Serum FTIR spectral features associated with HDRA-defined gemcitabine sensitivity in cholangiocarcinoma

Cholangiocarcinoma (CCA) exhibits diverse responses to chemotherapy, underscoring the need for drug sensitivity biomarkers. This proof-of-concept study utilized Fourier transform infrared (FTIR) spectral features to identify ex vivo gemcitabine sensitivity and resistance, as determined by the histoculture drug response assay (HDRA). We analyzed ten formalin-fixed paraffin-embedded tumor samples and 21 serum samples (including seven matched pairs) using synchrotron radiation-based FTIR microspectroscopy and attenuated total reflectance FTIR spectroscopy, respectively. Tissue and serum spectra were evaluated using partial least squares discriminant analysis and principal component analysis, respectively, alongside patient-level spectral ratio comparisons. Both sample types primarily displayed differences in the protein-associated amide I and II regions, with additional variations in carbohydrate- and nucleic acid-associated regions. Tissue spectra demonstrated partial group separation, while serum spectra showed exploratory separation with some overlap. Three serum intensity ratios (1633/1649 cm⁻¹, 1539/1649 cm⁻¹, and 1539/1633 cm⁻¹) remained significantly different after Benjamini-Hochberg correction (adjusted p = 0.041 for each), whereas no significant differences were observed in tissue ratios. Serum-based FTIR spectroscopy shows preliminary promise as a less invasive method for identifying spectral features linked to HDRA-defined gemcitabine sensitivity in CCA. However, these findings do not establish clinical predictive utility and require validation in larger cohorts with comprehensive treatment-response data.