Mouse Model Of Soft Tissue Sarcoma Research Articles

Abstract IA006: Immunobiology of sarcomas and therapeutic implications

Abstract Undoubtedly, the greatest breakthrough in cancer treatment over the past decade has been immunotherapy. However, the immunosuppressive nature of the tumor microenvironment (TME) remains the biggest obstacle to increasing the number of patients that respond to immunotherapy. Unfortunately, initial trials of immune checkpoint inhibitors in patients with soft tissue sarcoma (STS) have achieved very limited success, and the reasons for this are crudely unappreciated. Hence, it is critical to move beyond the current focus on targeting individual cell types of interest and rather adopt a more comprehensive systems-level approach in which we analyze and integrate all the TME components to identify and disable the critical nodes. Our team has characterized the immunobiology of STS via cutting–edge high-dimensional mapping platforms that we have established and standardized for analyzing specimens from patients with STS. We have discovered that tumor infiltrating myeloid cells (TIM) penetrate and dominate the TME of STS provoking the suppression of effective antitumoral T cell immune responses. Using a set of sophisticated multiscale techniques, we deconvoluted the TME of various STS creating a comprehensive map of all immune cell populations present and dissected out chemokine gradients of specific histological regions relevant for the recruitment and development of TIM in the TME of STS. STS TIM are regulated by tumor-derived cytokines to acquire a polarized immunosuppressive phenotype, which in turn de-activates the T cell compartment in the TME. In this way, we elucidated unique myeloid populations as key facilitators of STS progression and mediators of local tumor immunosuppression. Furthermore, we defined metabolic pathways utilized by TIM that contribute to their immunosuppressive properties in STS and manipulated them via glutamine antagonism in our mouse model of STS. Our intervention generated a TME that was less acidic, less hypoxic and more replete with nutrients leading to an intratumoral influx of T cells, both CD4+ and CD8+ cells, along with B cells. These modifications in the TME in combination with anti PD-1 therapy induced better endogenous anti-tumor responses and repurposed TIM markedly thereby reducing the tumor size and improving the survival of mice. Thus, we propose a metabolic strategy to therapeutically target the TME of STS and reprogram their immunosuppressive myeloid niche as a means of enhancing immunotherapy. Citation Format: Nicolas J. Llosa. Immunobiology of sarcomas and therapeutic implications [abstract]. In: Proceedings of the AACR Special Conference: Sarcomas; 2022 May 9-12; Montreal, QC, Canada. Philadelphia (PA): AACR; Clin Cancer Res 2022;28(18_Suppl):Abstract nr IA006.

Hybrid spectral CT reconstruction.

Current photon counting x-ray detector (PCD) technology faces limitations associated with spectral fidelity and photon starvation. One strategy for addressing these limitations is to supplement PCD data with high-resolution, low-noise data acquired with an energy-integrating detector (EID). In this work, we propose an iterative, hybrid reconstruction technique which combines the spectral properties of PCD data with the resolution and signal-to-noise characteristics of EID data. Our hybrid reconstruction technique is based on an algebraic model of data fidelity which substitutes the EID data into the data fidelity term associated with the PCD reconstruction, resulting in a joint reconstruction problem. Within the split Bregman framework, these data fidelity constraints are minimized subject to additional constraints on spectral rank and on joint intensity-gradient sparsity measured between the reconstructions of the EID and PCD data. Following a derivation of the proposed technique, we apply it to the reconstruction of a digital phantom which contains realistic concentrations of iodine, barium, and calcium encountered in small-animal micro-CT. The results of this experiment suggest reliable separation and detection of iodine at concentrations ≥ 5 mg/ml and barium at concentrations ≥ 10 mg/ml in 2-mm features for EID and PCD data reconstructed with inherent spatial resolutions of 176 μm and 254 μm, respectively (point spread function, FWHM). Furthermore, hybrid reconstruction is demonstrated to enhance spatial resolution within material decomposition results and to improve low-contrast detectability by as much as 2.6 times relative to reconstruction with PCD data only. The parameters of the simulation experiment are based on an in vivo micro-CT experiment conducted in a mouse model of soft-tissue sarcoma. Material decomposition results produced from this in vivo data demonstrate the feasibility of distinguishing two K-edge contrast agents with a spectral separation on the order of the energy resolution of the PCD hardware.

Myogenic transcription factors regulate pro-metastatic miR-182.

Approximately thirty percent of patients with soft-tissue sarcoma die from pulmonary metastases. The mechanisms that drive sarcoma metastasis are not well understood. Recently, we identified miR-182 as a driver of sarcoma metastasis in a primary mouse model of soft-tissue sarcoma. We also observed elevated miR-182 in a subset of primary human sarcomas that metastasized to the lungs. Here, we show that myogenic differentiation factors regulate miR-182 levels to contribute to metastasis in mouse models. We find that MyoD directly binds the miR-182 promoter to increase miR-182 expression. Furthermore, mechanistic studies revealed that Pax7 can promote sarcoma metastasis in vivo through MyoD-dependent regulation of pro-metastatic miR-182. Taken together, these results suggest that sarcoma metastasis can be partially controlled through Pax7/MyoD-dependent activation of miR-182 and provide insight into the role that myogenic transcription factors play in sarcoma progression.

Acute tissue injury activates satellite cells and promotes sarcoma formation via the HGF/c-MET signaling pathway.

Some patients with soft-tissue sarcoma (STS) report a history of injury at the site of their tumor. Although this phenomenon is widely reported, there are relatively few experimental systems that have directly assessed the role of injury in sarcoma formation. We recently described a mouse model of STS whereby p53 is deleted and oncogenic Kras is activated in muscle satellite cells via a Pax7(CreER) driver following intraperitoneal injection with tamoxifen. Here, we report that after systemic injection of tamoxifen, the vast majority of Pax7-expressing cells remain quiescent despite mutation of p53 and Kras. The fate of these muscle progenitors is dramatically altered by tissue injury, which leads to faster kinetics of sarcoma formation. In adult muscle, quiescent satellite cells will transition into an active state in response to hepatocyte growth factor (HGF). We show that modulating satellite cell quiescence via intramuscular injection of HGF increases the penetrance of sarcoma formation at the site of injection, which is dependent on its cognate receptor c-MET. Unexpectedly, the tumor-promoting effect of tissue injury also requires c-Met. These results reveal a mechanism by which HGF/c-MET signaling promotes tumor formation after tissue injury in a mouse model of primary STS, and they may explain why some patients develop a STS at the site of injury.

In vivo characterization of tumor vasculature using iodine and gold nanoparticles and dual energy micro-CT

Tumor blood volume and vascular permeability are well established indicators of tumor angiogenesis and important predictors in cancer diagnosis, planning and treatment. In this work, we establish a novel preclinical imaging protocol which allows quantitative measurement of both metrics simultaneously. First, gold nanoparticles are injected and allowed to extravasate into the tumor, and then liposomal iodine nanoparticles are injected. Combining a previously optimized dual energy micro-CT scan using high-flux polychromatic x-ray sources (energies: 40 kVp, 80 kVp) with a novel post-reconstruction spectral filtration scheme, we are able to decompose the results into 3D iodine and gold maps, allowing simultaneous measurement of extravasated gold and intravascular iodine concentrations. Using a digital resolution phantom, the mean limits of detectability (mean CNR = 5) for each element are determined to be 2.3 mg mL−1 (18 mM) for iodine and 1.0 mg mL−1 (5.1 mM) for gold, well within the observed in vivo concentrations of each element (I: 0–24 mg mL−1, Au: 0–9 mg mL−1) and a factor of 10 improvement over the limits without post-reconstruction spectral filtration. Using a calibration phantom, these limits are validated and an optimal sensitivity matrix for performing decomposition using our micro-CT system is derived. Finally, using a primary mouse model of soft-tissue sarcoma, we demonstrate the in vivo application of the protocol to measure fractional blood volume and vascular permeability over the course of five days of active tumor growth.

Uncoupling Cancer Mutations Reveals Critical Timing of p53 Loss in Sarcomagenesis

It is well accepted that cancer develops following the sequential accumulation of multiple alterations, but how the temporal order of events affects tumor initiation and/or progression remains largely unknown. Here, we describe a mouse model that allows for temporally distinct cancer mutations. By integrating a Flp-inducible allele of K-ras(G12D) with established methods for Cre-mediated p53 deletion, we were able to separately control the mutation of these commonly associated cancer genes in vitro and in vivo. We show that delaying p53 deletion relative to K-ras(G12D) activation reduced tumor burden in a mouse model of soft-tissue sarcoma, suggesting that p53 strongly inhibits very early steps of transformation in the muscle. Furthermore, using in vivo RNA interference, we implicate the p53 target gene p21 as a critical mediator in this process, highlighting cell-cycle arrest as an extremely potent tumor suppressor mechanism.

Efficacy of Sunitinib and Radiotherapy in Genetically Engineered Mouse Model of Soft-Tissue Sarcoma

Sunitinib (SU) is a multitargeted receptor tyrosine kinase inhibitor of the vascular endothelial growth factor and platelet-derived growth factor receptors. The present study examined SU and radiotherapy (RT) in a genetically engineered mouse model of soft tissue sarcoma (STS). Primary extremity STSs were generated in genetically engineered mice. The mice were randomized to treatment with SU, RT (10 Gy x 2), or both (SU+RT). Changes in the tumor vasculature before and after treatment were assessed in vivo using fluorescence-mediated tomography. The control and treated tumors were harvested and extensively analyzed. The mean fluorescence in the tumors was not decreased by RT but decreased 38-44% in tumors treated with SU or SU+RT. The control tumors grew to a mean of 1378 mm(3) after 12 days. SU alone or RT alone delayed tumor growth by 56% and 41%, respectively, but maximal growth inhibition (71%) was observed with the combination therapy. SU target effects were confirmed by loss of target receptor phosphorylation and alterations in SU-related gene expression. Cancer cell proliferation was decreased and apoptosis increased in the SU and RT groups, with a synergistic effect on apoptosis observed in the SU+RT group. RT had a minimal effect on the tumor microvessel density and endothelial cell-specific apoptosis, but SU alone or SU+RT decreased the microvessel density by >66% and induced significant endothelial cell apoptosis. SU inhibited STS growth by effects on both cancer cells and tumor vasculature. SU also augmented the efficacy of RT, suggesting that this combination strategy could improve local control of STS.