Approaches to identifying drug resistance mechanisms to clinically relevant treatments in childhood rhabdomyosarcoma

Abstract

Aim: Despite aggressive multiagent protocols, patients with metastatic rhabdomyosarcoma (RMS) have poor prognosis. In a recent high-risk trial (ARST0431), 25% of patients failed within the first year, while on therapy and 80% had tumor progression within 24 months. However, the mechanisms for tumor resistance are essentially unknown. Here we explore the use of preclinical models to develop resistance to complex chemotherapy regimens used in ARST0431. Methods: A Single Mouse Testing (SMT) protocol was used to evaluate the sensitivity of 34 RMS xenograft models to one cycle of vincristine, actinomycin D, cyclophosphamide (VAC) treatment. Tumor response was determined by caliper measurement, and tumor regression and event-free survival (EFS) were used as endpoints for evaluation. Treated tumors at regrowth were transplanted into recipient mice, and the treatment was repeated until tumors progressed during the treatment period (i.e., became resistant). At transplant, tumor tissue was stored for biochemical and omics analysis. Results: The sensitivity to VAC of 34 RMS models was determined. EFS varied from 3 weeks to > 20 weeks. Tumor models were classified as having intrinsic resistance, intermediate sensitivity, or high sensitivity to VAC therapy. Resistance to VAC was developed in multiple models after 2-5 cycles of therapy; however, there were examples where sensitivity remained unchanged after 3 cycles of treatment. Conclusion: The SMT approach allows for in vivo assessment of drug sensitivity and development of drug resistance in a large number of RMS models. As such, it provides a platform for assessing in vivo drug resistance mechanisms at a “population” level, simulating conditions in vivo that lead to clinical resistance. These VAC-resistant models represent “high-risk” tumors that mimic a preclinical phase 2 population and will be valuable for identifying novel agents active against VAC-resistant disease.

Contemporary preclinical mouse models for pediatric rhabdomyosarcoma: from bedside to bench to bedside

“…Although mixed aRMS/eRMS patient phenotypes are clinically possible (56,57), preclinical studies in our sample used aRMS and eRMS separately. Ghilu et al assessed drug sensitivity and resistance in different aRMS and eRMS CDX and PDX models using Single Mouse Testing protocol (58). Another example is the study conducted by Stewart et al, utilizing the orthotopic PDX model of both aRMS and eRMS to test therapeutic targets for RMS through genomic, epigenomic, and proteomic analyses (59).…”

Dose‐dependent bidirectional pharmacological effects of vinorelbine‐based metronomic combination chemotherapy on tumor growth and metastasis and mechanisms in melanoma mouse model

“…Conventional chemotherapy generally involves using the maximum tolerated dose (MTD) to kill as many tumor cells as possible and administering it every 2-4 weeks with a long drug-free break to enable patients to recover from the residual effects of chemotherapy [1,2]. Despite this strategy being supported by a high response rate of disease regression or stabilization, it seems to be less effective over the long term due to MTD-related toxicity, drug resistance, and even tumor progression [3,4]. About 20 years ago, preclinical studies demonstrated that cytotoxic drugs, given in short intervals at low doses and without interruption, could induce tumor regression by targeting tumor vascular endothelial cells [5][6][7].…”