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U Mahmood

Publications and source records attributed to U Mahmood.

18 recordsLinked to original sources
PubMed2001

[Progress in optical imaging].

Different optical imaging technologies have significantly progressed over the last years. Besides advances in imaging techniques and image reconstruction, new "smart" optical contrast agents have been developed which can be used to detect molecular targets (such as endogenous enzymes) in vivo. The combination of novel imaging technologies coupled with smart agents bears great diagnostic potential both clinically and experimentally. This overview outlines the basic principles of optical imaging and summarizes the current state of the art.

Animals↗
PubMed2001

Optical imaging of matrix metalloproteinase-2 activity in tumors: feasibility study in a mouse model.

PURPOSE: To develop an optical imaging method to determine the expression level of tumoral matrix metalloproteinase-2 (MMP-2) in vivo. MATERIALS AND METHODS: An optical contrast agent was developed that was highly activatable by means of MMP-2-induced conversion. Signal characteristics of the probe were quantified ex vivo with a recombinant enzyme. Animal tumor models were established with MMP-2-positive (human fibrosarcoma cell line, n = 4) and MMP-2-negative (well-differentiated mammary adenocarcinoma, n = 4) tumor cell lines. Both tumors were implanted into nude mice and were optically imaged after intravenous administration of the MMP-2-sensitive probe. RESULTS: The MMP-2-sensitive probe was activated by MMP-2 in vitro, producing up to an 850% increase in near-infrared fluorescent signal intensity. This activation could be blocked by MMP-2 inhibitors. MMP-2-positive tumors were easily identified as high-signal-intensity regions as early as 1 hour after intravenous injection of the MMP-2 probe, while contralateral MMP-2-negative tumors showed little to no signal intensity. A nonspecific control probe showed little to no activation in MMP-2-positive tumors. CONCLUSION: It is feasible to image MMP-2 enzyme activity in vivo by using near-infrared optical imaging technology and "smart" matrix metalloproteinase-sensitive probes.

Animals↗
PubMed2001

Molecular imaging.

The term molecular imaging can be broadly defined as the in vivo characterization and measurement of biologic processes at the cellular and molecular level. In contradistinction to "classical" diagnostic imaging, it sets forth to probe the molecular abnormalities that are the basis of disease rather than to image the end effects of these molecular alterations. While the underlying biology represents a new arena for many radiologists, concomitant efforts such as development of novel agents, signal amplification strategies, and imaging technologies clearly dovetail with prior research efforts of our specialty. Radiologists will play a leading role in directing developments of this embryonic but burgeoning field. This article presents some recent developments in molecular sciences and medicine and shows how imaging can be used, at least experimentally, to assess specific molecular targets. In the future, specific imaging of such targets will allow earlier detection and characterization of disease, earlier and direct molecular assessment of treatment effects, and a more fundamental understanding of the disease process.

Animals↗
PubMed2000

In vivo imaging of proteolytic enzyme activity using a novel molecular reporter.

The single biggest challenge facing in vivo imaging techniques is to develop biocompatible molecular beacons that are capable of specifically and accurately measuring in vivo targets at the protein, RNA, or DNA level. Our efforts have focused on developing activatable imaging probes to measure specific enzyme activities in vivo. Using cathepsin D as a model target protease, we synthesized a long-circulating, synthetic graft copolymer bearing near-infrared (NIR) fluorochromes positioned on cleavable substrate sequences. In its native state, the reporter probe was essentially nonfluorescent at 700 nm due to energy resonance transfer among the bound fluorochromes (quenching) but became brightly fluorescent when the latter were released by cathepsin D. NIR fluorescence signal activation was linear over at least 4 orders of magnitude and specific when compared with scrambled nonsense substrates. Using matched rodent tumor models implanted into nude mice expressing or lacking the targeted protease, it could be shown that the former generated sufficient NIR signal to be directly detectable and that the signal was significantly different compared with negative control tumors. The developed probes should find widespread applications for real-time in vivo imaging of a variety of clinically relevant proteases, for example, to detect endogenous protease activity in disease, to monitor the efficacy of protease inhibitors, or to image transgene expression.

Animals↗
PubMed1999

In vivo imaging of tumors with protease-activated near-infrared fluorescent probes.

We have developed a method to image tumor-associated lysosomal protease activity in a xenograft mouse model in vivo using autoquenched near-infrared fluorescence (NIRF) probes. NIRF probes were bound to a long circulating graft copolymer consisting of poly-L-lysine and methoxypolyethylene glycol succinate. Following intravenous injection, the NIRF probe carrier accumulated in solid tumors due to its long circulation time and leakage through tumor neovasculature. Intratumoral NIRF signal was generated by lysosomal proteases in tumor cells that cleave the macromolecule, thereby releasing previously quenched fluorochrome. In vivo imaging showed a 12-fold increase in NIRF signal, allowing the detection of tumors with submillimeter-sized diameters. This strategy can be used to detect such early stage tumors in vivo and to probe for specific enzyme activity.

Animals↗
PubMed1999

Near-infrared optical imaging of protease activity for tumor detection.

PURPOSE: To build and test an optical imaging system that is sensitive to near-infrared fluorescent molecular probes activated by specific enzymes in tumor tissues in mice. MATERIALS AND METHODS: The imaging system consisted of a source that delivered 610-650-nm excitation light within a lighttight chamber, a 700-nm longpass filter for selecting near-infrared fluorescence emission photons from tissues, and a charge-coupled device (CCD) for recording images. The molecular probe was a biocompatible autoquenched near-infrared fluorescent compound that was activated by tumor-associated proteases for cathepsins B and H. Imaging experiments were performed 0-72 hours after intravenous injection of the probe in nude mice that bore human breast carcinoma (BT-20). RESULTS: The imaging system had a maximal spatial resolution of 60 microns, with a field of view of 14 cm2. The detection threshold of the nonquenched near-infrared fluorescent dye was subpicomolar in the imaging phantom experiments. In tissue, 250 pmol of fluorochrome was easily detected during the 10-second image acquisition. After intravenous injection of the probe into the tumor-bearing animals, tumors as small as 1 mm became detectable because of tumor-associated enzymatic activation of the quenched compound. CONCLUSION: Tumor proteases can be used as molecular targets, allowing visualization of millimeter-sized tumors. The development of this technology, probe design, and optical imaging systems hold promise for molecular imaging, cancer detection, and evaluation of treatment.

Adenocarcinoma↗
PubMed1997

Study of the metabolism of choline and phosphatidylcholine in tumors in vivo using phosphonium-choline.

The results of an initial study on the feasibility of using the phosphonium analog of choline to follow the metabolism of phosphatidylcholine in tumors in vivo using 31P NMR are reported. C3H/He mice bearing a mammary carcinoma tumor on the foot pad were fed a choline-free diet supplemented with the phosphonium analog of choline. Metabolites of this compound, including the phosphonium analogs of phosphatidylcholine, phosphocholine, glycerophosphocholine, and betaine were observed noninvasively in vivo in tumors by 31P NMR after 2-3 weeks of feeding. Clearance of these phosphonium-labeled metabolites from tumors was measured after a change to a choline-containing diet. Significant decreases were seen in the levels of the analogs of betaine (P < 0.003) and phosphatidylcholine (P < 0.004) by Day 4. A significant increase in the level of authentic phosphocholine (P < 0.003) occurred over the same time period.

Adenocarcinoma↗
PubMed1996

13C and 31P NMR investigation of effect of 6-aminonicotinamide on metabolism of RIF-1 tumor cells in vitro.

The effect of 6-aminonicotinamide on the metabolism of RIF-1 tumor cells was investigated using 13C and 31P NMR spectroscopy. 6-Aminonicotinamide can be metabolized to 6-amino-NAD(P), a competitive inhibitor of NAD(P)-requiring processes. 40 microM 6-aminonicotinamide led to an inhibition of 6-phosphogluconate dehydrogenase and an accumulation of 6-phosphogluconate. A subsequent accumulation of the 6-phosphogluconate precursor 6-phosphoglucono-delta-lactone was observed in the 13C NMR spectrum. These metabolites were shown to be intracellular, although a small amount of leakage of 6-phosphoglucono-delta-lactone occurred. The intracellular concentrations of 6-phosphogluconate and 6-phosphoglucono-delta-lactone were 1.9 +/- 0.8 micromol/108 cells (+/-1 standard deviation) and 0.8 +/- 0.4 micromol/10(8) cells, respectively, after 15 h. Glucose utilization and lactate production were significantly inhibited by 6-aminonicotinamide (both p < 0.05), indicating inhibition of glycolysis. 31P NMR data showed that phosphocreatine was significantly depleted in cells exposed to 6-aminonicotinamide (p < 0.05). Exposure of RIF-1 cells to 6-aminonicotinamide prior to 3- or 6-Gy x-irradiation induced a supra-additive cell kill, indicating that 6-aminonicotinamide is acting as a radiosensitizer. There was no effect of 6-aminonicotinamide alone or when the drug was given postradiation, suggesting that its mechanism of action may be by inhibition of radiation-induced repair.

6-Aminonicotinamide↗
PubMed1996

In vivo detection by 31P NMR of pentose phosphate pathway block secondary to biochemical modulation.

The chemotherapeutic regimen of N-(phosphonacetyl)-L-aspartate (PALA) followed 17 h later by 6-methylmercaptopurine riboside (MMPR) and 6-aminonicotanamide (6AN) has been shown to be a potent sensitizer of anti-neoplastic therapy. We undertook this study to compare the therapeutic and metabolic effects of this triple drug combination vs one of its components, 6AN, in a murine mammary carcinoma. After treatment with PALA, MMPR and 6AN, a new peak was detected which was assigned to 6-phosphogluconate (6PG), which is a marker of inhibition of the pentose phosphate pathway at the 6-phosphogluconate dehydrogenase step. Treatment with PALA, MMPR and 6AN also induced a decrease in the ratios of nucleoside triphosphate/inorganic phosphate (NTP/Pi) and phosphocreatine/inorganic phosphate (PCr/Pi) similar to previous results with a different tumor model. These effects were most pronounced at 6 and 10 h. In addition, an increase in PME'/phosphocholine (PME' = downfield peak in the phosphomonoester region) was detected, which was expected because of the cytotoxic effect of this regimen. Treatment with 6AN alone also resulted in the detection of 6PG with a maximum intensity at 6 h post-6AN. Treatment with 6AN alone induced a smaller change in PME'/PC and failed to cause a decrease in PCr/Pi or NTP/Pi at 6 and 10 h. The enhanced response to the combination of PALA, MMPR and 6AN vs 6AN alone, both with regard to cytotoxicity and radiosensitization, may be due to energy depletion.

6-Aminonicotinamide↗
PubMed1995

In vitro and in vivo 31P nuclear magnetic resonance measurements of metabolic changes post radiation.

Radiation-induced metabolic changes previously observed in tumors using phosphorus nuclear magnetic resonance spectroscopy include changes in the relative amounts of the phospholipid precursors phosphoethanolamine and phosphocholine, increases in membrane catabolites, and increases in energy status. To elucidate the degree to which these in vivo alterations are a result of intrinsic cellular changes versus radiation-induced systemic effects, the Radiation-Induced Fibrosarcoma-1 tumor model was studied before and over the course of 7 days after a single dose of 17 Gy. In vivo studies were performed with tumors implanted in C3H/He mice; in vitro studies used cells that were perfused in agarose gel threads after being grown, radiated, and maintained in monolayer. The statistically significant increases in the downfield component of the phosphomonoester peak, which consists primarily of phosphoethanolamine, compared to the upfield component, phosphocholine, were qualitatively similar in vivo and in vitro post radiation. Statistically significant increases in the membrane catabolite glycerophosphocholine, a phosphodiester, were also observed in both tumors and cell culture after irradiation, with a greater percentage change in vitro. This suggests that changes in the phosphomonoester and phosphodiester concentrations are primarily an intrinsic effect of radiation on cellular metabolism, modulated to a lesser degree by systemic effects. In contrast, the statistically significant increases in energy status after the 17-Gy dose showed markedly different temporal responses in the two systems. Therefore, energy status changes observed in vivo are due largely to systemic changes, such as changes in blood flow. Flow cytometry data obtained from the cultured cells showed a sustained increase in the G2-M fraction starting at 24 h, the first time point measured after irradiation, which continued for the 7 days studied post radiation. These data indicate that the in vivo changes detected by nuclear magnetic resonance in phospholipid precursors and catabolites occur directly at the cellular level and may reflect cell death or growth inhibition after antineoplastic therapy.

Animals↗
PubMed1995

In vivo and in vitro studies of cyclophosphamide chemotherapy in a mouse mammary carcinoma by 31P NMR spectroscopy.

The effect of cyclophosphamide on the metabolic profile of a mammary carcinoma implanted on the foot of mouse was studied by 31P NMR spectroscopy both in vivo and in perchloric acid extracts. The ratio nucleotide triphosphate:P(i) was significantly elevated in cyclophosphamide treated tumours relative to untreated tumours after 96 h in vivo (p < 0.05). Phosphocreatine:P(i) was similarly elevated from 48 to 168 h (p < 0.01). Resolution of the phosphomonoester peak into two distinct resonances allowed us to estimate the ratio of PME' to phosphocholine (PC), where PME' is a composite peak consisting, in part, of phosphoethanolamine (PE). PME':PC was found to be significantly higher in treated animals relative to control animals in vivo (p < 0.01 from 48 to 168 h). Perchloric acid extract spectra suggest that the increase in PME':PC was in part due to a decrease in PC concentration and also due to an increase in a previously unidentified resonance which was coresonant with PE. Extract data show that there was a significant increase in the concentration of the phosphodiesters, glycerophosphocholine (p < 0.01) and glycerophosphoethanolamine (p < 0.05) in treated relative to control tumours. The changes in the phosphomonoester resonances are qualitatively similar to previously described changes following radiation and suggest that they may be a marker of cell kill or lack of cell growth after antineoplastic therapy.

Adenocarcinoma↗
PubMed1994

Radiation dose-dependent changes in tumor metabolism measured by 31P nuclear magnetic resonance spectroscopy.

The effects of radiation dose upon a hypoxic murine mammary carcinoma were followed using 31P nuclear magnetic resonance spectroscopy. Animals were studied before and over the course of 9 days after tumors were irradiated with a single dose of 0, 4, 8, or 17 Gy. The current data is compared to our previous studies of the effects of 32 or 65 Gy on the same tumor model. The energy status of the tumors, as reflected in nucleotide triphosphate:Pi and phosphocreatine:Pi ratios, improved after receiving a dose of 8 to 65 Gy and decreased after receiving 0 or 4 Gy doses. The energy status of the 8- to 65-Gy dose cohorts reached a maximum between 1 and 4 days after irradiation. Additionally, the change in the hypoxic cell fraction 48 h after a 17-Gy dose was determined; it was calculated from changes in the doses required to control 50% of the tumors post radiation for clamped (hypoxic) and unclamped (normoxic) tumors in parallel animal cohorts. A significant decrease compared to preirradiation values was observed in the hypoxic cell fraction following 17 Gy irradiation. This decrease was temporally coincident with increases in tumor energy status measured using nuclear magnetic resonance and was similar to our previously reported results of the change in hypoxic fraction 48 h after a 32-Gy dose. Changes in the relative ratio of phosphomonoesters showed a strong dose dependence after irradiation. The downfield component of the phosphomonoester peak, which consists largely of phosphoethanolamine, increased relative to the upfield component, phosphocholine. This dose-dependent ratio reached a maximum approximately 7 days post radiation. Changes in the levels of membrane phospholipid precursors may be related to alterations in cell proliferation or may be a result of radiation-induced membrane damage.

Animals↗
PubMed1993

Resolution enhanced NMR spectroscopy in biological systems via magnetic susceptibility matched sample immersion chambers.

A technique is described which reduced the magnetic susceptibility induced line broadening in NMR spectra obtained from three biological systems at 4.7 Tesla. Proton spectra from a sealed suspension of HL60 leukemic myeloblasts yielded minimum linewidths of 1.3 Hz at 200 MHz (0.0065 ppm) after 10 min of automated shimming. 31P spectra from an in vivo murine MCa mammary carcinoma yielded a well-resolved phosphorylcholine resonance without proton decoupling and with the resistive shim coil currents set to zero. 31P spectra from a perfused suspension of RIF-1 fibrosarcoma cells exhibited a gamma-nucleoside triphosphate resonance which was resolved into purine and pyrimidine components.

Animals↗
PubMed1992

Quantitative changes in tumor metabolism, partial pressure of oxygen, and radiobiological oxygenation status postradiation.

Hypoxia is considered to be a major cause of tumor radioresistance. Reoxygenation of previously hypoxic areas after a priming dose of radiation is associated with an increase in tumor radiosensitivity. In a study of a hypoxic mammary carcinoma, 31P nuclear magnetic resonance spectra showed statistically significant increases in metabolite ratios (phosphocreatine/Pi and nucleotide triphosphate/Pi) after 65 and 32 Gy. The maximum changes in metabolite ratios after 32 Gy occurred at 48 h, although significant changes were detected at 24 h. A corresponding increase in the mean tumor pO2 (polarographic microelectrode measurements) and a decrease in hypoxic cell fraction [changes in paired (clamped versus unclamped) tumor control dose for 50% of tumors] were also shown to occur 48 h after a priming dose of 32 Gy. A significant increase in the mean tumor pO2, phosphocreatine/Pi, and nucleotide triphosphate/Pi, compared to initial values, was noted at 24, 48, and 96 h post 65-Gy radiation. An increase in the downfield component of the phosphomonoester peak relative to the upfield component (phosphoethanolamine), is also noted after doses of 65 and 32 Gy. These are likely to be due to cell kill and/or decreased cell proliferation. In this tumor model, 31P nuclear magnetic resonance spectroscopic changes postradiation are temporally coincident with and may be indicative of tumor reoxygenation as measured by the tumor control dose for 50% of tumors and oxygen-sensitive microelectrodes.

Animals↗
PubMedDate not supplied

Quantitation of total metastatic tumor volume in the rat liver: correlation of MR and histologic measurements.

Assessing tumor response to chemotherapy in the liver has always been difficult. Most investigators estimate tumor volume as either a product of the two perpendicular diameters of a tumor nodule, or, in animal studies, simply count surface tumor nodules. The authors evaluated magnetic resonance (MR) imaging as a technique for determining absolute tumor volume in the liver in an animal model. Specifically, histologic volumetric and MR imaging measurements of tumor and liver volumes were quantitatively compared over a wide range of tumor burdens in a rat model of hepatic metastasis of a colorectal carcinoma. Twenty-three rats were imaged, with two different section thicknesses used in each animal. Both section thicknesses showed highly significant correlations between MR and histologic measurements for both tumor and liver volumes (P less than .001). MR imaging may be useful for noninvasively quantifying tumor burden and temporal response of metastatic disease in the liver to novel antineoplastic regimens.

Adenocarcinoma↗
PubMedDate not supplied

Preparation of a cathepsin D sensitive near-infrared fluorescence probe for imaging.

A variety of proteases are overexpressed or activated during pathogenesis and represent important targets for therapeutic drugs. We have previously shown that optical imaging probes sensitive in the near-infrared fluorescence (NIRF) spectrum can be used for in vivo imaging of enzyme activity. In the current study, we show that these probes can be designed with specificity for specific enzymes, for example, cathepsin D which is known to be overexpressed in many tumors. A NIR cyanine fluorochrome served as the optical reporter and was attached to the amino terminal of an 11 amino acid peptide sequence with specificity for cathepsin D. The peptides were subsequently attached to a synthetic graft copolymer for efficient tumoral delivery. The close spatial proximity of the multiple fluorochromes resulted in quenching of fluorescence in the bound state. A 350-fold signal amplification was observed post cleavage during in vitro testing. Cell culture experiments using a rodent tumor cell line stably transfected with human cathepsin D confirmed enzyme specific activation within cells. This sequence but not a scrambled control sequence showed enzyme specificity in vitro. We conclude that activatable NIRF optical probes can be synthesized to potentially probe for specific enzymes in living organisms.

Animals↗