Imaging of post-infarct myocardial inflammation with 68Ga-DOTATATE PET/MRI

Background

After myocardial infarction (MI), inflammation and its resolution modulate the extent of myocardial damage. 68Ga-DOTATATE is a PET tracer that binds to somatostatin receptor 2 (SST2), which is up-regulated in pro-inflammatory macrophages [1].

Purpose

We investigated 68Ga-DOTATATE PET/MRI for quantifying post-infarct myocardial inflammation.

Methods

In this prospective observational cohort study, participants with MI underwent 68Ga-DOTATATE PET/MRI at baseline (t0: <2 weeks post-MI) and 3 months (t3M). Patients with prior MI, heart failure, coronary revascularisation, or contraindication to PET/MRI, were excluded. Blood samples were taken at the time of imaging for high sensitivity CRP (hsCRP), high sensitivity troponin I (hsTnI), NTproBNP and peripheral blood monocyte subset counts measured by mass cytometry. 68Ga-DOTATATE maximum Standardised Uptake Values (SUV) and Tissue-to-Background Ratios (TBR) adjusted for blood pool activity were compared in the infarct defined by late gadolinium enhancement (LGE) MRI to remote myocardium at t0 and t3M.

Results

Thirty-two patients (mean age 59 [SD 9] years; 26 [81%] male and 6 [19%] female), comprised of 18 (56%) patients with ST elevation MI and 14 (44%) with non-ST elevation MI, were enrolled. Mean peak troponin was 16,953ng/L (range 408 to >25,000ng/L), and 16 (52%) patients had left ventricular impairment (ejection fraction <50%).

68Ga-DOTATATE PET signal co-localised with myocardial LGE and focal oedema (arrows) on T2-weighted MRI (Fig. 1; asterisk: culprit artery) and had excellent ability to discriminate infarct from remote regions (t0: infarct SUV 2.41 vs. remote 1.58, p<0.0001; t0: infarct TBR 5.08 vs. 3.35, p<0.0001; Fig. 2a).

At 100 (SD 13) days after MI (n=23 patients), residual 68Ga-DOTATATE uptake in the infarct remained higher than remote myocardium (t3M: infarct SUV 1.88 vs. remote 1.27, p<0.0001; t3M: infarct TBR 3.96 vs. remote 2.73, p<0.0001), but was reduced compared to baseline (SUV −22%, p<0.0001; TBR −22%, p=0.002; Fig. 2b).

Reduction in infarct 68Ga-DOTATATE uptake was consistent with overall decreases in hsCRP (2.16 vs. 8.76 mg/L), hsTnI (19 vs. 1365 ng/L) and NTproBNP (372 vs. 959 pg/mL) at t3M vs. t0 (n=23, all p<0.05). Focal oedema on MRI was resolved in 17 (74%) patients at t3M. Infarct-to-remote TBR ratio at t0 was correlated with hsTnI (r=0.35, p<0.05). At t3M (n=9 samples) vs t0 (n=20 samples), there was a reduction in % classical-to-non-classical ratio of peripheral monocytes (mean 6.5 [SD 3.8] vs. 14.4 [SD 11.2], p=0.005).

Conclusions

This is the first prospective study of serial 68Ga-DOTATATE PET/MRI in patients after MI. Here we show that 68Ga-DOTATATE tracks resolving myocardial inflammation. Ongoing work as part of this study seeks to confirm the cellular origin of infarct-related 68Ga-DOTATATE PET signal and SST2 expression within inflamed myocardial tissue, and test its longer-term association with ischaemic myocardial remodelling.

Funding Acknowledgement

Type of funding sources: Foundation. Main funding source(s): Wellcome TrustBritish Heart Foundation

Somatostatin receptor PET/MR imaging of large vessel inflammation in active compared with inactive vasculitis and atherosclerosis

Background

Use of 18F-FDG PET in large vessel vasculitis (LVV) is limited by non-specific uptake due to arterial remodelling and/or atherosclerosis leading to diagnostic uncertainty.

Purpose

To investigate somatostatin receptor 2 (SST2) as a novel inflammation-specific PET imaging target in LVV.

Methods

In a prospective observational cohort study, we tested the ability of PET/MRI using two somatostatin receptor tracers (68Ga-DOTATATE and 18F-FET-βAG-TOCA) to differentiate active from inactive LVV, and aortic atherosclerosis in patients with recent myocardial infarction. Ex vivo mapping of the imaging target was performed using immunofluorescence microscopy, imaging mass cytometry, and bulk, single-cell and single-nuclei RNA sequencing of temporal artery biopsies from LVV patients.

Results

Sixty-one participants were included (LVV, n=27; myocardial infarction ≤2 weeks, n=25; control subjects with an oncological indication for imaging, n=9). LVV patients (mean age 58 [SD 16] years; 78% female; 63% active or grumbling disease) had giant cell arteritis (n=13), Takayasu arteritis (n=13), or unspecified LVV (n=1). Baseline index vessel SST2 PET maximum tissue-to-blood ratio (TBRmax) was 61.8% (95% CI 31.5–99.0%, p<0.0001) higher in patients with active/grumbling LVV than inactive LVV, and 34.6% (95% CI 15.1–57.6%, p=0.0002) higher than recent myocardial infarction (Fig. 1a–c; arrow: PET signal; arrowhead: aortic thickening; asterisk: aortic atherosclerosis), with good diagnostic accuracy (AUC ≥0.86, p<0.001 for both). None of the control subjects without LVV or MI had increased arterial SST2 PET signal (Fig. 1d).

Mean aortic TBRmax was strongly correlated with Indian Takayasu Clinical Activity Score (r=0.82 [95% CI 0.46–0.95], p=0.001) and maximum wall thickness on MRI (r=0.68 [95% CI 0.31–0.87], p=0.002). SST2 PET/MRI was generally consistent with 18F-FDG PET/CT in LVV patients with contemporaneous scans (Fig. 1a, b), but with very low background signal in the brain and heart allowing for unimpeded assessment of nearby coronary, myocardial, and intracranial artery involvement. On follow-up imaging after a mean 9.3 (SD 3.2) months, clinically effective treatment for LVV was associated with a 0.49 ±SEM 0.24 (p=0.04; 22.3%) reduction in SST2 PET TBRmax, with good scan-scan repeatability in inactive LVV patients with no change in treatment (ICC 0.86, 95% CI 0.04–0.99).

SST2 localised to macrophages, pericytes, and perivascular adipocytes in inflamed arterial specimens (Fig. 2; a: H&E; b: imaging mass cytometry; arrow: SST2/CD68 co-staining). SSTR2-expressing macrophages co-expressed pro-inflammatory markers (S100A8, S100A9). Specific SST2 radioligand binding was confirmed by autoradiography in LVV specimens.

Conclusion

This is the first study to examine SST2 PET/MRI in LVV and to provide histological and gene expression data for validation. Here we show this novel approach holds major promise for diagnosis and therapeutic monitoring in LVV.

Funding Acknowledgement

Type of funding sources: Foundation. Main funding source(s): Wellcome Trust; Imperial NIHR Biomedical Research Centre

Physiological and molecular analysis of acid loading mechanisms in squamous and columnar-lined esophagus

Barrett's esophagus (BE) may be an adaptive cellular response to repeated acid exposure. The aims of this study were to compare intracellular acid loading in BE cells with normal squamous esophageal cells. Primary squamous and BE cells were obtained endoscopically and cultured for up to 24 h. Barrett's adenocarcinoma cell lines TE7 and OE-33 were compared with a normal esophageal (NE) cell line OE-21. Extracellular pH was lowered to 6.0 using HCl; specific ion exchangers were blocked pharmacologically and pH microfluorimetry was performed using 2'7'-bis(carboxyethyl)-5(6)-carboxyfluorescein. The effect of prolonged acid preincubations and repeated acid exposure on acid loading and recovery were examined. Acid loading was greater in primary BE than NE cells (DeltapHi -0.22 +/- 0.08 vs.-0.13 +/- 0.01) and maximal in the BE carcinoma cell line TE7 (DeltapHi -0.30 +/- 0.01). Whereas TE7 cells were able to recover fully from repeated acid exposure, OE-21 cells remained profoundly acidic. BE primary and transformed cells utilize DIDS inhibitable sodium-independent chloride/bicarbonate exchange as well as sodium/hydrogen ion exchange for acid loading. In contrast, SE only requires sodium-independent chloride/bicarbonate exchange for acidification. The degree of acid loading is greater in BE than NE cells and it occurs via dual ion exchangers similar to gastric mucosa. Only Barrett's epithelial cells can maintain a physiological pHi following prolonged and repeated reflux exposure, which may confer a teleological advantage.

Whole-body hyperthermia (41.8 degrees C) combined with bimonthly oxaliplatin, high-dose leucovorin and 5-fluorouracil 48-hour continuous infusion in pretreated metastatic colorectal cancer: a phase II study

BACKGROUND

Second- and third-line treatments remain a challenge in advanced colorectal cancer. Studies of bimonthly regimens of high-dose leucovorin (LV) and 5-fluorouracil (5-FU) by continuous infusion combined with oxaliplatin (L-OHP) have shown encouraging response rates in patients not responding to a bimonthly LV/5-FU regimen. Hyperthermic enhancement of L-OHP efficiency by increased DNA adduct formation has been demonstrated in vitro. This study was designed to address feasibility, toxicity and efficacy issues of whole-body hyperthermia (WBH) as an adjunct to L-OHP/LV/5-FU in pretreated patients after progression to first- and second-line treatments with LV/5-FU by continuous infusion and irinotecan.

PATIENTS AND METHODS

Forty-four patients with advanced colorectal cancer, who had progressed during or within 3 months after completion of chemotherapy with LV/5-FU 24-h infusion (LV/5-FU(24h)) (eight patients) or irinotecan combined with or after LV/5-FU(24h )(36 patients), were treated with L-OHP 85 mg/m(2), 2-h intravenous (i.v.) infusion, followed by LV 200 mg/m(2), 1-h i.v. infusion, and 5-FU 3 g/m(2), 48-h continuous infusion. Every second cycle of the biweekly regimen was combined with WBH, thus allowing a comparison of toxicity with and without WBH in the same patient. Whole-body hyperthermia was administered by a humidified radiant heat device. The target temperature of 41.8 degrees C was maintained for 60 min. L-OHP (2-h infusion) was started at a core body temperature of 39 degrees C.

RESULTS

All patients could be evaluated for toxicity, and 41 patients were evaluable for response. A total of 273 L-OHP-containing regimens were administered, 130 with and 143 without WBH. Hyperthermic treatment combined with L-OHP/LV/5-FU showed no unexpected toxicities. WHO grade 3 toxicities were rare and evenly balanced between cycles given with or without WBH. One early death occurred due to sepsis and tumor lysis. The overall response rate was 20%, with two complete and six partial responses. Twenty-three patients (56%) had stable disease and nine patients (22%) progressive disease. With a median observation time of 70 weeks, the median time to progression was 21 weeks [95% confidence interval (CI) 17-25 weeks] and the median survival was 50 weeks (95% CI 39-61 weeks) from the start of therapy.

CONCLUSIONS

This trial suggests some advantage of combining L-OHP/LV/5-FU with WBH. Results compare favorably with the activity of similar regimens without WBH in less extensively pretreated patients. These data support further evaluation and warrant phase III studies.

Amphotropic and VSV-G-pseudotyped retroviral vectors transduce human hematopoietic progenitor cells with similar efficiency

One restriction of retroviral gene transfer into hematopoietic stem cells is the low level of amphotropic virus receptor. In the present study, we examined whether retroviral vectors pseudotyped with the G-protein of vesicular stomatitis virus (VSV) can overcome this restriction. Human progenitor cells purified by magnetic beads and cell sorting were transduced with an amphotropic or VSV-G-pseudotyped retroviral vector containing the truncated human nerve growth factor receptor as a marker gene. Cells were prestimulated with flt-3 ligand, stem cell factor, and interleukin-3 and transduced on fibronectin. Marker gene expression was analyzed by flow cytometry. Transduction efficiencies of amphotropic and VSV-G-pseudotyped virus for CD34+ cells did not differ significantly. Gene transfer into CD34+CD38- cells, which are enriched in more immature progenitors, was not restricted and transfer efficiencies for this subset were also similar for both pseudotypes. The addition of fibronectin improved gene transfer with the amphotropic vector considerably (5- to 19.3-fold, mean 12.6), while the effect on the VSV-G-pseudotype was far less pronounced (1- to 3.9-fold, mean 2.1, P = 0.04). In conclusion, high levels of gene transfer to human hematopoietic progenitors were achieved with an optimized transduction protocol, and transduction efficiencies could not be improved further by the use of VSV-G-pseudotypes.