Purpose: Checkpoint kinase 1 (CHK1) inhibitors potentiate the DNA-damaging effects of cytotoxic therapies and/or promote elevated levels of replication stress, leading to tumor cell death. Prexasertib (LY2606368) is a CHK1 small-molecule inhibitor under clinical evaluation in multiple adult and pediatric cancers. In this study, prexasertib was tested in a large panel of preclinical models of pediatric solid malignancies alone or in combination with chemotherapy.Experimental Design: DNA damage and changes in cell signaling following in vitro prexasertib treatment in pediatric sarcoma cell lines were analyzed by Western blot and high content imaging. Antitumor activity of prexasertib as a single agent or in combination with different chemotherapies was explored in cell line-derived (CDX) and patient-derived xenograft (PDX) mouse models representing nine different pediatric cancer histologies.Results: Pediatric sarcoma cell lines were highly sensitive to prexasertib treatment in vitro, resulting in activation of the DNA damage response. Two PDX models of desmoplastic small round cell tumor and one malignant rhabdoid tumor CDX model responded to prexasertib with complete regression. Prexasertib monotherapy also elicited robust responses in mouse models of rhabdomyosarcoma. Concurrent administration with chemotherapy was sufficient to overcome innate resistance or prevent acquired resistance to prexasertib in preclinical models of neuroblastoma, osteosarcoma, and Ewing sarcoma, or alveolar rhabdomyosarcoma, respectively.Conclusions: Prexasertib has significant antitumor effects as a monotherapy or in combination with chemotherapy in multiple preclinical models of pediatric cancer. These findings support further investigation of prexasertib in pediatric malignancies.

Checkpoint kinase 1 (CHK1) is a key regulator of the DNA damage response and a mediator of replication stress through modulation of replication fork licensing and activation of S and G-M cell-cycle checkpoints. We evaluated prexasertib (LY2606368), a small-molecule CHK1 inhibitor currently in clinical testing, in multiple preclinical models of pediatric cancer. Following an initial assessment of prexasertib activity, this study focused on the preclinical models of neuroblastoma. We evaluated the antiproliferative activity of prexasertib in a panel of cancer cell lines; neuroblastoma cell lines were among the most sensitive. Subsequent Western blot and immunofluorescence analyses measured DNA damage and DNA repair protein activation. Prexasertib was investigated in several cell line-derived xenograft mouse models of neuroblastoma. Within 24 hours, single-agent prexasertib promoted γH2AX-positive double-strand DNA breaks and phosphorylation of DNA damage sensors ATM and DNA-PKcs, leading to neuroblastoma cell death. Knockdown of CHK1 and/or CHK2 by siRNA verified that the double-strand DNA breaks and cell death elicited by prexasertib were due to specific CHK1 inhibition. Neuroblastoma xenografts rapidly regressed following prexasertib administration, independent of starting tumor volume. Decreased Ki67 and increased immunostaining of endothelial and pericyte markers were observed in xenografts after only 6 days of exposure to prexasertib, potentially indicating a swift reduction in tumor volume and/or a direct effect on tumor vasculature. Overall, these data demonstrate that prexasertib is a specific inhibitor of CHK1 in neuroblastoma and leads to DNA damage and cell death in preclinical models of this devastating pediatric malignancy. .

Collectively, our data demonstrate that the antitumor effects of abemaciclib in preclinical ES models are multifaceted and include cell-cycle inhibition, DNA demethylation, and immunogenic changes.

Over the past decade, the development of new targeted therapeutics directed against specific molecular pathways involved in tumor cell proliferation and survival has allowed an essential improvement in carcinoma treatment. Unfortunately, the scenario is different for sarcomas, a group of malignant neoplasms originating from mesenchymal cells, for which the main therapeutic approach still consists in the combination of surgery, chemotherapy, and radiation therapy. The lack of innovative approaches in sarcoma treatment stems from the high degree of heterogeneity of this tumor type, with more that 70 different histopathological subtypes, and the limited knowledge of the molecular drivers of tumor development and progression. Currently, molecular therapies are available mainly for the treatment of gastrointestinal stromal tumor, a soft-tissue malignancy characterized by an activating mutation of the tyrosine kinase KIT. Since the first application of this approach, a strong effort has been made to understand sarcoma molecular alterations that can be potential targets for therapy. The low incidence combined with the high level of histopathological heterogeneity makes the development of clinical trials for sarcomas very challenging. For this reason, preclinical studies are needed to better understand tumor biology with the aim to develop new targeted therapeutics. Currently, these studies are mainly based on in vitro testing, since cell lines, and in particular patient-derived models, represent a reliable and easy to handle tool for investigation. In the present review, we summarize the most important models currently available in the field, focusing in particular on the three-dimensional spheroid/organoid model. This innovative approach for studying tumor biology better represents tissue architecture and cell–cell as well as cell–microenvironment crosstalk, which are fundamental steps for tumor cell proliferation and survival.

Purpose: Platelet-derived growth factor receptor α (PDGFRα) is implicated in several adult and pediatric malignancies, where activated signaling in tumor cells and/or cells within the microenvironment drive tumorigenesis and disease progression. Olaratumab (LY3012207/IMC-3G3) is a human mAb that exclusively binds to PDGFRα and recently received accelerated FDA approval and conditional EMA approval for treatment of advanced adult sarcoma patients in combination with doxorubicin. In this study, we investigated olaratumab in preclinical models of pediatric bone and soft tissue tumors. Experimental Design: PDGFRα expression was evaluated by qPCR and Western blot analysis. Olaratumab was investigated in in vitro cell proliferation and invasion assays using pediatric osteosarcoma and rhabdoid tumor cell lines. In vivo activity of olaratumab was assessed in preclinical mouse models of pediatric osteosarcoma and malignant rhabdoid tumor. Results: In vitro olaratumab treatment of osteosarcoma and rhabdoid tumor cell lines reduced proliferation and inhibited invasion driven by individual platelet-derived growth factors (PDGFs) or serum. Furthermore, olaratumab delayed primary tumor growth in mouse models of pediatric osteosarcoma and malignant rhabdoid tumor, and this activity was enhanced by combination with either doxorubicin or cisplatin. Conclusions: Overall, these data indicate that olaratumab, alone and in combination with standard of care, blocks the growth of some preclinical PDGFRα-expressing pediatric bone and soft tissue tumor models. Clin Cancer Res; 24(4); 847–57. ©2017 AACR.