Application of SPET using technetium-99m sestamibi in brain tumours and comparison with expression of the MDR-1 gene: is it possible to predict the response to chemotherapy in patients with gliomas by means of 99mTc-sestamibi SPET?

Incidental Pituitary Adenoma on MIBI Parathyroid Imaging

ABSTRACT

A 77-year-old man with a case of hyperthyroidism with high parathyroid hormone (41 pmol/L), low vitamin D, and normal thyroid-stimulating hormone. The SPECT/CT fused images confirmed the evidence of retrotracheal hyperdense mass approximately 1.0 cm of diameter below the lower pole of the right thyroid lobe with increased uptake, highly suggestive of typical parathyroid adenoma. The most significant point is that there was an incidental finding: high focal uptake in the sellar/suprasellar region corresponding to heterogenous soft tissue lesion suspicious for pituitary adenoma. According to the previous scans, nuclear medicine, CT scan, and the MRI scan indicated pituitary adenoma.

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.

Pituitary incidentalomas detected with technetium-99m MIBI in patients with suspected parathyroid adenoma: preliminary results

Tc-99m MIBI (MIBI) is a cationic lipophilic agent, which has traditionally been used for myocardial perfusion scintigraphy, detection and monitoring of different benign and malignant tumors. The objective of this study was to evaluate the frequency of pituitary incidentalomas detected on MIBI scans performed on patients with suspected parathyroid adenomas and to provide semiquantitative analysis of tracer uptake in the pituitary region. Tomographic images of MIBI scans on 56 patients with suspected parathyroid adenomas (2006–2007) were analyzed retrospectively. Semiquantitative analysis of abnormal uptake was performed by drawing identical regions of interest (ROI) over the pituitary area and the normal brain on one transverse section that demonstrates the lesion most clearly. Pituitary uptake to normal brain uptake ratio was calculated in all cases. We found statistically significant differences of MIBI uptake in patients with pituitary adenomas, mean ratio: 29.78±12.17 (median 29.77, and range 19-41), compared with patients with no pathologic changes in this region, mean ratio was 5.88±1.82 (median was 5.95 and range 2.0- 9.2). As the groups are too small for statistical analysis, these results need to be confirmed in a larger cohort and should include more detailed biochemical correlation. MIBI parathyroid scintigraphy should be taken into account as a potential source of identifying pituitary incidentalomas. Clinical significance of these findings needs further evaluation.

Investigation of blood perfusion and metabolic activity of brain tumours in adults by using 99mTc-methoxyisobutylisonitrile

OBJECTIVES

(i) To examine blood perfusion and metabolic activity of various brain tumours using radionuclide cerebral angiography (RCA) and single-photon emission tomography (SPET) after a single dose of Tc-methoxyisobutylisonitrile (MIBI). (ii) To examine if the inclusion of RCA can improve insight into the relative contribution of tumour perfusion to the uptake of MIBI shown by SPET, and to improve evaluation of tumour biology. (iii) To determine the value and the roles of MIBI in the management of brain tumour patients.

METHODS

Fifty adult patients (38 male, 12 female) with a total of 56 intracranial space-occupying lesions have been included prospectively, 37 of which were newly diagnosed and the remaining with signs of recurrence/rest of earlier resected and irradiated brain tumours. The control group consisted of nine volunteers with no evidence of organic cerebral disease. Scintigraphic examination consisted of a dynamic first-pass study lasting 60 s (3 s/frame) and two SPET studies (60 projections each, 25 s/projection), starting 15 min and 2 h after intravenous injection of MIBI. Regions of interest of the tumour and normal brain tissue were drawn on RCA and both early and delayed SPET slices. The following tumour/brain activity ratios have been calculated: (i) tumour perfusion index (P); (ii) early uptake index (E); (iii) delayed uptake index (D); and(iv) retention index (R). Analogous indices have been calculated from the same examinations performed in controls, reflecting maximal physiologic regional variations of perfusion and uptake in brain tissue.

RESULTS

Mean P of various brain tumours (low-grade gliomas 0.98, anaplastic gliomas 1.14, glioblastoma multiforme 1.20, metastases 1.09, lymphomas 1.08) differ little from each other and do not exceed maximal physiologic regional variations of cerebral perfusion (1.33), with the exception of meningioma (1.87, F=2.83, P=0.015). The receiver operating characteristics curve analysis of P showed that for the cut-off value of 1.45 the sensitivity for distinguishing meningioma from other tumours is 75%, specificity 87%, positive predictive value 33% and negative predictive value 97%. Mean E of malignant brain tumours (8.3, n=31, 23 primary, eight secondary), except anaplastic gliomas (3.5, n=5), differed significantly (P=0.02) from those of benign gliomas (3, n=9) but not from that of meningioma (11.9, n=4). The cut-off value for distinguishing malignant from benign lesions on the basis of E set at 4.8 resulted in sensitivity 67%, specificity 75%, accuracy 70%, positive predictive value 80% and negative predictive value 60%. D and R showed tendency of wash-out of MIBI from meningiomas, but otherwise did not improve the results substantially.

CONCLUSION

Integrated results of RCA and SPET with Tc-MIBI indicate that blood perfusion, blood-tumour barrier permeability and metabolic activity of the tumour are all very important for the resultant uptake shown by SPET. If the perfusion index is less than 1.45, then meningioma can be ruled out. Early SPET is recommendable for distinguishing glioblastoma from low-grade gliomas, as a complement to standard magnetic resonance imaging and/or computed tomography.

Technetium-99m-hexakis-2-methoxyisobutylisonitrile scintigraphy and multidrug resistance-related protein expression in human primary lung cancer

OBJECTIVE

The occurrence of multidrug resistance (MDR) is a major cause of resistance to chemotherapeutic agents in patients with lung cancer, in part owing to the overexpression of MDR-related proteins. Technetium-99m-hexakis-2-methoxyisobutylisonitrile ((99m)Tc-MIBI) has been shown to be a substrate for some MDR-related proteins. The aim of this study is to evaluate the role of (99m)Tc-MIBI scintigraphy for functional imaging of MDR-related protein phenotypes.

METHODS

To determine the correlation between (99m)Tc-MIBI scintigraphy and the expression level of P-glycoprotein (Pgp), multidrug-resistance protein (MRP), and glutathione-S-transferase Pi (GSTpi), 26 patients (17 men and 9 women, median age 57.5 years) with primary lung cancer were investigated. Following intravenous administration of 925 MBq (99m)Tc-MIBI, single-photon emission computed tomography (SPECT) and computed tomography (CT) were performed at 15 min and 2 h. On the basis of the fused images, tumor to background (T/B) ratio of both early and delayed images, and washout rate (WR%) of (99m)Tc-MIBI were calculated. The immunohistochemical staining of Pgp, MRP, and GSTpi was performed, and the expression level was semiquantitated using a pathoimage analysis system. The imaging results were compared with the status of Pgp, MRP, and GSTpi expression.

RESULTS

The WR% of (99m)Tc-MIBI showed a significant positive correlation with Pgp expression (r = 0.560, P = 0.003), as no correlation was observed between WR% and MRP or GSTpi (r = 0.354, P = 0.076; r = 0.324, P = 0.106). Neither early T/B nor delayed T/B correlated with the expression level of Pgp, MRP, and GSTpi. WR%, Pgp, and GSTpi expression showed significant differences between squamous cell carcinoma (group A) and adenocarcinoma (group B). There was no significant difference among Pgp, MRP, and GSTpi expression levels in any cases (P > 0.05).

CONCLUSIONS

Our data confirmed that (99m)Tc-MIBI scintigraphy is useful for determining the MDR caused by Pgp in patients with primary lung cancer.

(99m)Tc-MIBI imaging for prediction of therapeutic effects of second-generation MDR1 inhibitors in malignant brain tumors

The aim of this study was to explore whether (99m)Tc-methoxyisobutylisonitrile ((99m)Tc-MIBI) is suitable to elucidate multidrug resistance and prediction of potentiation of antitumor agents by second-generation MDR1 inhibitors (PSC833, MS-209) in malignant brain tumors in rat. Malignant tumor cells (RG2 and C6 gliomas, Walker 256 carcinoma) were incubated with low dose vincristine (VCR) to induce multidrug resistance. MTT assay demonstrated a significant increase of surviving fractions in VCR-resistant sublines compared to those of drug-naive cells. Reverse transcriptase polymerase chain reaction revealed higher expression of MDR1 mRNA in VCR-resistant cells than drug-naive cells in each line. Volume distribution (V(d)) of (99m)Tc-MIBI was negatively correlated with MDR1 mRNA expression among drug-naive and VCR-resistant cells. MDR1 inhibitors decreased surviving fractions and increased V(d) of (99m)Tc-MIBI significantly in VCR-resistant sublines, whereas MDR1 mRNA expression was unchanged. These findings indicate that (99m)Tc-MIBI efflux was functionally suppressed by MDR1 inhibitors. Autoradiographic images of (99m)Tc-MIBI revealed higher uptake in drug-naive cells at basal ganglia compared with VCR-resistant cells at the opposite basal ganglia of rats. Oral administration of the second-generation MDR1 inhibitors significantly increased (99m)Tc-MIBI accumulation of both tumors. Therapeutic effects of VCR with or without the MDR1 inhibitors were also evaluated autoradiographically using (14)C-methyl-L-methionine ((14)C-Met) and MIB-5 index. (14)C-Met uptake and MIB-5 index of both tumors treated with VCR following the MDR1 inhibitor treatment significantly decreased compared with tumors treated with VCR alone. Analysis of (99m)Tc-MIBI accumulation is considered informative for detecting MDR1-mediated drug resistance and for monitoring the therapeutic effects of MDR1 inhibitors in malignant brain tumors.

Technetium-99m sestamibi single photon emission computed tomography findings correlated with P-glycoprotein expression in pituitary adenoma

The aim of this study is to evaluate whether the technetium-99m sestamibi ((99m)Tc-MIBI) single photon emission computed tomography (SPECT) characteristics of pituitary adenomas might be correlated with cavernous sinus invasion, proliferative potential or the multidrug-resistance (MDR-1) gene product P-glycoprotein (Pgp) expression in pituitary adenomas. Fifteen patients with pituitary adenomas, including 10 nonfunctioning adenomas, two prolactinomas, two GH producing adenomas, and one ACTH producing adenomas was investigated for this study. SPECT images with (99m)Tc-MIBI were acquired 15 minutes (early) and 3 hours (delayed) after injection. The tumor-to-normal brain ratio was calculated both early (ER) and delayed (DR) images. Retention index (RI) was calculated using the following formula: (DR-ER)/ERx100%. The pituitary adenomas specimens were examined by immunohistochemistry using anti-Pgp and MIB-1 monoclonal antibodies.(99m)Tc-MIBI SPECT findings were not related to MIB-1 labeling index or cavernous sinus invasion. (99m)Tc-MIBI SPECT RI (-38.55+/-20.77) of the Pgp-positive group was significantly lower than that (-15.78+/-19.40) of Pgp-negative group (p=0.0494). No significant difference was observed in the ER and DR of (99m)Tc-MIBI SPECT between Pgp-positive and negative groups. Our study suggests that although (99m)Tc-MIBI SPECT is not useful to evaluate the proliferative potential or cavernous sinus invasion of pituitary adenomas. (99m)Tc-MIBI SPECT could predict anti-cancer drug resistance related to the expression of Pgp in pituitary adenomas.

MRP-1 Protein Expression and Glutathione Content of In Vitro Tumor Cell Lines Derived from Human Glioma Carcinoma U-87-MG Do Not Interact with 99mTc-Glucarate Uptake

The main cause of the multidrug resistance (MDR) of glioma cells is the overexpression of MRP-1, often associated with high levels of glutathione (GSH). We investigated whether MRP-1-related GSH content can influence (99m)Tc-glucarate entry by comparing its uptake with that of (99m)Tc-sestamibi (MIBI), an MRP- 1 probe, in an in vitro model of a sensitive cell line (U-87-MG) and a resistant derived cell line expressing MRP-1 (U-87-MG-R). Drug resistance was assessed by immunoblotting, GSH measurement, and Alamar Blue assay. To correlate MDR phenotype with tracer accumulation, uptakes were performed with and without modulators and after GSH depletion. Similar accumulation of (99m)Tc-glucarate was observed in the two cell lines, and the use of MDR reversals did not enhance its uptake. Our results clearly demonstrate that (99m)Tc-glucarate uptake is not related to MRP-1 expression or GSH levels. In contrast, (99m)Tc- MIBI accumulation is inversely proportional to the cell MDR phenotype. The combination of (99m)Tc-glucarate and (99m)Tc-MIBI may be a useful tool for the noninvasive detection of malignant sites and their chemoresistance status.

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.

Role of drug efflux transporters in the brain for drug disposition and treatment of brain diseases

The blood-brain barrier (BBB) serves as a protective mechanism for the brain by preventing entry of potentially harmful substances from free access to the central nervous system (CNS). Tight junctions present between the brain microvessel endothelial cells form a diffusion barrier, which selectively excludes most blood-borne substances from entering the brain. Astrocytic end-feet tightly ensheath the vessel wall and appear to be critical for the induction and maintenance of the barrier properties of the brain capillary endothelial cells. Because of these properties, the BBB only allows entry of lipophilic compounds with low molecular weights by passive diffusion. However, many lipophilic drugs show negligible brain uptake. They are substrates for drug efflux transporters such as P-glycoprotein (Pgp), multidrug resistance proteins (MRPs) or organic anion transporting polypeptides (OATPs) that are expressed at brain capillary endothelial cells and/or astrocytic end-feet and are key elements of the molecular machinery that confers the special permeability properties to the BBB. The combined action of these carrier systems results in rapid efflux of xenobiotics from the CNS. The objective of this review is to summarize transporter characteristics (cellular localization, specificity, regulation, and potential inhibition) for drug efflux transport systems identified in the BBB and blood-cerebrospinal fluid (CSF) barrier. A variety of experimental approaches available to ascertain or predict the impact of efflux transport on brain access of therapeutic drugs also are described and critically discussed. The potential impact of efflux transport on the pharmacodynamics of agents acting in the CNS is illustrated. Furthermore, the current knowledge about drug efflux transporters as a major determinant of multidrug resistance of brain diseases such as epilepsy is reviewed. Finally, we summarize strategies for modulating or by-passing drug efflux transporters at the BBB as novel therapeutic approaches to drug-resistant brain diseases.

Technetium-99m sestamibi single photon emission computed tomography findings correlated with P-glycoprotein expression, encoded by the multidrug resistance gene-1 messenger ribonucleic acid, in intracranial meningiomas

The present study evaluated whether technetium-99m sestamibi (99mTc-MIBI) single photon emission computed tomography (SPECT) characteristics of intracranial meningioma are correlated with the histological malignancy, proliferative potential, and P-glycoprotein (Pgp) expression, encoded by the multidrug resistance gene-1 (MDR-1) messenger ribonucleic acid (mRNA). Twenty-one patients with intracranial meningiomas, including 17 benign and four nonbenign meningiomas, underwent 99mTc-MIBI SPECT imaging at 15 minutes (early) and 3 hours (delayed) after injection. The tumor-to-normal pituitary gland ratio was calculated on both early (ER) and delayed (DR) images. Retention index (RI) was calculated using the following formula: (DR - ER)/ER x 100%. Meningioma specimens were examined by immunohistochemistry using anti-Pgp and MIB-1 monoclonal antibody. MDR-1 mRNA expression was also investigated using reverse transcription-polymerase chain reaction assay. 99mTc-MIBI was highly accumulated and retained in the tumors. 99mTc-MIBI SPECT findings were not related to MIB-1 labeling index. 99mTc-MIBI SPECT RI of the Pgp-positive group (-9.12 +/- 22.27%) was significantly lower than that of the Pgp-negative group (28.79 +/- 22.80%) (p = 0.0016). No significant difference was seen in ER and DR between the positive and negative groups. These results show that 99mTc-MIBI may not be useful for determining proliferative potential and histological malignancy, but could predict anticancer drug resistance related to the expression of MDR-1 mRNA and its gene product Pgp in patients with intracranial meningiomas.

Assessment of the P-glycoprotein expression by 99mTc-MIBI bone marrow imaging in patients with untreated leukaemia

The ability of cancer cells to become simultaneously resistant to different drugs is a significant impediment to successful chemotherapy. 99mTc-MIBI has been reported to be a transport substrate for P-glycoprotein (Pgp). The aim of the study was to ascertain the relationship between the degree of 99mTc-MIBI uptake and the level of Pgp expression in patients with newly diagnosed leukaemia. A total of 26 patients (12 female and 14 male; mean age 46.8+/-3.7 years) with newly diagnosed leukaemia were included in the study. None of the patients had been previously treated with chemotherapy. Images were obtained 20 min post-injection of 740 MBq 99mTc-MIBI. Whole-body and planar spot images of the pelvis and thorax were acquired. The uptake of the MIBI in the bone marrow was evaluated using a qualitative and also a quantitative scoring system with determination of the tumour-to-background (T/B) ratios. Flow cytometry was performed for determining the Pgp expression of the blast cells in the bone marrow aspiration samples. There was a statistically significant inverse relationship between the Pgp level in numeric values and both mean qualitative (P<0.001; r=-0.665) and quantitative (P=0.001; r=-0.606) results of 99mTc-MIBI imaging. Both the mean qualitative score and the T/B ratios were higher in patients who were Pgp negative than in those who were Pgp positive (P<0.001 and P<0.001, respectively). These data indicate that an increased level of Pgp expression is correlated with a low accumulation of 99mTc-MIBI in bone marrow of patients with leukaemia. 99mTc-MIBI bone marrow imaging, as a method of functional imaging, can give in vivo information concerning the functional expression of the MDR phenotype in patients with untreated leukaemia.

Imaging gliomas with positron emission tomography and single-photon emission computed tomography

Over the last two decades the large volume of research involving various brain tracers has shed invaluable light on the pathophysiology of cerebral neoplasms. Yet the question remains as to how best to incorporate this newly acquired insight into the clinical context. Thallium is the most studied radiotracer with the longest track record. Many, but not all studies, show a relationship between (201)Tl uptake and tumor grade. Due to the overlap between tumor uptake and histologic grades, (201)Tl cannot be used as the sole noninvasive diagnostic or prognostic tool in brain tumor patients. However, it may help differentiating a high-grade tumor recurrence from radiation necrosis. MIBI is theoretically a better imaging agent than (201)Tl but it has not convincingly been shown to differentiate tumors according to grade. MDR-1 gene expression as demonstrated by MIBI does not correlate with chemoresistance in high grade gliomas. Currently, MIBI's clinical role in brain tumor imaging has yet to be defined. IMT, a radio-labeled amino acid analog, may be useful for identifying postoperative tumor recurrence and, in this application, appears to be a cheaper, more widely available tool than positron emission tomography (PET). However, its ability to accurately identify tumor grade is limited. 18 F-2-Fluoro-2-deoxy-d-glucose (FDG) PET predicts tumor grade, and the metabolic activity of brain tumors has a prognostic significance. Whether FDG uptake has an independent prognostic value above that of histology remains debated. FDG-PET is effective in differentiating recurrent tumor from radiation necrosis for high-grade tumors, but has limited value in defining the extent of tumor involvement and recurrence of low-grade lesions. Amino-acid tracers, such as MET, perform better for this purpose and thus play a complementary role to FDG. Given the poor prognosis of patients with gliomas, particularly with high-grade lesions, the overall clinical utility of single photon emission computed tomography (SPECT) and PET in characterizing recurrent lesions remains dependent on the availability of effective treatments. These tools are thus mostly suited to the evaluation of treatment response in experimental protocols designed to improve the patients' outcome.

Tc-99m methoxyisobutylisonitrile bone marrow imaging for predicting the levels of myeloma cells in bone marrow in multiple myeloma: correlation with CD38/CD138 expressing myeloma cells

The percentage of myeloma cells in bone marrow is subsequently an important index of disease in patients with multiple myeloma (MM). Bone marrow myeloma cells can be detected by strong CD38/CD138 positivity and light scatter characteristics using flow cytometry. The aim of the study was to evaluate the relationship between the degree of Tc-99m methoxyisobutylisonitrile (MIBI) uptake and the percentage of CD38/CD138 expressing myeloma cells in the bone marrow of patients with MM. A total of 15 patients with MM (mean age: 61.7+/-2.4 years; 7 F and 8 M) were included in the study. Tc-99m MIBI imaging was obtained 20 min after injection of 740 MBq Tc-99m MIBI. Planar spot images of the pelvis and thorax were acquired. The uptake of Tc-99m MIBI in the bone marrow was evaluated using a qualitative and also a semiquantitative scoring system for the bone marrow in areas that included the proximal femurs, anterior iliac crest, and sternum. In all patients, flow cytometry was performed for assessing the percentage of CD38/CD138 expressing myeloma cells in the bone marrow samples. There was a statistically significant positive correlation between the percentage of CD38/CD138 expressing plasma cells in bone marrow and both mean qualitative (r=0.689, p=0.005) and semiquantitative (r=0.669, p=0.006) results of Tc-99m MIBI uptake. In conclusion, our results indicate that increased Tc-99m MIBI uptake of bone marrow is related to the percentage of plasma cell infiltration of bone marrow. Tc-99m MIBI bone marrow imaging may be a useful tool for predicting the levels of myeloma cells in bone marrow of patients with MM.

Tc-99m MIBI uptake and its relation to the proliferative potential of brain tumors

PURPOSE

Many studies have shown that the S-phase fraction is a reflection of the proliferation potential of tumors, and DNA aneuploidy is more common in malignant tumors. In this preliminary study, the authors assessed the Tc-99m MIBI uptake of brain tumors and its relation to tumor grade and DNA content of the tumor cells.

METHODS

Ten patients (eight male, two female; mean age, 53.2 +/- 6.11 years) with untreated brain tumors were included in the study. SPECT imaging was performed 20 minutes after injection of 740 MBq (20 mCi) Tc-99m MIBI. A single detector camera with a low-energy high-resolution collimator was used for image acquisition. A region of interest was drawn in the tumor area under magnetic resonance guidance. A Tc-99m MIBI uptake index was computed as the mean tumor-to-background ratio. Flow cytometric analysis of fresh tumor tissue specimens was performed immediately. The percentages of cells in the G0/G1, S, and G2/M phases were determined for each patient.

RESULTS

DNA aneuploidy was found in 4 (49%) patients, whereas diploidy was found in 6 (60%) patients. There was a significant positive correlation between the Tc-99m MIBI uptake and the percentage of the S-phase fraction of the cell cycle ( = 0.000, r = 0.95). The Tc-99m MIBI index was significantly greater in aneuploid tumors than in diploid tumors ( < 0.01).

CONCLUSIONS

High-grade brain tumors have increased Tc-99m MIBI uptake compared with that of low-grade tumors. Tc-99m MIBI uptake is correlated with the percentage of the S-phase fraction of the cell and the aneuploidy level of the brain tumor. This preliminary report suggests that Tc-99m MIBI imaging may be useful in the evaluation of the biologic characteristics of brain tumors.

99mTc-MIBI and 201Tl SPET in the detection of recurrent brain tumours after radiation therapy

The purpose of this study was to evaluate whether Tc-hexakis-2-methoxyisobutylisonitrile ( Tc-MIBI) or Tl single photon emission tomography (SPET) could detect recurrent tumours in patients with previous radiation therapy for brain tumours. Dual SPET with Tc-MIBI and Tl was performed in 21 patients suspected of having recurrent brain tumours. SPET images were acquired 15 min (early) and 2 h (delayed) after injection. The ratio of the average counts for the region of interest in the lesion area and its mirror image in normal brain tissue was obtained. Early and delayed ratios were calculated. On the basis of histological and/or clinical findings, the final diagnosis was considered as recurrent tumours in 15 patients and radiation necrosis in six. Both ratios using Tc-MIBI and Tl were significantly higher in recurrent tumours than in radiation necrosis. Based on a cut-off of 5.89 of the early ratio using Tc-MIBI to distinguish between recurrent tumours and radiation necrosis, the accuracy was 90%. Based on a cut-off of 6.77 of the delayed ratio using Tc-MIBI, the accuracy was 86%. The corresponding values using cut-offs of 2.40 and 1.85 with Tl were 90% and 86%, respectively. However, within recurrent tumours, both ratios for Tc-MIBI were significantly higher than those for Tl. Early Tc-MIBI SPET may be especially useful for the detection of recurrent tumours in patients who have previously undergone radiation therapy for brain tumours.

Localisation of breast cancer resistance protein in microvessel endothelium of human brain

Movement of substrates between blood and brain is known to be influenced by P-glycoprotein (P-gp) at the luminal surface of the endothelium lining brain microvessels and by multidrug resistance associated protein 1 (MRP1) at the basolateral surface of the choroid plexus epithelium. Here, using RT-PCR and Western blotting, we investigate other ABC transporters in both normal and tumour human brain tissue and demonstrate the presence of breast cancer resistance protein (BCRP). Immunofluorescence confocal microscopy demonstrates that BCRP is located at the blood-brain barrier, mainly at the luminal surface of microvessel endothelium. This localization closely resembles that of P-gp. BCRP has several substrates in common with P-gp and may pose an additional barrier to drug access to the brain.

Brain-tumour drug resistance: the bare essentials

Chemotherapy lacks efficacy in most histological types of primary human brain tumours and has, for most types, failed to improve outcome for patients. The unsatisfactory results with chemotherapeutic intervention in these cancers have been chiefly attributed to tumour-cell resistance. This review summarises some of the major molecular markers that, although neither exclusive for nor specific to brain tumours, have been associated with the formation of a chemoresistant phenotype. Elucidation of the cellular mechanisms involved in resistance regulation is needed for future progress in efficient approaches to selective modulation of drug resistance in these lesions.

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.

Comparison of 99Tcm-MIBI with 201Tl chloride SPET in patients with malignant brain tumours

The purpose of this study was to evaluate the usefulness of 99Tcm-MIBI accumulation for the differentiation of histological diagnosis of malignant brain tumours in comparison with the findings obtained using 201Tl chloride. A total of 25 patients with malignant brain tumours were investigated. The histological categories of tumours included glioblastoma multiforme (n = 5), anaplastic astrocytoma (n = 4), malignant lymphoma (n = 5), and metastatic tumour (n = 11). Simultaneous dual single photon emission tomography (SPET) images with 99Tcm-MIBI and 201Tl were acquired 15 min (early) and 2 h (delayed) after injection, and the early ratio, delayed ratio and retention index were measured. The new indices 201Tl/99Tcm-MIBI ratios and 201Tl/99Tcm-MIBI retention index were also calculated. With respect to the histological type, a higher retention index using 99Tcm-MIBI was noted in glioblastoma multiforme compared with metastatic tumour. Higher values of both ratios using 201Tl were noted in glioblastoma multiforme compared to metastatic tumour. The value of the delayed ratio obtained using 201Tl was higher in glioblastoma multiforme than in anaplastic astrocytoma, and the value was also higher in malignant lymphoma than in metastatic tumour. The 201Tl/99Tcm-MIBI early ratio of glioblastoma multiforme was significantly higher than that of metastatic brain tumour. The 201Tl/99Tcm-MIBI retention index of malignant lymphoma was significantly higher than that of glioblastoma multiforme. In the histological type of tumour, 99Tcm-MIBI is not superior to 201Tl, but the combined indices using 201Tl/99Tcm-MIBI may add new information about differential diagnosis.

Technetium-99m-sestamethoxyisobutylisonitrile scan as a predictor of chemotherapy response in malignant lymphomas compared with P-glycoprotein expression, multidrug resistance-related protein expression and other prognosis factors

The purpose of the present study was to predict the response of malignant lymphomas (MLs) to chemotherapy using technetium-99m methoxyisobutylisonitrile (Tc-MIBI) scan and to compare it with the predictive ability of P-glycoprotein (P-gp) expression, multidrug resistance-related protein (MRP) expression and other prognosis factors. Twenty-five ML patients were enrolled in this study prior to initiation of chemotherapy. Images were obtained 10 min after intravenous injection of Tc-MIBI, interpreted visually and the tumour-to-background (T/B) ratios calculated. Immunohistochemical analyses were performed on sections of the biopsy specimens to determine P-gp and MRP expression. Chemotherapy response was evaluated in the first 1-2 years after completion of chemotherapy. The mean T/B ratio of the 15 patients with a good response (3.3 +/- 0.6) was significantly higher than that of the 10 patients with a poor response (1.2 +/- 0.1). All 15 patients with a good chemotherapy response had positive Tc-MIBI scan results and negative P-gp and MRP expression. All 10 patients with a poor response had negative Tc-MIBI scan results and either positive P-gp or MRP expression. Other prognosis factors showed no significant difference in the incidence of good and poor responses. Tc-MIBI scan results represent P-gp or MRP expression more accurately than other prognosis factors and predict the chemotherapy response in ML patients.

Anticancer drug resistance in primary human brain tumors

The difficult clinical situation still associated with most types of primary human brain tumors has fostered significant interest in defining novel therapeutic modalities for this heterogeneous group of neoplasms. Beginning in the 1980s chemotherapy has been incorporated into the treatment protocol of a number of intractable brain tumors. However, it has predominantly failed to improve patient outcome. The unsatisfactory results with chemotherapeutic intervention have chiefly been attributed to tumor cell resistance. In recent years, there has been a literal explosion in our understanding about the mechanisms by which cancer cells become chemoresistant. During the course of their evolution (intrinsic resistance) or in response to chemotherapy (acquired resistance) these cells may follow a number of pathways of genetic alterations to possess a common (multidrug) or drug-specific (individual drug) resistant phenotype. Genomic aberrations, deregulation of membrane transporting proteins and cellular enzymes, and an altered susceptibility to commit to apoptosis are among the steps on the way that contribute to the genesis of chemotherapeutic treatment failure. Although, through the years we have come to yield information and inferences as to the roles that different molecular events may have in the resistance phenotype of cancer cells, the actual involvement of single genetic alterations in conferring drug resistance in primary brain tumors remains debatable. This uncertainty and, besides, the lack of proper drug resistance diagnostics, in a vicious circle, hinder the development of effective resistance-modulation strategies. Clinical non-responsiveness to chemotherapy remains a formidable obstacle to the successful treatment of brain tumors and one of the most serious problems to be solved in the therapy of these lesions. Future advances in the chemotherapeutic management of these neoplasms will come with an improved understanding of the significance and interrelationship of the multiple biological systems operative in promoting resistance to this treatment modality. The focus of this review is to summarize current knowledge concerning major drug resistance-related markers, to describe their functional interaction en route to chemoresistance, and to discuss their implication in rendering human brain tumor cells resistant to chemotherapy.

The usefulness of Tc-99m MIBI for evaluating brain tumors: comparative study with Tl-201 and relation with P-glycoprotein

PURPOSE: This study was undertaken to determine the usefulness of Tc-99m methoxyisobutylisonitrile (MIBI) in brain tumors compared with TI-201 imaging. The authors evaluated the correlation between MIBI uptake and the presence of P-glycoprotein, and also the relation between MIBI uptake in response to combined radiotherapy and chemotherapy in glioblastoma. MATERIALS AND METHODS: Thirty-four brain tumors composed of 15 glioblastoma multiforme (GBM), 5 anaplastic astrocytomas, 5 low-grade astrocytomas, and 9 metastases were evaluated. Early and delayed images were obtained for MIBI and Tl-201 scintigraphy. P-glycoprotein status in all GBM, 2 anaplastic astrocytomas, 2 low-grade astrocytomas, and 2 metastases were evaluated immunohistochemically. Patients with GBM were divided into an effective and a noneffective group according to the change in tumor size. MIBI uptake indices were compared for these two groups. RESULTS: Both radiopharmaceuticals accumulated in all GBM and anaplastic astrocytomas. In low-grade astrocytomas, only one case showed tracer uptake. In metastasis, two cases showed high uptake on early images and marked washout on delayed images. Uptake ratio values (early uptake ratio and delayed uptake ratio) in all tumors were significantly higher in MIBI than in Tl-201. Immunohistochemical studies showed that the metastases were positive for P-glycoprotein but the GBM were not. In low-grade astrocytomas, a few cells were positively stained. In relation to the therapeutic outcome of GBM, both the early and delayed uptake ratios of MIBI were significantly greater in the noneffective group. CONCLUSIONS: Although diagnostic ability was comparable in MIBI and Tl-201, the imaging quality was better in MIBI. Both radiopharmaceuticals are useful in differentiating low-grade glioma from high-grade glioma. MIBI delayed imaging could also reflect the presence of P-glycoprotein. Intense MIBI uptake was also predictive of a poor clinical outcome in GBM.