Intercomparison of conventional and QuickScan dicentric scoring for the validation of individual biodosimetry analysis in Taiwan.

PURPOSE: The dicentric chromosome assay (DCA), the gold standard for radiation biodosimetry, evaluates an individual absorbed radiation dose by the analysis of DNA damage in human lymphocytes. The conventional (C-DCA) and QuickScan (QS-DCA) scoring methods are sensitive for estimating radiation dose. The Biodosimetry Laboratory at Institute of Nuclear Energy Research (INER), Taiwan, participated in intercomparison exercises conducted by Health Canada (HC) in 2014, 2015 and 2018 to validate the laboratory's accuracy and performance. MATERIAL AND METHODS: Blood samples for the conventional dose response curve for Taiwan were irradiated with 0, 0.25, 0.5, 1, 2, 3, 4 and 5 Gy. Ten blind blood samples were provided by HC. Either or both of two methods of conventional (C) or QuickScan (QS) scoring could be chosen for the HC's intercomparison. For C-DCA triage scoring, only cells with 46 centromeres were counted and each scorer recorded the number of dicentrics in the first 50 metaphases or stopped scoring when 30 dicentrics were reached. Scorers also recorded how much time it took to analyze 10, 20, and 50 cells. Subsequently, the data were entered into the Dose Estimate software (DoseEstimate_v5.1) and dose estimates were calculated. With QS-DCA scoring, a minimum of 50 metaphase cells (or 30 dicentrics) were scored in apparently complete metaphases without verification of exactly 46 centromeres. RESULTS: For the blinded blood samples irradiated at HC and shipped to INER, the mean absolute deviation (MAD) derived after scoring 50 cells for C-DCA and QS-DCA was <0.5 Gy for all three intercomparisons, meeting the criteria for acceptance. CONCLUSION: The results indicated that the Biodosimetry Laboratory at INER can provide reliable dose estimates in the case of a large-scale radiation accident.

External beam radiotherapy synergizes ¹88Re-liposome against human esophageal cancer xenograft and modulates ¹88Re-liposome pharmacokinetics.

External beam radiotherapy (EBRT) treats gross tumors and local microscopic diseases. Radionuclide therapy by radioisotopes can eradicate tumors systemically. Rhenium 188 ((188)Re)-liposome, a nanoparticle undergoing clinical trials, emits gamma rays for imaging validation and beta rays for therapy, with biodistribution profiles preferential to tumors. We designed a combinatory treatment and examined its effects on human esophageal cancer xenografts, a malignancy with potential treatment resistance and poor prognosis. Human esophageal cancer cell lines BE-3 (adenocarcinoma) and CE81T/VGH (squamous cell carcinoma) were implanted and compared. The radiochemical purity of (188)Re-liposome exceeded 95%. Molecular imaging by NanoSPECT/CT showed that BE-3, but not CE81T/VGH, xenografts could uptake the (188)Re-liposome. The combination of EBRT and (188)Re-liposome inhibited tumor regrowth greater than each treatment alone, as the tumor growth inhibition rate was 30% with EBRT, 25% with (188)Re-liposome, and 53% with the combination treatment at 21 days postinjection. Combinatory treatment had no additive adverse effects and significant biological toxicities on white blood cell counts, body weight, or liver and renal functions. EBRT significantly enhanced the excretion of (188)Re-liposome into feces and urine. In conclusion, the combination of EBRT with (188)Re-liposome might be a potential treatment modality for esophageal cancer.

Correlation between radioactivity and chemotherapeutics of the (111)In-VNB-liposome in pharmacokinetics and biodistribution in rats.

BACKGROUND: The combination of a radioisotope with a chemotherapeutic agent in a liposomal carrier (ie, Indium-111-labeled polyethylene glycol pegylated liposomal vinorelbine, [(111)In-VNB-liposome]) has been reported to show better therapeutic efficiency in tumor growth suppression. Nevertheless, the challenge remains as to whether this therapeutic effect is attributable to the combination of a radioisotope with chemotherapeutics. The goal of this study was to investigate the pharmacokinetics, biodistribution, and correlation of Indium-111 radioactivity and vinorelbine concentration in the (111)In-VNB-liposome. METHODS: The VNB-liposome and (111)In-VNB-liposome were administered to rats. Blood, liver, and spleen tissue were collected to determine the distribution profile of the (111)In-VNB-liposome. A liquid chromatography tandem mass spectrometry system and gamma counter were used to analyze the concentration of vinorelbine and radioactivity of Indium-111. RESULTS: High uptake of the (111)In-VNB-liposome in the liver and spleen demonstrated the properties of a nanosized drug delivery system. Linear regression showed a good correlation (r = 0.97) between Indium-111 radioactivity and vinorelbine concentration in the plasma of rats administered the (111)In-VNB-liposome. CONCLUSION: A significant positive correlation between the pharmacokinetics and biodistribution of (111)Indium radioactivity and vinorelbine in blood, spleen, and liver was found following administration of the (111)In-VNB-liposome. The liposome efficiently encapsulated both vinorelbine and Indium-111, and showed a similar concentration-radioactivity time profile, indicating the correlation between chemotherapy and radiotherapy could be identical in the liposomal formulation.

Biodistribution and pharmacokinetics of 188Re-liposomes and their comparative therapeutic efficacy with 5-fluorouracil in C26 colonic peritoneal carcinomatosis mice.

BACKGROUND: Nanoliposomes are designed as carriers capable of packaging drugs through passive targeting tumor sites by enhanced permeability and retention (EPR) effects. In the present study the biodistribution, pharmacokinetics, micro single-photon emission computed tomography (micro-SPECT/CT) image, dosimetry, and therapeutic efficacy of (188)Re-labeled nanoliposomes ((188)Re-liposomes) in a C26 colonic peritoneal carcinomatosis mouse model were evaluated. METHODS: Colon carcinoma peritoneal metastatic BALB/c mice were intravenously administered (188)Re-liposomes. Biodistribution and micro-SPECT/CT imaging were performed to determine the drug profile and targeting efficiency of (188)Re-liposomes. Pharmacokinetics study was described by a noncompartmental model. The OLINDA|EXM computer program was used for the dosimetry evaluation. For therapeutic efficacy, the survival, tumor, and ascites inhibition of mice after treatment with (188)Re-liposomes and 5-fluorouracil (5-FU), respectively, were evaluated and compared. RESULTS: In biodistribution, the highest uptake of (188)Re-liposomes in tumor tissues (7.91% ± 2.02% of the injected dose per gram of tissue [%ID/g]) and a high tumor to muscle ratio (25.8 ± 6.1) were observed at 24 hours after intravenous administration. The pharmacokinetics of (188)Re-liposomes showed high circulation time and high bioavailability (mean residence time [MRT] = 19.2 hours, area under the curve [AUC] = 820.4%ID/g*h). Micro-SPECT/CT imaging of (188)Re-liposomes showed a high uptake and targeting in ascites, liver, spleen, and tumor. The results were correlated with images from autoradiography and biodistribution data. Dosimetry study revealed that the (188)Re-liposomes did not cause high absorbed doses in normal tissue but did in small tumors. Radiotherapeutics with (188)Re-liposomes provided better survival time (increased by 34.6% of life span; P < 0.05), tumor and ascites inhibition (decreased by 63.4% and 83.3% at 7 days after treatment; P < 0.05) in mice compared with chemotherapeutics of 5-fluorouracil (5-FU). CONCLUSION: The use of (188)Re-liposomes for passively targeted tumor therapy had greater therapeutic effect than the currently clinically applied chemotherapeutics drug 5-FU in a colonic peritoneal carcinomatosis mouse model. This result suggests that (188)Re-liposomes have potential benefit and are safe in treating peritoneal carcinomatasis of colon cancer.

Multimodality imaging and preclinical evaluation of 177Lu-AMBA for human prostate tumours in a murine model.

AMBA (DO3A-CH(2)CO-G-(4-aminobenzoyl)-QWAVGHLM-NH(2)) is a bombesin (BN)-like peptide having high affinity with gastrin-releasing peptide receptors (GRPr).(177)Lu-AMBA is currently undergoing clinical trial as a systemic radiotherapy for hormone refractory prostate cancer (HRPC) patients. This study evaluated the biodistribution, pharmacokinetics, bioluminescent imaging (BLI) and microSPECT/CT imaging of (177)Lu-AMBA in PC-3M-luc-C6 luciferase-expressing human prostate tumour-bearing mice. Plasma stability of (177)Lu-AMBA could be maintained up to 55.67±6.07% at 24 h in a protection buffer. High positive correlations of PC-3M luc-C6 tumour growth in SCID mice between caliper measurement and BLI were observed (R(2)=0.999). Both the biodistribution and microSPECT/CT imaging in PC-3M-luc-C6 bearing-tumour mice showed that (177)Lu-AMBA in tumour uptake could be retained for 24 h. The distribution half-life (t(1/2α)) and the elimination half-life (t(1/2ß)) of (177) Lu-AMBA in mice were 0.52 h and 26.6 h, respectively. These results indicated that BLI could be used to monitor the growth of tumour. High uptake of (177)Lu-AMBA in PC-3M-luc-C6 tumour-bearing mice by microSPECT/CT imaging can further evaluate the potential of (177)Lu-AMBA therapy for PC-3M-luc-C6 tumours.

Preliminary evaluation of acute toxicity of (188) Re-BMEDA-liposome in rats.

Liposomes can selectively target cancer sites and carry payloads, thereby improving diagnostic and therapeutic effectiveness and reducing toxicity. To evaluate therapeutic strategies, it is essential to use animal models reflecting important safety aspects before clinical application. The objective of this study was to investigate acute radiotoxicity of ¹88Re-N,N-bis (2-mercaptoethyl)-N',N'-diethylethylenediamine (BMEDA)-labeled pegylated liposomes (¹88Re-BMEDA-liposome) in Sprague-Dawley rats. Rats were administered with ¹88Re-BMEDA-liposome, normal saline as blank or non-radioactive liposome as vehicle control via intravenous injection and observed for 14 days. Examinations were conducted with respect to mortality, clinical signs, food consumption, body weight and hematological and biochemical analyses. In addition, gross necropsy, histopathological examinations and cytogenetic analyses were also performed. None of the rats died and no clinical sign was observed during the 14-day study period. Rats administered with ¹88Re-BMEDA-liposome at dosage of 185 MBq displayed a significant weight loss compared with the control from study day (SD) 1 to SD 4, and the white blood cell count reduced to 5-10% of initial value (female: 18.55 ± 6.58 to 0.73 ± 0.26 x 10³ µl⁻¹; male: 14.52 ± 5.12 to 1.43 ± 0.54 x 10³ µl⁻¹) 7 days-post injection, but were found to have recovered on SD 15. There were no significant differences in biochemical parameters and histopathological assessments between the ¹88Re-BMEDA-liposome-treated and control groups. The frequencies of dicentric chromosomes were associated with dosage of ¹88Re-BMEDA-liposome. The information generated from this study on acute toxicity will serve as a safety reference for further subacute toxicity study in rats and human clinical trials.

Therapeutic efficacy and microSPECT/CT imaging of 188Re-DXR-liposome in a C26 murine colon carcinoma solid tumor model.

Nanocarriers can selectively target cancer sites and carry payloads, thereby improving diagnostic and therapeutic effectiveness and reducing toxicity. The objective of this study was to investigate the therapeutic efficacy of a new co-delivery radiochemotherapeutics of (188)Re-N,N-bis (2-mercaptoethyl)-N',N'-diethylethylenediamine (BMEDA)-labeled pegylated liposomal doxorubicin (DXR) ((188)Re-DXR-liposome) in a C26 murine colon carcinoma solid tumor model. To evaluate the targeting and localization of (188)Re-DXR-liposome in C26 murine tumor-bearing mice, biodistribution, microSPECT/CT imaging and pharmacokinetic studies were performed. The antitumor effect of (188)Re-DXR-liposome was assessed by tumor growth inhibition, survival ratio and histopathological hematoxylin-eosin staining. The tumor target and localization of the nanoliposome delivery radiochemotherapeutics of (188)Re-DXR-liposome were demonstrated in the biodistribution, pharmacokinetics and in vivo nuclear imaging studies. In the study on therapeutic efficacy, the tumor-bearing mice treated with bimodality radiochemotherapeutics of (188)Re-DXR-liposome showed better mean tumor growth inhibition rate (MGI) and longer median survival time (MGI=0.048; 74 days) than those treated with radiotherapeutics of (188)Re-liposome (MGI=0.134; 60 days) and chemotherapeutics of Lipo-Dox (MGI=0.413; 38 days). The synergistic tumor regression effect was observed with the combination index (CI) exceeding 1 (CI=1.145) for co-delivery radiochemotherapeutics of (188)Re-DXR-liposome. Two (25%) of the mice treated with radiochemotherapeutics were completely cured after 120 days. The therapeutic efficacy of radiotherapeutics of (188)Re-liposome and the synergistic effect of the combination radiochemotherapeutics of (188)Re-DXR-liposome have been demonstrated in a C26 murine solid tumor animal model, which pointed to the potential benefit and promise of the co-delivery of nanoliposome radiochemotherapeutics for adjuvant cancer treatment on oncology applications.

Noninvasive bioluminescent and microPET imaging for the regulation of NF-kappaB in human hepatoma-bearing mice.

UNLABELLED: The activity of nuclear factor-kappaB (NF-kappaB), a nuclear transcription factor, influences both critical tumor promotion and host-tumor interactions. Preventing NF-kappaB activation may thus inhibit the development of cancer. Therefore, development of easy and rapid methods to evaluate the regulation of NF-kappaB is needed for drug discovery. The aim of this study was to visualize the regulation of NF-kappaB by real-time, noninvasive bioluminescence and microPET imaging in vivo. MATERIALS AND METHODS: A highly responsive HepG2/NF-kappaB/luc clone L for 12-O-tetradecanoylphorbol-13-acetate (TPA)-induced tumor promotion inhibited by methotrexate (MTX) was selected by high-throughput bioluminescent imaging (BLI) in vitro. BLI and microPET using (18)F-fluorodeoxyglucose (FDG) imaging were performed in HepG2/NF-kappaB/Luc/L hepatoma-bearing SCID mice. RESULTS: The luciferase expression by BLI assay reflected that the TPA-induced NF-kappaB activity was suppressed by MTX after 16 h treatment. A positive correlation between in vitro and in vivo MTX-suppressed TPA-induced NF-kappaB activity was indicated. MicroPET imaging could not demonstrate any decrease in FDG uptake during the early stage at 24 h after TPA and MTX treatment. CONCLUSION: BLI directly revealed that MTX inhibited cellular transformation by suppressing NF-kappaB activity. Molecular imaging would accelerate the validation of the gene regulation of tumor cells in preclinical cellular and mouse models.

Biodistribution, pharmacokinetics and PET imaging of [(18)F]FMISO, [(18)F]FDG and [(18)F]FAc in a sarcoma- and inflammation-bearing mouse model.

UNLABELLED: 2-Deoxy-2-[(18)F]fluoro-d-glucose ([(18)F]FDG), [(18)F]fluoroacetate ([(18)F]FAc) and [(18)F]fluoromisonidazole ([(18)F]FMISO) were all considered to be positron emission tomography (PET) probes for tumor diagnosis, though based on different rationale of tissue uptake. This study compared the biodistribution, pharmacokinetics and imaging of these three tracers in a sarcoma- and inflammation-bearing mouse model. METHODS: C3H mice were inoculated with 2x10(5) KHT sarcoma cells in the right thigh on Day 0. Turpentine oil (0.1 ml) was injected in the left thigh on Day 11 to induce inflammatory lesion. Biodistribution, pharmacokinetics and microPET imaging of [(18)F]FMISO, [(18)F]FDG and [(18)F]FAc were performed on Day 14 after tumor inoculation. RESULTS: The inflammatory lesions were clearly visualized by [(18)F]FDG/microPET and autoradiography at 3 days after turpentine oil injection. The tumor-to-muscle and inflammatory lesion-to-muscle ratios derived from microPET imaging were 6.79 and 1.48 for [(18)F]FMISO, 8.12 and 4.69 for [(18)F]FDG and 3.72 and 3.19 for [(18)F]FAc at 4 h post injection, respectively. Among these, the tumor-to-inflammation ratio was the highest (4.57) for [(18)F]FMISO compared with that of [(18)F]FDG (1.73) and [(18)F]FAc (1.17), whereas [(18)F]FAc has the highest bioavailability (area under concentration of radiotracer vs. time curve, 116.2 hxpercentage of injected dose per gram of tissue). CONCLUSIONS: MicroPET images and biodistribution studies showed that the accumulation of [(18)F]FMISO in the tumor is significantly higher than that in inflammatory lesion at 4 h post injection. [(18)F]FDG and [(18)F]FAc delineated both tumor and inflammatory lesions. Our results demonstrated the potential of [(18)F]FMISO/PET in distinguishing tumor from inflammatory lesion.

Comparative dosimetric evaluation of nanotargeted (188)Re-(DXR)-liposome for internal radiotherapy.

UNLABELLED: A dosimetric analysis was performed to evaluate nanoliposomes as carriers of radionuclides ((188)Re-liposomes) and radiochemotherapeutic drugs [(188)Re-doxorubicin (DXR)-liposomes] in internal radiotherapy for colon carcinoma, as evaluated in mice. METHODS: Pharmacokinetic data for (188)Re-N, N-bis (2-mercaptoethyl)-N',N'-diethylethylenediamine (BMEDA), (188)Re-liposome, and (188)Re-DXR-liposome were obtained for the estimation of absorbed doses in tumors and normal organs. Two colon carcinoma mouse models were employed: subcutaneous growing solid tumor and malignant ascites pervading tumor models. Radiation-dose estimates for normal tissues and tumors were calculated by using the OLINDA/EXM program. An evaluation of a recommended maximum administered activity (MAA) for the nanotargeted drugs was also made. RESULTS: Mean absorbed doses derived from (188)Re-liposome and (188)Re-DXR-liposome in normal tissues were generally similar to those from (188)Re-BMEDA in intraperitoneal and intravenous administration. Tissue-absorbed dose in the liver was 0.24-0.40 and 0.17-0.26 (mGy/MBq) and in red marrow was 0.033-0.050 and 0.038-0.046 (mGy/MBq), respectively, for (188)Re-liposome and (188)Re-DXR-liposome. Tumor-absorbed doses for the nanotargeted (188)Re-liposome and (188)Re-DXR-liposome were higher than those of (188)Re-BMEDA for both routes of administration (4-26-fold). Dose to red marrow defined the recommended MAA. CONCLUSIONS: Our results suggest that radionuclide and chemoradiotherapeutic passive targeting delivery, using nanoliposomes as the carrier, is feasible and promising in systemic-targeted radionuclide therapy.

Biodistribution and pharmacokinetics of transgenic pig-produced recombinant human factor IX (rhFIX) in rats.

BACKGROUND: Recombinant human factor IX (rhFIX) is a 56 kDa glycoprotein with full biological activity providing a guarantee of freedom from blood-borne viral contamination in the therapy of hemophilia B, but no data are available on the distribution of transgenic pig-produced rhFIX post injection (p.i.). Therefore, an 131I-radiolabeled rhFIX was developed to evaluate the distribution of rhFIX in rats. MATERIALS AND METHODS: rhFIX was labeled with the lodogen method. 131I-rhFIX (25 microCi/25 microg/200 microl/rat) was intravenously injected through the tail vein in normal Sprague-Dawley (SD) rats and the biodistribution was examined from 5 min to 72 h p.i.. The pharmacokinetics were also evaluated from 5 min to 96 h p.i. RESULTS: The radiolabeled efficiency and radiochemical purity of 131I-rhFIX was over 96% and 98%, respectively. The biodistribution study showed that the rhFIX chiefly accumulated in the liver. The distribution and elimination half-life (t(1/2alpha) and t(1/2beta)) of 131I-rhFIX were 0.82 and 9.34 h, respectively. The maximum concentration in the plasma (Cmax) and the area under the concentration versus time curve (AUC(INF)) of 131I-rhFIX in rats were 3.09% injected dose (ID)/g and 15.3 h x % ID/g. CONCLUSION: The transgenic pig-produced rhFIX is mostly retained in the liver and the preclinical biodistribution and pharmacokinetic studies of 131I radiolabeled rhFIX are helpful for researching its biological effect in vivo.

Longitudinal microSPECt/CT imaging and pharmacokinetics of synthetic luteinizing hormone-releasing hormone (LHRH) vaccine in rats.

BACKGROUND: Luteinizing hormone-releasing hormone (LHRH)-derived decapeptide-based vaccines have been used in studies of immunocastration and immunotherapy of prostate cancer, but no image data are available on the kinetics of vaccines post injection (p.i.). Therefore, an 131I radiolabeled LHRH-derived immunogen was developed to visualize and evaluate the retention of LHRH-derived vaccines in rats. MATERIALS AND METHODS: The LHRH immunogens, which contained equal moles of 131I-p607E, p667 and p500, were formulated with an equal volume of an adjuvant, Montanide ISA50. MicroSPECT/CT imaging was performed to visualize the retention of the radiolabeled immunogen up to 30 days after intramuscular inoculation of 25 microg immunogens. The pharmacokinetics, distribution and excretion were also evaluated. RESULTS: The radiochemical purity of 131I-p607E was 97.85+/-2.12%. The longitudinal microSPECT/CT imaging revealed that most 131I-p607E was retained at the injected muscle site until 30 days p.i.. Biodistribution showed that 34.56+/-4.27% of radioactivity remained at the injected muscle site at 28 days p.i.. The cumulative radioactivity excreted via urine was 30.02+/-3.82% up to day 28 p.i.. The elimination half-life (t1/2), Tmax and Cmax were 158.67 h, 24 h, and 0.026 percentage of injected dose per gram (%ID/g), respectively. CONCLUSION: The LHRH immunogen, 131I-p607E, was mainly retained at the intramuscular injection site during the whole study period. The microSPECTICT imaging modality can be used to monitor the location and distribution of the LHRH immunogen, 131I-p607E, in a rat model.

Biodistribution, pharmacokinetics and microSPECT/CT imaging of 188Re-bMEDA-liposome in a C26 murine colon carcinoma solid tumor animal model.

Nanoliposomes are useful carriers in drug delivery. Radiolabeled nanoliposomes have potential applications in radiotherapy and diagnostic imaging. In this study, the biodistribution and pharmacokinetics of 188Re-BMEDA-labelled pegylated liposomes (RBLPL) and unencapsulated 188Re-BMEDA administered by the i.v. route in murine C26-colon tumour-bearing mice were investigated. MicroSPECT/CT images were performed to evaluate the distribution and tumor targeting of RBLPL in mice. For the biodistribution study, the highest uptake of liposome in tumors was 3.62% +/- 0.73% at 24 h after RBLPL administration, and the tumor to muscle ratio of RBLPL was 7.1-fold higher than that of 188Re-BMEDA. With image analysis, the highest SUV in tumor was 2.81 +/- 0.26 at 24 h after injection of RBLPL. The Pearson correlation analysis showed a positive correlation of tumor targeting or uptake of RBLPL between biodistribution and microSPECT semi-quantification imaging analysis (r = 0.633). The results of the pharmacokinetics revealed that the area under the tissue concentration-time curve (AUC) of RBLPL was 4.7-fold higher than that of unencapsulated 188Re-BMEDA. These results suggested the potential benefit and advantage of 188Re-labeled nanoliposomes for imaging and treatment of malignant diseases.

Insulin-like growth factor 1 stimulates KCl cotransport, which is necessary for invasion and proliferation of cervical cancer and ovarian cancer cells.

The mechanisms by which insulin-like growth factor 1 (IGF-1) cooperates with membrane ion transport system to modulate epithelial cell motility and proliferation remain poorly understood. Here, we investigated the role of electroneutral KCl cotransport (KCC), in IGF-1-dependent invasiveness and proliferation of cervical and ovarian cancer cells. IGF-1 increased KCC activity and mRNA expression in a dose- and time-dependent manner in parallel with the enhancement of regulatory volume decrease. IGF-1 treatment triggers phosphatidylinositol 3-kinase and mitogen-activated protein kinase cascades leading to the activation of Akt and extracellular signal-regulated kinase1/2 (Erk1/2), respectively. The activated Erk1/2 mitogen-activated protein kinase and phosphatidylinositol 3-kinase signaling pathways are differentially required for IGF-1-stimulated biosyn-thesis of KCC polypeptides. Specific reduction of Erk1/2 protein levels with small interference RNA abolishes IGF-1-stimulated KCC activity. Pharmacological inhibition and genetic modification of KCC activity demonstrate that KCC is necessary for IGF-1-induced cancer cell invasiveness and proliferation. IGF-1 and KCC colocalize in the surgical specimens of cervical cancer (n = 28) and ovarian cancer (n = 35), suggesting autocrine or paracrine IGF-1 stimulation of KCC production. Taken together, our results indicate that KCC activation by IGF-1 plays an important role in IGF-1 signaling to promote growth and spread of gynecological cancers.

Competitive inhibition of the capsaicin receptor-mediated current by dehydroepiandrosterone in rat dorsal root ganglion neurons.

The effects of dehydroepiandrosterone (5-androsten-3beta-ol-17-one; DHEA) and related steroids on the capsaicin receptor-mediated current were studied in acutely dissociated rat dorsal root ganglion neurons using the whole-cell voltage-clamp technique. DHEA rapidly and reversibly inhibited the capsaicin-induced current in a concentration-dependent manner, with an EC(50) of 6.7 microM and a maximal inhibition of 100%. DHEA increased the capsaicin EC(50) with little effect on the capsaicin maximal response, suggesting that the blocking action of DHEA is competitive. Neither the capsaicin response nor inhibition of the capsaicin response by extracellularly applied DHEA was significantly affected by inclusion of a saturating concentration of DHEA in the electrode buffer, arguing that DHEA acted at the extracellular surface of the membrane. Moreover, DHEA did not act through protein phosphatases to inhibit the capsaicin-induced current. Furthermore, the stereoisomer of DHEA, 5-androsten-3alpha-ol-17-one, failed to inhibit the capsaicin-induced current, producing instead a potentiating effect on the capsaicin response, demonstrating that the interaction of steroids with the capsaicin receptor is stereospecific. The inhibitory action of DHEA on the capsaicin-induced current may provide a basis for reducing capsaicin receptor-mediated nociception.