The application of radiation therapy to the pediatric preclinical testing program (PPTP): Results of a pilot study in rhabdomyosarcoma

Abstract

Background The Pediatric Preclinical Testing Program (PPTP) has been successfully used to determine the efficacy of novel agents against solid tumors by testing them within a mouse-flank in vivo model. To date, radiation therapy has not been applied to this system. We report on the feasibility and biologic outcomes of a pilot study using alveolar and embryonal rhabdomyosarcoma xeno-graft lines. Procedures We developed a high-throughput mouse-flank irradiation device that allows the safe delivery of radiotherapy in clinically relevant doses. For our pilot study, two rhabdomyosarcoma xenograft lines from the PPTP, Rh30 (alveolar) and Rh18 (embryonal) were selected. Using established methods, xenografts were implanted, grown to appropriate volumes, and were subjected to fractionated radiotherapy. Tumor response-rates, growth kinetics, and event-free survival time were measured. Results Once optimized, the rate of acute toxicity requiring early removal from study in 93 mice was only 3%. During the optimization phase, it was observed that the alveolar Rh30 xenograft line demonstrated a significantly greater radiation resistance than embryonal Rh18 in vivo. This finding was validated within the standardized 30 Gy treatment phase, resulting in overall treatment failure rates of 10% versus 60% for the embryonal versus alveolar subtype, respectively. Conclusions Our pilot study demonstrated the feasibility of our device which enables safe, clinically relevant focal radiation delivery to immunocompromised mice. It further recapitulated the expected clinical radiobiology.

FANCD2 Is a Potential Therapeutic Target and Biomarker in Alveolar Rhabdomyosarcoma Harboring the PAX3–FOXO1 Fusion Gene

“…The xenograft lines used for the preclinical testing experiments (obtained from the Pediatric Preclinical Testing Program, Nationwide Children’s Hospital, Columbus, Ohio) were two rhabdomyosarcoma (RMS) lines: Rh18 (embryonal) and Rh30 (alveolar) which were propagated and grown in mouse flanks as previously described (18). These two lines express the two major RMS genotypes: Rh30 (t-ARMS-Rh30) expresses the fusion transcription factor PAX3-FOXO1, while Rh18 (ERMS-Rh18) does not.…”

“…Thereafter, body weights were measured weekly for dose calculation. Mice received fractionated flank-irradiation treatments in clinically-relevant 2-Gy daily doses as previously described using our proprietary mouse-flank irradiation device (18,20). For mice receiving concurrent therapy, radiation was given 2–4 hours after drug administration on days 8–12; irradiation treatment resumed on days 15–19 after a two-day break (reflecting the weekends off of typical treatment courses).…”

Radiation therapy may increase metastatic potential in alveolar rhabdomyosarcoma

“…In the irradiation group, mice received daily 2 Gy fractionated doses to total 20-30 Gy to the flank tumor, while shielding the host, using the apparatus and technique previously described by Kaplon et al [2]. Although one group of five mice did tolerate 40 Gy in the previous study, the rest received doses ranging from 20-30 Gy and developed metastatic events, providing the rationale for the chosen dose.…”

“…A pilot and optimization radiation study for rhabdomyosarcoma involving alveolar (Rh30) and embryonal (Rh18) rhabdomyosarcoma xenografts of the Pediatric Preclinical Testing Program (PPTP)[1], as described by Kaplon et al[2], demonstrated that clinically relevant radiation doses of 2 Gy per fraction up to a total of 40 Gy can be administered to mice with acceptable toxicities. During these experiments, some of the mice from each tumor line developed metastases.…”

“…Low doses of radiotherapy have been shown to induce VEGF expression in hypoxia-mimicking conditions and to activate vascular endothelial growth factor (VEGF) receptor 2, which promotes endothelial cell migration leading to metastasis formation [6]. Kaplon et al described metastatic events in mice without spontaneous recurrence of local disease at the original xenograft site, suggesting that another mechanism other than an irradiated microenvironment contributed to formation of distant metastases [2]. We hypothesized that radiotherapy induced changes in genomic expression were an integral part of the metastatic process along with the altering of the tumor microenvironment.…”