Photon and Proton irradiation in Patient-derived, Three-Dimensional Soft Tissue Sarcoma Models

Abstract

Background: Despite their heterogeneity, the current standard preoperative radiotherapy regimen for localized high-grade soft tissue sarcoma (STS) follows a one fits all approach for all STS subtypes. Sarcoma patient-derived three-dimensional cell culture models represent an innovative tool to overcome challenges in clinical research enabling reproducible subtype-specific research on STS. In this pilot study, we present our methodology and preliminary results using STS patient-derived 3D cell cultures that were exposed to different doses of photon and proton radiation. Our aim was: (i) to establish a reproducible method for irradiation of STS patient-derived 3D cell cultures and (ii) to explore the differences in tumor cell viability of two different STS subtypes exposed to increasing doses of photon and proton radiation at different time points.

Methods: Two patient-derived cell cultures of untreated localized high-grade STS (an undifferentiated pleomorphic sarcoma (UPS) and a pleomorphic liposarcoma (PLS)) were exposed to a single fraction of photon or proton irradiation using doses of 0 Gy (sham irradiation), 2 Gy, 4 Gy, 8 Gy and 16 Gy. Cell viability was measured and compared to sham irradiation at two different time points (four and eight days after irradiation).

Results: The proportion of viable tumor cells four days after photon irradiation for UPS vs. PLS were significantly different with 85% vs. 65% (4 Gy), 80% vs. 50% (8 Gy) and 70% vs. 35% (16 Gy). Proton irradiation led to similar diverging viability curves between UPS vs. PLS four days after irradiation with 90% vs. 75% (4 Gy), 85% vs. 45% (8 Gy) and 80% vs. 35% (16 Gy). Photon and proton radiation displayed only minor differences in cell-killing properties within each cell culture (UPS and PLS). The cell-killing effect of radiation sustained at eight days after irradiation in both cell cultures.

Conclusions: Pronounced differences in radiosensitivity are evident among UPS and PLS 3D patient-derived sarcoma cell cultures which may reflect the clinical heterogeneity. Photon and proton radiation showed similar dose-dependent cell-killing effectiveness in both 3D cell cultures. Patient-derived 3D STS cell cultures may represent a valuable tool to enable translational studies towards individualized subtype-specific radiotherapy in patients with STS.

Keywords: Organoid; Patient-derived; Photon; Proton; Radiotherapy; Sarcoma, 3D cell culture; Soft tissue sarcoma.

Fig. 1

Depth dose curve of the spread out proton Bragg peak. After the Lucite pre-absorber (light grey) the beam enters the measurement chamber. The depth dose curve remains steady as it passes through the polylactide sample holder (grey), the Eppendorf tube with soft tissue sarcoma cells (light blue), reaches the exit dosimetry (vertical dark grey line at 19.8 mm depth) and displays a steep decline in the Lucite phantom (light grey).

Fig. 2

Effect of transportation on PD3D viability. Viability of UPS cell culture (A) and PLS cell culture (B) samples retained in the cell culture laboratory (Control) vs. sham irradiation (0 Gy) after four or eight days of incubation. Mean ± standard error of the mean; ns, not significant; 3 independent experiments with 4 technical replicates in each.

Fig. 3

Dose response and kinetics of cancer cell viability following photon and proton irradiation of UPS (Sarc-P-53). Viability of UPS cell culture after four and eight days of incubation following increasing dosages of photon (A) or proton (B) irradiation. Mean ± standard error of the mean; *, p < 0.05 vs. sham irradiation (0 Gy) after four days; #, p < 0.05 vs. sham irradiation (0 Gy) after eight days; at least 1 experiment with 4 technical replicates in each.

Fig. 4

Dose response and kinetics of cancer cell viability following photon and proton irradiation of PLS (Sarc-P-117). Viability of PLS cell culture after four and eight days of incubation following increasing dosages of photon (A) or proton (B) irradiation. Mean ± standard error of the mean; empty circles, cells overgrown; *, p < 0.05 vs. sham irradiation (0 Gy) after four days; #, p < 0.05 vs. sham irradiation (0 Gy) after eight days; at least 1 experiment with 4 technical replicates in each.

Fig. 5

Effects of photon and proton irradiation on UPS (Sarc-P-53) vs. PLS (Sarc-P-117). Viability of UPS and PLS cell culture after four (A, C) and eight (B, D) days of incubation following increasing dosages of photon (A, B) or proton (C, D) irradiation. Mean ± standard error of the mean; *, p < 0.05 comparison between the same dosages of irradiation between UPS and PLS; at least 1 experiment with 4 technical replicates in each.