Itraconazole synergistically increases therapeutic effect of paclitaxel and 99mTc-MIBI accumulation, as a probe of P-gp activity, in HT-29 tumor-bearing nude mice

P-glycoprotein (P-gp), is an important efflux pump involved in chemotherapy resistance in human colon cancer. We investigated the efficacy of itraconazole as a P-gp inhibitor and its therapeutic synergistic relationship to paclitaxel through 99mTc-MIBI accumulation in HT-29 tumor-bearing nude mice. Histopathological screening along with in vitro experiments was done for further assessment. Itraconazole successfully inhibited P-gp mediated 99mTc-MIBI efflux, increasing its in vitro accumulation in itraconazole-receiving dishes. Notably, the co-administration of itraconazole with paclitaxel significantly enhanced the in vitro cytotoxicity effect of paclitaxel in itraconazole + paclitaxel wells containing HT-29 cells. Compared to the control, tumor volume in mice treated with itraconazole, paclitaxel and itraconazole +paclitaxel showed growth suppression approximately by 36.21, 60.02, and 73.3% respectively. And compared to paclitaxel group, the nude mice co-treated with paclitaxel and itraconazole showed suppression of tumor growth by about 33.31 % at the end of the treatment period. Also the biodistribution result showed that the co-administration of itraconazole with paclitaxel raised the mean tumor radioactivity accumulation compared to control and paclitaxel group. When given paclitaxel alone, the ID% of hepatic and cardiac tissue was reduced while co-administration of itraconazole with paclitaxel increased 99mTc-MIBI accumulation in these organs. Furthermore, the histopathological findings confirmed the biodistribution results. These results demonstrate that although monotherapy with itraconazole or paclitaxel has anti-tumor activity against HT-29 human colorectal cancer, a synergistic anti-tumor activity can be achieved when itraconazole is co-administered with paclitaxel. Also, 99mTc-MIBI is an effective radiotracer for monitoring response to treatment in MDR tumors.

Upfront F18-choline PET/CT versus Tc99m-sestaMIBI SPECT/CT guided surgery in primary hyperparathyroidism: the randomized phase III diagnostic trial APACH2

BACKGROUND

The common endocrine disorder primary hyperparathyroidism (PHPT) can be cured by surgery. Preoperative localization of parathyroid adenoma (PTA) by imaging is a prerequisite for outpatient minimally invasive parathyroidectomy (MIP). Compared to inpatient bilateral cervical exploration (BCE) which is performed if imaging is inconclusive, MIP is superior in terms of cure and complication rates and less costly. The imaging procedure F18-choline (FCH) PET/CT outperforms Tc99m-sestaMIBI (MIBI) SPECT/CT for PTA localization, but it is much costlier. The aim of this study is to identify the most efficient first-line imaging modality for optimal patient care in PHPT without added cost to society.

METHODS

We will conduct a multicenter open diagnostic intervention randomized phase III trial comparing two diagnostic strategies in patients with PHPT: upfront FCH PET/CT versus MIBI SPECT/CT. The primary endpoint is the proportion of patients in whom the first-line imaging method results in successful MIP and cure. Follow-up including biological tests will be performed 1 and 6 months after surgery. The main secondary endpoint is the social cost of both strategies. Other secondary endpoints are as follows: FCH PET/CT and MIBI SPECT/CT diagnostic performance, performance of surgical procedure and complication rate, FCH PET/CT inter- and intra-observer variability and optimization of FCH PET/CT procedure. Fifty-eight patients will be enrolled and randomized 1:1.

DISCUSSION

FCH PET/CT is a highly efficient but expensive imaging test for preoperative PTA localization and costs three to four times more than MIBI SPECT/CT. Whether FCH PET/CT improves patient outcomes compared to the reference standard MIBI SPECT/CT is unknown. To justify its added cost, FCH PET/CT-guided parathyroid surgery should lead to improved patient management, resulting in higher cure rates and fewer BCEs and surgical complications. In the previous phase II APACH1 study, we showed that second-line FCH PET/CT led to a cure in 88% of patients with negative or inconclusive MIBI SPECT/CT. BCE could be avoided in 75% of patients and surgical complication rates were low. We therefore hypothesize that upfront FCH PET/CT would improve patient care in PHPT and that the reduction in clinical costs would offset the increase in imaging costs.

TRIAL REGISTRATION

NCT04040946 , registered August 1, 2019.  Protocol version Version 2.1 dated from 2020/04/23.

99mTc-MIBI uptake as a marker of mitochondrial membrane potential in cancer cells and effects of MDR1 and verapamil

We investigated the relation of ^99mTc-MIBI uptake to mitochondrial membrane potential (MMP) in cancer cell lines and patient-derived tumor cells (PDCs). In T47D and HT29 cells with low MDR1 expression, FCCP dose-dependently reduced MMP and ^99mTc-MIBI accumulation in similar patterns with nearly perfect linear relationships. T47D and HT29 cells with high MDR1 expression had low ^99mTc-MIBI accumulation that was minimally affected by FCCP dose. In these cells, verapamil markedly increased ^99mTc-MIBI accumulation to magnitudes that were excessive compared to MMP increase. Decreased plasma membrane potential by verapamil and its recovery by FCCP suggested that enhanced ^99mTc-MIBI transport through modified plasma membranes contributed to the excess accumulation. Evaluation of three different colon cancer PDCs with low to modest MDR1 expression verified that FCCP significantly suppressed MMP and similarly reduced ^99mTc-MIBI accumulation. Verapamil partially recovered both MMP and ^99mTc-MIBI accumulation that was lowered by FCCP. Importantly, a high linear correlation was found (r = 0.865) between ^99mTc-MIBI accumulation and MMP in these cells. These findings indicate that low baseline ^99mTc-MIBI uptake that is markedly increased by verapamil represents cancer cells with high levels of MDR1 expression. However, in cancer cells with low or modest levels of MDR1 expression that do not markedly increase ^99mTc-MIBI uptake by verapamil, the magnitude of uptake is largely dependent on cellular MMP.

Prognostic value of primary tumor SUVmax on F-18 FDG PET/CT compared with semi-quantitative tumor uptake on Tc-99m sestamibi breast-specific gamma imaging in invasive ductal breast cancer

OBJECTIVE

This study aimed to evaluate the prognostic value of F-18 FDG PET/CT in comparison with Tc-99m sestamibi breast-specific gamma imaging (BSGI) and previously established clinical prognostic parameters of invasive ductal breast carcinoma (IDC).

METHODS

We retrospectively included 157 female IDC patients (mean age 49.2 years, range 29.9-78.9) who underwent PET/CT and BSGI. The maximum standardized uptake value (SUV_max) and tumor to normal background ratios (TNRs) of their primary tumors were measured on PET/CT and BSGI, respectively. Univariate and multivariate survival analyses were performed to evaluate the prognostic value of the measured parameters and other clinical prognostic factors: age, menopausal status, breast density, pathologic tumor size (pTS), axillary nodal status (ANS), nuclear grade, histologic grade, hormone receptor status of estrogen (ER) and progesterone receptors (PR) and HER-2 expression.

RESULTS

Among 157 patients, recurrences occurred in 22 patients (14.0 %). In univariate analyses, pTS (p < 0.0001), ANS (p < 0.0001), nuclear grade (p = 0.0046), histologic grade (p = 0.0001), ER status (p < 0.0001), PR status (p = 0.0037), HER-2 status (p = 0.0007), primary tumor SUV_max (p < 0.0001) and TNR (p = 0.0001) were significant predictors of recurrence. Among them, pTS (p = 0.0172), ANS (p = 0.0416), ER status (p = 0.0375) and primary tumor SUV_max (p = 0.0239) were independent prognostic factors in multivariate regression analysis.

CONCLUSIONS

High primary tumor SUV_max of PET/CT and high TNR of BSGI were poor prognostic factors in IDC patients; in addition, primary tumor SUV_max was an independent prognostic factor along with pTS, ANS and ER status.

The importance of the incidental thyroid gland uptake during Tc-99m MIBI myocardial perfusion scintigraphy

OBJECTIVE

The purpose of study was to investigate whether incidental thyroid gland uptake had an important during Tc-99m sestamibi (MIBI) myocardial perfusion scintigraphy (SPECT).

PATIENTS AND METHODS

In the presented study, 968 consecutive patients were evaluated for the presence or absence of thyroid gland uptake in the raw data of the Tc-99m MIBI SPECT. All of the patients had thyroid gland uptake of the Tc-99m MIBI underwent laboratory evaluation of thyroid function, ultrasonographic imaging, and hystopathological examination.

RESULTS

The thyroid gland uptake was detected in 14 of 968 (1.4%) consecutive patients during the evaluation of raw images of Tc-99m MIBI SPECT studies. Among these 14 patients, 4 had subacute thyroiditis, 7 multinodular goiter, 3 Graves disease by ultrasonographic imaging and hystopathological examination. TSH levels of all of these patients were < 0.01 U/ml.

CONCLUSIONS

Tc-99m MIBI uptake by thyroid gland has been explained with associated clinical thyrotoxicosis. Although the primary goal of myocardial perfusion imaging is the evaluation of myocardial perfusion, the interpretation of myocardial perfusion imaging should not be limited to the heart. Because, it is possible to observe extracardiac radioactivity accumulation, which may then lead to the diagnosis of a noncardiac disease during this detailed examination.

Myocardial washout rate of resting ⁹⁹mTc-Sestamibi (MIBI) uptake to differentiate between normal perfusion and severe three-vessel coronary artery disease documented with invasive coronary angiography

OBJECTIVES

Patients with severe coronary artery disease (CAD) may present impaired mitochondrial function to enhance (99m)Tc-sestamibi (MIBI) washout from ischemic myocardium. In this study, we aimed to study the MIBI washout rate (WR) between patients with three-vessel CAD (3V-CAD) confirmed by invasive coronary angiography and healthy normal volunteers (HNV) to evaluate the potential utility of MIBI WR to differentiate between these two populations and to stratify the CAD severity.

METHODS

Ten HNV (male = 5, age = 56 ± 10 years) and eight 3V-CAD patients (male = 4, age = 62 ± 8 years) with 3V lumen stenosis ≥50% were enrolled for this study. Each study subject had a resting MIBI perfusion scan at 90 min and a repeated scan at 4 h post the MIBI injection. Global WR (GWR) and regional WR (RWR) were quantified with the percentage difference of decay-corrected polar maps obtained from the two scans and compared between the HNV and 3V-CAD groups. For the 3V-CAD group, the severity of CAD was assessed with CAD severity scores (CADSS) utilizing degree and location of obstructive lesions (stenosis ≥50%) for quantification and compared with WR to evaluate the correlation between these two variables.

RESULTS

Significantly higher GWR was observed in the 3V-CAD (21.1 ± 4.6 %) group than the HNV group (9.5 ± 4.9%) (p < 0.001). RWR values in left anterior descending (LAD), right coronary artery (RCA) and left circumflex (LCX) in the 3V-CAD group were also higher than those of the HNV group (LAD 20.7 ± 5.9 vs 9.4 ± 5.6, p < 0.001; RCA 21.3 ± 4.8 vs 9.2 ± 5.8, p < 0.001; LCX 20.5 ± 7.2 vs 10.1 ± 4.4, p = 0.002). Additionally, the linear correlation of GWR and total CADSS for the whole myocardium was strong and statistically significant (y = 0.86x - 1.12, r (2) = 0.73, p = 0.006).

CONCLUSION

Patients with impaired mitochondrial function due to 3V-CAD had consistently higher global and regional rest (99m)Tc-sestamibi washout rates than those of healthy normal volunteers. The global rest (99m)Tc-sestamibi washout rate is a sensitive indicator to stratify the severity of 3V-CAD and to differentiate between severe 3V-CAD and normal perfusion populations.

Nuclear scintigraphy findings for Askin tumor with In111-pentetreotide, Tc99m-MIBI and F18-FDG

Askin tumor is a rare disease which had previously been reported as being thallium-201 and gallium-67 avid. Varying data regarding 18F- fluorodeoxyglucose metabolism has been described with Ewing family of soft tissue tumors. In this case, we present a patient found to have an Askin tumor of the left chest wall which demonstrated indium-111 pentetreotide and technetium-99m MIBI avidity. The lesion did not show 18F- fluorodeoxyglucose hypermetabolism in this case despite the aggressiveness of the tumor. The patient was treated with surgical excision of the tumor and chemotherapy. Subsequently, contrast enhanced CT, indium-111 pentetreotide and technetium 99m-MIBI showed that the lesion had regressed. These findings suggest that Askin tumor can demonstrate Indium-111 pentetreotide and technetium 99m-MIBI uptake and need not be hypermetabolic on 18F-fluorodeoxyglucose exam.

Mediastinal parathyroid carcinoma presenting with severe skeletal manifestations

Parathyroid carcinoma is a rare malignancy, accounting for about 1% of primary hyperparathyroidism. We report the case of a 23-year-old man who presented with poorly united mid-shaft fracture of the left femur with severe hypercalcaemia in the setting of 99 mTc sestamibi-avid lesions in the mediastinal and thoracic vertebrae. The patient underwent surgery, and histopathology revealed a low-grade parathyroid carcinoma. After surgery, the patient developed severe hungry bone syndrome requiring intensive calcium, magnesium and active vitamin D supplementation. A review of the literature was undertaken with regards to mediastinal parathyroid carcinoma, management of refractory hypercalcaemia in this setting and hungry bone syndrome.

Predictors of Vinorelbine Pharmacokinetics and Pharmacodynamics in Patients With Cancer

Purpose

Marked interindividual variation in drug disposition and toxicity pose an ongoing challenge to chemotherapy dosage individualization. The aim of this study was to evaluate pretreatment clinical features, genotype and functional indicators of drug clearance as predictors of vinorelbine clearance, and myelotoxicity that could inform dosage optimization.

Patients and Methods

Forty-one patients with cancer received a 60 mg intravenous dose of vinorelbine. Pretreatment routine body size measurements and blood tests were performed. Midazolam clearance and hepatic technetium labeled sestamibi (99mTc-MIBI) clearance were used to investigate CYP3A and ABCB1 (MDR1, P-glycoprotein) phenotype respectively and selected single nucleotide polymorphisms in CYP3A and ABCB1 were documented. A limited blood sampling strategy was employed and vinorelbine concentrations were determined by high-performance liquid chromatography. Posterior Bayesian estimates of vinorelbine clearance were obtained for each patient using population pharmacokinetic modeling. Myelotoxicity was estimated from the fractional survival of neutrophils post-treatment.

Results

There was 4.3-fold variation in vinorelbine clearance across the cohort. In a multivariable analysis, pretreatment estimated creatinine clearance (P < .01) and hepatic 99mTc-MIBI clearance (P = .01) were independent predictors of vinorelbine clearance. Fractional survival of neutrophils ranged from 1.3% to 100% and was significantly correlated with vinorelbine clearance (P < .01). Body-surface area was the only pretreatment predictor of fractional survival of neutrophils independent of vinorelbine clearance (P = .02).

Conclusion

Specific indicators of drug clearance provide predictive information about vinorelbine pharmacokinetics, and body-surface area, probably reflecting normal bone marrow reserve, provides an additional pharmacodynamic indicator. Use of a fixed dose of vinorelbine with modifications guided by pretreatment measures is worthy of prospective evaluation.

Paclitaxel modifies the accumulation of tumor-diagnostic tracers in different ways in P-glycoprotein-positive and negative cancer cells

AIM

To study how paclitaxel treatment modifies the accumulation of tumor-diagnostic radiotracers in P-glycoprotein (P-gp) positive and negative cancer cells.

METHODS

The accumulations of different P-gp substrates, including rhodamine 123, daunorubicin and [(99m)Tc]hexakis-2-methoxybutyl isonitrile ((99m)Tc-MIBI), were measured in P-gp-positive (A2780AD) and P-gp-negative human ovarian carcinoma cells (A2780) and JY human lymphoid B cells. The uptakes of the tumor-diagnostic tracers (11)C-choline and 2-[(18)F]fluoro-2-deoxy-d-glucose ((18)FDG) were measured in the same cell lines. The P-gp expression and function were demonstrated by flow-cytometry.

RESULTS

The (18)FDG measurements revealed that the glucose metabolic rate was significantly higher (p<0.01) in the P-gp-positive A2780AD cells than in the P-gp-negative cells. Paclitaxel (1-70microM) increased the (18)FDG uptake (up to 200%) of both P-gp-positive and P-gp-negative cells, whereas it did not modulate their (11)C-choline uptake. Paclitaxel reinstated the (99m)Tc-MIBI accumulation of the A2780AD cells (to 1500% of the control) in a concentration-dependent manner, while it increased the uptake of the P-gp-negative cells to a lesser extent (to a maximum of 200% of the control).

CONCLUSION

Paclitaxel modifies the uptake of tumor-diagnostic tracers in both P-gp-dependent and independent manners. Interpretation of the multifactorial effects of paclitaxel may promote a correct in vivo diagnosis of P-gp-positive and P-gp-negative tumors.

Slow coronary flow and stress myocardial perfusion imaging. Different patterns in acute patients

OBJECTIVE

We investigated myocardial perfusion in acute patients with slow coronary flow (SCF) at angiography. Whether impaired myocardial perfusion occurs in acute patients with SCF is unknown.

METHODS

We enrolled 28 consecutive patients with SCF in the epicardial coronary arteries with no evidence of significant stenosis. SCF affected a single coronary artery in 14 patients (group A) and all three coronary vessels in 14 others (group B). Coronary angiography was repeated after dipyridamole infusion and single photon emission computed tomography was performed using dipyridamole as the stress agent. The Thrombolysis in Myocardial Infarction frame count was measured in SCF vessels at baseline and after dipyridamole infusion.

RESULTS

Mean Thrombolysis in Myocardial Infarction frame count significantly decreased after dipyridamole in both groups. At baseline, mean values of the single photon emission computed tomography score were 31.5 +/- 1.6 and 25.1 +/- 2.1 in groups A and B, respectively. After dipyridamole, they increased from 31.5 +/- 1.6 to 37.8 +/- 1.4 (P < 0.001) in group A, whereas a further decrease to 15.0 +/- 1.2 (P < 0.005) was observed in group B.

CONCLUSIONS

An opposite behavior of myocardial perfusion was observed after dipyridamole infusion: a normal response in patients with SCF affecting one single coronary artery versus an ischemic-like response in those with CSF affecting all three coronary arteries.

Assessment of brown adipose tissue activity in rats by 99mTc-sestamibi uptake

Brown adipose tissue (BAT) physiology and imaging have recently attracted considerable attention. BAT is characterized both by enhanced perfusion and increased mitochondrial activity. (99m)Tc-sestamibi is a lipophilic cationic tracer that concentrates in mitochondria. Data on the accumulation of (99m)Tc-sestamibi in BAT are currently lacking. This study investigates the in vivo (99m)Tc-sestamibi uptake in rat BAT. (99m)Tc-sestamibi was administered in male Wistar rats of various age and body size. (99m)Tc-sestamibi uptake was measured in vitro in BAT and white fat (WF) together with cytochrome c oxidase activity. Both (99m)Tc-sestamibi uptake and cytochrome c oxidase activity were higher in BAT than in WF (P<0.05). (99m)Tc-Sestamibi uptake in both BAT and WF was negatively related to body weight (r = -0.96 and -0.89, respectively) as was the BAT/WF uptake ratio (r = -0.85). These data show a higher (99m)Tc-sestamibi uptake in BAT compared to WF, in agreement with the high mitochondrial content and respiratory activity of the former. The strong negative correlation between (99m)Tc-sestamibi uptake in BAT and body weight (negative allometry), is in accordance to increased needs of thermogenesis in smaller animals. Implications of increased (99m)Tc-sestamibi uptake in BAT in radionuclide imaging are also discussed.

Study of Monoglutathionyl Conjugates TC-99MSestamibi and TC-99M-Tetrofosmin Transport Mediated by the Multidrug Resistance–Associated Protein Isoform 1 in Glioma Cells

The emergence of multidrug resistance (MDR) is a major obstacle to successful chemotherapy of malignant glioma tumors. Overexpression of the multidrug resistance-associated protein isoform 1 (MRP1), associated with a high level of intracellular glutathione (GSH), is a well-characterized mechanism of MDR in glioma cells. Previously, we have investigated the role of GSH and MRP1 in the accumulation of two radiopharmaceuticals classically used in nuclear medicine: (99m)Tc-sestamibi (MIBI) and (99m)Tc-tetrofosmin (TFOS), in a model of glioma cell lines. Although the involvement of GSH in MRP1-mediated transport of the two radiopharmaceuticals has been demonstrated, the exact transport mechanisms involving phase II (conjugation) and phase III (efflux) detoxification of these lipophilic cations has not been fully elucidated. To clarify the difference of release kinetics observed between MIBI and TFOS, we have studied the efficiency of formation of monogluthationyl conjugates mediated by glutathione S-transferses (GSTs). Our results clearly demonstrate that, in our model, the main efflux mechanism for radiopharmaceuticals is on monoglutathionyl-conjugates of MIBI (MIBI-SG) and TFOS (TFOS-SG). These mechanisms involving MRP1, and the phase II of detoxification is not efficient for TFOS in resistant glioma cells. A relatively slower catalytic efficiency of formation of TFOS-SG conjugate (0.006%.s(-1)) prevents its expulsion, contrary to MIBI (0.133%.s(-1)), suggesting that TFOS should be interesting in the detection and management of patients with high-grade glioma.

A New High Affinity Technetium-99m-Bombesin Analogue with Low Abdominal Accumulation

99mTc-labeled bombesin analogues have shown promise for noninvasive detection of many tumors that express bombesin (BN)/gastrin-releasing peptide (GRP) receptors. 99mTc-labeled peptides, however, have a tendency to accumulate in the liver and intestines due to hepatobiliary clearance as a result of the lipophilicity of the 99mTc chelates. This makes the imaging of lesions in the abdominal area difficult. In this study, we have synthesized a new high affinity 99mTc-labeled BN analogue, [DTPA1, Lys3(99mTc-Pm-DADT), Tyr4]BN, having a built-in pharmacokinetic modifier, DTPA, and labeled with 99mTc using a hydrophilic diaminedithiol chelator (Pm-DADT) to effect low hepatobiliary clearance. In vitro binding studies using human prostate cancer PC-3 cell membranes showed that the inhibition constant (Ki) for [DTPA1, Lys3(99Tc-Pm-DADT), Tyr4]BN was 4.1 +/- 1.4 nM. Biodistribution studies of [DTPA1, Lys3(99mTc-Pm-DADT), Tyr4]BN in normal mice showed very low accumulation of radioactivity in the liver and intestines (1.32 +/- 0.13 and 4.58 +/- 0.50% ID, 4 h postinjection, respectively). There was significant uptake (7.71 +/- 1.37% ID/g, 1 h postinjection) in the pancreas which expresses BN/GRP receptors. The uptake in the pancreas could be blocked by BN, partially blocked by neuromedin B, but not affected by somatostatin, indicating that the in vivo binding was BN/GRP receptor specific. Scintigraphic images showed specific, high contrast delineation of prostate cancer PC-3 xenografts in SCID mice. Thus, the new peptide has a great potential for imaging BN/GRP receptor-positive cancers located even in the abdomen.

Does 99mTc-sestamibi uptake discriminate breast tumors?

The aim of this work was to investigate 99mTc-sestamibi uptake and histopathological characteristics of breast tumors. Static 99mTc-sestamibi scintimammography (SMM) has been performed in 101 breast tumors (98 patients). SMM were scored from 0 to 4 according to intensity of 99mTc-sestamibi uptake and classified in two groups: SMM with absence or low tumor uptake (0, 1, 2) and SMM with high tumor uptake (3, 4). Tumor histopathological characteristics have been determined on core or excisional biopsy. The 99mTc-sestamibi uptake (low vs. high) correlated to classical prognostic factors: positively with Scarff-Bloom and Richardson (SBR) grade (p < 0.0005), axillary involvement (p < 0.0005), and tumor size (p < 0.0005) and negatively with estrogen receptors (p < 0.001). Fixation of 99mTc-sestamibi in invasive lobular carcinoma was lower than in invasive ductal carcinoma (p < 0.01) despite a similar mean tumor size (28 +/- 14 mm vs. 24 +/- 14 mm). Relations between 99mTc-sestamibi uptake and tumor size, histologic type, and axillary involvement were independent variables also significant in multivariate analysis (p < 0.0005, p < 0.005, p < 0.05, respectively). Moreover, the five-year survival rate was higher when 99mTc-sestamibi breast tumor uptake was low (p < 0.005). This difference is also significant using the Cox model (p < 0.05). Uptake of 99mTc-sestamibi (low vs. high) discriminates breast tumors with different histopathological characteristics and prognosis.

High prevalence of Chlamydia pneumoniae seropositivity in Mexican patients with ischemic heart disease

BACKGROUND

Risk factors for development of atherosclerosis, such as hyperlipidemia, high blood pressure, smoking habit, and diabetes mellitus, have been identified. The possibility that infectious agents may unchain biological and biochemical reactions related to inflammation, atherogenesis, and vascular thromboses events have recently been described. Chlamydia pneumoniae has been associated with coronary artery disease in some seroepidemiology studies. Reports of this association are limited in the Latin American population; therefore, we conducted a case-control study to explore this issue in the Mexican population.

METHODS

Eighty nine patients with scintigraphic evidence of coronary artery disease compared with a control group of 105 individuals were analyzed. Serum levels of IgA, IgM, and IgG against Chlamydia pneumoniae were determined using enzyme immunoassay method in all subjects. Conventional risk factors were also analyzed.

RESULTS

High seroprevalence of IgA and IgG with no significant difference between the two groups was found. Prevalence of antibodies was as follows: IgA 56.2% (50/89 patients); IgG 66.3% (59/ 89 patients) in coronary artery disease group; IgA 56.2% (59/105 patients), and IgG 70.5% (74/105 patients) in control group. Among common risk factors for coronary artery disease, significant differences were found in males, in patients with diabetes, and in habitual smokers.

CONCLUSIONS

These results suggest a high prevalence of C. pneumoniae infection in the studied population. However, in this series seroprevalence was not evidently associated with coronary artery disease (CAD). To clarify the possible relation between C. pneumoniae and coronary atherosclerosis, additional studies must be performed.

Relationship between sestamibi uptake, parathyroid hormone assay, and nuclear morphology in primary hyperparathyroidism1

BACKGROUND

Technetium-99m-sestamibi scanning and the intraoperative intact parathyroid hormone (iPTH) assay have permitted development of focused parathyroid techniques for treatment of primary hyperparathyroidism. The purpose of this study was to assess if any pre- and intraoperative factors (degree of sestamibi uptake and iPTH levels) were associated with postoperative results (resected gland weight and parathyroid nuclear morphology).

STUDY DESIGN

We performed a retrospective analysis of 101 consecutive patients who underwent preoperative sestamibi scintigraphy and a targeted parathyroid exploration for primary hyperparathyroidism. Sestamibi uptake was graded visually on a 4-point scale of 0 (no uptake or false-negative result) to 3 (high uptake) and compared with respect to iPTH levels, gland morphology, and specimen weight. A Kruskal-Wallis test and a Pearson test were used for the statistical analysis.

RESULTS

Degree of sestamibi uptake was associated with gland weight (median weight of 250 mg, 340 mg, 655 mg, 1,400 mg for grades 0, 1, 2, and 3, respectively, p < 0.001). The uptake of sestamibi was also associated with preoperative PTH levels (median PTH levels of 113, 151, 129, and 170 pg/mL for grades 0, 1, 2, and 3, respectively, p = 0.02), but not with the other parameters. The weight of resected gland(s) was associated with preoperative PTH levels (p = 0.02), and with some of the morphologic nuclear data (mean surface area (p = 0.02), maximum diameter (p = 0.01), and perimeter of the nuclei (p = 0.01).

CONCLUSIONS

These data suggest that false-negative sestamibi scanning (visual score of 0) might result when hypersecreting parathyroid glands are small. Preoperative PTH level might be useful to estimate the amount of hypersecreting tissue to be resected.

Noninvasive imaging of myocardial angiogenesis following experimental myocardial infarction

Noninvasive imaging strategies will be critical for defining the temporal characteristics of angiogenesis and assessing efficacy of angiogenic therapies. The alphavbeta3 integrin is expressed in angiogenic vessels and represents a potential novel target for imaging myocardial angiogenesis. We demonstrated the localization of an indium-111-labeled ((111)In-labeled) alphavbeta3-targeted agent in the region of injury-induced angiogenesis in a chronic rat model of infarction. The specificity of the targeted alphavbeta3-imaging agent for angiogenesis was established using a nonspecific control agent. The potential of this radiolabeled alphavbeta3-targeted agent for in vivo imaging was then confirmed in a canine model of postinfarction angiogenesis. Serial in vivo dual-isotope single-photon emission-computed tomographic (SPECT) imaging with the (111)In-labeled alphavbeta3-targeted agent demonstrated focal radiotracer uptake in hypoperfused regions where angiogenesis was stimulated. There was a fourfold increase in myocardial radiotracer uptake in the infarct region associated with histological evidence of angiogenesis and increased expression of the alphavbeta3 integrin. Thus, angiogenesis in the heart can be imaged noninvasively with an (111)In-labeled alphavbeta3-targeted agent. The noninvasive evaluation of angiogenesis may have important implications for risk stratification of patients following myocardial infarction. This approach may also have significant clinical utility for noninvasively tracking therapeutic myocardial angiogenesis.

Correlation of expression of multidrug resistance protein and messenger RNA with 99mTc-methoxyisobutyl isonitrile (MIBI) imaging in patients with hepatocellular carcinoma

AIM

To explore whether P-glycoprotein (Pgp) and other pumps, multidrug resistance-associated protein (MRP) and lung resistance protein (LRP), could affect tumor accumulation and efflux of 99mTc-MIBI in liver cancer.

METHODS

Surgically treated 78 liver cancer patients were included in this study. Before surgery, 99mTc-MIBI SPECT was performed 15 min and 120 min after injection of 20 mCi 99mTc-MIBI, respectively. Early uptake, delayed uptake (L/Nd), and washout rate (L/Nwr) of 99mTc-MIBI were obtained. Expressions of Pgp, MRP and LRP were investigated with Western blotting and immunohistochemistry. Messenger RNA (mRNA) level of Pgp, MRP and LRP was determined by RT-PCR.

RESULTS

No 99mTc-MIBI uptakes in tumor lesions of 68 of 78 (87.2%) patients with hepatocellular carcinoma were found on 99mTc-MIBI SPECT. P-gp expression was observed in tumor tissues of the patients with no uptake of 99mTc-MIBI (P<0.017). No appreciable correlation was found between liver cancer 99mTc-MIBI images and expression of MRP or LRP on the level of protein or mRNA.

CONCLUSION

99mTc-MIBI SPECT is noninvasive, and useful in predicting the presence of MDR1 gene-encoded Pgp in patients with hepatocellular carcinoma.

Correlation between myocardial uptake of technetium-99m-sestamibi and pressure-derived myocardial fractional flow reserve

OBJECTIVES

Development of the coronary pressure wire has facilitated the measurement of fractional flow reserve (FFR) to assess the functional severity of coronary artery stenoses.

METHODS

This study evaluated the correlations between FFR and myocardial direct counts of technetium-99m(99mTc)-sestamibi in 20 patients (16 men, 4 women, mean age 66 +/- 8 years) who underwent 99mTc-sestamibi single-photon emission computed tomography (SPECT) with the 2-day protocol using 740 MBq of 99mTc-sestamibi each day. Visual assessment of myocardial imaging and quantitative analysis with the measurement of percent uptake and direct count of 99mTc-sestamibi were performed.

RESULTS

Visual assessment of myocardial imaging revealed that reversibility of 99mTc-sestamibi perfusion defects was correlated with FFR of < 0.75, which is regarded as functionally important stenosis (17/20 vs 3/20, kappa = 0.71, p < 0.002). Regional reversibility score did not correlate with FFR (r = -0.40, p = NS). Quantitative analysis revealed that the change in 99mTc-sestamibi percent uptake with pharmacologic stress using adenosine triphosphate disodium (ATP) also did not correlate with FFR (r = 0.35, p = NS). In contrast, percent increase in 99mTc direct counts with ATP was lower in patients with FFR of < 0.75 than in those with FFR of > = 0.75 (-4 +/- 16% vs 24 +/- 30%, p < 0.01). In addition, a significant correlation (r = 0.70, p < 0.001) was observed between percent increase in 99mTc direct counts with ATP and FFR.

CONCLUSIONS

These results suggest that quantitative analysis of 99mTc-sestamibi scintigraphy enables the assessment of the magnitude of functional significance of coronary stenosis.

Functional Imaging of Multidrug Resistant Phenotype by 99mTc-MIBI Scan in Patients with Multiple Myeloma

Overexpression of P-glycoprotein (Pgp) is one of the primary mechanisms of multidrug resistance (MDR) in several diseases, including multiple myeloma. The aim of this study was to investigate whether the washout of 99mTc-MIBI, a transport substrate of Pgp, is enhanced in the bone marrow of patients with multiple myeloma overexpressing Pgp. Seventeen (17) patients were i.v. injected with 555 MBq of 99mTc-MIBI, and whole-body scans were performed at 10 and 60 minutes. A region of interest (ROI) was drawn over the thoracic spine of each scan, and the washout of 99mTc-MIBI was calculated, after decay correction, as: (10-minute counts/pixel minus 60-minute counts/pixel) divided by 10-minute counts/pixel. Pgp expression was determined in 17 bone marrow samples obtained from the same patients immediately before the 99mTc-MIBI scan. Following centrifugation over the Ficoll-Hypaque gradient, cytospins were obtained and immunostained with C219 monoclonal antibody. The immunostaining of Pgp was graded as 1, 2, or 3 when a faint, moderate, or intense reaction, respectively, was observed in infiltrating plasma cells. Washout of 99mTc-MIBI ranged between 5% and 26%. A statistically significant direct correlation was found between the washout of the tracer and Pgp expression (Spearman rank correlation coefficient r = 0.74, p < 0.001). A partial overlap of washout values was observed in different classes of Pgp expression, thus preventing the discrimination of individual patients. Washout of 99mTc-MIBI, expressed as the percentage of radioactivity cleared from the bone marrow over a 1-hour period, may be used as a noninvasive tool for in vivo whole-body imaging of Pgp expression and function in multiple myeloma patients.

Relationship of cell proliferation (Ki-67) to 99mTc-(V)DMSA uptake in breast cancer

INTRODUCTION

The aim of the present study was to identify the relationships between the uptake of radiotracers - namely pentavalent dimercaptosuccinic acid [(V)DMSA] and sestamibi (MIBI) - and the following parameters in primary breast cancer: steroid receptor concentrations (i.e. estrogen receptor [ER] and progesterone receptor [PR]), Ki-67 expression, tumor size, tumor grade, age, and levels of expression of p53 and c-erbB-2. In addition, by multivariate regression analysis, we further isolated those factors with independent associations with (V)DMSA and/or MIBI uptake in primary breast cancer.

METHODS

Thirty-four patients with histologically confirmed breast carcinoma underwent preoperative scintimammography with technetium-99m (99mTc)-(V)DMSA and/or 99mTc-MIBI in consecutive sessions 10 and 60 min after administration of 925-1110 MBq of each radiotracer. The tumor-to-background ratio was calculated and correlated with the presence of ER, PR, Ki-67, tumor size, tumor grade, p53, and c-erbB-2. ER, PR, p53, and c-erbB-2 were determined immunohistochemically. The analysis included tumor-to-background ratio of (V)DMSA and MIBI uptake as dependent and all of the other parameters as independent variables.

RESULTS

Correlation was positive between Ki-67 and (V)DMSA (r = 0.37 at 10 min, P = 0.038; r = 0.42 at 60 min, P = 0.018) and inverse between PR and (V)DMSA uptake (r = -0.46 at 10 min, P = 0.010; r = -0.51 at 60 min, P = 0.003). Multivariate regression analysis demonstrated a positive correlation between Ki-67 and (V)DMSA at 60 min (P = 0.045). Ki-67 was not significantly correlated with MIBI uptake, whereas tumor size was positively correlated with MIBI uptake at 60 min both in univariate (r = 0.45, P = 0.027) and multivariate analysis (P = 0.024). Negative correlations were observed between (V)DMSA uptake and ER, as well as between ER/PR and MIBI uptake, but these were not significant.

CONCLUSION

Ki-67 appears to represent the major independent factor affecting (V)DMSA uptake in breast cancer. Tumor size was the only independent parameter influencing MIBI uptake in breast cancer. (V)DMSA appears to have an advantage over MIBI in that it can be used to visualize tumors with intense proliferative activity, and thus it can identify those tumors that are more aggressive.

The Multidrug Resistance ofIn VitroTumor Cell Lines Derived from Human Breast Carcinoma MCF-7 Does Not Influence Pentavalent Technetium-99m-Dimercaptosuccinic Acid Uptake

The main causes of multidrug resistance (MDR) are overexpression of P-glycoprotein (P-gp) and multidrug resistance-associated protein isoform 1 (MRP1) often associated with high levels of glutathione (GSH). We investigated whether MDR phenotype can influence Tc-99m-(V)-DMSA [pentavalent technetium-99m-dimercaptosuccinic acid] entry by comparing its uptake with that of Tc-99m-sestamibi (MIBI) on an in vitro model of sensitive (MCF-7) and variant resistant cell lines. Drug resistance was assessed by immunoblotting, GSH measurement, and 3-[4,5-dimethylthiazol-2-yl]-2,5,diphenyl tetrazolium bromide (MTT) assay. To correlate MDR phenotype with tracer accumulation, uptakes were performed with and without P-gp and MRP1 inhibitors and after GSH modulation. Similar accumulation of Tc-99m-(V)-DMSA was observed in all cell lines and the use of MDR reversals did not enhance its uptake. Our results demonstrate clearly that Tc-99m-(V)-DMSA uptake is not related to either P-gp and MRP1 expression, or GSH levels. In contrast, Tc-99m-MIBI accumulation is inversely proportional to the cell MDR phenotype. The combination of Tc-99m-(V)-DMSA and Tc-99m-MIBI may be a useful tool for noninvasive detection of malignant sites and their chemoresistance status.

Tetrofosmin as predictors of tumour response

Non-invasive imaging methods in the evaluation of chemotherapy response in malignant tumours are currently being explored. Standard Nuclear Medicine procedures seem to offer the clinician a promising tool in the management of those oncologic patients, who might benefit from chemotherapy. Early studies focused on the relationship between radionuclides used in tumour diagnosis and factors associated with multidrug resistance (MDR). The tumour expression of P-glycoprotein (Pgp) and multidrug resistance-related protein-1 expression (MRP) have been suggested as important factors in the failure of chemotherapy. Most studies found an association between Pgp levels and (99m)Tc-sestamibi ((99m)Tc-MIBI) or (99m)Tc-Tetrofosmin uptake ((99m)Tc-TF). Currently investigations in nuclear medicine oncology are focusing on the potential role of radionuclide imaging in the assessment of chemotherapy. Recent papers discuss the usefulness of radionuclides as (99m)Tc-MIBI and (99m)Tc-TF as non-invasive procedures to predict and to monitor therapy response in patients affected by malignant tumours treatable using chemotherapy. This chapter will review the latest development in (99m)Tc-TF, giving an overview of recent investigations carried out using this radiotracer in therapy oncology, with emphasis on its potential role as predictor of tumour response.

Effect of P-glycoprotein and multidrug resistance associated protein gene expression on Tc-99m MIBI imaging in hepatocellular carcinoma

P-glycoprotein (Pgp) and multidrug resistance-associated protein (MRP) expressions as well as Tc-99m methoxisobutylisonitrile (MIBI) images were assessed in 25 patients hepatocellular carcinoma (HCC). Tc-99m MIBI imaging was performed 10 minutes after intravenous injection of 20 mCi Tc-99m MIBI. Using immunohistochemical staining, 60% of the HCC lesions showed positive for Pgp and 64% showed positive for MRP. In 3 patients with MIBI uptake, immunohistochemical study of tumor tissue showed no Pgp stained cells. Nevertheless, they were all positive for MRP. The result of Tc-99m MIBI imaging is more related to the expression of Pgp than MRP gene. It is possible that other membrane transporters as well as Pgp and MRP are involved in the efflux of Tc-99m MIBI.

Minimally invasive video-assisted parathyroidectomy and intraoperative parathyroid hormone monitoring. The first 36 cases and some pitfalls

BACKGROUND

The success of parathyroid surgery depends on the identification and removal of all hyperactive parathyroid tissue. At this writing, bilateral cervical exploration and identification of all parathyroid glands represent the operative standard for primary hyperparathyroidism (pHPT). However, improved preoperative localization techniques and the availability of intraoperative parathyroid hormone monitoring prepare the way for minimally invasive procedures.

METHODS

Patients with pHPT and one unequivocally enlarged parathyroid gland on preoperative ultrasound and 99mTc-SestaMIBI scintigraphy underwent minimally invasive video-assisted parathyroidectomy by an anterior approach. Intraoperatively, a rapid chemiluminescense immunoassay was used to measure intact parathyroid hormone (iPTH) levels shortly before and then 5, 10, and 15 min after excision of the adenoma. The operation was considered successful when more than a 50% decrease in preexcision iPTH levels was observed after 5 min.

RESULTS

Between October 1999 and November 2001, 36 of 82 patients with pHPT were eligible for a minimally invasive approach. A conversion to open surgery became necessary in five patients because of technical problems. In three cases, intraoperative iPTH monitoring showed no sufficient decrease in iPTH values. In these cases, subsequent cervical exploration showed one double adenoma and two hyperplasias, respectively. In two patients we had difficulty interpreting intraoperative iPTH values, resulting in persistent pHPT.

CONCLUSIONS

Despite the use of high-resolution ultrasound and 99mTc-SestaMIBI scintigraphy, the presence of multiple glandular disease cannot be ruled out completely. Intraoperative iPTH monitoring to ensure operative success is indispensible for a minimally invasive approach. Despite our problems with iPTH monitoring in two patients, we believe that in selected cases, minimally invasive parathyroidectomy represents an attractive alternative to conventional surgery.

[Correlation of the uptake of technetium-99m methoxyisobutyl isonitrile with expression of multidrug resistance genes mdr-1 and MRP in human lung cancer]

OBJECTIVE

To investigate the relationship between the uptake of technetium-99m methoxyisobutyl isonitrile ((99m)Tc-MIBI) and the expression of multidrug resistance genes mdr-1 and MRP in lung cancer so as to guide chemotherapy.

METHODS

Eighteen lung cancer patients were given 1 110 MBq(99m)Tc-MIBI intravenously. Chest single-photon emission-computed tomography was performed 60 and 120 min after the injection. The early and delay uptake rates and retain index of (99m)Tc-MIBI were calculated by the count ratio of the lung lesion to contralateral normal lung tissue. The expressions of mdr-1 and MRP genes in specimens of lung cancer and normal lung tissues near the cancers resected during operation among the 27 patients were detected with RT-PCR method.

RESULTS

The positive rate of (99m)Tc-MIBI in the chest of lung cancer patients was 83.3% (15/18). The early uptake ratio of imaging in lung cancer patients was 1.99 +/- 0.64. After time decay correction, the rate of target to background and the retain index in 13 delay imagings were 2.06 +/- 0.69 and -45% approximately 33% respectively. In specimens of lung cancer, the positive expression rates of mdr-1 and MRP were 22.2%(6/27) and 63%(17/27) with the expression amount of 0.39 +/- 0.1 and 0.23 +/- 0.17 respectively. In specimens of normal lung tissues near lung cancer, the positive expression rates of mdr-1 and MRP genes were 35%(7/20) and 45.0%(9/20) with the expression amount of 0.44 +/- 0.14 and 0.17 +/- 0.18 respectively. In lung cancer tissues, the positive rate of MRP was higher than that of mdr-1 (P < 0.05), however, in the tissues near lung cancer, no significant difference was found between the positive rate of MRP and that of mdr-1 (P >< 0.05). There was no marked correlation (P >< 0.05) among the co-expression or expression of mdr-1 and/or MRP and the early uptake or retain index in lung cancer.

CONCLUSION

The primary chemoresistance of lung cancer has not significant correlation to the expression of multidrug resistance genes mdr-1 and MRP. Other resistance mechanism may exist. (99m)Tc-MIBI imaging has not much clinical value in predicting the expression of mdr-1 and MRP genes.

Modulation of the multidrug resistance of glioma by glutathione levels depletion--interaction with Tc-99M-Sestamibi and Tc-99M-Tetrofosmin

We have investigated the effect of glutathione (GSH) depletion on the chemosensitivity of human malignant glioma cell lines: G111, G5 and G152. All the cell lines showed a multidrug resistant (MDR) phenotype associated with MRP1 expression, high intracellular levels of GSH, and depolarized plasma membranes. Tc-99M-Sestamibi (MIBI) and Tc-99M-Tetrofosmin (Tfos) were used for monitoring the MDR mechanisms. Modulation of GSH content was performed with butoxysulfoximide (BSO) pre-treatment alone or in combination with GSH ethyl ester. MIBI and Tfos accumulation in the cells was inversely correlated to the GSH content, a higher accumulation was found after BSO pre-treatment and addition of GSH ethyl ester reversed this process. BSO could therefore play a role as a chemosensitizing drug and thus help to overcome MDR. However, higher accumulation of MIBI and Tfos was observed even in the sensitive cells suggesting another effect of BSO on the cell physiological characteristics. No sign of apoptosis has been found indicating a possible direct effect on the plasma membrane fluidity and permeability. MIBI and Tfos don't follow the expected behavior of a MDR probe in the glioma cells and given the particular morpho-physiological characteristics of these types of tumors, Tfos could be rather used as a marker of the tumor growth and proliferation.

Could 99mTc-MIBI be used to visualize the apoptotic MCF7 human breast cancer cells?

Defects in key components of apoptotic pathways provide a survival advantage to cells and have been implicated as important factors in tumorogenesis. As therapeutic drug-induced apoptosis is a key component in treatment of most cancers, alterations in apoptotic pathways may be critical to drug resistance. The question is: would it be possible to distinguish apoptotic cells and resistant cells with a same radiotracer? In this study, we investigated the ability of sodium phenylacetate (NaPa), a natural cytostatic proapoptotic metabolite, to induce apoptosis in MCF7 human breast cancer cells. Then, we tested the 99mTc-MIBI accumulation in these apoptotic cells. Annexin V-FITC was used to identify apoptotic cells by flow cytometry. Ours results demonstrated that a 72 hr treatment of MCF7 cells with 40 mM NaPa induced apoptosis in 60% of cells. In a parallel way, 99mTc-MIBI accumulation in NaPa treated cells decreased for concentrations higher than 20 mM NaPa. Thus, 99mTc-MIBI accumulation decreased correlatively with the increasing percentage of apoptotic cells obtained by treatment of MCF7 cells with NaPa. These data demonstrate that NaPa induced apoptosis in MCF7 cells and that 99mTc-MIBI is a negative tracer of apoptosis: the more MCF7 cells were engaged in the apoptotic pathway, the more 99mTc-MIBI accumulation decreased in these MCF7 apoptotic cells.

Detection of minimal residual disease in acute leukemia by Tc-99m MIBI femoral marrow imaging

To determine the potential of Tc-99m MIBI femoral marrow imaging for detecting minimal residual disease in acute leukemia, MIBI images of 68 patients with acute leukemia and 110 control patients were examined. MIBI accumulation was classified into three patterns: not detectable, mild accumulation, and clearly visualized accumulation. Clearly visualized accumulation was interpreted as abnormal. The mean uptake ratio of the femoral marrow to muscle was calculated. Forty-five patients who were in complete remission (CR) at the time of MIBI imaging had a follow-up study (mean interval, 23 months). Clearly visualized accumulation was demonstrated in 35 patients with acute leukemia: in 7 patients before starting induction chemotherapy, in 12 patients after relapse, and in 16 of the 49 patients in the CR group. Mild accumulation was demonstrated in 14 patients in the CR group and in 13 control group patients. No detectable accumulation was observed in 19 patients in the CR group and in 97 control patients. The marrow and muscle uptake ratio of patients before starting chemotherapy (2.29 +/- 0.26) was greater compared with that in patients after relapse (1.78 +/- 0.44, P < 0.02) and in patients with abnormal accumulation despite complete remission (1.84 +/- 0.36, P < 0.01). The uptake ratio in patients with abnormal accumulation despite CR was higher compared with patients with mild accumulation in CR (1.26 +/- 0.13, P < 0.001) and controls (1.23 +/- 0.10, P < 0.001) who had mild accumulation. Fifteen patients with abnormal accumulation despite CR had a markedly greater relapse rate (66.7% > 10.0%, P < 0.005), a higher mortality rate (46.7% > 6.7%, P < 0.01), and shorter remission time (8.7 +/- 10.2 months < 35.9 +/- 20.1 months, P < 0.001) compared with 30 patients without abnormal accumulation in CR. MIBI femoral marrow imaging may be a useful and simple method for monitoring levels of residual leukemic cells. Clearly visualized MIBI accumulation may be a marker for relapse.

Technetium-99m-tetrofosmin would be a substrate for multidrug resistance-associated protein (MRP): comparison between a leukemia cell line with high MRP gene expression and its parental cell line

The kinetics of cellular accumulation and retention of technetium-99m-tetrofosmin (99mTc-TF) were investigated in wild type HL60/WT cell line and in its doxorubicin-resistant HL60/DOX cell line with multidrug resistance-associated protein (MRP), but without P-gp overexpression, to determine whether 99mTc-TF is a substrate for MRP.

METHODS

The accumulation and washout of 99mTc-TF were observed in both cell lines at 37 degrees C. The effect of verapamil on the kinetics was also assessed.

RESULTS

99mTc-TF net accumulation was significantly lower in HL60/DOX (1.35 +/- 0.23%) than in HL60/WT (12.79 +/- 0.47%) at 60 min (P < 0.001). Three minutes after exchanging the incubation solution to the tracer-free medium, only 18.20 +/- 0.34% of 99mTc-TF remained in HL60/DOX, whereas 84.74 +/- 0.65% did in HL60/WT (P < 0.001). In the presence of 10 microM verapamil, 99mTc-TF net accumulation in HL60/DOX was 302% of the control and the washout was significantly delayed.

CONCLUSION

99mTc-TF would be a substrate for MRP and 99mTc-TF may be used as a functional imaging agent of MRP in vivo.

Accumulation of sestamibi in lymphoma cell lines in vitro

Although some authors have suggested that sestamibi imaging is useful in evaluation of patients with lymphoma, others have obtained equivocal results. This discrepancy has been further investigated in vitro using two patient-derived non-Hodgkin's lymphoma cell lines, OCI-Ly3 and OCI-Ly18. Sestamibi (0.2 MBq/ml) was added to a suspension of OCI-Ly3 or OCI-Ly18 cells and aliquots were removed over 1 h and centrifuged to determine cell-associated radioactivity. Further experiments studied the effect of addition of a P-glycoprotein (Pgp) modulator or alteration in plasma and/or mitochondrial membrane potentials. Accumulation of sestamibi reached plateau values within 30 min, but these values were 6-fold higher in OCI-Ly3 than in OCI-Ly18. Inhibition of Pgp function with GG918 or PSC833 did not affect OCI-Ly3 cells but increased accumulation in OCI-Ly18 cells 3-fold, indicating a moderate level of Pgp. However, both cell lines responded similarly to membrane potential alterations: hyperpolarization of the mitochondrial membrane with nigericin had little effect on accumulation: in contrast, depolarization of the plasma membrane with an isotonic high potassium buffer reduced accumulation of sestamibi to 52% of control and additional depolarization of the mitochondrial membrane with valinomycin further reduced accumulation to 12% of control levels. These studies suggest that there can be wide differences in accumulation between cell lines, in part due to Pgp-mediated efflux, but that both of these cell lines have highly polarized mitochondria with little further capacity for hyperpolarization.

In vitro comparison of sestamibi, tetrofosmin, and furifosmin as agents for functional imaging of multidrug resistance in tumors

Sestamibi, tetrofosmin, and furifosmin are 99mTc-labeled myocardial perfusion imaging agents which have been shown to be substrates for P-glycoprotein (Pgp), the multidrug-resistance transporter which is overexpressed in some tumors. The three tracers were directly compared in vitro in the human breast cancer cell line MCF7-WT and two multidrug-resistant variants, MCF7-BC19 (MDR1 gene transfected) and MCF7-AdrR (doxorubicin selected). Tracer accumulation over the course of 60 minutes was determined. Dose-response curves were generated for two modulators of Pgp function, GG918 and PSC833. The general shape of accumulation curves for the three tracers in MCF7-WT cells was similar, with accumulation levels being sestamibi > tetrofosmin > furifosmin. Accumulation of sestamibi and furifosmin in MCF7-BC19 cells was reduced to 10% and 21% of MCF7-WT levels, respectively, but this accumulation deficit could be completely reversed by addition of 0.1 microM GG918 or 2 microM PSC833. Accumulation of sestamibi and tetrofosmin in MCF7-AdrR cells was 1.6% and 12% of MCF7-WT levels, respectively, and could only be enhanced to 30% and 45% of MCF7-WT levels by addition of GG918 or PSC833. In contrast, furifosmin showed similar levels of accumulation in MCF7-WT and MCF7-BC19 cells, slightly lower levels in MCF7-AdrR cells, and no consistent response to Pgp modulators. These results support the continued investigation of sestamibi and tetrofosmin as agents for functional imaging of multidrug resistance in human cancer.

Effects of cholesterol and enantiomeric cholesterol on P-glycoprotein localization and function in low-density membrane domains

Multidrug resistance P-glycoprotein (Pgp) has been reported to localize in low-density, cholesterol-enriched membranes. However, effects of low-density membrane domains on function of Pgp remain unexplored in whole cell systems. In cells that express modest levels of the protein endogenously or through drug selection, Pgp predominantly localized to low-density membranes following separation on a sucrose gradient. When highly overexpressed in NIH 3T3 cells, a prominent amount of Pgp also was detected in high-density membranes. Removing cholesterol from cells with beta-methylcyclodextrin (CD), a sterol acceptor molecule, shifted fractions that contained Pgp from low toward high density, and this effect was reversed to a similar extent by restoring sterols with either cholesterol or enantiomeric cholesterol. However, function of human MDR1 Pgp as probed with Tc-Sestamibi, a transport substrate for Pgp, was not dependent on localization of Pgp in cholesterol-enriched membranes. Specific inhibition of MDR1 Pgp with GF120918 or LY335979 also was independent of cholesterol. Cell-type-specific effects of cholesterol content on function of human Pgp were detected by use of daunomycin, another substrate for Pgp, although efficacy of inhibitors remained independent of cholesterol. Conversely, both function and inhibition of hamster Pgp as measured with Tc-Sestamibi and daunomycin were in part dependent on normal cell content of cholesterol. These data show that Pgp preferentially localizes to low-density, cholesterol-enriched membrane domains, but acute depletion of cholesterol impacts Pgp-mediated drug transport in a substrate- and cell-type-specific manner.

Involvement of the glutathione S-conjugate compounds and the MRP protein in Tc-99m-tetrofosmin and Tc-99m-sestamibi uptake in glioma cell lines

The objective of this study was to compare the accumulation of Tc-99m-tetrofosmin and Tc-99m-sestamibi in four grade IV glioma cell lines and to correlate their accumulation with the multidrug resistance of the cells. Tc-99m-tetrofosmin in all glioma cell lines showed slightly higher uptake and more efficient release beyond 150 min than Tc-99m-sestamibi and the retention of both tracers in the cells was to a certain extend inversely proportional to their degree of multidrug resistance. The results obtained showed that the efflux of both tracers was carried out only in part through the MRP/GS-X pump system. Tc-99m-tetrofosmin showed good potential as a marker of recurrent malignant glioma and in vivo studies are currently underway to confirm these observations.

Effects of ion channel modulators in the influx and efflux of Tc-99m-MIBI

Possible involvement of cell membrane ion transport systems in the uptake and extrusion of Tc-99m-MIBI was investigated by using various buffers with or without Na+ and Ca++, and ion transport inhibitors in a tumor cell line. The ion transport modulators dimethyl amiloride (DMA), verapamil, flunarizine and monensin were used. The uptake of Tc-99m-MIBI was significantly increased in all buffers containing either Na+ or Ca++ alone or none of them. There was significantly increased uptake of Tc-99m-MIBI especially in buffers without Na+. Verapamil, a L-type Ca++ channel blocker, increased Tc-99m-MIBI uptake in all buffers. Flunarizine, which inhibits Na+/ Ca++ channels, caused significantly increased accumulation of Tc-99m-MIBI only in buffer containing both Na+ and Ca++. Monensin, a sodium ionophore, significantly increased uptake of Tc-99m-MIBI. DMA, a potent Na+/H+ antiport inhibitor, significantly inhibited the uptake of Tc-99m-MIBI in all buffers. In conclusion, Tc-99m-MIBI behaves like Na+ during its uptake and extrusion. Extrusion of Tc-99m-MIBI may involve both verapamil- and flunarizine-sensitive pathways.

99mTc-sesta-(2-methoxy-isobutyl-isonitrile) uptake by pancreatic islets, parotid cells, and mammary carcinoma cells

99mTc-sesta-(2-methoxy-isobutyl-isonitrile)(Tc-MIBI) is currently used for imaging of several organs. In the present study, its uptake by rat pancreatic islets, rat parotid cells, and human breast adenocarcinoma cells (MCF-7 cells) was found to be grossly proportional to its concentration (up to 0.1 microM), time-related (with a fractional turnover rate close to 2-3 10(-2).min(-1)), and stimulated by D-glucose. Comparable values for the fractional turnover rate were found in prelabeled islets and MCF-7 cells, D-glucose failing to affect Tc-MIBI efflux from prelabeled islets. In the islets, the uptake of Tc-MIBI was decreased at low temperature, in the presence of mitochondrial poisons and at high extracellular K+ concentration, unaffected by the absence of extracellular Ca2+, and increased by nutrient secretagogs, such as 2-ketoisocaproate and the association of L-leucine and L-glutamine. These findings are consistent with the view that Tc-MIBI uptake is ruled by its extracellular concentration, and the polarization of both plasma and mitochondrial membranes. It is proposed that this lipophilic cation may be useful to detect alteration of nutrient metabolism in pancreatic islets deprived of any exogenous fuel.

Characterization of P-glycoprotein transport and inhibition in vivo

The P-glycoprotein is an energy-dependent efflux pump capable of decreasing the intracellular concentration of a broad range of chemotherapeutic agents. [99mTc]Sestamibi, a P-glycoprotein transport substrate, is a sensitive probe of P-glycoprotein function both in vitro and in vivo. A human tumor model in nude mice was evaluated to determine whether [99mTc]Sestamibi could detect in vivo differences in P-glycoprotein expression and P-glycoprotein modulation by the reversal agent SDZ PSC 833. Differential [99mTc]Sestamibi accumulation based upon P-glycoprotein expression was demonstrated in xenografts in vivo. Dose-dependent inhibition of P-glycoprotein function was achieved with SDZ PSC 833. Administration of the reversal agent increased [99mTc]Sestamibi accumulation in the xenografts expressing P-glycoprotein. These observations show that [99mTc]Sestamibi as capable of detecting the modulation of P-glycoprotein in a solid tumor model by the reversal agent SDZ PSC 833.

Three-year follow-up on scintigraphically assessed cardiac sympathetic denervation in patients with long-term insulin-dependent (type I) diabetes mellitus

Scintigraphy using I-123-metaiodobenzylguanidine (I-123-MIBG) and Tc-99m-methoxyisobutylisonitrile (Tc-99m-MIBI) allows assessment of the cardiac sympathetic innervation and the myocardial perfusion. To investigate the natural history of cardiac sympathetic denervation in long-term diabetic patients without myocardial perfusion defects, global and regional I-123-MIBG and Tc-99m-MIBI uptake was determined (score 1-6; 1 = normal uptake, 6 = no uptake) in 22 patients with insulin-dependent (type I) diabetes mellitus (IDDM) at 3-year follow-up. All patients were treated with intensive insulin therapy and HbA1c was 8.0% +/- 1.0% at entry compared with 7.9% +/- 1.1% at follow-up. Cardiac sympathetic denervation (I-123-MIBG uptake score > 2), initially observed in 18 patients, was detectable in 21 patients at follow-up. The global myocardial I-123-MIBG uptake score deteriorated in eight patients, remained unchanged in 11 and improved in three patients. The changes in mean global I-123-MIBG uptake score (3.5 +/- 1.0 versus 3.8 +/- 0.8) were not significant. Reduction of the anterior, lateral, posterior, septal, and apical I-123-MIBG uptake did not progress significantly during follow-up. The mean uptake score of the posterior myocardial region (4.7 +/- 0.8) was smaller than the uptake score of the anterior (3.0 +/- 1.1, p = 0.001), lateral (3.2 +/- 0.9, p < 0.001) and septal (4.1 +/- 1.1, p < 0.05) myocardial regions. At follow-up, moderate myocardial perfusion defects (global Tc-99m-MIBI uptake score = 3) were detectable in four patients. Our study demonstrates that scintigraphically assessed cardiac sympathetic denervation does neither significantly regress nor progress on the average in a group of long-term IDDM patients during a 3-year follow-up. Thus, it is concluded that cardiac sympathetic abnormalities are a persistent, yet frequent phenomenon in long-term IDDM patients.

Characterization of functional assays of multidrug resistance P-glycoprotein transport activity

P-glycoprotein-mediated multidrug resistance has emerged as one of the most attractive targets to improve anticancer therapy. The P-glycoprotein functions as an energy-dependent, membrane transport pump capable of decreasing the intracellular concentration of a broad range of chemotherapeutic agents. Pharmaceuticals which inhibit P-glycoprotein transport activity are currently being evaluated in clinical trials. Characterization of P-glycoprotein functional activity is critical in determining if these multidrug resistance reversal agents improve therapeutic responses of tumors expressing P-glycoprotein. In this report, we directly compare and characterize assays using rhodamine 123, dimethyloxadicarbocyanine iodide (DiOC2), [3H]daunorubicin and hexakis(2-methoxyisobutyl isonitrile)technetium(I) ([(99m)Tc]Sestamibi) as P-glycoprotein transport probes to quantitate functional activity. The accumulation of certain substrates is concentration dependent and the parameters which determine probe accumulation are impacted by the level of P-glycoprotein expression. In addition, higher concentrations of reversal agents are required to inhibit multidrug resistance in cell lines expressing higher levels of P-glycoprotein. Furthermore, the concentration of reversal agents required to inhibit completely P-glycoprotein transport activity is higher than generally recognized. Thus, the level of P-glycoprotein expression may confound intersample comparisons unless sensitive probes are used in combination with saturating concentrations of potent reversal agents. These results highlight the importance of carefully characterizing assay systems under uniform conditions to quantitate P-glycoprotein function.

Characterization of multidrug resistance P-glycoprotein transport function with an organotechnetium cation

Multidrug resistance (MDR) in mammalian cells and tumors is associated with overexpression of an approximately 170 kDa integral membrane efflux transporter, the MDR1 P-glycoprotein. Hexakis (2-methoxyisobutyl isonitrile)technetium(I) (Tc-SESTAMIBI), a gamma-emitting lipophilic cationic metallopharmaceutical, has recently been shown to be a P-glycoprotein transport substrate. Exploiting the negligible lipid membrane adsorption properties of this organometallic substrate, we studied the transport kinetics, pharmacology, drug binding, and modulation of P-glycoprotein in cell preparations derived from a variety of species and selection strategies, including SW-1573, V79, Alex, and CHO drug-sensitive cells and in 77A, LZ-8, and Alex/A.5 MDR cells. Rapid cell accumulation (t1/2 approximately 6 min) of the agent to a steady state was observed which was inversely proportional to immunodetectable levels of P-glycoprotein. Many MDR cytotoxic agents inhibited P-glycoprotein-mediated Tc-SESTAMIBI efflux, thereby enhancing organometallic cation accumulation. Median effective concentrations (EC50; microM) were as follows: vinblastine, 13; daunomycin, 55; idarubicin, 65; actinomycin D, 235; colchicine, minimal inhibition; adriamycin, no effect. P-glycoprotein modulators generally demonstrated significantly greater potency (EC50; microM): SDZ PSC 833, 0.08; cyclosporin A, 1.3; verapamil, 4.1; quinidine, 6.4; prazosin, > 300. Modulator-induced enhancement up to 100-fold was observed with Hill coefficients approximately 1, consistent with simple Michaelis-Menten kinetics. Vanadate was an efficacious transport inhibitor, while agents usually not included in the MDR phenotype were without effect. Scatchard analysis showed quinidine to be a noncompetitive inhibitor of P-glycoprotein-mediated Tc-SESTAMIBI transport, indicating allosteric effector sites on P-glycoprotein. The lipid bilayer adsorbing agents tetraphenyl borate and phloretin induced large increases in final Tc-SESTAMIBI accumulation, showing maximal accumulations 2-fold greater than classic MDR modulators and Hill coefficients >> 2. In V79 and 77A cells, modulators of PKC activity altered Tc-SESTAMIBI accumulation, while there was no indication of modulation of P-glycoprotein-mediated Tc-SESTAMIBI transport by hypotonic buffer, extracellular ATP, Cl-, or K+ (membrane potential). While recognized and avidly transported by the P-glycoprotein at buffer concentrations as low as 7 pM, Tc-SESTAMIBI at up to 100 microM only minimally modulated the cytotoxic action of colchicine, doxorubicin, or vinblastine in MDR cells. In conclusion, transport analysis with Tc-SESTAMIBI is a sensitive assay for detecting functional expression of low levels of P-glycoprotein and for the quantitative characterization of transporter modulation and regulation. The biochemical data favor a high Km, high capacity allosterically modulated translocation mechanism for P-glycoprotein-mediated transport of this organometallic cation.

99Tcm-MIBI uptake in green plants

Uptake of 99mTcm-sestamibi by biological structures depends on delivery and concentration by electrochemical gradients through the biological membranes and can be simply studied using a green plant model in which photosynthesis tightly modulates water and solute regional flow. Photosynthesis creates electrochemical gradients inside chloroplasts and mitochondria. Moreover, it is the driving force for the movement of water and solutes through induction of pore opening which causes capture of CO2 and loss of water vapour. Thus osmotic pressure increases thereby drawing water from the roots. Hypoestes sanguinolenta was used as an experimental model. This plant displays green zones (with several chloroplasts) and red zones (where they are absent). To detect the uptake differences between these zones we used a new, high-resolution gamma camera. Our results show that (a) 99mTcm-sestamibi is actively transported with water and ions by xylem to leaves where it may diffuse at cellular levels; (b) activation of photosynthesis by light strongly influences the total uptake and the selective compartmentation in green zones; and (c) the green plant's particular physiology tremendously enhances the differences between 99Tcm-sestamibi and 201Tl uptake. We suggest that viable cells, able to create and maintain electrochemical gradients, selectively take up 99Tcm-sestamibi.

In vivo metabolism of the technetium isonitrile complex [Tc(2-ethoxy-2-methyl-1-isocyanopropane)6]+

Technetium(2-ethoxy-2-methyl-1-isocyanopropane)6+, [Tc-EIBT] is a complex of technetium(I) structurally similar but slightly more lipophilic than the commercial myocardial perfusion agent Cardiolite [Tc-MIBI]. Tc-EIBI exhibits rapid extraction from the blood into heart, liver, kidney and striated muscle and rapid hepatobiliary clearance. In the guinea pig, unlike Tc-MIBI, this compound is almost completely enzymatically metabolized to numerous cationic complexes containing a mixture of ethyl other and hydroxy isonitrile ligands. Substitution of the ethyl other group for a methyl ether produces an agent that shows selective in vivo metabolism and more rapid clearance from the liver.

Tumor uptake of 99mTc-MIBI and 201Tl by a 9L gliosarcoma brain tumor model in rats

There have been several recent case reports of the accumulation of 99mTc-MIBI [hexakismethoxyisobutylisonitriletechnetium(I), Cardiolite, Sestamibi] in tumors, but no reports of the uptake of this radiopharmaceutical in an animal model. To address this question, the biodistributions of 99mTc-MIBI and 201Tl were compared in Fisher rats bearing 9L gliosarcomas. The results showed that, although the absolute uptake of the tracers by the tumor is relatively low (< 1% ID/g), the tumor-to-normal brain ratios are greater than 6:1 because of low uptake by normal brain. The tumor-to-normal brain ratio of 99mTc-MIBI exceeds that of other currently available 99mTc radiopharmaceuticals suggesting that 99mTc-MIBI may be of particular value in the clinical evaluation of brain tumors and that further investigation of this class of compounds as tumor-avid radiopharmaceuticals is necessary.