Anticancer Drug Doxorubicin Spontaneously Reacts with GTP and dGTP.

Here, we reported a spontaneous reaction between anticancer drug doxorubicin and GTP or dGTP. Incubation of doxorubicin with GTP or dGTP at 37 °C or above yields a covalent product: the doxorubicin-GTP or -dGTP conjugate where a covalent bond is formed between the C14 position of doxorubicin and the 2-amino group of guanine. Density functional theory calculations show the feasibility of this spontaneous reaction. Fluorescence imaging studies demonstrate that the doxorubicin-GTP and -dGTP conjugates cannot enter nuclei although they rapidly accumulate in human SK-OV-3 and NCI/ADR-RES cells. Consequently, the doxorubicin-GTP and -dGTP conjugates are less cytotoxic than doxorubicin. We also demonstrate that doxorubicin binds to ATP, GTP, and other nucleotides with a dissociation constant (Kd) in the sub-millimolar range. Since human cells contain millimolar levels of ATP and GTP, these results suggest that doxorubicin may target ATP and GTP, energy molecules that support essential processes in living organisms.

Radiomicrosphere Dosimetry: Principles and Current State of the Art.

Radiomicrosphere Therapy (RMT) refers to a liver-directed therapeutic modality based on the intrahepatic arterial administration of radiolabeled microspheres. There is a need for standardization of the terminology of RMT. A descriptive identifier should first name the radioisotope, then the chemical formulation of the microsphere, and lastly add the term RMT that indicates the therapeutic modality. At present, clinically available options include |Y-90| |Resin| |RMT|, |Y-90| |Glass| |RMT| and |Ho-166| |PLLA| |RMT|. The latter is available in Europe and is being considered for clearance by the FDA in the United States. Preclinical studies with |Re-188| |PLLA| |RMT| are underway. Dosimetric considerations are strongly tied to both the type of the radioisotope and the chemical composition of the microsphere type. This review will focus on Y-90 resin and glass RMT, the history, dosimetry, clinical use, and controversies.

Computational model of silica nanoparticle penetration into tumor spheroids: Effects of methoxy and carboxy PEG surface functionalization and hyperthermia.

Drug delivery to tumors suffers from poor solubility, specificity, diffusion through the tumor micro-environment and nonoptimal interactions with components of the extracellular matrix and cell surface receptors. Nanoparticles and drug-polymer complexes address many of these problems. However, large size exasperates the problem of slow diffusion through the tumor. Three-dimensional tumor spheroids are good models to evaluate approaches to mitigate these difficulties and aid in design strategies to improve the delivery of drugs to treat cancer effectively. Diffusion of drug carriers is highly dependent on cell uptake rate parameters (association/dissociation) and temperature. Hyperthermia increases molecular transport and is known to act synergistically with chemotherapy to improve treatment. This study presents a new inverse estimation approach based on Bayesian probability for estimating nanoparticle cell uptake rates from experiments. The parameters were combined with a finite element computational model of nanoparticle transport under hyperthermia conditions to explore its effect on tumor porosity, diffusion and particle binding (association and dissociation) at cell surfaces. Carboxy-PEG-silane (cPEGSi) nanoparticles showed higher cell uptake compared to methoxy-PEG-silane (mPEGSi) nanoparticles. Simulations were consistent with experimental results from Skov-3 ovarian cancer spheroids. Amorphous silica (cPEGSi) nanoparticles (58 nm) concentrated at the periphery of the tumor spheroids at 37°C but mild hyperthermia (43°C) increased nanoparticle penetration. Thus, hyperthermia may enhance cancer treatment by improving blood delivery to tumors, enhancing extravasation and penetration into tumors, trigger release of drug from the carrier at the tumor site and possibly lead to synergistic anti-cancer activity with the drug.

Magneto-plasmonic nanostars for image-guided and NIR-triggered drug delivery.

Smart multifunctional nanoparticles with magnetic and plasmonic properties assembled on a single nanoplatform are promising for various biomedical applications. Owing to their expanding imaging and therapeutic capabilities in response to external stimuli, they have been explored for on-demand drug delivery, image-guided drug delivery, and simultaneous diagnostic and therapeutic (i.e. theranostic) applications. In this study, we engineered nanoparticles with unique morphology consisting of a superparamagnetic iron oxide core and star-shaped plasmonic shell with high-aspect-ratio gold branches. Strong magnetic and near-infrared (NIR)-responsive plasmonic properties of the engineered nanostars enabled multimodal quantitative imaging combining advantageous functions of magnetic resonance imaging (MRI), magnetic particle imaging (MPI), photoacoustic imaging (PAI), and image-guided drug delivery with a tunable drug release capacity. The model drug molecules bound to the core-shell nanostars were released upon NIR illumination due to the heat generation from the core-shell nanostars. Moreover, our simulation analysis showed that the specific design of the core-shell nanostars demonstrated a pronounced multipolar plasmon resonance, which has not been observed in previous reports. The multimodal imaging and NIR-triggered drug release capabilities of the proposed nanoplatform verify their potential for precise and controllable drug release with different applications in personalized medicine.

Optimization and Characterization of Protein Nanoparticles for the Targeted and Smart Delivery of Cytochrome c to Non-Small Cell Lung Carcinoma.

The delivery of Cytochrome c (Cyt c) to the cytosol stimulates apoptosis in cells where its release from mitochondria and apoptotic induction is inhibited. We developed a drug delivery system consisting of Cyt c nanoparticles decorated with folate-poly(ethylene glycol)-poly(lactic-co-glycolic acid)-thiol (FA-PEG-PLGA-SH) to deliver Cyt c into cancer cells and tested their targeting in the Lewis Lung Carcinoma (LLC) mouse model. Cyt c-PLGA-PEG-FA nanoparticles (NPs) of 253 ± 55 and 354 ± 11 nm were obtained by Cyt c nanoprecipitation, followed by surface decoration with the co-polymer SH-PLGA-PEG-FA. The internalization of Cyt c-PLGA-PEG-FA nanoparticles (NPs) in LLC cells was confirmed by confocal microscopy. NP caspase activation was more efficient than the NP-free formulation. Caspase activity assays showed NPs retained 88-96% Cyt c activity. The NP formulations were more effective in decreasing LLC cell viability than NP-free formulation, with IC50 49.2 to 70.1 µg/mL versus 129.5 µg/mL, respectively. Our NP system proved to be thrice as selective towards cancerous than normal cells. In vivo studies using near infrared-tagged nanoparticles show accumulation in mouse LLC tumor 5 min post-injection. In conclusion, our NP delivery system for Cyt c shows superiority over the NP-free formulation and reaches a folic acid-overexpressing tumor in an immune-competent animal model.

Speciation of thioarsenicals through application of coffee ring effect on gold nanofilm and surface-enhanced Raman spectroscopy.

Thioarsenicals, such as dimethylmonothioarsinic acid (DMMTAV) and dimethyldithioarsinic acid (DMDTAV), have been increasingly discovered as important arsenic metabolites, yet analysis of these unstable arsenic species remains a challenging task. A method based on surface-enhanced Raman spectroscopy (SERS) detection in combination with the coffee ringeffect for separation is expected to be particularly useful for analysis of thioarsenicals, thanks to minimal sample pretreatment and unique fingerprint Raman identification. Such a method would offer an alternative approach that overcomes limitations of conventional arsenic speciation techniques based on high performance liquid chromatography separation and mass spectrometry detection. A novel analytical method based on combination of the coffee ringeffect and SERS was developed for the speciation of thiolated arsenicals. A gold nanofilm (AuNF) was employed not only as a SERS substrate, but also as a platform for the separation of thioarsenicals. Once a drop of the thioarsenicals solution was placed onto the AuNF and evaporation of the solvent and the ring stamp formation onto AuNF began, the SERS signal intensity substantially increased from center to edge regions of the evaporated droplet due to the presence of the coffee ring effect. Through calculating the pKa's of DMMTAV and DMDTAV and accordingly manipulating the chemical environment, separation of these thioarsenicals was realized as they travelled different distances during the development of the coffee ring. The migration distances of individual species were influenced by a radial outward flow of a solute, the thioarsenicals-AuNF interactions and a thermally induced Marangoni flow. The separation of DMMTAV (center) and DMDTAV (edge) on the coffee ring, in combination with fingerprint SERS spectra, enables the identification of these thioarsenicals by this AuNF-based coffee ring effect-SERS method.

Perspectives on the Future of Nanomedicine to Impact Patients: An Analysis of US Federal Funding and Interventional Clinical Trials.

The US and governments around the world, and companies, have made a considerable investment in nanomedicine, and there have been important discoveries. Nevertheless, there has been considerable debate as to whether the investment, both in money and in time, has been worth it. That question is not yet definitively answerable. However, investigators (and investors) might also wonder if the efforts in nanomedicine are likely to continue at the same pace as over the past decade. For this paper, an analysis was done by searching Medline, RePORT, the DOD (CDMRP), the NSF, and ClinicalTrials.gov. The major findings from the analysis are as follows: (1) The number of journal articles on the subject of nanomedicine continues to steadily rise and the areas "Drug Carriers" and "Drug Delivery Systems" are experiencing particularly rapid growth. (2) The level of funding from the Department of Health and Human Services (NIH and others) for indications other than cancer has been greater than that for cancer. (3) Funding for applications in HIV/AIDS has been strong. (4) Most of the cancers are being impacted. (5) The number of clinical trials are more highly focused in breast, skin, metastatic, and ovarian cancers, though the noncancer indications of pain and infections are also highly represented. The trials are primarily in Phases I and II, suggesting a long horizon before translating to a high impact on patients. (6) The vast majority of the clinical trials are for the evaluation of established nanomedicine formulations (liposomes and nab-paclitaxel/Abraxane) in combination with other therapies. Nevertheless, the number of clinical trials with other nanomedicine formulations has been increasing since 2009. Relatively few of the trials are for micelles or dendrimers. Taken as a whole, the analysis provides a picture that nanomedicine continues to be highly funded and highly studied but with few recent breakthroughs. Nanomedicine has yet to provide the "silver bullet" for therapy in cancer or other diseases, and it remains unclear whether it ever will.

Meta-Analysis of Efficacy of Chemotherapy Delivered by Mesoporous Silica Nanoparticles to Tumor-Bearing Mice.

Nanomedicines have played an important role in the management of cancer patients with PEGylated liposomal doxorubicin (e.g., Doxil) and nab-paclitaxel (Abraxane) being two examples that have been commercially successful. However, the number of patients benefitting from these therapies is small compared with the potential impact. While off-site toxicities have been reduced, long term survival has not been realized. Thus, there continues to be a need for improved therapies and nanomedicine (delivery of drugs using nanoparticle carriers) that provide advantages over the delivery of free drug. Mesoporous silica nanoparticles (MSNs) are a unique class of nanomedicine that offers high loading capacity, the ability of targeting specificity, potential for stimulated drug release and are considered generally safe and non-toxic. This paper provides a comprehensive analysis of 166 published studies in which MSNs were evaluated in vivo and tumor response was reported. Eleven studies with liposomal doxorubicin and 3 studies with Abraxane are also included in the analysis. The MSN formulations exhibit a wide range of size, charge, drug loading and drug release. The tumor inhibition ratio (TIR) of some MSN formulations compared favorably to the FDA approved nanomedicines. However, TIR reached at least 99% in only 14 MSN formulations reported. On average, targeted MSNs and MSNs with combined therapy (multiple drugs, or drugs combined with thermal therapy) performed best. Survival was reported in 14 MSN studies. The reported increased life survival (ILS) tended to be longer for liposomal doxorubicin and Abraxane than for the MSN formulations. The paper also provides an overview of MSN synthesis strategies and compares the development timeline of MSNs to that of Doxil and Abraxane, discussing the barriers to commercialization. Finally, the paper provides recommendations to advance the development and commercialization of MSNs for cancer therapy.

Recalcitrant Issues and New Frontiers in Nano-Pharmacology.

Packaging of old pharma drugs into new packaging "nanoparticles" is called nano-pharmacology and the products are called nano-based drugs. The inception of nano-pharmacology research and development (R&D) is marked by the approval of the first nano-based drug Doxil® in 1995 by the Food and Drug Administration. However, even after more than two decades, today, there are only ∼20 nano-based drugs in the market to treat cancers and brain diseases. In this article we share the perspectives of nanotechnology scientists, engineers, and clinicians on the roadblocks in nano-pharmacology R&D. Also, we share our opinion on new frontiers in the field of nano-pharmacology R&D that may allow rapid and efficient transfer of nano-pharma technologies from R&D to market.

Arsenic Speciation on Silver Nanofilms by Surface-Enhanced Raman Spectroscopy.

Surface-enhanced Raman spectroscopy (SERS), as a nondestructive and fast detection technique, is a promising alternative approach for arsenic detection, particularly for in situ applications. SERS-based speciation analysis according to the fingerprint SERS signals of different arsenicals has the potential to provide a superior technique in species preservation over the conventional chromatographic separation methods, albeit with some difficulties due to the similarity in SERS patterns. In this study, we explored a novel SERS method for arsenic speciation by using the separation potential of the coffee ring effect on negatively charged silver nanofilms (AgNFs). Four arsenic species, including arsenite (AsIII), arsenate (AsV), monomethylarsonic acid (MMAV), and dimethylarsinic acid (DMAV), were measured for fingerprint SERS signals in solution and on the films. Significant enhancement of SERS signals on the dried coffee ring stains by the AgNFs were observed except for AsIII, and more importantly, arsenicals migrated varying distances during coffee ring development, promoting better speciation. Sodium dodecyl sulfate was then introduced into the droplet to reduce the droplet surface tension, facilitating the migration of solution into the peripheral region. Under the combined interactions of arsenicals with the AgNFs, solvent, and surfactant, enhanced separation between arsenicals was observed as a result of the formation of two concentric rings. Combining the SERS fingerprint signals and physical separation of arsenicals on the surface, arsenic speciation was achieved using the AgNFs substrate-based SERS technology, demonstrating the potential of the coffee ring effect for rapid separation and analysis of small molecules by SERS.

90 Y SPECT/CT quantitative study and comparison of uptake with pretreatment 99 m Tc-MAA SPECT/CT in radiomicrosphere therapy.

INTRODUCTION: Yttrium-90 (90 Y) microsphere post-treatment imaging reflects the true distribution characteristics of microspheres in the tumor and liver compartments. However, due to its decay spectra profile lacking a pronounced photopeak, the bremsstrahlung imaging for 90 Y has inherent limitations. The absorbed dose calculations for 90 Y microspheres radiomicrosphere therapy (RMT) sustain a limitation due to the poor quality of 90 Y imaging. The aim of this study was to develop quantitative methods to improve the post-treatment 90 Y bremsstrahlung single photon emission tomography (SPECT)/computed tomography (CT) image analysis for dosimetric purposes and to perform a quantitative comparison with the 99m Tc-MAA SPECT/CT images, which is used for theranostics purposes for liver and tumor dosimetry. METHODS: Pre and post-treatment SPECT/CT data of patients who underwent RMT for primary or metastatic liver cancer were acquired. A Jasczak phantom with eight spherical inserts of various sizes was used to obtain optimal iteration number for the contrast recovery algorithm for improving 90 Y bremsstrahlung SPECT/CT images. Comparison of uptake on 99m Tc-MAA and 90 Y microsphere SPECT/CT images was assessed using tumor to healthy liver ratios (TLRs). The voxel dosimetry technique was used to estimate absorbed doses. Absorbed doses within the tumor and healthy part of the liver were also investigated for correlation with administered activity. RESULTS: Improvement in CNR and contrast recovery coefficients on patient and phantom 90 Y bremsstrahlung SPECT/CT images respectively were achieved. The 99m Tc-MAA and 90 Y microspheres SPECT/CT images showed significant uptake correlation (r = 0.9, P = 0.05) with mean TLR of 9.4 ± 9.2 and 5.0 ± 2.2, respectively. The correlation between the administered activity and tumor absorbed dose was weak (r = 0.5, P > 0.05), however, healthy liver absorbed dose increased with administered activity (r = 0.8, P = 0.0). CONCLUSIONS: This study demonstrated correlation in mean TLR between 99m Tc-MAA and 90 Y microsphere SPECT/CT.

4-N-Alkanoyl and 4-N-alkyl gemcitabine analogues with NOTA chelators for 68-gallium labelling.

The conjugation of 4-N-(3-aminopropanyl)-2'-deoxy-2',2'-difluorocytidine with 2-(p-isothiocyanatobenzyl)-1,4,7-triazacyclononane-1,4,7-triacetic acid (SCN-Bn-NOTA) ligand in 0.1 M Na2CO3 buffer (pH 11) at ambient temperature provided 4-N-alkylgemcitabine-NOTA chelator. Incubation of latter with excess of gallium(III) chloride (GaCl3) (0.6 N AcONa/H2O, pH = 9.3) over 15 min gave gallium 4-N-alkylgemcitabine-NOTA complex which was characterized by HRMS. Analogous [68Ga]-complexation of 4-N-alkylgemcitabine-NOTA conjugate proceeded with high labeling efficiency (94%-96%) with the radioligand almost exclusively found in the aqueous layer (∼95%). The high polarity of the gallium 4-N-alkylgemctiabine-NOTA complex resulted in rapid renal clearance of the 68Ga-labelled radioligand in BALB/c mice.

Raman spectra of thiolated arsenicals with biological importance.

Surface enhanced Raman scattering (SERS) has great potential as an alternative tool for arsenic speciation in biological matrices. SERS measurements have advantages over other techniques due to its ability to maintain the integrity of arsenic species and its minimal requirements for sample preparation. Up to now, very few Raman spectra of arsenic compounds have been reported. This is particularly true for thiolated arsenicals, which have recently been found to be widely present in humans. The lack of data for Raman spectra in arsenic speciation hampers the development of new tools using SERS. Herein, we report the results of a study combining the analysis of experimental Raman spectra with that obtained from density functional calculations for some important arsenic metabolites. The results were obtained with a hybrid functional B3LYP approach using different basis sets to calculate Raman spectra of the selected arsenicals. By comparing experimental and calculated spectra of dimethylarsinic acid (DMAV), the basis set 6-311++G** was found to provide computational efficiency and precision in vibrational frequency prediction. The Raman frequencies for the rest of organoarsenicals were studied using this basis set, including monomethylarsonous acid (MMAIII), dimethylarsinous acid (DMAIII), dimethylmonothioarinic acid (DMMTAV), dimethyldithioarsinic acid (DMDTAV), S-(Dimethylarsenic) cysteine (DMAIII(Cys)) and dimethylarsinous glutathione (DMAIIIGS). The results were compared with fingerprint Raman frequencies from As─O, As─C, and As─S obtained under different chemical environments. These fingerprint vibrational frequencies should prove useful in future measurements of different species of arsenic using SERS.

Polyethylene glycol modified ORMOSIL theranostic nanoparticles for triggered doxorubicin release and deep drug delivery into ovarian cancer spheroids.

A novel pegylated multifunctional probe of Ormosil nanoparticles (PEGCDSIR820) loaded with Near Infrared dye (NIR; IR820) and a chemotherapeutic drug, Doxorubicin (DOX) was developed for cancer theranostic applications. PEGCDSIR820 nanoparticles had an average diameter of 58.2±3.1nm, zeta potential of -6.9±0.1mV in cell culture media and stability against aggregation in physiological buffers. The encapsulation efficiency of DOX was 65.0±3.0%, and that of IR820 was 76.0±2.1%. PEGCDSIR820 showed no cytotoxicity in ovarian cancer cells (Skov-3). The cytotoxicity markedly increased when Skov-3 cells incubated with PEGCDSIR820 particles were exposed to 808nm laser due to the combination of adjuvant hyperthermia (43°C) and enhanced DOX release. Exposure to laser enhanced the release of DOX, 45% of DOX release was observed in 3h compared to 23% without laser exposure. Confocal imaging in Skov-3 cells showed that the combination of hyperthermia due to NIR exposure and release of DOX caused cell necrosis. Furthermore, in spheroids exposed to NIR laser penetration of DOX was deeper compared to the absence of laser exposure. Skov-3 spheroids incubated with pegylated nanoparticles for 24h and exposed to laser showed 94% reduction in cell viability. Encapsulation of IR820 in PEGCDSIR820 increased the in-vivo elimination half-life to 41.0±7.2h from 30.5±0.5h of free IR820.

Potential application of SERS for arsenic speciation in biological matrices.

Speciation of arsenic is usually carried out using chromatography-based methods coupled with spectroscopic determination; however, the inevitable procedures involving sample preparation and separation could potentially alter the integrity of the arsenic metabolites present in biological samples. Surface-enhanced Raman spectroscopy (SERS) could be a promising alternative for providing a reliable arsenic analysis under the influence of a cellular matrix. A method for arsenic speciation using SERS in cellular matrix was developed in this study and four arsenicals were selected, including arsenite (AsIII), arsenate (AsV), monomethylarsonic acid (MMAV) and dimethylarsinic acid (DMAV). Silver nanoparticles in the form of colliodal suspension with different surface charges, i.e., coated with citrate (AgNPs-Citrate) and spermine (AgNPs-Spermine) were employed as SERS substrates. Adsorption of arsenicals on nanoparticles in colloidal suspensions and the cellular matrix and the pH, size, and zeta potential of the colloidal suspensions were investigated for a better understanding of the SERS signal response of arsenicals in the colloidal suspensions or under the influence of cellular matrix. Arsenicals showed substantially different SERS responses in the two colloidal suspensions, mainly because of the distinct difference in the interaction between the arsenicals and the nanoparticles. Arsenic speciation in cell lysate could be successfully carried out in AgNPs-Spermine suspension, while AgNPs-Citrate could not yield significant SERS signals under the experimental conditions. This study proved that AgNPs-Spermine colloidal suspension could be a promising SERS substrate for studying arsenic metabolism in a biological matrix, reducing the bias caused by traditional techniques that involve sample extraction and pretreatment.

Multifunctional organically modified silica nanoparticles for chemotherapy, adjuvant hyperthermia and near infrared imaging.

We report a novel system of organically modified silica nanoparticles (Ormosil) capable of near infrared fluorescence and chemotherapy with adjuvant hyperthermia for image guided cancer therapy. Ormosil nanoparticles were loaded with a chemotherapeutic, Doxorubicin (DOX) and cyanine dye, IR820. Ormosil particles had a mean diameter of 51.2±2.4 nanometers and surface charge of -40.5±0.8mV. DOX was loaded onto Ormosil particles via physical adsorption (FDSIR820) or covalent linkage (CDSIR820) to the silanol groups on the Ormosil surface. Both formulations retained DOX and IR820 over a period of 2 days in aqueous buffer, though CDSIR820 retained more DOX (93.2%) compared to FDSIR820 (77.0%) nanoparticles. Exposure to near infrared laser triggered DOX release from CDSIR820. Uptake of nanoparticles was determined by deconvolution microscopy in ovarian carcinoma cells (Skov-3). CDSIR820 localized in the cell lysosomes whereas cells incubated with FDSIR820 showed DOX fluorescence from the nucleus indicating leakage of DOX from the nanoparticle matrix. FDSIR820 nanoparticles showed severe toxicity in Skov-3 cells whereas CDSIR820 particles had the same cytotoxicity profile as bare (No DOX and IR820) Ormosil particles. Furthermore, exposure of CDSIR820 nanoparticles to Near Infrared laser at 808 nanometers resulted in generation of heat (to 43°C from 37°C) and resulted in enhanced cell killing compared to Free DOX treatment. Bio-distribution studies showed that CDSIR820 nanoparticles were primarily present in the organs of Reticuloendothelial (RES) system.

18F-FLT Positron Emission Tomography/Computed Tomography Imaging in Pancreatic Cancer: Determination of Tumor Proliferative Activity and Comparison with Glycolytic Activity as Measured by 18F-FDG Positron Emission Tomography/Computed Tomography Imaging.

OBJECTIVE: This phase-I imaging study examined the imaging characteristic of 3'-deoxy-3'-(18F)-fluorothymidine (18F-FLT) positron emission tomography (PET) in patients with pancreatic cancer and comparisons were made with (18F)-fluorodeoxyglucose (18F-FDG). The ultimate aim was to develop a molecular imaging tool that could better define the biologic characteristics of pancreas cancer, and to identify the patients who could potentially benefit from surgical resection who were deemed inoperable by conventional means of staging. METHODS: Six patients with newly diagnosed pancreatic cancer underwent a combined FLT and FDG computed tomography (CT) PET/CT imaging protocol. The FLT PET/CT scan was performed within 1 week of FDG PET/CT imaging. Tumor uptake of a tracer was determined and compared using various techniques; statistical thresholding (z score=2.5), and fixed standardized uptake value (SUV) thresholds of 1.4 and 2.5, and applying a threshold of 40% of maximum SUV (SUVmax) and mean SUV (SUVmean). The correlation of functional tumor volumes (FTV) between 18F-FDG and 18F-FLT was assessed using linear regression analysis. RESULTS: It was found that there is a correlation in FTV due to metabolic and proliferation activity when using a threshold of SUV 2.5 for FDG and 1.4 for FLT (r=0.698, p=ns), but a better correlation was obtained when using SUV of 2.5 for both tracers (r=0.698, p=ns). The z score thresholding (z=2.5) method showed lower correlation between the FTVs (r=0.698, p=ns) of FDG and FLT PET. CONCLUSION: Different tumor segmentation techniques yielded varying degrees of correlation in FTV between FLT and FDG-PET images. FLT imaging may have a different meaning in determining tumor biology and prognosis.