Inhibition of fatty acid synthase sensitizes prostate cancer cells to radiotherapy

Many common human cancers, including colon, prostate and breast cancer, express high levels of fatty acid synthase compared to normal human tissues. This elevated expression is associated with protection against apoptosis, increased metastasis and poor prognosis. Inhibitors of fatty acid synthase, such as the cerulenin synthetic analog C75, decrease prostate cancer cell proliferation, increase apoptosis and decrease tumor growth in experimental models. Although radiotherapy is widely used in the treatment of prostate cancer patients, the risk of damage to neighboring normal organs limits the radiation dose that can be delivered. In this study, we examined the potential of fatty acid synthase inhibition to sensitize prostate cancer cells to radiotherapy. The efficacy of C75 alone or in combination with X irradiation was examined in monolayers and in multicellular tumor spheroids. Treatment with C75 alone decreased clonogenic survival, an effect that was abrogated by the antioxidant. C75 treatment also delayed spheroid growth in a concentration-dependent manner. The radiosensitizing effect of C75 was indicated by combination index values between 0.65 and 0.71 and the reduced surviving fraction of clonogens, in response to 2 Gy X irradiation, from 0.51 to 0.30 and 0.11 in the presence of 25 and 35 μM C75, respectively. This increased sensitivity to radiation was reduced by the presence of the antioxidant. The C75 treatment also enhanced the spheroid growth delay induced by X irradiation in a supra-additive manner. The level of radiation-induced apoptosis in prostate cancer cells was increased further by C75, which induced cell cycle arrest in the G2/M phase, but only at a concentration greater than that required for radiosensitization. Radiation-induced G2/M blockade was not affected by C75 treatment. These results suggest the potential use of fatty acid synthase inhibition to enhance the efficacy of radiotherapy of prostate carcinoma and that C75-dependent cell cycle arrest is not responsible for its radiosensitizing effect

Preparation and evaluation of tumor-targeting peptide - Oligonucleotide conjugates

Enormous progress has been made in the development of antisense oligodeoxynucleotides (ODNs) as therapeutic agents inhibiting gene expression. Unfortunately, the therapeutical application of ODNs is still held back because of the low cellular uptake and the lack of specific transport into particular cells. In this paper, we report a drug-targeting system using somatostatin receptors (SSTRs) which are overexpressed in various tumors. Phosphorothioate ODNs were covalently linked to Tyr3-octreotate, an analogue of somatostatin. The peptide was assembled by solid-phase synthesis, oxidized to form the cyclic disulfide, and subsequently derivatized with a N-terminal maleimido functionality. 5'-Thiol derivatized phosphorothioate-ODNs directed against the protooncogene bcl-2 were conjugated to this maleimido-modified peptide. Binding studies revealed that the conjugates retain specific binding with nanomolar affinities to SSTRs (IC50-values between 1.83 and 2.52 nM). Furthermore, melting studies with complementary DNA revealed that the terminal conjugation of the ODNs did not significantly affect their hybridization affinity.This project was supported by a grant from the Deutsche Forschungsgemeinschaft (Ei 130/15-3). The authors would like to thank D. Keane and M. Wiersma for skilful assistance in ODN synthesis. Essential support for the establishment of receptor binding assays from Dr. Barbara Stolz, Novartis Pharma AG, Switzerland, is gratefully acknowledged.Peer reviewe

Peptide-PNA conjugates: Targeted transport of antisense therapeutics into tumors

Tumor-specific accumulation of antisense therapeutics: The conjugation of a receptor-binding peptide allows for the first time the selective transport of oligonucleotide analogues into tumor tissue. By using the tert-butyloxycarbonyl (Boc) protecting group stratergy, hybrids of peptide nucleic acids and peptides are accessible that accumulate in tumor tissue at a tenfold higher concentration than the free peptide nucleic acid.Peer reviewe

Influence of 68Ga-DOTATOC on sparing of normal tissue for radiation therapy of skull base meningioma: differential impact of photon and proton radiotherapy

Background: To evaluate the impact of 68Ga-DOTATOC-PET on treatment planning and sparing of normal tissue in the treatment of skull base meningioma with advanced photons and protons. Methods: From the institutional database consisting of 507 skull base meningiomas 10 patients were chosen randomly for the present analysis. Target volume definition was performed based on CT and MRI only, as well as with additional 68Ga-DOTATOC-PET. Treatment plans were performed for Intensity Modulated Radiotherapy (IMRT) and proton therapy using active raster scanning on both target volumes. We calculated doses to relevant organs at risk (OAR), conformity indices as well as differences in normal tissue sparing between both radiation modalities based on CT/MRI planning as well as CT/MRI/PET planning. Results: For photon treatment plans, PET-based treatment plans showed a reduction of brain stem Dmax and Dmedian for different levels of total dose. At the optic chiasm, use of 68Ga-DOTATOC significantly reduces Dmax; moreover, the Dmedian is reduced in most cases, too. For both right and left optic nerve, reduction of dose by addition of 68Ga-DOTATOC-PET is minimal and depends on the anatomical location of the meningioma. In protons, the impact of 68Ga-DOTATOC-PET is minimal compared to photons. Conclusion: Addition of 68Ga-DOTATOC-PET information into treatment planning for skull base meningiomas has a significant impact on target volumes. In most cases, PET-planning leads to significant reductions of the treatment volumes. Subsequently, reduced doses are applied to OAR. Using protons, the benefit of additional PET is smaller since target coverage is more conformal and dose to OAR is already reduced compared to photons. Therefore, PET-imaging has the greatest margin of benefit in advanced photon techniques, and combination of PET-planning and high-precision treatment leads to comparable treatment plans as with protons

Feasibility and robustness of dynamic F-18-FET PET based tracer kinetic models applied to patients with recurrent high-grade glioma prior to carbon ion irradiation

The aim of this study was to analyze the robustness and diagnostic value of different compartment models for dynamic F-18-FET PET in recurrent high-grade glioma (HGG). Dynamic F-18-FET PET data of patients with recurrent WHO grade III (n:7) and WHO grade IV (n: 9) tumors undergoing re-irradiation with carbon ions were analyzed by voxelwise fitting of the time-activity curves with a simplified and an extended one-tissue compartment model (1TCM) and a two-tissue compartment model (2TCM), respectively. A simulation study was conducted to assess robustness and precision of the 2TCM. Parameter maps showed enhanced detail on tumor substructure. Neglecting the blood volume V-B in the 1TCM yields insufficient results. Parameter K-1 from both 1TCM and 2TCM showed correlation with overall patient survival after carbon ion irradiation (p = 0.043 and 0.036, respectively). The 2TCM yields realistic estimates for tumor blood volume, which was found to be significantly higher in WHO IV compared to WHO III (p = 0.031). Simulations on the 2TCM showed that K1 yields good accuracy and robustness while k(2) showed lowest stability of all parameters. The 1TCM provides the best compromise between parameter stability and model accuracy;however application of the 2TCM is still feasible and provides a more accurate representation of tracer-kinetics at the cost of reduced robustness. Detailed tracer kinetic analysis of F-18-FET PET with compartment models holds valuable information on tumor substructures and provides additional diagnostic and prognostic value

CONTRAST-ENHANCED ULTRASOUND MONITORING OF PERFUSION CHANGES IN HEPATIC NEUROENDOCRINE METASTASES AFTER SYSTEMIC VERSUS SELECTIVE ARTERIAL 177LU/90Y-DOTATOC AND 213BI-DOTATOC RADIOPEPTIDE THERAPY

Radiopeptide therapy with beta emitter labeled 177Lu/90Y- DOTA(0)-Phe(1)-Tyr(3)-octreotide (DOTATOC) and more recently also alpha emitting 213Bi-DOTATOC are promising new treatments for neuroendocrine tumors. No early predictors for treatment response have been recognized and tumor-shrinkage after radiation therapy appears slowly. In some solid tumors a decline in tumor perfusion was found predictive of final treatment response but the gold standard multiphase computed tomography (CT) has a high radiation burden. Therefore we evaluated the ability of contrast-enhanced ultrasound (CEUS) to evaluate tumor perfusion as a response criteria. Materials and Methods: 14 patients with hepatic neuroendocrine tumor (NET) metastases were enrolled in the retrospective study. Eleven patients were treated with beta-emitting 177Lu/90Y-DOTATOC, either intravenous (i.v.) (n = 5) or intra-arterial (i.a.) (n = 6) and three patients received alpha-emitting 213Bi-DOTATOC (i.a.). CEUS and contrast-enhanced CT (CE-CT) were performed before and 3 months after treatment. Results: CE-CT and CEUS presented comparable results in the baseline study and in the assessment of perfusion changes due to the different treatment regimes. A therapy related decrease in tumor perfusion is an early predictor of longterm morphologic response. Conclusion: CEUS is a cheap, ubiquitary available and radiation free technique which showed comparable results for perfusion and diameter of liver metastases compared to CE-CT. Intensity reduction in an arterial phase CEUS can be seen as a positive sign indicating long term tumor response to treatment. Therefore CEUS may be considered as an imaging modality for monitoring early treatment after focal alpha and beta targeted therapy.JRC.E.5-Nuclear chemistr

Comparison between 68Ga-bombesin (68Ga-BZH3) and the cRGD tetramer 68Ga-RGD4 studies in an experimental nude rat model with a neuroendocrine pancreatic tumor cell line

BACKGROUND: Serotonergic neurons in the rodent hypothalamus are implicated in key neuroendocrine and metabolic functions, including circadian rhythmicity. However, the assessment of the serotonergic system in the human hypothalamus in vivo is difficult as delineation of the hypothalamus is cumbersome with conventional region-of-interest analysis. In the present study, we aimed to develop a method to visualize serotonin transporters (SERT) in the hypothalamus. Additionally, we tested the hypothesis that hypothalamic SERT binding ratios are different between patients with hypothalamic impairment (HI), pituitary insufficiency (PI), and control subjects (C). METHODS: SERT availability was determined in 17 subjects (6 HI, 5 PI, and 6 healthy controls), 2 h after injection of 123I-N-ω-fluoropropyl-2β-carboxymethoxy-3β-(4-iodophenyl) nortropane ([123I]FP-CIT), using single-photon emission computed tomography (performed on a brain-dedicated system) fused with individual magnetic resonance imaging (MRI) scans of the brain. The hypothalamus (representing specific SERT binding) and cerebellum (representing nonspecific binding) were manually delineated on each MRI to assess [123I]FP-CIT binding and specific-to-nonspecific binding ratios. RESULTS: In each healthy subject, [123I]FP-CIT binding was higher in the hypothalamus than in the cerebellum, and the mean hypothalamic binding ratio of SERT was 0.29 ± 0.23. We found no difference in hypothalamic binding ratios between HI, PI, and control subjects (HI 0.16 ± 0.24, PI 0.45 ± 0.39, C 0.29 ± 0.23, p value 0.281). CONCLUSIONS: We were able to demonstrate SERT binding in the human hypothalamus in vivo. However, we did not find altered hypothalamic SERT binding in patients with hypothalamic impairment. TRIAL REGISTRATION: Netherlands Trial Register: NTR2520