The hematological malignancies classified as Mixed Lineage leukemias (MLL) harbor fusions of the MLL1 gene to partners that are members of transcriptional elongation complexes. MLL-rearranged leukemias are associated with extremely poor prognosis and response to conventional therapies and efforts to identify molecular targets are urgently needed. Using mouse models of MLL-rearranged acute myeloid leukemia (AML), here we show that genetic inactivation or small molecule inhibition of the protein arginine methyltransferase PRMT5 exhibit anti-tumoral activity in MLL-fusion protein driven transformation. Genome wide transcriptional analysis revealed that inhibition of PRMT5 methyltransferase activity overrides the differentiation block in leukemia cells without affecting the expression of MLL-fusion direct oncogenic targets. Furthermore, we find that this differentiation block is mediated by transcriptional silencing of the cyclin-dependent kinase inhibitor p21 (CDKN1a) gene in leukemia cells. Our study provides pre-clinical rationale for targeting PRMT5 using small molecule inhibitors in the treatment of leukemias harboring MLL-rearrangements.

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Blood cell formation must be appropriately maintained throughout life to provide robust immune function, hemostasis, and oxygen delivery to tissues, and to prevent disorders that result from over- or underproduction of critical lineages. Persistent inflammation deregulates hematopoiesis by damaging hematopoietic stem and progenitor cells (HSPCs), leading to elevated myeloid cell output and eventual bone marrow failure. Nonetheless, antiinflammatory mechanisms that protect the hematopoietic system are understudied. The transcriptional regulator STAT3 has myriad roles in HSPC-derived populations and nonhematopoietic tissues, including a potent antiinflammatory function in differentiated myeloid cells. STAT3 antiinflammatory activity is facilitated by STAT3-mediated transcriptional repression of , which encodes the E2 ubiquitin-conjugating enzyme Ubc13 involved in proinflammatory signaling. Here we demonstrate a crucial role for STAT3 antiinflammatory activity in preservation of HSPCs and lineage-balanced hematopoiesis. Conditional removal from the hematopoietic system led to depletion of the bone marrow lineage Sca-1 c-Kit CD150 CD48 HSPC subset (LSK CD150 CD48 cells), myeloid-skewed hematopoiesis, and accrual of DNA damage in HSPCs. These responses were accompanied by intrinsic transcriptional alterations in HSPCs, including deregulation of inflammatory, survival and developmental pathways. Concomitant /Ubc13 deletion from-deficient hematopoietic cells enabled lineage-balanced hematopoiesis, mitigated depletion of bone marrow LSK CD150 CD48 cells, alleviated HSPC DNA damage, and corrected a majority of aberrant transcriptional responses. These results indicate an intrinsic protective role for STAT3 in the hematopoietic system, and suggest that this is mediated by STAT3-dependent restraint of excessive proinflammatory signaling via Ubc13 modulation.

Non-small cell lung cancer (NSCLC) brain metastasis cell lines and in vivo models are not widely accessible. Herein we report on a direct-from patient-derived xenograft (PDX) model system of NSCLC brain metastases with genomic annotation useful for translational and mechanistic studies. Both heterotopic and orthotopic intracranial xenografts were established and RNA and DNA sequencing was performed on patient and matching tumors. Morphologically, strong retention of cytoarchitectural features was observed between original patient tumors and PDXs. Transcriptome and mutation analysis revealed high correlation between matched patient and PDX samples with more than more than 95% of variants detected being retained in the matched PDXs. PDXs demonstrated response to radiation, response to selumetinib in tumors harboring KRAS G12C mutations and response to savolitinib in a tumor with MET exon 14 skipping mutation. Savolitinib also demonstrated in vivo radiation enhancement in our MET exon 14 mutated PDX. Early passage cell strains showed high consistency between patient and PDX tumors. Together, these data describe a robust human xenograft model system for investigating NSCLC brain metastases. These PDXs and cell lines show strong phenotypic and molecular correlation with the original patient tumors and provide a valuable resource for testing preclinical therapeutics.

FGFRs are commonly altered in non-small cell lung cancer (NSCLC). FGFRs activate multiple pathways including RAS/RAF/MAPK, PI3K/AKT, and STAT, which may play a role in the cellular response to radiation. We investigated the effects of combining the selective FGFR 1-3 tyrosine kinase inhibitor AZD4547 with radiation in cell line and xenograft models of NSCLC. NSCLC cell lines were assessed with proliferation, clonogenic survival, apoptosis, autophagy, cell cycle, and DNA damage signaling and repair assays. In vivo xenografts and IHC were used to confirm in vitro results. NSCLC cell lines demonstrated varying degrees of FGFR protein and mRNA expression. In vitro clonogenic survival assays showed radiosensitization with AZD4547 in two NSCLC cell lines. In these two cell lines, an increase in apoptosis and autophagy was observed with combined radiation and AZD4547. The addition of AZD4547 to radiation did not significantly affect gH2AX foci formation. Enhanced xenograft tumor growth delay was observed with the combination of radiation and AZD4547 compared with radiation or drug alone. IHC results revealed inhibition of pMAPK and pS6 and demonstrated an increase in apoptosis in the radiation plus AZD4547 group. This study demonstrates that FGFR inhibition by AZD4547 enhances the response of radiation in FGFR-expressing NSCLC in vitro and in vivo model systems. These results support further investigation of combining FGFR inhibition with radiation as a clinical therapeutic strategy.

The bone is essential for locomotion, calcium storage, and harboring the hematopoietic stem cells (HSCs) that supply the body with mature blood cells throughout life. HSCs reside at the interface of the bone and bone marrow (BM), where active bone remodeling takes place. Although the cellular components of the BM niche have been characterized, little is known about its epigenetic regulation. Here we find that the histone methylation regulator PTIP (Pax interaction with transcription-activation domain protein-1) is required to maintain the integrity of the BM niche by promoting osteoclast differentiation. PTIP directly promotes chromatin changes required for the expression of Pparγ (peroxisome proliferator-activated receptor-γ), a transcription factor essential for osteoclastogenesis. PTIP deletion leads to a drastic reduction of HSCs in the BM and induces extramedullary hematopoiesis. Furthermore, exposure of acute myeloid leukemia cells to a PTIP-deficient BM microenvironment leads to a reduction in leukemia-initiating cells and increased survival upon transplantation. Taken together, our data identify PTIP as an epigenetic regulator of osteoclastogenesis that is required for the integrity of the BM niche to sustain both normal hematopoiesis and leukemia.

M6620, a selective ATP-competitive inhibitor of the ATM and RAD3-related (ATR) kinase, is currently under investigation with radiation in patients with non–small cell lung cancer (NSCLC) brain metastases. We evaluated the DNA damage response (DDR) pathway profile of NSCLC and assessed the radiosensitizing effects of M6620 in a preclinical NSCLC brain metastasis model. Mutation analysis and transcriptome profiling of DDR genes and pathways was performed on NSCLC patient samples. NSCLC cell lines were assessed with proliferation, clonogenic survival, apoptosis, cell cycle, and DNA damage signaling and repair assays. NSCLC brain metastasis patient-derived xenograft models were used to assess intracranial response and overall survival. In vivo IHC was performed to confirm in vitro results. A significant portion of NSCLC patient tumors demonstrated enrichment of DDR pathways. DDR pathways correlated with lung squamous cell histology; and mutations in ATR, ATM, BRCA1, BRCA2, CHEK1, and CHEK2 correlated with enrichment of DDR pathways in lung adenocarcinomas. M6620 reduced colony formation after radiotherapy and resulted in inhibition of DNA DSB repair, abrogation of the radiation-induced G2 cell checkpoint, and formation of dysfunctional micronuclei, leading to enhanced radiation-induced mitotic death. The combination of M6620 and radiation resulted in improved overall survival in mice compared with radiation alone. In vivo IHC revealed inhibition of pChk1 in the radiation plus M6620 group. M6620 enhances the effect of radiation in our preclinical NSCLC brain metastasis models, supporting the ongoing clinical trial (NCT02589522) evaluating M6620 in combination with whole brain irradiation in patients with NSCLC brain metastases.

Patient-derived model systems are important tools for studying novel anti-cancer therapies. Patient-derived xenografts (PDXs) have gained favor over the last 10 years as newer mouse strains have improved the success rate of establishing PDXs from patient biopsies. PDXs can be engrafted from head and neck cancer (HNC) samples across a wide range of cancer stages, retain the genetic features of their human source, and can be treated with both chemotherapy and radiation, allowing for clinically relevant studies. Not only do PDXs allow for the study of patient tissues in an in vivo model, they can also provide a renewable source of cancer cells for organoid cultures. Herein, we review the uses of HNC patient-derived models for radiation research, including approaches to establishing both orthotopic and heterotopic PDXs, approaches and potential pitfalls to delivering chemotherapy and radiation to these animal models, biological advantages and limitations, and alternatives to animal studies that still use patient-derived tissues.