Tumor-targeting Salmonella typhimurium A1-R arrests a doxorubicin-resistant PDGFRA-amplified patient-derived orthotopic xenograft mouse model of pleomorphic liposarcoma

Abstract

Pleomorphic liposarcoma (PLPS) is a recalcitrant soft-tissue sarcoma (STS) subtype in need of transformative therapy. We have previously established a patient-derived orthotopic xenograft (PDOX) model, of PLPS with PDGFRA amplification, using surgical orthotopic implantation. In the current study, the PLPS PDOX model was randomized into 3 groups of 7 mice each: untreated control; doxorubicin (DOX)-treated; and treated with Salmonella typhimurium A1-R (S. typhimurium A1-R) expressing green fluorescent protein (GFP). Tumor volume and body weight were monitored during the treatment period. The PLPS PDOX was resistant to DOX. In contrast, the PLPS PDOX was highly sensitive to S. typhimurium A1-R. There was no significant body-weight loss among these 3 groups. Fluorescence imaging demonstrated that S. typhimurium A1-R-GFP was very effective to target the PLPS PDOX tumor. The current study demonstrates that a PLPS PDOX, resistant to first-line therapy DOX, was highly sensitive to tumor targeting S. typhimurium A1-R.

Keywords: PDGFRA amplification; Salmonella typhimurium A1-R; green fluorescent protein; patient-derived orthotopic xenograft; pleomorphic liposarcoma; soft-tissue sarcoma; tumor targeting.

Figure 1. Treatment protocol of pleomorphic liposarcoma (PLPS) PDOX

Treatment protocol. Group 1, untreated control (n =7); Group 2, treated with doxorubicin (DOX) (3 mg/kg, i.v., weekly, 2 weeks, n = 7); Group 3, treated with S. typhimurium A1-R (5×10⁷CFU/100 ml, i.v., weekly, 2 weeks, n = 7). All mice included in this study were sacrificed on day 15 to harvest tumor for further histological evaluation.

Figure 2. Efficacy of S. typhimurium A1-R vs. DOX on the PLPS PDOX

The line graphs show relative tumor volume on each time point. Relative tumor is the tumor volume at any given time point at the beginning of the treated period divided by the tumor volume. Error bars: ± SD. * p < 0.05.

Figure 3. Macroscopic imaging of control and treated tumor

Images were obtained at the end of the treatment period. Scale bar: 10mm.

Figure 4. Tumor targeting S. typhimurium A1-R-GFP of the PLPS PDOX

S. typhimurium, expressing green fluorescent protein (GFP), was cultivated in serial dilution from supernatants of tumor homogenates by mincing tumor tissue on agar medium. Grown colonies of bacterial were imaged by GFP fluorescence. Fluorescent bacteria were detected at all dilutions in the tumor treated with S. typhimurium A1-R. Scale bar: 10 mm, 2.5 mm at high magnification. BF: Bright field, GFP: Green fluorescent protein.

Figure 5. Body weight of treated PLPS PDOX mouse models

Bar graphs show the relative body weight of mice treated with each agent. Relative body weight as the body weight at any given time divided by the inhibited body weight. Error bars: ± SD. N.S.: not significant.

Figure 6. Tumor histology

(A) Control tumor (B) Untreated PLPS PDOX. (C) DOX group. (D) S. typhimurium A1-R group. Scale bars: 100μm.