Release of volatile organic compounds (VOCs) from the lung cancer cell line CALU-1 in vitro

Abstract

Background: The aim of this work was to confirm the existence of volatile organic compounds (VOCs) specifically released or consumed by lung cancer cells.

Methods: 50 million cells of the human non-small cell lung cancer (NSCLC) cell line CALU-1 were incubated in a sealed fermenter for 4 h or over night (18 hours). Then air samples from the headspace of the culture vessel were collected and preconcentrated by adsorption on solid sorbents with subsequent thermodesorption and analysis by means of gas chromatography mass spectrometry (GC-MS). Identification of altogether 60 compounds in GCMS measurement was done not only by spectral library match, but also by determination of retention times established with calibration mixtures of the respective pure compounds.

Results: The results showed a significant increase in the concentrations of 2,3,3-trimethylpentane, 2,3,5-trimethylhexane, 2,4-dimethylheptane and 4-methyloctane in the headspace of CALU-1 cell culture as compared to medium controls after 18 h. Decreased concentrations after 18 h of incubation were found for acetaldehyde, 3-methylbutanal, butyl acetate, acetonitrile, acrolein, methacrolein, 2-methylpropanal, 2-butanone, 2-methoxy-2-methylpropane, 2-ethoxy-2-methylpropane, and hexanal.

Conclusion: Our findings demonstrate that certain volatile compounds can be cancer-cell derived and thus indicative of the presence of a tumor, whereas other compounds are not released but seem to be consumed by CALU-1 cells.

Figure 1

An exemplary chromatogram of volatile compounds in headspace of the cancer cells CALU-1. 200 ml of headspace from cells cultured in 100 ml medium were collected on a sorption trap filled with Tenax TA, Carboxen 569, Carboxen 1000 and subsequently thermal desorbed into the GC-MS system. The peaks that correspond to compounds discussed in this paper are labeled with letters (see Table 1). Peaks exceeding the range of scale are cut off.

Figure 2

Comparison of VOCs concentrations present at higher concentration in the headspace of CALU-1 cells in culture (blue columns) as compared to medium control (red columns) after 18 h of incubation. Presented are average concentrations (n = 3) with standard deviations. Significant differences are labeled with asterisks.

Figure 4

A and B: Comparison of VOCs concentrations present at lower level in the headspace of cell culture (CALU-1) solution (blue columns) as compared with medium only (red columns) after 4 h (Fig. 4A) and 18 h (Fig. 4B) of incubation. Presented are average concentrations (n = 4 for 4 h of incubation, n = 3 for 18 h of incubation) with standard deviation. Significant differences are labeled with asterisks.

Figure 3

Comparison of VOCs present at lower concentrations present in the headspace of cells in culture (CALU-1) (bright blue and dark blue columns) as compared to medium control (yellow and red columns) after 4 h and 18 h of incubation. Presented are average concentrations (n = 4 for 4 h of incubation, n = 3 for 18 h of incubation) with standard deviations. Significant differences are labeled with asterisks.