Maroun Karam

Tumor Targeting of MMP-2/9 Activatable Cell-Penetrating Imaging Probes Is Caused by Tumor-Independent Activation

Activatable cell-penetrating peptides (ACPPs) are a new class of promising molecular imaging probes for the visualization of enzymes in vivo. The cell-penetrating function of a polycationic peptide is efficiently blocked by intramolecular electrostatic interactions with a polyanionic peptide. Proteolysis of a cleavable linker present between the polycationic cell-penetrating peptide and polyanionic peptide affords dissociation of both domains and enables the activated cell-penetrating peptide to enter cells. Here, we aimed to develop an ACPP sensitive to matrix metalloproteinase-2 and -9 (MMP-2/9) for nuclear imaging purposes. Methods: MMP-2/9 ACPPs and nonactivatable cell-penetrating peptides (non-ACPP) were prepared by 9-fluorenylmethyloxycarbonyl solid-phase peptide synthesis and labeled with 177Lu or 177Lu/125I for dual-isotope studies. The in vivo biodistribution of these probes was assessed in MMP-2/9–positive tumor-bearing mice (n = 6) and healthy mice (n = 4) using γ-counting. Furthermore, a radiolabeled cell-penetrating peptide serving as a positive control was evaluated in tumor-bearing mice (n = 6). Results: Biodistribution studies showed a 5-fold-higher retention of ACPP in tumor than in muscle (P < 0.01) and a 6-fold-higher tumor retention relative to non-ACPP (P < 0.01), supporting earlier studies on fluorescently labeled ACPPs proposing activation by tumor-associated MMP-2/9. Surprisingly, however, the uptake of ACPP was significantly higher than that of non-ACPP in almost all tissues (P < 0.01). To unravel the activation process of ACPP in vivo, we developed dual-isotope ACPP analogs (dACPPs) that allowed us to discriminate between uncleaved dACPP and activated dACPP. In vivo biodistribution of dACPP indicated that the tissue-associated counts originated from activated dACPP. Interestingly, dACPP administration to healthy mice, compared with MMP-2/9–positive tumor-bearing mice, resulted in a similar dACPP biodistribution. Furthermore, a radiolabeled cell-penetrating peptide showed tumor-to-tissue ratios equal to those found for ACPP (P > 0.05). Conclusion: This study demonstrates that the tumor targeting of radiolabeled MMP-2/9 ACPPs is most likely caused by the activation in the vascular compartment rather than tumor-specific activation, as suggested earlier. The results in the present paper indicate that different and more tissue-specific enzyme–ACPP combinations are needed to unleash the full potential of the elegant ACPP concept in living animals.

Bilateral Hilar Foci on 18F-FDG PET Scan in Patients Without Lung Cancer: Variables Associated with Benign and Malignant Etiology

Bilateral hilar 18F-FDG–avid foci are often noted on PET studies of patients without lung cancer. This finding may lead to diagnostic uncertainty about the presence of metastatic disease. Our objective was to evaluate features of these foci associated with benign or malignant etiology. Methods: We performed a retrospective study of patients with cancer with bilateral hilar foci on 1 or 2 sequential 18F-FDG PET studies between 2002 and 2006. Patients with lung cancer, sarcoidosis, or anthracosis/silicosis were excluded. Variables evaluated were maximum standard uptake values (SUV max), purity (absence of 18F-FDG–avid foci in nonhilar mediastinal nodes), symmetry (difference between left and right side SUV max), the primary tumor, node size determined by CT, and, in those who participated in 2 studies, stability of uptake over time. The gold standard was histologic diagnosis or long-term clinical follow-up (range, 19–41 mo; mean, 25 mo). Results: Fifty-one patients with the finding of bilateral hilar 18F-FDG–avid foci underwent a staging-only PET study; 52 scans from an additional set of patients demonstrated this abnormality on at least 1 of 2 sequential studies, the first of which was performed for staging. On univariate analysis, variables associated with malignancy were SUV max (6.6 ± 4.1 vs. 3.5 ± 1.0 for benign, P < 0.001; t test); impurity (P < 0.001; χ2 test), with 79% of impure scans versus 18% of pure scans being malignant; node size determined by CT (P = 0.027); and change in uptake between scans 1 and 2 (change in SUV = 2.7 ± 2.1 vs. 0.73 ± 1.1 for benign, P < 0.01; t test). Variables associated with benign etiology were: symmetry (difference between left and right sides = 0.57 ± 0.54 for benign vs. 1.8 ± 1.7 for malignant, P < 0.01), purity, and colorectal primary (75% of colorectal were benign vs. 34% of breast, 49% of lymphoma, and 37% of other, P = 0.030; χ2 test). After multivariate analysis, SUV max and purity were found to be independent predictors, with the odds of malignancy increasing by 1.54 (95% confidence interval, 1.16–2.05) for each unit increase in SUV and decreasing by 0.08 (95% confidence interval, 0.03–0.22) if pure. Conclusion: In patients with nonlung cancer, in particular colorectal, foci of symmetric and mild uptake limited to the hilar regions that are stable on 2 sequential PET studies despite intervening anticancer therapy are likely related to a benign etiology.

Fdg positron emission tomography/computed tomography scan may identify mantle cell lymphoma patients with unusually favorable outcome

ObjectivePatients diagnosed with mantle cell lymphoma (MCL) have generally poor prognosis, but a minority have a longer survival. There are no markers to identify this group and no generally established prognostic index for MCL. Our objective was to assess the prognostic value of the staging FDG PET/computed tomography (CT) scan. MethodsWe retrospectively analyzed initial scans performed at three institutions on biopsy-proven, cyclin D (+) MCL patients. The association of the SUVmax of the ‘hottest focus’ with overall survival (OS) and failure-free survival (FFS) was evaluated. Receiver operating characteristic analysis of SUVmax versus survival was used to establish a cut-off point of 4.83. In addition, PET findings were compared with contrast-enhanced CT performed within 3 weeks in patients from one institution. ResultsBoth the OS and FFS for patients with SUVmax greater than 5 were significantly decreased (P<0.01 and <0.001, respectively) as compared with the patients with SUV ≤5. The 5-year OS for group with SUVmax ≤5 was 87.7% and for SUVmax greater than 5 it was 34%. For SUVmax ≤5, the median FFS was 45.3 months as compared with 10.6 months for SUVmax greater than 5. PET changed the stage as compared with CT alone in 45% of patients. ConclusionStaging FDG PET/CT is superior to CT and may be used in the future for identification of a subset of MCL patients with a better outcome than otherwise expected.

Diuretic renogram clearance half-times in the diagnosis of obstructive uropathy: effect of age and previous surgery

&NA; Diuretic renography with radiotracers has been used successfully to diagnose obstruction in patients with hydronephrosis. Controversy persists with regard to the best approach for the interpretation of renogram curves: visual analysis or a quantitative index, i.e. the clearance half‐time. The latter is often reported to be in the intermediate or non‐diagnostic range. It is important to measure the incidence of equivocal half‐times in various subsets of patients with hydronephrosis in order to determine in which settings the measurement of this index may be clinically useful. We performed a retrospective study of diuretic renograms performed at our institution between 1997 and 2000 for the evaluation of suspected ureteropelvic junction (UPJ) obstruction. Vigorous intravenous hydration, exceeding current guidelines, was employed in these patients. Three hundred and seventy‐seven renogram curves in 205 patients were analysed. Patients were divided into three groups: >1 year of age; ≤1 year of age; and those who had previously undergone surgical correction of obstruction regardless of age. Patients with reflux or anatomical abnormalities of the urinary tract, those with chronic renal failure, those with bilateral normal clearances before furosemide administration and those with unilateral normal clearances before furosemide administration with contralateral poor renal function were excluded. In the remaining 119 patients, 205 clearance half‐times were classified as normal before furosemide, normal after furosemide (half‐time, <10 min), prolonged (half‐time, >20 min) or intermediate (half‐time, 10–20 min). In patients >1 year of age, 37% of 101 renograms showed normal half‐times before furosemide, 20% showed normal half‐times after furosemide, 44% showed prolonged half‐times and none (0%) showed an intermediate half‐time. In patients ≤1 year of age, there was a statistically significantly different distribution, with 48% of 64 renograms showing normal washout before furosemide, 16% showing normal clearance after furosemide, 19% showing abnormal half‐times and 17% showing intermediate half‐times. In 33 renograms from patients who had undergone corrective surgery, 49% had normal half‐times, 24% had prolonged half‐times and 27% had intermediate half‐times. It can be concluded that, when using the selection criteria, hydration, acquisition and processing protocols and half‐time definition employed in this study, the addition of a clearance measurement in patients older than 1 year with suspected UPJ disease enhances patient classification and may improve the diagnostic confidence. There was a significantly higher incidence of intermediate half‐times in patients with native disease aged <1 year than in those >1 year. Caution is advised when interpreting this finding in this age group. The measurement of washout was less useful in patients who had undergone a corrective procedure, because of the high rate of ‘indeterminate’ and ‘abnormal’ values in spite of successful surgery. Vigorous intravenous hydration, exceeding current standards, may have contributed to the lower incidence of intermediate half‐times than reported previously.

The role of bone scintigraphy in treatment planning, and predicting pain relief after kyphoplasty.

BackgroundThe role of whole-body 99mTc-MDP bone scanning in the management of vertebral compression fractures with kyphoplasty has not been clearly established. ObjectiveTo determine the accuracy of bone scanning in patient selection, planning treatment and predicting response to kyphoplasty. MethodsRetrospective chart reviews were undertaken of all kyphoplasties performed by the same orthopaedic surgeon between June 2000 and June 2004. All patients who underwent plain radiographs (X-ray) of the spine and bone scanning within 4 weeks of treatment were included. Response to treatment was assessed via a questionnaire administered to the patient 3 weeks after intervention and concomitant objective assessment. Response was graded as excellent, intermediate or poor. Each bone scan was reviewed by two nuclear physicians blinded to the initial scan results, level of treatment and therapeutic response. The readers were asked to indicate the level(s) to be treated according to the bone scan findings. Sites of chronic fractures were also recorded. ResultsSixty-six procedures on 60 patients fulfilled the selection criteria. Fifty-three patients were managed by X-ray and bone scanning (A) and seven were managed by X-ray only (B). There was a significant difference in the rates of sub-optimal results between (A) and (B) (11/53 vs. 7/7, P=0.0001). There was also a significant difference in chronic fracture rates between patients with excellent outcome and those with sub-optimal results (3/42 vs. 7/11, P=0.0002). A high rate of incorrect level selection (3/7) was found in (B). In 12 patients (20%) X-ray showed multiple fractures but the bone scanning demonstrated only one level of acute disease. ConclusionsBone scanning is an excellent predictor of response to kyphoplasty and decreases the number of vertebrae to be treated as suggested by X-ray. Preoperative bone scanning is recommended to avoid incorrect selection of treatment level. Even when the appropriate level has been selected an incomplete response can be expected if additional chronic fracture is seen on bone scanning. In the event of unexpected incomplete response, re-evaluation with bone scanning may demonstrate new disease amenable to therapy.

Increasing the radiochemical purity of 99mTc sestamibi commercial preparations results in improved sensitivity of dual-phase planar parathyroid scintigraphy.

BackgroundPoor results for dual-phase parathyroid scintigraphy have recently prompted increased use of dual-tracer imaging. We noticed that seminal studies used higher radiochemical purity than provided by current commercial preparations meeting US Pharmacopea (USP) specifications (90% of technetium bound to sestamibi). We surmised that the presence of unbound Tc (non-MIBI tracer) might hamper dual-phase detection that is dependent on rapid wash-out of technetium from thyroid tissue. PurposeTo test the hypothesis that reducing non-MIBI tracer will enhance thyroid wash-out and improve sensitivity of dual-phase imaging. MethodsStarting in April 2003 we decreased the technetium to sestamibi ratio. This resulted in a significant decrease of non-MIBI tracer from 8.1±2.2% (SD) (group 1, n=42) to 3.5±1.1% (group 2, n=47) (P<0.05 t-test). We performed a retrospective review of 89 patients with primary hyperparathyroidism who underwent imaging and subsequent surgery. The pathological findings served as the ‘gold standard’. ResultsScanning detected 21/39 diseased glands (sensitivity=54%) in group 1 patients. In group 2 imaging detected 38/45 diseased glands (sensitivity=84%). An improvement in sensitivity (P<0.01) was achieved by modifying the radiopharmaceutical preparation. ConclusionsElevated levels of non-MIBI tracer in Tc-MIBI commercial preparations result in persistent thyroid background activity that may interfere with detection of parathyroid pathology. Achieving a higher degree of radiochemical purity (at least 95% bound, 5% impurities) than required by USP may be needed for optimal results. The large variation in sensitivity reported in the literature may be related in part to non-uniform radiopharmaceutical preparation.

Features of large cell transformation of indolent lymphomas as observed on sequential PET/CT.

ObjectiveDetection of large cell transformation (LCT) has been reported with the increasing use of PET/computed tomography (CT) in patients with indolent lymphomas. However, there is little information on PET/CT characteristics, specifically, the distribution of lesion maximum standardized uptake value (SUVmax) within a patient, or SUVmax changes before and after LCT. Our objectives were to compare SUVmax values and distribution between nontransformed and LCT patients; to compare SUVmax of LCT and nontransformed lesions in patients with documented focal transformation; and to measure the SUVmax changes in patients before and after LCT. MethodsRetrospective study of patients with LCT (n=29)compared with nontransformed (n=41), and comparison of LCT and nontransformed lesions within patients and over time. ResultsOn average, the highest SUVmax was greater in LCT patients than in nontransformed patients. In addition, there was a wider range of SUVmax values in the LCT group compared with the nontransformed group (P<0.05). The median ratio of the SUVmax of 12 LCT to nontransformed biopsy-proven lesions in the same patient was 4.3, P value of less than 0.05 (range 2.6–15.5). In 10 of 12 patients it was greater than or equal to 3. No change in highest SUVmax and distribution was shown on serial PET in untreated nontransformed patients. ConclusionLCT is often focal and is associated with higher SUVmax than nontransformed. The emergence of a focus with SUVmax three times or higher than others on asingle scan, or that has tripled or more in value on serial scans, should raise suspicion for LCT.

Successful thyroid tissue ablation as defined by a negative whole-body scan or an undetectable thyroglobulin: a comparative study.

BackgroundSuccessful thyroid tissue ablation of patients with well-differentiated thyroid cancer can be defined by a negative whole-body scan (WBS) and/or an undetectable thyroglobulin (Tg). Variables associated with success are poorly understood. Tg measurement, although more sensitive than WBS, has not been firmly established as the sole monitoring method. In a previous study, we retrospectively evaluated the variables associated with scintigraphic success. Ablation dose (AD) was the only variable associated with success (odds ratio (OR): 1.96 per 1.85 GBq increment; 95% confidence interval (CI)=1.11–3.46). Objectives(1) To determine if the variables associated with success are the same using Tg. (2) To determine whether Tg measurement can become the sole method for assessing ablation success. MethodsWe performed the analysis using a Tg level <2 ng · ml−1 as a criterion for completed ablation. Data were available from 109 patients. ResultsUnivariate analysis showed an effect of stage (OR=0.05; 95% CI=0.01–0.23) and female sex (OR=2.8; 95% CI=1.14–6.89). Multivariate analysis demonstrated only stage to be a significant predictor of success. Ablation was successful by both methods in 62/109 patients and it failed by both in 10/109. There were 21 WBS− Tg+ and 16 WBS+ Tg− patients. ConclusionsInvestigation of the variables associated with successful ablation yields different results depending on the definition of success. There was a significant incidence of WBS+ Tg− cases after initial ablation. Until it is firmly established that such patients have a benign course both monitoring methods should be used.