Limitations the authors state:
  • The healthy reference group (51 people) was much smaller than that of an earlier study (409). The authors used this to explain why their SMRP reference range was narrower.
  • OPN values were somewhat lower than the manufacturer's suggested range (53–195 ng/mL). The authors suggested this may reflect their small cohort or a different patient population.
  • The before-and-after surgery comparison involved only seven patients and was not statistically significant.

Topics

The National Library of Medicine indexes this study under subjects our site covers: Mesothelioma.

Medical terms in this study, explained in our Lexicon: Mesothelin, Soluble Mesothelin-Related Peptides (SMRP), Osteopontin, Biomarker, Malignant Mesothelioma, Mesothelioma, Extrapleural Pneumonectomy (EPP).

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