P16. Localized Drug Delivery for Retroperitoneal Sarcoma (RPS): An Organotypic Model

Introduction: RPS exhibit a high locoregional recurrence rate after macroscopically complete resection. Systemic therapies have limited efficacy and significant adverse effects. Localized drug delivery platforms delivering these same systemic therapies lead to decreased recurrence and improved survival in small animal models. This study employed organotypic culture to characterize the mechanism of action of paclitaxel (PTX) delivered at sustained supratherapeutic doses.

Submitted to SUS ASC Feb 2026


Methods: 2 million liposarcoma cells (LP6) were subcutaneously inoculated into NU/J mice and allowed to grow until 1,000 mm3. Tumors were harvested, sliced with a vibratome (250 μm), and cultured. LP6 monolayer culture served as a control. Model viability (days 0-10) was established with MTS, trypan blue, and amine reactive dye via flow cytometry. Tumor slice microenvironment characterization was performed via staining with CD44, a cell surface adhesion protein overexpressed in sarcoma. Tumor slice cell viability in response to varying concentrations (0.1-30,000 ng/mL) and exposure time (day 1-4) of PTX was established via MTS and flow cytometry. Differential gene expression was examined using a qPCR cancer gene array. Functional validation of caspase 8 activity was performed with fluorescence inhibitor of caspase staining via flow cytometry.


Results: Organotypic culture viability was maintained up to 7 days with greater than 50% viability. Tumor slices were composed of 82% human liposarcoma cells by CD44 staining with the remainder being mouse stroma. A decrease in tumor slice cell viability was seen only at 30,000 ng/mL and 4-day treatment with PTX (24%) with a 7,000X right shift in IC50 as compared to monolayer (57,505 vs 8.17 ng/mL, p< 0.001), while lower concentrations or shorter exposure did not lead to cell death, contrary to monolayer behavior. A subset of 17 genes was significantly differentially expressed as compared to untreated controls after 4 days of treatment, while no genes were differentially expressed after 1 day. Gene set enrichment analysis demonstrated enrichment in apoptotic, extracellular matrix, cell motility, and cell cycle pathways. Caspase 8 activation occurred at ≥10,000 ng/mL PTX after 4 days of treatment (39% & 75% for 10,000 & 30,000 ng/mL PTX of dying or dead cells, respectively).


Conclusions: A reproducible, representative organotypic culture model of liposarcoma was established. This model exhibited drug resistance at conditions mimicking systemic administration, but demonstrated susceptibility at sustained supratherapeutic conditions, such as those achieved by localized drug delivery systems, via modulation of apoptotic and drug resistance pathways.