99mTc-MIBI scintigraphy in metastatic renal cell carcinoma: clinical validation of the relationship between 99mTc-MIBI uptake and P-glycoprotein expression in tumour tissue

Imaging techniques to study drug transporter function in vivo

Transporter systems involved in the permeation of drugs and solutes across biological membranes are recognized as key determinants of pharmacokinetics. Typically, the action of membrane transporters on drug exposure to tissues in living organisms is inferred from invasive procedures, which cannot be applied in humans. In recent years, imaging methods have greatly progressed in terms of instruments, synthesis of novel imaging probes as well as tools for data analysis. Imaging allows pharmacokinetic parameters in different tissues and organs to be obtained in a non-invasive or minimally invasive way. The aim of this overview is to summarize the current status in the field of molecular imaging of drug transporters. The overview is focused on human studies, both for the characterization of transport systems for imaging agents as well as for the determination of drug pharmacokinetics, and makes reference to animal studies where necessary. We conclude that despite certain methodological limitations, imaging has a great potential to study transporters at work in humans and that imaging will become an important tool, not only in drug development but also in medicine. Imaging allows the mechanistic aspects of transport proteins to be studied, as well as elucidating the influence of genetic background, pathophysiological states and drug-drug interactions on the function of transporters involved in the disposition of drugs.

99mTc-sestamibi SPECT/CT for the characterization of renal masses: a pictorial guide

In parallel to the increased utilization of cross-sectional imaging, the incidence of small renal masses has steadily risen in recent years. At the present time, anatomical imaging techniques are limited in their ability to differentiate benign from malignant renal masses. Moreover, renal mass biopsy has a high non-diagnostic rate, poor negative-predictive ability, and carries potential risks as well as substantial costs. As a result, benign renal masses are often unnecessarily resected for the false presumption of cancer. ^99mTc-sestamibi single photon emission computed tomography/computed tomography (SPECT/CT) is a molecular imaging test that allows for the differentiation of benign renal oncocytomas and hybrid oncocytomic/chromophobe tumours apart from malignant renal cell carcinomas on the basis of differences in mitochondrial content as well as multidrug resistant pump expression. Herein, we review the principles of ^99mTc-sestamibi SPECT/CT administration and image interpretation for the purpose of renal mass characterization.

Initial experience using 99mTc-MIBI SPECT/CT for the differentiation of oncocytoma from renal cell carcinoma

Purpose

The differentiation of oncocytoma from renal cell carcinoma (RCC) remains a challenge with currently available cross-sectional imaging techniques. As a result, a large number of patients harboring a benign oncocytoma undergo unnecessary surgical resection. In this study, we explored the utility of ^99mTc-MIBI SPECT/CT for the differentiation of these tumors based on the hypothesis that the large number of mitochondria in oncocytomas would lead to increased ^99mTc-MIBI uptake.

Patients and Methods

In total, 6 patients (3 with oncocytoma and 3 with RCC) were imaged with ^99mTc-MIBI SPECT/CT. Relative quantification was performed by measuring tumor-to-normal renal parenchyma background ratios.

Results

All 3 oncocytomas demonstrated radiotracer uptake near or above the normal renal parenchymal uptake (range of uptake ratios, 0.85–1.78). In contrast, the 3 RCCs were profoundly photopenic relative to renal background (range of uptake ratios, 0.21–0.31).

Conclusions

^99mTc-MIBI SPECT/CT appears to be of value in scintigraphically distinguishing benign renal oncocytoma from RCC.

Predictive value of (99m)Tc sestamibi scintigraphy in the evaluation of doxorubicin based chemotherapy response in patients with advanced breast cancer

Resistance to doxorubicin based chemotherapy is a major therapeutic problem limiting advanced breast cancer treatment. 99mTc hexakis-2-methoxyisobutylisonitrile ((99m)Tc-MIBI) has been reported to be extruded from tumour cells by the P-glycoprotein and multidrug resistance protein encoded by MDR1 and MRP1 genes, respectively. These proteins are involved in the cellular efflux of several chemotherapeutic agents including doxorubicin. The aim of this study was to investigate the clinical value of a standard (99m)Tc-MIBI scintimammography technique in the prediction of response to chemotherapy in advanced breast cancer patients. Fifty-six lesions from 33 female patients with locally advanced (n=27) or recurrent breast cancer (n=6) were included in the study. MIBI scintigraphy was performed 2-8 days prior to chemotherapy (FAC regimen). Images were acquired 10 min and 1 h post-injection of 740-1110 MBq of (99m)Tc-MIBI. Tumour-to-normal background tissue uptake ratios were calculated on each lesion in the early (T/B(e)) and delayed phase of the study (T/B(d)). Both T/B(e) and T/B(d) ratios were significantly higher (P<0.0001) in responders (n=43) than nonresponders (n=13). Diagnostic values of (99m)Tc-MIBI in the prediction of chemotherapy response were evaluated using the arbitrary cut-off values of 1.5 for T/B(e) and 1.4 forT/B(d). Sensitivity, specificity, positive and negative predictive values were 88.4%, 92.3%, 97.4%, 70.6%; and 90.7%, 100.0%, 100.0%, 76.6%, for T/B(e) and T/B(d), respectively. We conclude that (99m)Tc-MIBI scintigraphy may be a clinically valuable tool for guiding chemotherapy in advanced breast cancer patients.

Detection of cold bone metastasis by Tc-99m MIBI imaging

We present a case of renal cell carcinoma metastasis to the skull, appearing as a photopenic area on Tc-99m MDP bone scan and with focal uptake in the same region on Tc-99m MIBI imaging.

Prediction of chemotherapeutic response by Technetium 99m--MIBI scintigraphy in breast carcinoma patients

BACKGROUND

Significance of Technetium 99m ((99m)Tc)-MIBI scintigraphy in the prediction of response to anthracylines and taxanes (both are substrates for P-glycoprotein [P-gp]) as well as relation between (99m)Tc-MIBI uptake and P-gp or MDR1 mRNA expression in tumors were studied in patients with breast carcinoma.

METHODS

Forty-six female patients with locally advanced (n = 15) or metastatic (n = 31) breast carcinoma were recruited in this study. Before chemotherapy (epirubicin and cyclophosphamide [n = 20] or decetaxel [n = 26]), (99m)Tc-MIBI scintigraphy was performed to obtain the T/N (tumor to normal tissue) ratios of (99m)Tc-MIBI uptake at 10 minutes (T/N[e]) and at 180 minutes (T/N[d]) after the (99m)Tc-MIBI injection. Expression of MDR1 mRNA and P-gp in tumors (n = 32) were determined by a quantitative real-time polymerase chain reaction and immunohistochemistry, respectively.

RESULTS

Clinical significance of T/N(e) and T/N(d) ratios in the prediction of chemotherapeutic response was evaluated using the arbitrary cutoff values of 3.0 for T/N(e) ratios and 2.0 for T/N(d) ratios. Positive predictive value, negative predictive value, and diagnostic accuracy of T/N(d) ratios (81.0%, 96.0%, and 89.1%, respectively) were higher, although statistically not significant, than those of T/N(e) ratios (73.3%, 77.4%, and 76.1%, respectively), and these values were not affected by type of chemotherapy. MDR1 mRNA levels were not significantly different between the lesions with high (> or = 2.0) and low (< 2.0) T/N(d) ratios, but P-gp expression was significantly (P < 0.01) higher in the lesions with low T/N(d) ratios than in those with high T/N(d) ratios.

CONCLUSIONS

T/N(d) ratios determined by (99m)Tc-MIBI scintigraphy are useful in the prediction of response to chemotherapy with epirubicin and cyclophosphamide or docetaxel as well as in the in vivo evaluation of P-gp expression status in tumors in patients with locally advanced or recurrent breast carcinoma.

Technetium-99m MIBI single photon emission computed tomography as an indicator of prognosis for patients with lung cancer-preliminaly report

PURPOSE

We performed technetium-99m hexakis-2-methoxyisobutylisonitrile (Tc-99m MIBI) single photon emission computed tomography (SPECT) in 23 patients with primary lung cancer between July 1993 and March 1996. We evaluated the relationships among the uptake ratio, retention index and the prognosis after radiation therapy and/or chemotherapy.

MATERIALS AND METHODS

Tc-99m MIBI SPECT was performed at 30 minutes and at 3 hours after intravenous injection of 600 MBq of Tc-99m MIBI with three gamma camera detectors (GCA-9300A/HG) on transverse SPECT images. Regions of interest were set in the area of abnormal uptake of Tc-99m MIBI and in the contralateral normal lung. The ratio of uptake in the lesion to that in the contralateral normal lung was obtained on early images (early ratio; ER) as well as delayed images (delayed ratio: DR). The retention index (RI) was calculated as follows: RI = (DR - ER)/ER x 100. The ratio was compared with survival time and prognostic factors.

RESULTS

There was no correlation between ER and DR. The patients with high RI survived longer than those with low RI (median survival, 19.4 months vs. 9.4 months; p = 0.0104 by the Mantel-Cox test).

CONCLUSION

These results suggest that RI is the most useful among Tc-99m MIBI indices of primary lung cancer in predicting prognosis.

Tc-99m MIBI SPECT is useful for noninvasively predicting the presence of MDR1 gene-encoded P-glycoprotein in patients with hepatocellular carcinoma

PURPOSE

Resistance to chemotherapeutic drugs continues to be one of the major unsolved problems in the treatment of cancer. Multidrug resistance is defined as the ability of cells exposed to a single drug to develop resistance to a broad range of structurally and functionally unrelated drugs as a result of enhanced outward transport of drugs mediated by P-glycoprotein that is encoded by multidrug resistance genes. Recent evidence has shown that Tc-99m MIBI is a suitable transport substrate for P-glycoprotein. A potential advantage of Tc-99m MIBI SPECT is its superiority to diagnose noninvasively the presence of P-glycoprotein overexpression in vivo. In this study, the authors determined the association of enhanced MIBI efflux in Tc-99m MIBI SPECT with overexpression of P-glycoprotein in hepatocellular carcinoma.

MATERIALS AND METHODS

Thirty-five patients with hepatocellular carcinoma were enrolled in the study. Tc-99m MIBI SPECT was performed 10 minutes after intravenous injection of 20 mCi Tc-99m MIBI. All patients had liver biopsy or surgery within 1 week of MIBI imaging. Immunohistochemical study of the biopsy or resected hepatocellular carcinoma specimens was performed using the avidin-biotin-peroxidase technique with monoclonal antibody JSB-1 directed against P-glycoprotein.

RESULTS

On Tc-99m MIBI SPECT, 30 of 35 (85.7%) patients with hepatocellular carcinoma had no Tc-99m MIBI uptake in tumor lesions, whereas five patients with hepatocellular carcinoma had Tc-99m MIBI uptake in tumor lesions. P-glycoprotein expression was observed in tumor tissues of all the patients without Tc-99m MIBI uptake, whereas among the five patients with Tc-99m MIBI uptake, no P-glycoprotein expression was seen in tumor lesions (P < 0.015).

CONCLUSION

Tc-99m MIBI SPECT is useful for noninvasively predicting the presence of MDR1 gene-encoded P-glycoprotein in patients with hepatocellular carcinoma.

False-negative scintigraphy with Tc-99m sestamibi in stage IV neuroblastoma

Tc-99m sestamibi, originally developed for myocardial studies, has been used as a tumor-seeking agent. Recently, the agent also was reported to be a functional tracer to predict multidrug resistance-related p-glycoprotein expression in tumor tissue. The current report presents the authors' experience with sestamibi tumor scintigraphy in a neuroblastoma. Although I-131 MIBG tumor imaging and Tc-99m MDP bone scanning accurately demonstrated the extent of the disease, Tc-99m sestamibi showed no accumulation in primary and metastatic foci. Lack of sestamibi uptake was initially thought to be suggestive of failure to respond to chemotherapy because of p-glycoprotein expression. However, the patient responded well to chemotherapy and complete remission was achieved. The failure of Tc-99m sestamibi to detect a neuroblastoma and the lack of sestamibi accumulation in the tumor may not always be related to chemotherapy resistance.

Technetium-99m methoxyisobutylisonitrile chest imaging of small cell lung carcinoma: relation to patient prognosis and chemotherapy response--a preliminary report

BACKGROUND

The purpose of this preliminary study was to evaluate retrospectively the relation between chemotherapy response and survival time, using technetium-99m methoxyisobutylisonitrile (Tc-99m MIBI) uptake in small cell lung carcinoma (SCLC) to detect the expression of multidrug resistance (mdr)-mediated 170-kDa P-glycoprotein (PgP).

METHODS

Before the administration of chemotherapy (which consisted of cisplatin 25 mg and etoposide 125 mg every day per 3-day course), 15 male patients (ages 54-64 years) with SCLC were enrolled in this study to undergo Tc-99m MIBI chest imaging, including single photon emission computed tomography (SPECT) and planar imaging, for qualitative and quantitative assessments of PgP in their SCLC.

RESULTS

In 12 of 15 cases (80%), SCLC could be detected by visual interpretation of the Tc-99m MIBI chest SPECT images. In 13 of 15 cases (87%), Tc-99m MIBI chest SPECT images (either positive SPECT with good response or negative SPECT with poor response) correctly predicted chemotherapy response. The correlation between tumor uptake ratios obtained by planar images (total counts in the region of interest [ROI] of the tumor divided by total counts in the same size ROI of the contralateral normal lung) and survival days (from the time of SCLC diagnosis to the time of the patient's death) was both positive and good (correlation coefficient=0.83).

CONCLUSIONS

Tc-99m MIBI chest images have the potential to demonstrate mdr-PgP expression in SCLC and to predict patient prognosis and chemotherapy response.

Challenging drug resistance in cancer therapy--review of the First Nordic Conference on Chemoresistance in Cancer Treatment, October 9th and 10th, 1997

The First Nordic Conference on Chemoresistance in Cancer Treatment was held in the Danish town of Helsingør on October 9th and 10th, 1997, under the auspices of the Nordic Cancer Chemoresistance Group (NCCG). The meeting focused on biochemical chemoresistance in a multidisciplinary approach. There were 19 oral and 15 poster presentations documenting recent advances in experimental and clinical research of drug transport mechanisms, DNA repair systems, detoxifying enzymes, drug target regulation, in vitro sensitivity tests, apoptosis inhibition, and strategies to circumvent chemoresistance. In the present paper we review the main issues that were addressed and discuss the findings with reference to the current literature in the field. The meeting demonstrated the plurality and the complexity of chemoresistance, which is a major obstacle to successful chemotherapy in cancer patients. The new insights to mechanisms of drug resistance and sensitization represent a useful basis for further development of strategies to circumvent chemoresistance in clinical practice.