Eckhard Friedrich

Imaging of tumors by time-delayed laser-induced fluorescence

A technique to improve signal-to-background ratio in fluorescence images of superficially growing tumors marked with photosensitizers is described. Time-delayed detection of fluorescence following pulsed-laser excitation allows suppression of the autofluorescence background falling into the fluorescence band of the photosensitizer. This technique exploits the longer fluorescence-decay times of porphyrin-based photosensitizers compared to average decay times of tissue autofluorescence. The feasibility of time-delayed fluorescence imaging of tumors has been demonstrated in vitro. From time-delayed fluorescence spectra the authors infer that the ratio between photosensitizer signal and autofluorescence background can be improved by about one order of magnitude.

Kupffer cells recognize trinitrobenzene-labeled erythrocytes

Chemical-modified erythrocytes (trinitrobenzene-modified erythrocytes (TNB-RBC)) are trapped in vivo rapidly by liver macrophages (Kupffer cells). The liver homing of TNB-RBC is dependent on the concentration of TNB-residues coupled to the surface of RBC. High concentrations induce liver homing, low concentrations spleen homing.

The injection of heparin prolongs the plasma clearance of oxidized low density lipoprotein in the rat

There is evidence that oxidized-LDL plays an important role in atherogenesis. We now report on the in vivo interaction between unfractionated heparin and oxidized LDL in rats. The recovery rates of the native LDL particles ranged between 75% and 85% of the injected dose. Heparin did not interfere with the clearance rates of native LDL. After administration of radioactive labeled oxidized-LDL particles, 26% of the material was measured in circulation after 5 minutes, 8% after 20 minutes, and 3% after 60 minutes. After injection of heparin 2 minutes prior to oxidized-LDL tracer particles, 44% of the tracer was found in blood after 5 minutes, 23% after 20 minutes, and 9% after 60 minutes. Oxidized-LDL tracer particles disappeared from blood with an alpha half-life of 5 minutes and a beta half-life of 7.5 minutes. After receptor blocking with unfractionated heparin the alpha half-life of the oxidized-LDL tracer was prolonged to 17.5 minutes and the beta half-life to 27.5 minutes. These results indicate that heparin molecules of a comparatively small molecular weight competed the scavenger receptor mediated uptake of oxidized-LDL particles in vivo. Oxidized-LDL particles are known to mediate their pro-atherosclerotic activity in part by stimulating smooth muscle cell proliferation by a scavenger receptor-mediated pathway. It can be speculated, if heparins interfere with the uptake of oxidized-LDL, heparins might thus in part exert their known antiatherosclerotic properties.

Serum albumin (SA) accumulation by bronchogenic tumours : a tracer technique may help with patient selection for SA-delivered chemotherapy

Systemic toxicity and inadequate tumour uptake of chemotherapeutic agents limit effective therapy of disseminated malignant disease. We seek to use macromolecules for improved delivery of therapeutic agents to tumours, and hope to use radiotracer procedures to identify those malignancies able to accumulate the transport molecule. A literature search identified in vitro and animal experimental data which indicated that serum albumin is taken up in malignancies. Selected cytostatic drugs can be bound to albumin, which suggests the suitability of the molecule as a potential transport vehicle. We therefore evaluated indium-111 labelled human serum albumin (HSA) to determine the frequency of its accumulation in bronchogenic tumours. Single-photon emission tomographic (SPET) images were obtained in 23 patients 48 h after intravenous injection of 1.5 mCi111In diethylenetriamine penta-acetic acid (DTPA)-HSA. SPET imaging with technetium-99m labelled erythrocytes was included in the protocol to assess the influence which vascularity has on the HSA-based images. All patients went on to surgery. We documented the histological diagnosis, T-stage and differentiation grade. The scintigraphic examination demonstrated HSA uptake in three squamous cell carcinomas and four adenocarcinomas. Of these, six malignancies accumulating HSA had 2.2–5.4 times the tracer concentrations observed in comparable background regions. Small cell carcinoma failed to accumulate the labelled HSA during the 2-day scintigraphic evaluation. The HSA images did not appear to represent tumour vascularity. T-stage and differentiation grade failed to predict which tumours would demonstrate HSA uptake. Initial results suggest that HSA merits evaluation as a potential transport molecule for inmour-directed therapeutic agents, since approximately 35% of the examined malignancies showed HSA uptake. At the same time the relatively infrequent tumour HSA incorporation may mandate using scintigraphy and labelled HSA for selecting those individuals who may profit from HSA-delivered drug therapy. The described selection and therapy approach was tried in two patients who had an111In-DTPA-HSA tumour to background ratio of 1.45:1 and 5.3:1 respectively. Both received experimental chemotherapy with methotrexate (MTX)-HSA.

Homing kinetics of indium-111 labelled bacteria: detection of organ specificities as revealed by scintigraphy.

Abstract “Homing” of 111In labelled bacteria to the liver was quantitatively studied using scintigraphy and liver perfusion. Salmonella typhimurium (rough) and Staphylococcos aureus were rapidly and efficiently trapped by the rat liver. In contrast Salmonella typhimurium (smooth) was trapped only at poor rates by liver and spleen. Serum dependency of the filtering process was studied using perfusion techniques.

A rapid new method of measuring phagocytosis and cytotoxicity in macrophage tissue cultures.

111Indium as a radioactive tracer for labelling cells has advantages of 51 chromium: very low leakage after 24 h, superior counting properties of the radionuclide 111indium, and a labelling yield of greater than 70%. Tissue culture chamber slides combine the advantage of tissue culture micromethods with simple preparation techniques used in histology. We report here results with peritoneal macrophages as effector cells and erythrocytes and tumor cells as targets. Phagocytosis and cytotoxicity were measured easily and rapidly.

Studies on intravascular phagocytosis in the lung.

SummaryIn this paper we have shown for the first time endocytosis by intravascular lung phagocytes. Glutaraldehyde-treated erythrocytes (discocytes) homed rapidly to the rat lung as measured by scintigraphic procedures. Transmission and scanning electron microscopy showed that the discocytes are phagocytosed by macrophages, blood monocytes and granulocytes as whole cells. This process could not be inhibited by silica treatment.

Tumor cells adhere to intraperitoneal injection sites

SummaryTumor cells injected intraperitoneally form cell plaques at injection sites in the abdominal wall of mice within a few minutes. Tumor cells appear to be transported passively and chemotactic factors are not involved. Dihydrocortisol blocks cell adherence and silica particles, assumed to destroy macrophages, abolish cell plaque formation.

Studies of erythrocyte sequestration

SummaryHeat altered erythrocytes are taken up by spleen macrophages without any signs of mechanical strain as revealed by light and scanning electron microscopy. There was no scintigraphic evidence for changed flow rates within the spleen after sequestration of erythrocytes.

Enhancement of porphyrin tumor accumulation by inhibition of porphyrin liver pathway

Photodynamic therapy has attracted attention by its potential for selective tumor destruction. However, selectivity is limited by unsatisfactory accumulation of porphyrin derivatives in tumors. Porphyrins injected intravenously are rapidly cleared from circulation by the liver. We examined the possibility of inhibiting the liver uptake of porphyrins by using the non-phototoxic hemin to compete for liver accumulation. The tumor model was an ovarian carcinoma (O-342, Zeller) transplanted in the muscle of the left hind leg of BDIX rats. To monitor the biodistribution of the photosensitizer various porphyrins were labelled with 111Indium. The distribution of the radioactivity was imaged by a gamma camera (Phogamma IV; Searle/Siemens) and biopsies measured in a gamma counter (Berthold, Freiburg). An injection of 5 mg/kg hemin prior to introduction of the porphyrin caused competition for uptake of the photosensitizer by the liver. Consequently, the plasma half-life for all 111Indium-porphyrins investigated was increased by 30 - 50%. The liver competition was possible both by preinjection of 5 mg/kg hemin 5 minutes before administration of the photosensitizer or by injection of hemin within 15 minutes post injection of the photosensitizer. This saturable process suggests distinct binding sites for hematoporphyrin in the liver. However, tumor uptake of the radio-labelled porphyrins was not blocked by hemin. Tumor accumulation of the porphyrins demonstrated a positive correlation to plasma retention time. Preinjection of hemin induced higher tumor uptake rates, up to a factor of 5 within 24 hours post injection. Pretreatment of the animals with hemin caused better therapeutic ratios for all porphyrins. The tumor to skin ratio of Photofrin II was raised from 4:1 to 7:1 by preinjection of hemin. This effect may be useful to reduce skin phototoxicity of PDT in man by dose reduction of the applied photosensitizers.