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Multimodal imaging identifies inflammation and fibrosis in response to pressure overload-induced heart failure and detects alleviation of cardiac remodeling following ventricular unloading (#15)
Aylina Glasenapp1, 2, Katja Derlin2, Gutberlet Marcel2, Laura B. N. Langer1, Hans-Jürgen Wester3, Tobias Ross1, Frank M. Bengel1, James T. Thackeray1
1 Hannover Medical School, Department of Nuclear Medicine , Hannover, Lower Saxony, Germany
Inflammation plays a crucial role in the progression of ischemic heart failure and contributes to fibroblast activation and scar formation. But the role of inflammation in non-ischemic heart failure is less well characterized. We hypothesized that non-invasive multimodality imaging would reveal parallel development of inflammation and fibrosis in response to pressure overload and heart failure. Mechanical unloading of the ventricle would attenuate inflammation and lower interstitial fibrosis resulting in restored contractile function.
C57Bl/6 mice underwent transverse aortic constriction (TAC, n=41) or sham surgery (n=20). To model mechanical unloading, the aortic banding was removed at 3wk post-surgery (rTAC, n=10). Serial PET images using the chemokine receptor CXCR4 ligand 68Ga-pentixafor were acquired at 1 and 3wk after TAC and 1wk and 3wk after rTAC to quantify cardiac inflammation. Cardiac magnetic resonance (CMR) at identical timepoints measured left ventricle (LV) geometry, ejection fraction (EF) and diffuse interstitial fibrosis by T1 mapping. Autoradiography and immunohistochemistry validated regional 68Ga-pentixafor distribution and inflammatory cell infiltration. Interstitial and perivascular fibrosis were confirmed by picrosirius red histology.
TAC increased LV mass (131±20 vs 87±7mg, p<0.001) and lowered ejection fraction (EF, 44±12 vs 66±6%, p<0.001) compared to sham. Failing hearts exhibited diffuse CXCR4 PET signal at 1wk after TAC (% injected dose (ID)/g, 0.96±0.20 vs 0.74±0.25, p<0.001) which declined by 3wk. Early CXCR4 PET signal predicted late EF (r=-0.42, p=0.01). Autoradiography confirmed tracer uptake (p=0.006), with proportional increase of CD68+ macrophages (p<0.01). Macrophage content inversely correlated with LV function (r=-0.82, p<0.01), and corresponded to regions of interstitial fibrosis. CMR T1 mapping revealed prolonged relaxation time after TAC (1151±139 vs 1006±34ms, p=0.003), proportional to EF (r=0.76, p<0.001) and histologic fibrosis (r=0.69, p=0.006). Ventricle unloading led to rapid EF recovery (57±13 vs 44±15%, p=0.022). Both CXCR4 PET signal and T1 relaxation were decreased after rTAC (0.75±0.19 vs 0.96±0.19%ID/g, p=0.026; 1002±61 vs 1151±139ms, p=0.004).
Inflammation and fibrosis occur early after pressure overload heart failure, which can be measured by 68Ga-pentixafor PET and CMR T1 mapping. These findings underscore the crucial relationship between inflammation and fibrosis in the failing heart. Ventricular unloading alleviates both inflammation and fibrosis which can be detected by imaging, suggesting the possibility to monitor therapeutic intervention in heart failure.
Multimodal imaging of inflammation and fibrosis after pressure overload heart failure
Figure 1 (A) Representative short axis PET images of chemokine receptor CXCR4 inflammation with 68Ga-pentixafor in the left ventricle defined by 18F-FDG; T1 maps at corresponding time points display relaxation time. (B) Quantification displays mild elevation of CXCR4 expression in the left ventricle after transverse aortic constriction (TAC) which is alleviated via reverse TAC unloading. (C) Mean T1 relaxation time is elevated after TAC and normalized by reverse TAC unloading.
Keywords: PET, MRI, Preclinical imaging, Inflammation, Heart failure
Boiling Histotripsy Increases Systemic Immune Response against Murine Neuroblastoma Tumor and leads to Long-Term Survival (#9)
Avinash Eranki1, Mario Ries2, Priya Srinivasan1, Anthony Sandler1, AeRang Kim1, Karun Sharma1, Peter Kim7, Bradford Wood8, Chrit Moonen9
1 Children’s National Medical Center, The Sheikh Zayed Institute for Pediatric Surgical Innovation, Washington, United States of America
Neuroblastoma (NBL) is a solid tumor that arises from the developing sympathetic nervous system and represents the most common solid childhood cancer with survival rates of only 20-40%. We previously demonstrated that high intensity focused ultrasound (HIFU) -mediated boiling histotripsy (BH) canproduce controlled, spatially precise mechanical tissue fractionation. The goal of this study was to evaluate the effect of BH to immunotherapy on improving survival in mice.
Mouse NBL tumors (Neuro2a) were grown in A/J mice via subcutaneous hind limb injection of 1×106 tumor cells. Tumors of 13-15 mm were treated with 1) BH alone (day 8), 2) ɑ-CTLA-4 + ɑ-PD-L1 (day 9, 12 and 15), or 3) BH + ɑ-CTLA-4 + ɑ-PD-L1 (N=10 each group). Mice were anesthetized and positioned using a custom-built holder and a 3-axis linear stage, and three foci (1.5×1.5×6 mm @-6dB) were treated within each tumor (fc=1.5 MHz, PRF=1 Hz, total sonication time/focus=15 s, and pulse length = 13 ms). Pain medication was administered in all mice. ELISA of cardiac blood serum, and flow cytometry of splenocytes were performed at three time points (Figure1a). Tumor sections were stained with H&E, CD4+ (helper T-cells), and CD68+ (macrophages) antibodies.
BH + ɑ-CTLA-4 + ɑ-PD-L1 significantly increased survival (62.5%), compared to BH alone or ɑ-CTLA-4 + ɑ-PD-L1 only (0% for both groups), with no recurrence (Figure1). BH resulted in ~40% tumor necrosis at 24-hrs (Figure2a,d). There was a significant increase in CD4+ and CD68+ population 24-hrs post BH (Figure2b,e, Figure2c,f, respectively). In addition, BH significantly reduced concentration of interleukin-10 (IL-10) at 24, 48, & 72-hrs, reflecting a significant increase in macrophages (Figure 2f). In addition, there was a significant increase in IL-2 at 24-hrs, strongly mirroring natural killer cells (NK-cells) activity presenting a similar trend. Interferon-gamma (IFN-ɣ) significantly increases at 72-hrs. Regulatory T-cells (FoxP3+) in the spleen significantly decrease by 72-hrs, and the ratio of CD8+/FoxP3+ significantly increases at 72-hrs post BH. All these results suggest that BH converts the NBL tumor from non-immunogenic to highly immunogenic.
We demonstrated that BH + ɑ-CTLA-4 + ɑ-PD-L1 is capable of treating large established NBL tumors in mice, resulting in long-term survival. BH increased CD8+ populations while reducing FoxP3+ populations and other immune suppressive cytokines, making the tumor more immunogenic. Our approach of using BH + checkpoint inhibitors, and demonstrating BH on a clinical HIFU system, potentially allows for rapid clinical translation of BH therapy (1).
1) Eranki et al. Clin. Cancer Res. in press
Keywords: Focussed Ultrasound, Histotripsy, Immune System Stimulation, Checkpoint Inhibition Therapy