Feasibility of induced metabolic bioluminescence imaging in advanced ovarian cancer patients: first results of a pilot study

Abstract

Purpose: The precise determination of energy metabolites is challenged by the heterogeneity of their distribution, their rapid changes after surgical resection and the architectural complexity of malignancies. Induced metabolic bioluminescence imaging (imBI) allows to determine energy metabolites in tissue sections and to co-localize these with histological structures based on consecutive sections stained with HE. In this prospective pilot study patients with suspected advanced ovarian cancer (OC) were enrolled to prove the feasibility of imBI.

Methods: During surgery, suspicious peritoneal metastases were resected and transferred in liquid nitrogen within 30 s. ATP, glucose and lactate concentrations were measured. Furthermore, the expression of monocarboxylate transporters MCT1 and MCT4 was determined by immunofluorescence staining.

Results: 16 patients were screened, 12 entered the study. Final histological assessment revealed ten malignant and two benign peritoneal lesions. In all 12 cases high concentrations of ATP suggested that energy metabolism was not altered by the surgical and transport procedures (mean 0.56 μmol/g, range 0.24-1.21 μmol/g). The mean concentration of glucose was 1.95 μmol/g (range 0.58-4.71 μmol/g). The concentration of lactate was drastically higher in the ten OC cases (mean 24.79 μmol/g, range 17.51-37.16 μmol/g) compared to the benign samples (mean 5.98 μmol/g, range 5.43-6.54 μmol/g). Lactate concentrations seem to correlate with MCT1 (spearman rank correlation ρ = 0.624, 0.05 > p > 0.025), but not with MCT4 (spearman rank correlation ρ = 0.018, p > 0.1).

Conclusions: ImBI is feasible in peritoneal metastases of OC and encourages further effort to elucidate the role of glucose, lactate, MCT1 and MCT4 in OC.

Keywords: ATP; Glucose; Induced metabolic bioluminescence imaging (imBI); Lactate; Monocarboxylate transporters (MCT); Ovarian cancer.

Fig. 1

imBI measurements in human peritoneal metastases of ovarian cancer and in two benign tissue samples. a Representative images of one benign reference (sample no. 3) and one sample of a peritoneal metastasis of a high-grade serous ovarian cancer (sample no. 6) are shown. Adjacent sections were used for hematoxylin and eosin (HE) staining and induced metabolic bioluminescence imaging. These were then color-coded with every color representing a concentration range of ATP, glucose and lactate in µmol/g. Concentrations in µmol/g ATP (b), glucose (c) or lactate (d) of all advanced ovarian cancer patients and the benign references are shown as boxplots: mean (square), median (line), box (25 and 75 % percentile), ±SD (whisker)

Fig. 2

Variance in metabolite concentrations in benign and tumor tissue samples. One benign (3) and one malignant tumor tissue sample (6) were chosen to illustrate intratumoral heterogeneity. From each representative tissue sample three smaller sections were chosen for analyses and measured in triplicate (=9 measurements per metabolite). The corresponding boxplots represent: mean (square), median (line), box (25 and 75 % percentile), ±SD (whisker)

Fig. 3

Monocarboxylate transporter (MCT) 1 and MCT4 expression in benign and OC tissue. Representative images of immunofluorescence stained expression of MCT1 (a) and MCT4 (b) in one human high-grade ovarian cancer (sample no. 6) and one benign tissue sample (sample no. 3) (scale bar 20 µm). The relative MCT intensity of all measured tissue sections is shown as boxplots: mean (square), median (line), box (25 and 75 % percentile), ±SD (whisker)

Fig. 4

Correlation of relative Monocarboxylate transporter (MCT) intensity with lactate concentrations by spearman rank correlation. a Probable correlation between MCT1 staining intensity and lactate concentration (ρ = 0.624, 0.05 > p > 0.025). b No correlation between MCT4 expression and lactate concentration (ρ = 0.018, p > 0.1). Spearman rank correlation was analyzed for all tumor samples (squares) without the benign references (circles), standard deviation (whisker)