Imaging recognition of inhibition of multidrug resistance in human breast cancer xenografts using 99mTc-labeled sestamibi and tetrofosmin

Astragalus polysaccharides can regulate cytokine and P-glycoprotein expression in H22 tumor-bearing mice

AIM: To investigate the adjunct anticancer effect of Astragalus polysaccharides in H22 tumor-bearing mice.

METHODS: To establish a solid tumor model, 5.0 × 10⁶/mL H22 hepatoma cells were inoculated subcutaneously into the right armpit region of Kunming mice (6-12 wk old, 18-22 g). When the tumors reached a size of 100 mm³, the animals were treated as indicated, and the mice were randomly assigned to seven groups (n = 10 each). After ten days of treatment, blood samples were collected from mouse eyes, and serum was harvested by centrifugation. Mice were sacrificed, and the whole body, tumor, spleen and thymus were weighed immediately. The rate of tumor inhibition and organ indexes were calculated. The expression levels of serum cytokines, P-glycoprotein (P-GP) and multidrug resistance (MDR) 1 mRNA in tumor tissues were detected using enzyme-linked immunosorbent assay, Western blotting, and quantitative myeloid-derived suppressor cells reverse transcription-polymerase chain reaction, respectively.

RESULTS: The tumor inhibition rates in the treatment groups of Adriamycin (ADM) + Astragalus polysaccharides (APS) (50 mg/kg), ADM + APS (100 mg/kg), and ADM + APS (200 mg/kg) were significantly higher than in the ADM group (72.88% vs 60.36%, P = 0.013; 73.40% vs 60.36%, P = 0.010; 77.57% vs 60.36%, P = 0.001). The spleen indexes of the above groups were also significantly higher than in the ADM group (0.65 ± 0.22 vs 0.39 ± 0.17, P = 0.023; 0.62 ± 0.34 vs 0.39 ± 0.17, P = 0.022; 0.67 ± 0.20 vs 0.39 ± 0.17, P = 0.012), and the thymus indexes of the ADM + APS (100 mg/kg) and ADM + APS (200 mg/kg) groups were significantly higher than in the ADM group (0.20 ± 0.06 vs 0.13 ± 0.04, P = 0.029; 0.47 ± 0.12 vs 0.13 ± 0.04, P = 0.000). APS was found to exert a synergistic anti-tumor effect with ADM and to alleviate the decrease in the sizes of the spleen and thymus induced by AMD. The expression of interleukin-1α (IL-1α), IL-2, IL-6, and tumor necrosis factor-α (TNF-α) was significantly higher in the ADM + APS (50 mg/kg), ADM + APS (100 mg/kg) and ADM + APS (200 mg/kg) groups than in the ADM group; and IL-10 was significantly lower in the above groups than in the ADM group. APS could increase IL-1α, IL-2, IL-6, and TNF-α expression and decrease IL-10 levels. Compared with the ADM group, APS treatment at a dose of 50-200 mg/kg could down-regulate MDR1 mRNA expression in a dose-dependent manner (0.48 ± 0.13 vs 4.26 ± 1.51, P = 0.000; 0.36 ± 0.03 vs 4.26 ± 1.51, P = 0.000; 0.21 ± 0.04 vs 4.26 ± 1.51, P = 0.000). The expression level of P-GP was significantly lower in the ADM + APS (200 mg/kg) group than in the ADM group (137.35 ± 9.20 mg/kg vs 282.19 ± 20.54 mg/kg, P = 0.023).

CONCLUSION: APS exerts a synergistic anti-tumor effect with ADM in H22 tumor-bearing mice. This may be related to its ability to enhance the expression of IL-1α, IL-2, IL-6, and TNF-α, decrease IL-10, and down-regulate MDR1 mRNA and P-GP expression levels.

64Cu-labeled phosphonium cations as PET radiotracers for tumor imaging

Alteration in mitochondrial transmembrane potential (ΔΨ(m)) is an important characteristic of cancer. The observation that the enhanced negative mitochondrial potential is prevalent in tumor cell phenotype provides a conceptual basis for development of mitochondrion-targeting therapeutic drugs and molecular imaging probes. Since plasma and mitochondrial potentials are negative, many delocalized organic cations, such as rhodamine-123 and (3)H-tetraphenylphosphonium, are electrophoretically driven through these membranes, and able to localize in the energized mitochondria of tumor cells. Cationic radiotracers, such as (99m)Tc-Sestamibi and (99m)Tc-Tetrofosmin, have been clinically used for diagnosis of cancer by single photon emission computed tomography (SPECT) and noninvasive monitoring of the multidrug resistance (MDR) transport function in tumors of different origin. However, their diagnostic and prognostic values are often limited due to their insufficient tumor localization (low radiotracer tumor uptake) and high radioactivity accumulation in the chest and abdominal regions (low tumor selectivity). In contrast, the (64)Cu-labeled phosphonium cations represent a new class of PET (positron emission tomography) radiotracers with good tumor uptake and high tumor selectivity. This review article will focus on our recent experiences in evaluation of (64)Cu-labeled phosphonium cations as potential PET radiotracers. The main objective is to illustrate the impact of radiometal chelate on physical, chemical, and biological properties of (64)Cu radiotracers. It will also discuss some important issues related to their tumor selectivity and possible tumor localization mechanism.

Pgp inhibition by UIC2 antibody can be followed in vitro by using tumor-diagnostic radiotracers, 99mTc-MIBI and 18FDG

P-glycoprotein (Pgp, ABCB1) is one of the active efflux pumps that are able to extrude a large variety of chemotherapeutic drugs from the cells, causing the phenomenon of multidrug resistance. It has been shown earlier that the combined application of a class of Pgp modulators (e.g. cyclosporine A and SDZ PSC 833) used at low concentrations and UIC2 antibody is a novel, specific, and effective way of blocking Pgp function (Goda et al., 2007). In the present work we study the UIC2 antibody mediated Pgp inhibition in more detail measuring the accumulation of tumor diagnostic radiotracers, 2-[(18)F]fluoro-2-deoxy-d-glucose ((18)FDG) and [(99m)Tc]hexakis-2-methoxybutyl isonitrile ((99m)Tc-MIBI), into Pgp(+) (A2780AD) and Pgp(-) (A2780) human ovarian carcinoma cells. Co-incubation of cells with UIC2 and cyclosporine A (CSA, 2μM) increased the binding of UIC2 more than 3-fold and reverted the rhodamine 123 (R123), daunorubicin (DNR) and (99m)Tc-MIBI accumulation of the Pgp(+) 2780AD cells to approx. the same level as observed in Pgp(-) cells. Similarly, 50μM paclitaxel (Pacl) increased UIC2 binding, and consequently reinstated the uptake of R123, DNR and (99m)Tc-MIBI into the Pgp(+) cells. Blocking Pgp by combined treatments with CSA+UIC2 or Pacl+UIC2 also decreased the glucose metabolic rate of the A2780AD Pgp(+) cells measured in (18)FDG accumulation experiments suggesting that the maintenance of Pgp activity requires a considerable amount of energy. Similar treatments of the A2780 Pgp(-) cells did not result in significant change in the R123, DNR, (99m)Tc-MIBI and (18)FDG accumulation demonstrating that the above effects are Pgp-specific. Thus, combined treatment with the UIC2 antibody and Pgp modulators can completely block the function of Pgp in human ovarian carcinoma cells and this effect can be followed in vitro by using tumor-diagnostic radiotracers, (99m)Tc-MIBI and (18)FDG.

Glucose-induced alteration of accumulation of organotechnetium complexes accumulation in Pgp-negative tumor-bearing mice

The biologic and microenvironmental factors determining (99m)Tc sestamibi (MIBI) and (99m)Tc tetrofosmin (TF) uptake in breast tumors are incompletely understood, especially in P-glycoprotein (Pgp)-negative tumors. We analyzed the influence of glucose administration on the uptake and retention of MIBI and TF in Pgp-negative tumor-bearing mice in vivo. Twenty (20) mice bearing Ehrlich ascites tumor cell (EATC) xenografts were divided into four groups: (1) MIBI, (2) MIBI+glucose, (3) TF, and (4) TF+glucose. Glucose was administered (5.0 g/kg body weight) intraperitoreally (i.p.) 1 hour before scintigraphy. There were significant differences between the E-UPR MIBI and MIBI+glucose groups (p = 0.009) and minor differences in L-UPR between these groups (p = 0.04). There was a significant inverse correlation between E-UPR of MIBI and glucose levels (r = 0.71, p = 0.02). Comparing the four groups, the highest E-UPR was obtained in the MIBI group (p = 0.006). Other parameters were not different in the MIBI and MIBI+glucose groups and in the TF and TF+glucose groups. Increased blood glucose level affected the MIBI uptake of tumor tissue, particularly for E-UPR. We suggest that these findings were due to basically decreased blood flow and secondarily decreased extracellular pH. However, glucose administration did not affect TF.

Mechanism for myocardial localization and rapid liver clearance of Tc-99m-N-MPO: a new perfusion radiotracer for heart imaging

BACKGROUND

[Tc-99m-N(mpo)(PNP5)](+) (Tc-99m-N-MPO: Hmpo = 2-mercaptopyridine N-oxide and PNP5 = N-ethoxyethyl-N,N-bis[2-(bis(3-methoxypropyl)phosphino)ethyl]amine) is a new Tc-99m radiotracer useful for myocardial perfusion imaging. The main objective of this study is to elucidate the mechanism for myocardial localization and fast liver clearance of Tc-99m-N-MPO in comparison with Tc-99m-sestamibi ([Tc-99m-(MIBI)(6)](+): MIBI = 2-methoxy-2-methylpropylisonitrile).

METHODS AND RESULTS

Subcellular distribution of Tc-99m-N-MPO and Tc-99m-sestamibi was examined in the excised Sprague-Dawley (SD) rat myocardium. Biodistribution and planar imaging studies were performed using SD rats in the absence/presence of Cyclosporin-A. Due to negative plasma and mitochondrial potentials, 84.5% +/- 3.2% of Tc-99m-N-MPO was found in the mitochondrial fraction as compared to 88.0% +/- 1.5% of Tc-99m-sestamibi. There was no significant difference in their mitochondrial accumulation. Tc-99m-N-MPO was also able to retain its chemical integrity in rat myocardium. Pre-treatment of SD rats with Cys-A result in significant increase in the kidney and liver uptake of Tc-99m-N-MPO.

CONCLUSION

Tc-99m-N-MPO and Tc-99m-sestamibi share almost identical subcellular distribution and localization mechanism. The MDR transport function of hepatocytes and renal cells is responsible for the fast clearance kinetics of Tc-99m-N-MPO from liver and kidneys, respectively. Tc-99m-N-MPO is a very promising myocardial perfusion radiotracer with favorable biodistribution properties and rapid liver clearance.

Evaluation of (64)Cu(DO3A-xy-TPEP) as a potential PET radiotracer for monitoring tumor multidrug resistance

In this study, we evaluated the potential of (64)Cu(DO3A-xy-TPEP) (DO3A-xy-TPEP = (2-(diphenylphosphoryl)ethyl)diphenyl(4-((4,7,10-tris(carboxymethyl)-1,4,7,10-tetraazacyclododecan-1-yl)methyl)benzyl)phosphonium) as a PET (positron emission tomography) radiotracer for noninvasive monitoring of multidrug resistance (MDR) transport function in several xenografted tumor models (MDR-negative: U87MG; MDR-positive: MDA-MB-435, MDA-MB-231, KB-3-1, and KB-v-1). It was found that (64)Cu(DO3A-xy-TPEP) has a high initial tumor uptake (5.27 +/- 1.2%ID/g at 5 min p.i.) and shows a steady uptake increase between 30 and 120 min p.i. (2.09 +/- 0.53 and 3.35 +/- 1.27%ID/g at 30 and 120 min p.i., respectively) in the MDR-negative U87MG glioma tumors. (64)Cu(DO3A-xy-TPEP) has a greater uptake difference between U87MG glioma and MDR-positive tumors (MDA-MB-231: 1.57 +/- 0.04, 1.00 +/- 0.17, and 0.93 +/- 0.15; MDA-MB-435: 1.15 +/- 0.19, 1.12 +/- 0.20, and 0.81 +/- 0.11; KB-3-1: 1.45 +/- 0.31, 1.43 +/- 0.16, and 1.08 +/- 0.19; and KB-v-1: 1.63 +/- 0.47, 1.81 +/- 0.31, and 1.14 +/- 0.22%ID/g at 30, 60, and 120 min p.i., respectively) than (99m)Tc-Sestamibi. Regardless of the source of MDR, the overall net effect is the rapid efflux of (64)Cu(DO3A-xy-TPEP) from tumor cells, which leads to a significant reduction of its tumor uptake. It was concluded that (64)Cu(DO3A-xy-TPEP) is more efficient than (99m)Tc-Sestamibi as the substrate for MDR P-glycoproteins (MDR Pgps) and multidrug resistance-associated proteins (MRPs), and might be a more efficient radiotracer for noninvasive monitoring of the tumor MDR transport function. (64)Cu(DO3A-xy-TPEP) and (99m)Tc-Sestamibi share almost identical subcellular distribution patterns in U87MG glioma tumors. Thus, it is reasonable to believe that (64)Cu(DO3A-xy-TPEP), like (99m)Tc-Sestamibi, is able to localize in mitochondria due to the increased plasma and mitochondrial transmembrane potentials in tumor cells.

64Cu-labeled 2-(diphenylphosphoryl)ethyldiphenylphosphonium cations as highly selective tumor imaging agents: effects of linkers and chelates on radiotracer biodistribution characteristics

Radiolabeled organic cations, such as triphenylphosphonium (TPP), represents a new class of radiotracers for imaging cancers and the transport function of multidrug resistance P-glycoproteins (particularly MDR1 Pgp) by single photon emission computed tomography (SPECT) or positron emission tomography (PET). This report presents the synthesis and biological evaluation of (64)Cu-labeled 2-(diphenylphosphoryl)ethyldiphenylphosphonium (TPEP) cations as novel PET radiotracers for tumor imaging. Biodistribution studies were performed using the athymic nude mice bearing subcutaneous U87MG human glioma xenografts to explore the impact of linkers, bifunctional chelators (BFCs), and chelates on biodistribution characteristics of the (64)Cu-labeled TPEP cations. Metabolism studies were carried out using normal athymic nude mice to determine the metabolic stability of four (64)Cu radiotracers. It was found that most (64)Cu radiotracers described in this study have significant advantages over (99m)Tc-Sestamibi for their high tumor/heart and tumor/muscle ratios. Both BFCs and linkers have significant impact on biological properties of (64)Cu-labeled TPEP cations. For example, (64)Cu(DO3A-xy-TPEP) has much lower liver uptake and better tumor/liver ratios than (64)Cu(DO3A-xy-TPP), suggesting that TPEP is a better mitochondrion-targeting molecule than TPP. Replacing DO3A with DO2A results in (64)Cu(DO2A-xy-TPEP) (+), which has a lower tumor uptake than (64)Cu(DO3A-xy-TPEP). Substitution of DO3A with NOTA-Bn leads to a significant decrease in tumor uptake for (64)Cu(NOTA-Bn-xy-TPEP). The use of DOTA-Bn to replace DO3A has little impact on the tumor uptake, but the tumor/liver ratio of (64)Cu(DOTA-Bn-xy-TPEP) (-) is not as good as that of (64)Cu(DO3A-xy-TPEP), probably due to the aromatic benzene ring in DOTA-Bn. Addition of an extra acetamido group in (64)Cu(DOTA-xy-TPEP) results in a lower liver uptake, but tumor/liver ratios of (64)Cu(DOTA-xy-TPEP) and (64)Cu(DO3A-xy-TPEP) are comparable due to a faster tumor washout of (64)Cu(DOTA-xy-TPEP). Substitution of xylene with the PEG 2 linker also leads to a significant reduction in both tumor and liver uptake. MicroPET imaging studies on (64)Cu(DO3A-xy-TPEP) in athymic nude mice bearing U87MG glioma xenografts showed that the tumor was clearly visualized as early as 1 h postinjection with very high T/B contrast. There was very little metabolite (<2%) detectable in the urine and feces samples for (64)Cu(DO3A-xy-TPEP), (64)Cu(DOTA-Bn-xy-TPEP)(-), and (64)Cu(NOTA-Bn-xy-TPEP). Considering both tumor uptake and T/B ratios (particularly tumor/heart, tumor/liver, and tumor/muscle), it was concluded that (64)Cu(DO3A-xy-TPEP) is a promising PET radiotracer for imaging the MDR-negative tumors.

(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.

Functional imaging of multidrug resistance in an orthotopic model of osteosarcoma using 99mTc-sestamibi

PURPOSE

The purpose of this work was the development of an orthotopic model of osteosarcoma based on luciferase-expressing tumour cells for the in vivo imaging of multidrug resistance (MDR) with (99m)Tc-sestamibi.

METHODS

Doxorubicin-sensitive (143B-luc(+)) and resistant (MNNG/HOS-luc(+)) osteosarcoma cell lines expressing different levels of P-glycoprotein and carrying a luciferase reporter gene were inoculated into the tibia of nude mice. Local tumour growth was monitored weekly by bioluminescence imaging and X-ray. After tumour growth, a (99m)Tc-sestamibi dynamic study was performed. A subset of animals was pre-treated with an MDR inhibitor (PSC833). Images were analysed for calculation of (99m)Tc-sestamibi washout half-life (t (1/2)), percentage washout rate (%WR) and tumour/non-tumour (T/NT) ratio.

RESULTS

A progressively increasing bioluminescent signal was detected in the proximal tibia after 2 weeks. The t (1/2) of (99m)Tc-sestamibi was significantly shorter (p < 0.05) in drug-resistant MNNG/HOS-luc(+) tumours (t (1/2) = 87.3 +/- 15.7 min) than in drug-sensitive 143B-luc(+) tumours (t (1/2) = 161.0 +/- 47.4 min) and decreased significantly with PSC833 (t (1/2) = 173.0 +/- 24.5 min, p < 0.05). No significant effects of PSC833 were observed in 143B-luc(+) tumours. The T/NT ratio was significantly lower (p < 0.05) in MNNG/HOS-luc(+) tumours than in 143B-luc(+) tumours at early (1.55 +/- 0.22 vs 2.14 +/- 0.36) and delayed times (1.12 +/- 0.11 vs 1.62 +/- 0.33). PSC833 had no significant effects on the T/NT ratios of either tumour.

CONCLUSION

The orthotopic injection of tumour cells provides an animal model suitable for functional imaging of MDR. In vivo bioluminescence imaging allows the non-invasive monitoring of tumour growth. The kinetic analysis of (99m)Tc-sestamibi washout provides information on the functional activity of MDR related to P-glycoprotein expression and its pharmacological inhibition in osteosarcoma.

Mechanism of uptake and retention of F-18 BMS-747158-02 in cardiomyocytes: a novel PET myocardial imaging agent

BACKGROUND

BMS-747158-02 is a novel fluorine 18-labeled pyridazinone derivative designed for cardiac imaging. The uptake and retention mechanisms of F-18 BMS-747158-02 in cardiac myocytes were studied in vitro, and the biodistribution of F-18 BMS-747158-02 was studied in vivo in mice.

METHODS AND RESULTS

Fluorine 19 BMS-747158-01 inhibited mitochondrial complex I (MC-I) in bovine heart submitochondrial particles with an IC(50) of 16.6 +/- 3 nmol/L that was comparable to the reference inhibitors of MC-1, rotenone, pyridaben, and deguelin (IC(50) of 18.2 +/- 6.7 nmol/L, 19.8 +/- 2.6 nmol/L, and 23.1 +/- 1.5 nmol/L, respectively). F-18 BMS-747158-02 had high uptake in monolayers of neonatal rat cardiomyocytes (10.3% +/- 0.7% of incubated drug at 60 minutes) that was inhibited by 200 nmol/L of rotenone (91% +/- 2%) and deguelin (89% +/- 3%). In contrast, an inactive pyridaben analog, P-070 (IC(50) value >4 micromol/L in MC-1 assay), did not inhibit the binding of F-18 BMS-747158-02 in cardiomyocytes. Uptake and washout kinetics for F-18 BMS-747158-02 in rat cardiomyocytes indicated that the time to half-maximal (t((1/2))) uptake was very rapid (approximately 35 seconds), and washout t((1/2)) for efflux of F-18 BMS-747158-02 was greater than 120 minutes. In vivo biodistribution studies in mice showed that F-18 BMS-747158-02 had substantial myocardial uptake (9.5% +/- 0.5% of injected dose per gram) at 60 minutes and heart-to-lung and heart-to-liver ratios of 14.1 +/- 2.5 and 8.3 +/- 0.5, respectively. Positron emission tomography imaging in the mouse allowed clear cardiac visualization and demonstrated sustained myocardial uptake through 55 minutes.

CONCLUSIONS

F-18 BMS-747158-02 is a novel positron emission tomography cardiac tracer targeting MC-I in cardiomyocytes with rapid uptake and slow washout. These characteristics allow fast and sustained accumulation in the heart.