Exploring cisplatin resistance in cancer using mass spectrometry-based bioanalytical tools and patient-derived xenograft cell models

Osteosarcomas (OST) and ovarian cancer (OC) are heterogeneous aggressive malignancies affecting the bones and the female reproductive system, respectively. Their limited treatment options, mainly consisting of chemotherapeutic agents like cisplatin and doxorubicin drugs, often result in the development of drug-resistant phenotypes and metastasis, compromising the treatment efficacies and therefore the patient's survival. Here we aimed at applying bioanalytical tools (mass spectrometry, MS, and inductively coupled plasma MS, ICP-MS) to understand better the cellular mechanisms mediating drug resistance in cancer.

Five commercial and eight primary OST patient-derived xenograft cell lines (PDXCL), and four commercial OC cell lines were subjected to cisplatin-resistance induction by continuous exposure to stepwise increasing drug concentrations. The viability of cell lines was assayed (n=3) after 72h of drug exposure using a cell proliferation reagent to determine the resistance index (RI=IC50resistant/IC50parental). The cellular incorporation of cisplatin within the parental and resistant cell lines and the formation of platinum-DNA adducts were investigated by single cell- and flow injection analysis (FIA)-ICP-MS approaches, respectively. Additionally, MS-based proteomics analyses (LC-Q-TOF) were performed to identify treatment-response predictors at the protein level.

After 1-8 months of cisplatin exposure, ~47% of the cell lines (6/9 commercial and 2/8 PDXCL) developed a stable drug resistance with similar RI values (3.82±1.21) for cisplatin treatment. Up to 10.4 times more platinum was detected in parental cellular cells compared to their cisplatin-resistant counterparts (0.228 ft Pt/cell vs 0.022 ft Pt/cell, respectively). Proteomics analysis reported 8,033 proteins in common for parental and cisplatin-resistant models and a 192-protein treatment response signature. Different proteomics phenotypes were also observed for each cell line and cancer type.

In summary, high heterogeneity for drug resistance development was observed, with the OST PDX cells showing greater drug sensitivity. Moreover, both OST and OC parental cells depicted higher Pt cellular incorporation, which might relate to increased cell death rates. Finally, high-throughput proteomics identified cisplatin-treatment response signatures for OST and OC, which could serve as potential markers for targeted screening. Altogether, this study evidenced the need to employ patient-derived models to better resemble the clinical settings, together with the co-existence of common and case-dependent phenotypic features associated with developing drug resistance in cancer.