Constitutive activation of NF-κB inducing kinase (NIK) in the mesenchymal lineage using Osterix (Sp7)- or Fibroblast-specific protein 1 (S100a4)-Cre drives spontaneous soft tissue sarcoma.

Aberrant NF-κB signaling fuels tumor growth in multiple human cancer types including both hematologic and solid malignancies. Chronic elevated alternative NF-κB signaling can be modeled in transgenic mice upon activation of a conditional NF-κB-inducing kinase (NIK) allele lacking the regulatory TRAF3 binding domain (NT3). Here, we report that expression of NT3 in the mesenchymal lineage with Osterix (Osx/Sp7)-Cre or Fibroblast-Specific Protein 1 (FSP1)-Cre caused subcutaneous, soft tissue tumors. These tumors displayed significantly shorter latency and a greater multiple incidence rate in Fsp1-Cre;NT3 compared to Osx-Cre;NT3 mice, regardless of sex. Histological assessment revealed poorly differentiated solid tumors with some spindled patterns, as well as robust RelB immunostaining, confirming activation of alternative NF-κB. Even though NT3 expression also occurs in the osteolineage in Osx-Cre;NT3 mice, we observed no bony lesions. The staining profiles and pattern of Cre expression in the two lines pointed to a mesenchymal tumor origin. Immunohistochemistry revealed that these tumors stain strongly for alpha-smooth muscle actin (αSMA), although vimentin staining was uniform only in Osx-Cre;NT3 tumors. Negative CD45 and S100 immunostains precluded hematopoietic and melanocytic origins, respectively, while positive staining for cytokeratin 19 (CK19), typically associated with epithelia, was found in subpopulations of both tumors. Principal component, differential expression, and gene ontology analyses revealed that NT3 tumors are distinct from normal mesenchymal tissues and are enriched for NF-κB related biological processes. We conclude that constitutive activation of the alternative NF-κB pathway in the mesenchymal lineage drives spontaneous sarcoma and provides a novel mouse model for NF-κB related sarcomas.

Genome-wide CRISPR Screen to Identify Genes that Suppress Transformation in the Presence of Endogenous KrasG12D.

Cooperating gene mutations are typically required to transform normal cells enabling growth in soft agar or in immunodeficient mice. For example, mutations in Kras and transformation-related protein 53 (Trp53) are known to transform a variety of mesenchymal and epithelial cells in vitro and in vivo. Identifying other genes that can cooperate with oncogenic Kras and substitute for Trp53 mutation has the potential to lead to new insights into mechanisms of carcinogenesis. Here, we applied a genome-wide CRISPR/Cas9 knockout screen in KrasG12D immortalized mouse embryonic fibroblasts (MEFs) to search for genes that when mutated cooperate with oncogenic Kras to induce transformation. We also tested if mutation of the identified candidate genes could cooperate with KrasG12D to generate primary sarcomas in mice. In addition to identifying the well-known tumor suppressor cyclin dependent kinase inhibitor 2A (Cdkn2a), whose alternative reading frame product p19 activates Trp53, we also identified other putative tumor suppressors, such as F-box/WD repeat-containing protein 7 (Fbxw7) and solute carrier family 9 member 3 (Slc9a3). Remarkably, the TCGA database indicates that both FBXW7 and SLC9A3 are commonly co-mutated with KRAS in human cancers. However, we found that only mutation of Trp53 or Cdkn2a, but not Fbxw7 or Slc9a3 can cooperate with KrasG12D to generate primary sarcomas in mice. These results show that mutations in oncogenic Kras and either Fbxw7 or Slc9a3 are sufficient for transformation in vitro, but not for in vivo sarcomagenesis.

Loss of atrx cooperates with p53-deficiency to promote the development of sarcomas and other malignancies.

The SWI/SNF-family chromatin remodeling protein ATRX is a tumor suppressor in sarcomas, gliomas and other malignancies. Its loss of function facilitates the alternative lengthening of telomeres (ALT) pathway in tumor cells, while it also affects Polycomb repressive complex 2 (PRC2) silencing of its target genes. To further define the role of inactivating ATRX mutations in carcinogenesis, we knocked out atrx in our previously reported p53/nf1-deficient zebrafish line that develops malignant peripheral nerve sheath tumors and gliomas. Complete inactivation of atrx using CRISPR/Cas9 was lethal in developing fish and resulted in an alpha-thalassemia-like phenotype including reduced alpha-globin expression. In p53/nf1-deficient zebrafish neither peripheral nerve sheath tumors nor gliomas showed accelerated onset in atrx+/- fish, but these fish developed various tumors that were not observed in their atrx+/+ siblings, including epithelioid sarcoma, angiosarcoma, undifferentiated pleomorphic sarcoma and rare types of carcinoma. These cancer types are included in the AACR Genie database of human tumors associated with mutant ATRX, indicating that our zebrafish model reliably mimics a role for ATRX-loss in the early pathogenesis of these human cancer types. RNA-seq of p53/nf1- and p53/nf1/atrx-deficient tumors revealed that down-regulation of telomerase accompanied ALT-mediated lengthening of the telomeres in atrx-mutant samples. Moreover, inactivating mutations in atrx disturbed PRC2-target gene silencing, indicating a connection between ATRX loss and PRC2 dysfunction in cancer development.

Targeted Delivery of miRNA 155 to Tumor Associated Macrophages for Tumor Immunotherapy.

Tumor associated macrophages (TAMs) are important components residing in the tumor microenvironment. They are immunosuppressive and promote tumor progression. Targeting TAMs and reprogramming their phenotype may be a promising strategy that can restore antitumor immune responses. In this study, we developed a microRNA delivery system based on lipid-coated calcium phosphonate nanoparticles (CaP/miR@pMNPs) containing conjugated mannose and sterically shielded with a pH-responsive material. The nanocarrier could respond to the low pH in the tumor microenvironment and expose mannose to promote cellular internalization in TAMs. The carrier could reactivate TAMs and reprogram their functions, reverse the immunosuppressive tumor microenvironment, and inhibit tumor growth in a tumor-bearing mouse model. In summary, redirecting the polarization of TAMs is a potential therapeutic strategy for tumor immunotherapy.

Nicotinamide Phosphoribosyltransferase Acts as a Metabolic Gate for Mobilization of Myeloid-Derived Suppressor Cells.

Cancer induces alteration of hematopoiesis to fuel disease progression. We report that in tumor-bearing mice the macrophage colony-stimulating factor elevates the myeloid cell levels of nicotinamide phosphoribosyltransferase (NAMPT), the rate-limiting enzyme in the NAD salvage pathway, which acts as negative regulator of the CXCR4 retention axis of hematopoietic cells in the bone marrow. NAMPT inhibits CXCR4 through a NAD/Sirtuin 1-mediated inactivation of HIF1α-driven CXCR4 gene transcription, leading to mobilization of immature myeloid-derived suppressor cells (MDSC) and enhancing their production of suppressive nitric oxide. Pharmacologic inhibition or myeloid-specific ablation of NAMPT prevented MDSC mobilization, reactivated specific antitumor immunity, and enhanced the antitumor activity of immune checkpoint inhibitors. Our findings identify NAMPT as a metabolic gate of MDSC precursor function, providing new opportunities to reverse tumor immunosuppression and to restore clinical efficacy of immunotherapy in patients with cancer. SIGNIFICANCE: These findings identify NAMPT as a metabolic gate of MDSC precursor function, providing new opportunities to reverse tumor immunosuppression and to restore clinical efficacy of immunotherapy in cancer patients.

Murine Models of Bone Sarcomas.

This chapter describes the procedures for inducing bone sarcoma in mice. Two models based on inoculation of cancer cells in paraosseous and intraosseous site will be described. In addition to providing technical aspects of anesthesia and surgical options, key information of cell preparation and postoperative follow-up will be discussed.

Circulating MicroRNA-92b-3p as a Novel Biomarker for Monitoring of Synovial Sarcoma.

The lack of useful biomarkers is a crucial problem for patients with soft tissue sarcomas (STSs). Emerging evidence has suggested that circulating microRNAs (miRNAs) in body fluids have novel impact as biomarkers for patients with malignant diseases, but their significance in synovial sarcoma (SS) patients remains unknown. Initial global miRNA screening using SS patient serum and SS cell culture media identified a signature of four upregulated miRNAs. Among these candidates, miR-92b-3p secretion from SS cells was confirmed, which was embedded within tumour-derived exosomes rather than argonaute-2. Animal experiments revealed a close correlation between serum miR-92b-3p levels and tumour dynamics. Clinical relevance was validated in two independent clinical cohorts, and we subsequently identified that serum miR-92b-3p levels were significantly higher in SS patients in comparison to that in healthy individuals. Moreover, serum miR-92b-3p was robust in discriminating patients with SS from the other STS patients and reflected tumour burden in SS patients. Overall, liquid biopsy using serum miR-92b-3p expression levels may represent a novel approach for monitoring tumour dynamics of SS.

Immunohistochemical Characterization of Sarcomas in Trp53+/- Haploinsufficient Mice.

The use of immunohistochemical (IHC) staining in determining and/or confirming the cellular origin of poorly differentiated sarcomas was evaluated in this study. Sarcomatous neoplasms were evaluated in a research study conducted in 2 strains of p53+/- haploinsufficient mice. The most common neoplasms were undifferentiated sarcomas, followed by osteosarcomas and rhabdomyosarcomas (RMSs). The RMSs were poorly differentiated and appeared similar to the pleomorphic, or adult type, RMS of humans. All sarcomas stained positive by IHC for the mesenchymal cell intermediate filament vimentin. The RMSs were identified by positive IHC staining for myogenin, a transcription factor specific to skeletal muscle. Osteosarcomas were easily identifiable on hematoxylin and eosin-stained slides; no generally accepted IHC stain specific for bone is presently available. Some of the undifferentiated sarcomas contained numerous macrophages that stained positive for F4/80, a macrophage marker; the positive-staining cells were considered to be infiltrating macrophages. One-third of the neoplasms observed in this study were associated with subcutaneous implanted electronic microchips used for animal identification. Based upon histopathologic evaluation and IHC staining, it was not possible to distinguish neoplasms associated with subcutaneous microchips from neoplasms not associated with microchips.

Generation and comparison of CRISPR-Cas9 and Cre-mediated genetically engineered mouse models of sarcoma.

Genetically engineered mouse models that employ site-specific recombinase technology are important tools for cancer research but can be costly and time-consuming. The CRISPR-Cas9 system has been adapted to generate autochthonous tumours in mice, but how these tumours compare to tumours generated by conventional recombinase technology remains to be fully explored. Here we use CRISPR-Cas9 to generate multiple subtypes of primary sarcomas efficiently in wild type and genetically engineered mice. These data demonstrate that CRISPR-Cas9 can be used to generate multiple subtypes of soft tissue sarcomas in mice. Primary sarcomas generated with CRISPR-Cas9 and Cre recombinase technology had similar histology, growth kinetics, copy number variation and mutational load as assessed by whole exome sequencing. These results show that sarcomas generated with CRISPR-Cas9 technology are similar to sarcomas generated with conventional modelling techniques and suggest that CRISPR-Cas9 can be used to more rapidly generate genotypically and phenotypically similar cancers.

Oncopig Soft-Tissue Sarcomas Recapitulate Key Transcriptional Features of Human Sarcomas.

Human soft-tissue sarcomas (STS) are rare mesenchymal tumors with a 5-year survival rate of 50%, highlighting the need for further STS research. Research has been hampered by limited human sarcoma cell line availability and the large number of STS subtypes, making development of STS cell lines and animal models representative of the diverse human STS subtypes critical. Pigs represent ideal human disease models due to their similar size, anatomy, metabolism, and genetics compared to humans. The Oncopig encodes inducible KRAS G12D and TP53 R167H transgenes, allowing for STS modeling in a spatial and temporal manner. This study utilized Oncopig STS cell line (fibroblast) and tumor (leiomyosarcoma) RNA-seq data to compare Oncopig and human STS expression profiles. Altered expression of 3,360 and 7,652 genes was identified in Oncopig STS cell lines and leiomyosarcomas, respectively. Transcriptional hallmarks of human STS were observed in Oncopig STS, including altered TP53 signaling, Wnt signaling activation, and evidence of epigenetic reprogramming. Furthermore, master regulators of Oncopig STS expression were identified, including FOSL1, which was previously identified as a potential human STS therapeutic target. These results demonstrate the Oncopig STS model's ability to mimic human STS transcriptional profiles, providing a valuable resource for sarcoma research and cell line development.

Immune deficiency augments the prevalence of p53 loss of heterozygosity in spontaneous tumors but not bi-directional loss of heterozygosity in bone marrow progenitors.

p53 loss of heterozygosity (LOH) is a frequent event in tumors of somatic and Li-Fraumeni syndrome patients harboring p53 mutation. Here, we focused on resolving a possible crosstalk between the immune-system and p53 LOH. Previously, we reported that p53 heterozygous bone-marrow mesenchymal progenitor cells undergo p53 LOH in-vivo. Surprisingly, the loss of either the wild-type p53 allele or mutant p53 allele was detected with a three-to-one ratio in favor of losing the mutant allele. In this study, we examined whether the immune-system can affect the LOH directionality in bone marrow progenitors. We found that mesenchymal progenitor cells derived from immune-deficient mice exhibited the same preference of losing the mutant p53 allele as immune-competent matched cells, nevertheless, these animals showed a significantly shorter tumor-free survival, indicating the possible involvement of immune surveillance in this model. Surprisingly, spontaneous tumors of p53 heterozygous immune-deficient mice exhibited a significantly higher incidence of p53 LOH compared to that observed in tumors derived of p53 heterozygous immune-competent mice. These findings indicate that the immune-system may affect the p53 LOH prevalence in spontaneous tumors. Thus suggesting that the immune-system may recognize and clear cells that underwent p53 LOH, whereas in immune-compromised mice, those cells will form tumors with shorter latency. In individuals with a competent immune-system, p53 LOH independent pathways may induce malignant transformation which requires a longer tumor latency. Moreover, this data may imply that the current immunotherapy treatment aimed at abrogating the inhibition of cellular immune checkpoints may be beneficial for LFS patients.

Multimodal targeting of tumor vasculature and cancer stem-like cells in sarcomas with VEGF-A inhibition, HIF-1α inhibition, and hypoxia-activated chemotherapy.

Vascular endothelial growth factor A (VEGF-A) inhibition with pazopanib is an approved therapy for sarcomas, but likely results in compensatory pathways such as upregulation of hypoxia inducible factor 1α (HIF-1α). In addition, cancer stem-like cells can preferentially reside in hypoxic regions of tumors and be resistant to standard chemotherapies. In this study, we hypothesized that the combination of VEGF-A inhibition, HIF-1α inhibition, and hypoxia-activated chemotherapy with evofosfamide would be an effective multimodal strategy. Multimodal therapy was examined in one genetically engineered and two xenograft mouse models of sarcoma. In all three models, multimodal therapy showed greater efficacy than any single agent therapy or bimodality therapy in blocking tumor growth. Even after cessation of therapy, tumors treated with multimodal therapy remained relatively dormant for up to 2 months. Compared to the next best bimodality therapy, multimodal therapy caused 2.8-3.3 fold more DNA damage, 1.5-2.7 fold more overall apoptosis, and 2.3-3.6 fold more endothelial cell-specific apoptosis. Multimodal therapy also decreased microvessel density and HIF-1α activity by 85-90% and 79-89%, respectively, compared to controls. Sarcomas treated with multimodal therapy had 95-96% depletion of CD133(+) cancer stem-like ells compared to control tumors. Sarcoma cells grown as spheroids to enrich for CD133(+) cancer stem-like cells were more sensitive than monolayer cells to multimodal therapy in terms of DNA damage and apoptosis, especially under hypoxic conditions. Thus multimodal therapy of sarcomas with VEGF-A inhibition, HIF-1α inhibition, and hypoxia-activated chemotherapy effectively blocks sarcoma growth through inhibition of tumor vasculature and cancer stem-like cells.

Inhibition of SP1 by the mithramycin analog EC-8042 efficiently targets tumor initiating cells in sarcoma.

Tumor initiating cells (TICs), responsible for tumor initiation, and cancer stem cells (CSCs), responsible for tumor expansion and propagation, are often resistant to chemotherapeutic agents. To find therapeutic targets against sarcoma initiating and propagating cells we used models of myxoid liposarcoma (MLS) and undifferentiated pleomorphic sarcoma (UPS) developed from human mesenchymal stromal/stem cells (hMSCs), which constitute the most likely cell-of-origin for sarcoma. We found that SP1-mediated transcription was among the most significantly altered signaling. To inhibit SP1 activity, we used EC-8042, a mithramycin (MTM) analog (mithralog) with enhanced anti-tumor activity and highly improved safety. EC-8042 inhibited the growth of TIC cultures, induced cell cycle arrest and apoptosis and upregulated the adipogenic factor CEBPα. SP1 knockdown was able to mimic the anti-proliferative effects induced by EC-8042. Importantly, EC-8042 was not recognized as a substrate by several ABC efflux pumps involved in drug resistance, and, opposite to the chemotherapeutic drug doxorubicin, repressed the expression of many genes responsible for the TIC/CSC phenotype, including SOX2, C-MYC, NOTCH1 and NFκB1. Accordingly, EC-8042, but not doxorubicin, efficiently reduced the survival of CSC-enriched tumorsphere sarcoma cultures. In vivo, EC-8042 induced a profound inhibition of tumor growth associated to a strong reduction of the mitotic index and the induction of adipogenic differentiation and senescence. Finally, EC-8042 reduced the ability of tumor cells to reinitiate tumor growth. These data suggest that EC-8042 could constitute an effective treatment against both TIC and CSC subpopulations in sarcoma.

Prenyl Ammonium Salts--New Carriers for Gene Delivery: A B16-F10 Mouse Melanoma Model.

PURPOSE: Prenyl ammonium iodides (Amino-Prenols, APs), semi-synthetic polyprenol derivatives were studied as prospective novel gene transfer agents. METHODS: AP-7, -8, -11 and -15 (aminoprenols composed of 7, 8, 11 or 15 isoprene units, respectively) were examined for their capacity to form complexes with pDNA, for cytotoxicity and ability to transfect genes to cells. RESULTS: All the carriers were able to complex DNA. The highest, comparable to commercial reagents, transfection efficiency was observed for AP-15. Simultaneously, AP-15 exhibited the lowest negative impact on cell viability and proliferation--considerably lower than that of commercial agents. AP-15/DOPE complexes were also efficient to introduce pDNA to cells, without much effect on cell viability. Transfection with AP-15/DOPE complexes influenced the expression of a very few among 44 tested genes involved in cellular lipid metabolism. Furthermore, complexes containing AP-15 and therapeutic plasmid, encoding the TIMP metallopeptidase inhibitor 2 (TIMP2), introduced the TIMP2 gene with high efficiency to B16-F10 melanoma cells but not to B16-F10 melanoma tumors in C57BL/6 mice, as confirmed by TIMP2 protein level determination. CONCLUSION: Obtained results indicate that APs have a potential as non-viral vectors for cell transfection.

Eliminating roles for T-bet and IL-2 but revealing superior activation and proliferation as mechanisms underpinning dominance of regulatory T cells in tumors.

Foxp3(+) regulatory T cells (Tregs) are often highly enriched within the tumor-infiltrating T cell pool. Using a well-characterised model of carcinogen-induced fibrosarcomas we show that the enriched tumor-infiltrating Treg population comprises largely of CXCR3(+) T-bet(+) 'TH1-like' Tregs which are thymus-derived Helios(+) cells. Whilst IL-2 maintains homeostatic ratios of Tregs in lymphoid organs, we found that the perturbation in Treg frequencies in tumors is IL-2 independent. Moreover, we show that the TH1 phenotype of tumor-infiltrating Tregs is dispensable for their ability to influence tumor progression. We did however find that unlike Tconvs, the majority of intra-tumoral Tregs express the activation markers CD69, CD25, ICOS, CD103 and CTLA4 and are significantly more proliferative than Tconvs. Moreover, we have found that CD69(+) Tregs are more suppressive than their CD69- counterparts. Collectively, these data indicate superior activation of Tregs in the tumor microenvironment, promoting their suppressive ability and selective proliferation at this site.

Coamplification of Myc/Pvt1 and homozygous deletion of Nlrp1 locus are frequent genetics changes in mouse osteosarcoma.

Osteosarcomas (OSs) are characterized by high levels of genomic instability (GI). To gain insights into the GI and its contribution toward understanding the genetic basis of OS, we characterized 19 primary and 13 metastatic mouse tumors in a genetically engineered novel mouse model of OS by a combination of genomic techniques. Through the bone-specific deletion of the wild-type Trp53 locus or activation of a metastatic-promoting missense R172Hp53 allele, C57BL/6 mice developed either localized or metastatic OS. Subsequent tumors were isolated and primary cultures created from primary bone and/or distal metastatic lesions, for example, lung and liver. These tumors exhibited high levels of GI with complex chromosomal rearrangements, amplifications, and deletions comparable to human OS. The combined genomic approaches identified frequent amplification of chromosome 15D1 and loss of 11B4 by CGH and/or SKY. Both 15D1 and 11B4 have homology with frequently altered chromosomal bands 8q24 and 17p13 in human OS, respectively. Subsequent array CGH, FISH, and qRT-PCR analysis identified coamplification and overexpression of Myc/Pvt1 transcripts from the 15D1 amplicon and loss and decreased expression of the Nlrp1b from 11B4. The Nlrp1 gene is the key mediator of apoptosis and interacts strongly with caspase 2.

Anti-tumor effect investigation of obtustatin and crude Macrovipera lebetina obtusa venom in S-180 sarcoma bearing mice.

Over the last few decades, research on snake venom toxins has provided not only new tools to decipher molecular details of various physiological processes, but also inspiration to design and develop a number of therapeutic agents. Isolated from the venom of Macrovipera lebetina obutusa (MLO), obtustatin represents the shortest known snake venom monomeric disintegrin specific inhibitor of α1ß1 integrin. This low molecular weight peptide revealed a potent therapeutic effect on melanoma progression. Its oncostatic effect was related to the inhibition of angiogenesis. The aim of the proposed investigation was to study the influence of obtustatin and crude MLO venom on the S-180 sarcoma growth in vitro and in vivo. A S-180 sarcoma bearing mouse model, histological examination, DNA retardation assay were utilized to investigate the anti-tumor effects of MLO and obtustatin. In addition, some biochemical tests (chemiluminescence-ChL, TBA-test) were applied to elucidate the influence of obtustatin and crude MLO venom on the S-180 sarcoma. The size of tumor was significantly inhibited by MLO venom and obtustatin with the inhibitory rate of 50% and 33% at the doses of 10 µg/mouse and 1mg/kg/day respectively. Both ChL and MDA decrease in the two treated groups. Both obtustatin and MLO venom have an anticancer activity and might be candidates for the treatment of malignant sarcoma. All our results have shown that both obtustatin and MLO venom have an anticancer activity and might be candidates for the treatment of malignant sarcoma.

Targeting tumors with a killer-reporter adenovirus for curative fluorescence-guided surgery of soft-tissue sarcoma.

Fluorescence-guided surgery (FGS) of cancer is an area of intense interest. However, FGS of cancer has not yet been shown to be curative due to residual microscopic disease. Human fibrosarcoma HT1080 expressing red fluorescent protein (RFP) was implanted orthotopically in the quadriceps femoris muscle of nude mice. The tumor-bearing mice were injected with high and low-dose telomerase-dependent, green fluorescent protein (GFP)-containing adenovirus OBP-401, which labeled the tumor with GFP. Fluorescence-guided surgery (FGS) or bright light surgery (BLS) was then performed. OBP-401 could label soft-tissue sarcoma (STS) with GFP in situ, concordant with RFP. OBP-401-based FGS resulted in superior resection of STS in the orthotopic model of soft-tissue sarcoma, compared to BLS. High-dose administration of OBP-401 enabled FGS without residual sarcoma cells or local or metastatic recurrence, due to its dual effect of cancer-cell labeling with GFP and killing. High-dose OBP-401 based-FGS improved disease free survival (p = 0.00049) as well as preserved muscle function compared with BLS. High-dose OBP-401-based FGS could cure STS, a presently incurable disease. Since the parent virus of OBP-401, OBP-301, has been previously proven safe in a Phase I clinical trial, it is expected the OBP-401-FGS technology described in the present report should be translatable to the clinic in the near future.

Initial testing (stage 1) of the tubulin binding agent nanoparticle albumin-bound (nab) paclitaxel (Abraxane(®)) by the Pediatric Preclinical Testing Program (PPTP).

BACKGROUND: Nanoparticle albumin-bound paclitaxel (nab-paclitaxel, Abraxane(®)) is FDA approved for the treatment of several adult cancers. Antimitotic agents are essential components for curative therapy of pediatric solid tumors, although taxanes have shown limited activity. Because of the novel formulation, nab-paclitaxel was evaluated against a limited series of Pediatric Preclinical Testing Program (PPTP) solid tumors. PROCEDURES: Nab-paclitaxel was tested against a limited subset of PPTP solid tumor xenograft models at a dose of 50 mg/kg using a q4d × 3 schedule intravenously. RESULTS: Nab-paclitaxel was well tolerated in vivo, producing maximum weight loss of approximately 10% with recovery to baseline weight in the week following the third dose. All 20 xenograft models tested were considered evaluable for efficacy. Nab-paclitaxel induced statistically significant differences in event-free survival (EFS) distribution compared to control in 19 of 20 (95%) of the solid tumors. Objective responses were observed in 12 of 20 (60%) solid tumor xenografts. Complete responses (CR) or maintained CR were observed in 5 of 8 Ewing sarcoma models and 6 of 8 rhabdomyosarcomas. There were no objective regressions in either neuroblastoma (n = 2) or osteosarcoma (n = 2) xenograft panels. At the dose tested, systemic exposures of nab-paclitaxel in mice were somewhat greater than those tolerated in humans. CONCLUSIONS: The high level of activity observed against the rhabdomyosarcoma and Ewing sarcoma PPTP preclinical models makes nab-paclitaxel an interesting agent to consider for pediatric evaluation.

A versatile modular vector system for rapid combinatorial mammalian genetics.

Here, we describe the multiple lentiviral expression (MuLE) system that allows multiple genetic alterations to be introduced simultaneously into mammalian cells. We created a toolbox of MuLE vectors that constitute a flexible, modular system for the rapid engineering of complex polycistronic lentiviruses, allowing combinatorial gene overexpression, gene knockdown, Cre-mediated gene deletion, or CRISPR/Cas9-mediated (where CRISPR indicates clustered regularly interspaced short palindromic repeats) gene mutation, together with expression of fluorescent or enzymatic reporters for cellular assays and animal imaging. Examples of tumor engineering were used to illustrate the speed and versatility of performing combinatorial genetics using the MuLE system. By transducing cultured primary mouse cells with single MuLE lentiviruses, we engineered tumors containing up to 5 different genetic alterations, identified genetic dependencies of molecularly defined tumors, conducted genetic interaction screens, and induced the simultaneous CRISPR/Cas9-mediated knockout of 3 tumor-suppressor genes. Intramuscular injection of MuLE viruses expressing oncogenic H-RasG12V together with combinations of knockdowns of the tumor suppressors cyclin-dependent kinase inhibitor 2A (Cdkn2a), transformation-related protein 53 (Trp53), and phosphatase and tensin homolog (Pten) allowed the generation of 3 murine sarcoma models, demonstrating that genetically defined autochthonous tumors can be rapidly generated and quantitatively monitored via direct injection of polycistronic MuLE lentiviruses into mouse tissues. Together, our results demonstrate that the MuLE system provides genetic power for the systematic investigation of the molecular mechanisms that underlie human diseases.