Biomedical subjects

A I Kassis

Publications and source records attributed to A I Kassis.

At least 91 records · Page 5Linked to original sources

PubMed1989

Monoclonal antibody internalization by tumor cells: an experimental model for potential radioimmunotherapy applications.

The monoclonal IgM 3G5, which reacts with the surface membranes of rat insulinoma cells RINm5F, was purified by HPLC and labeled with 125I using Protag-125; bovine IgG (bIgG) was similarly radiolabeled, and used as a control. 125I-3G5 was incubated with RINm5F cells either at 4 degrees C or at 37 degrees C. 125I-3G5 bound onto RINm5F cells growing in Petri dishes remained approx. constant over 44 h when incubated at 4 degrees C, whereas at 37 degrees C radioactivity was released back in the medium starting at 3 h (plateau at approx. 20 h). At the end of incubation at 37 degrees C, activity in the medium included a high percentage of free 125I (15.69 vs 2.62% for bIgG, and 1% for 3G5 at 4 degrees C). In a cell suspension experiment, cell-bound 125I-3G5 also remained constant over a 24 h incubation at 4 degrees C, whereas at 37 degrees C it decreased to 37.5% of its initial value (64.1% at 4 h). Concomitant microautoradiography showed diffuse radioactive deposits within the RINm5F cells following incubation with 125I-3G5 (but not 125I-bIgG) at 37 degrees C. These results indicate that 3G5-IgM reacts with a surface antigen on the RINm5F cells, but is rapidly internalized by the cells: within the cells, this antibody undergoes some metabolic processing which results in the release of free 125I outside the cells.

Animals↗

PubMed1989

Radiotoxicity of an 125I-labeled DNA intercalator in mammalian cells.

To explore the effect of the Auger electron emitter 125I attached to a DNA intercalator, we have synthesized 125I- and 127I-labeled 3-acetamido-5-iodoproflavine (AIP) and have examined the uptake, intracellular distribution, and radiotoxicity of A125IP in Chinese hamster V79 cells. After incubation with AIP, the nuclei of V79 cells become fluorescent. Uptake of A125IP is directly proportional to its extracellular radioactive concentration and reaches a plateau at about 10 h. Of the cell-associated radioactivity, 60% is retained by the cells after extensive washing. When the survival of V79 cells is plotted as a function of radioactive cell content, the curve has no shoulder with a mean lethal dose (DN) of about 1.3 Gy to the cell nucleus. Because the DN of these cells when irradiated with 250 kVp X rays is 5.8 Gy, the relative biological effectiveness (RBE) of A125IP is about 4.5. The dependence of the RBE values on the localization of the Auger emitter is discussed on the basis of our extended studies on the same cell line.

Animals↗

PubMed1989

Radiotoxicity of 5-[123I]iodo-2'-deoxyuridine in V79 cells: a comparison with 5-[125I]iodo-2'-deoxyuridine.

The toxic effects of the short-lived (T 1/2 = 13.2 h) Auger-electron-emitting isotope 123I, incorporated in the form of 123IUdR into the DNA of V79 cells in vitro, have been investigated and compared to those of 125IUdR. For the concentrations tested, the rate of incorporation of 123IUdR at any time is proportional to the concentration of extracellular radioactivity. The curve for survival of clonogenic cells decreases exponentially and exhibits no shoulder at low doses. The mean lethal dose (D37) to the nucleus is 79 +/- 9 cGy and is about the same as that obtained previously with 125IUdR. However, the total number of decays needed to produce this D37 with 123IUdR is about twice that required with 125IUdR, approximately equal to the ratio of the energy deposited in microscopic volumes by 125I and 123I, respectively. This correlation suggests that nuclear recoil, electronic excitation, and chemical transmutation are probably of minor importance to the observed biological toxicity with either isotope. The results also indicate that there are no saturation effects in the decay of 125IUdR in the DNA of V79 cells (i.e., all of the emitted energy is biologically effective) and that each of the two steps involved in the 125I decay is equally effective in causing biological damage.

Animals↗

PubMed1989

Limitations of conventional internal dosimetry at the cellular level.

A theoretic examination of the validity at the cellular level of assumptions used in classic internal dosimetry has been undertaken. An alternate dosimetric model accounting for the consequences of selective uptake of a radiolabeled compound by specific cells in a multicellular cluster of hexagonal geometry has been developed. At the cellular level, derived dose estimates for electrons have been compared to dose estimates obtained employing the assumptions of conventional internal dosimetry. The study has been performed for all electron energies and then applied specifically to electrons emitted by 99mTc, 201Tl, 111In, and 123I. The dosimetric consequences of altering (a) the intracellular-to-extracellular radionuclide concentration, (b) the labeled cell density, and (c) the cell size have been examined for the labeled and nonlabeled cells in a cell cluster, and the conditions in which conventional dosimetry underestimates or overestimates the dose to individual cells have been indicated. It is shown that when selective intracellular uptake of a radiolabeled compound occurs in specific cells within a cell cluster, conventional dosimetry underestimates the radiation dose delivered to the labeled cells by twofold to more than 25-fold if the emitted electrons have ranges of a few micrometers or less, i.e., energies smaller than approximately 10 keV. Under the same conditions, conventional dosimetry overestimates slightly (20% to 50%) the electron radiation dose to the nonlabeled cells of the cell cluster. It is shown that inclusion of photons in the calculation of the total dose to individual cells does not alter significantly the conclusions of the present investigation.

Electrons↗

PubMed1988

Radioimmunotherapy with alpha-particle-emitting immunoconjugates.

Alpha particles are energetic short-range ions whose higher linear energy transfer produces extreme cytotoxicity. An alpha-particle-emitting radioimmunoconjugate consisting of a bismuth-212-labeled monoclonal immunoglobulin M specific for the murine T cell/neuroectodermal surface antigen Thy 1.2 was prepared. Analysis in vitro showed that the radioimmunoconjugate was selectively cytotoxic to a Thy 1.2+ EL-4 murine tumor cell line. Approximately three bismuth-212-labeled immunoconjugates per target cell reduced the uptake of [3H]thymidine by the EL-4 target cells to background levels. Mice inoculated intraperitoneally with EL-4 cells were cured of their ascites after intraperitoneal injection of 150 microcuries of the antigen-specific radioimmunoconjugate, suggesting a possible role for such conjugates in intracavitary cancer therapy.

Alpha Particles↗

PubMed1988

Radioiododemercuration: a simple synthesis of 5-[123/125/127I]iodo-2'-deoxyuridine.

Through the use of iododemercuration, 5-[123/125I]iodo-2'-deoxyuridine was synthesized rapidly and with high radiochemical purity from 5-chloromercuri-2'-deoxyuridine. The synthesis of radioiodinated 2'-deoxyuridine was achieved in one step in the presence of Iodogen in 50% yield after isolation by reverse phase high performance column chromatography. The radiochemical purity was greater than 99%. The ease and the absence of any starting material, suggests that radiohalodemercuration may be the method of choice for this and structurally similar compounds.

Idoxuridine↗

PubMed1988

Efficient conjugation of DTPA to an IgM monoclonal antibody in ascites fluid.

We have developed a simple, rapid, and reproducible method for conjugating the bifunctional metal chelator diethylenetriaminepentaacetic acid (DTPA) to an IgM monoclonal antibody (MoAb) without first isolating the MoAb from the ascites fluid. Treatment of the protein mixture in the ascites fluid with cyclic DTPA anhydride (cDTPAA) followed by HPLC purification on a size exclusion column allowed isolation of the DTPA-IgM conjugate which could then be labeled with 111In in greater than or equal to 80% yield. Over the range of total protein concentrations used (11-44 mg/mL), the number of DTPA molecules per molecule of IgM was approximately one-half the molar ratio of cDTPAA to total protein. We have used this method to prepare an 111In labeled anti-Thy 1.2 IgM, a MoAb with specificity for a murine cell-surface antigen found on normal and malignant T cells and neuroectodermal tissues. Analysis of the DTPA-IgM conjugate prior to and after 111In labeling using indirect immunofluorescence flow cytometry and a target-cell binding assay showed that the antigen specificity of this anti-Thy 1.2 MoAb is not substantially altered by the presence of up to 8 DTPA molecules per IgM molecule.

Animals↗

PubMed1988

Biodistribution studies of anti-Thy 1.2 IgM immunoconjugates: implications for radioimmunotherapy.

We have prepared 111In radioimmunoconjugates (RICs) of the IgM isotype with specificity for the murine T cell/neuroectodermal surface antigen, Thy 1.2. Using gamma camera immunoscintigraphy, we have analyzed the biodistribution patterns of the RICs after intravenous and intraperitoneal injection into normal Thy 1.2+ and Thy 1.2- mice. Both routes of administration show antigen-specific uptake by the splenic T lymphocyte population. A high degree of nonspecific uptake by the reticuloendothelial system is also observed. Analysis of the specific activity of various segments of spleens from RIC-injected animals shows inhomogeneous uptake of the RIC not readily apparent by immunoscintigraphy. Animals injected with the RIC and then given high dose total body irradiation showed rapid shifts in radionuclide distribution away from the target cell population and into the general reticuloendothelial system, suggesting that death of the target cell can alter RIC biodistribution. Analyses of RIC biodistribution patterns will contribute to optimization of treatment by radioimmunotherapy.

Animals↗

PubMed1987

HPLC analysis of the dissociation and recombination of rabbit immunoglobulin G.

Rabbit immunoglobulin G (RIgG) was reduced with dithioerythritol and analyzed by high performance liquid chromatography. A quantitative method for determining the percentage of reduced half-molecules in the mixture was developed. An acetic acid concentration-dependent rate of dissociation of reduced half-molecules was observed. The specific optical absorptivity was determined for whole molecules and half-molecules and found to be significantly greater for the half-molecules. Purified half-molecules were reconstituted into RIgG with a yield greater than 90% following a 16 h incubation at pH 8.0 and room temperature.

Acetates↗

PubMed1987

Radiobiologic implications of the microscopic distribution of energy from radionuclides.

A significant increase in our understanding of the dosimetry and therapeutic potential of various types of radioactive decay has augmented the possibility of utilizing specific radiolabeled carriers in tumor therapy. At least three types of radioactive decay lend themselves to this approach. Most fastidious in their distribution requirements are the Auger electron emitters whose radiotoxicity can only be realized with their intranuclear localization. Alpha emitters irradiate regions of several cell diameters. Beta emitters are less stringent as far as proximity to the total tumor mass, but doses to normal tissues can be high. The advantages and the limitations of each type of decay are presented.

Alpha Particles↗

PubMed1987

Efficient radiolabeling of mammalian cells using 111In-tagged liposomes.

When indium-111 oxine labeled neutral liposomes were incubated with Chinese hamster V79 cells in the presence of 100 mM calcium, the cell-associated radioactivity increased approximately 75-fold over that observed in the absence of calcium. This is considerably higher (approximately 20 times) than the cellular uptake obtained when these cells are incubated in the presence of 111In-oxine alone. The highest uptake of radioactivity occurred when no bovine serum albumin was present in the medium, while as little as 0.001% of the protein greatly reduced the cell-liposome association. These efficient cell labeling conditions were not found to affect the survival of the cells.

Animals↗

PubMed1987

Synthesis and biological studies of iodinated (127/125I) derivatives of rhodamine 123.

Rhodamine 123, a mitochondrial stain that preferentially accumulates in certain cancer cells, has been reduced and iodinated by using NaI in the presence of N-chlorosuccinimide. The various mono-, di-, and triiodo derivatives have been isolated and characterized. These nonfluorescent compounds are taken up by mammalian cells, become fluorescent within the cytoplasm (presumably following oxidation), and show the same pattern of localization as the parent compound. Iodination with no-carrier-added Na125I yields the same mixture of compounds. All 125I derivatives accumulate preferentially in PC3 adenocarcinoma cells compared with V79 lung fibroblasts, with the differential being greatest for the monoiodo compound, followed by the di- and triiodo derivatives.

Adenocarcinoma↗

PubMed1987

Radiotoxicity of 125I in mammalian cells.

The radiotoxicity of 125I in Chinese hamster V79 lung fibroblasts has been studied following extracellular (Na125I), cytoplasmic [125I]iododihydrorhodamine (125I-DR), and nuclear (125IUdR) localization of the radionuclide. Exposure of the cells for 18 h to Na125I (less than or equal to 7.4 MBq/ml) had no effect on survival. A similar exposure to 125I-DR produced a survival curve with a distinct shoulder and with a mean lethal dose (D37) of 4.62 Gy to the nucleus. While this value compares well with the 5.80 Gy X-ray D37 dose, it is in contrast to the survival curve obtained with DNA-bound 125IUdR which is of the high LET type and has a D37 of 0.80 Gy to the nucleus. Furthermore, when the uptake of 125I into DNA is reduced by the addition of nonradioactive IUdR or TdR to the medium and the survival fraction is determined as a function of 125I contained in the DNA, a corresponding increase in survival is observed. This work demonstrates the relative inefficiency of the Auger electron emitter 125I when located in the cytoplasm or outside the cell. It indicates that a high dose deposited within the cytoplasm contributes minimally to radiation-induced cell death and that radiotoxicity depends not upon the specific activity of IUdR but upon the absolute amount of 125I that is associated with nuclear DNA.

Animals↗

PubMed1987

Kinetics of uptake, retention, and radiotoxicity of 125IUdR in mammalian cells: implications of localized energy deposition by Auger processes.

The kinetics of uptake, retention, and radiotoxicity of 125IUdR have been studied in proliferating mammalian cells in culture. The radioactivity incorporated into the DNA is directly proportional to the duration of incubation and to the extracellular concentration of 125I. The rate of proliferation of cells is related to the intracellular radioactive concentration and is markedly reduced at medium concentrations greater than or equal to 0.1 mu Ci/ml. At 37% survival the high LET type cell survival curve is characterized by an uptake of 0.035 pCi/cell, and the cumulated mean lethal dose to the cell nucleus is about 80 rad compared to 580 rad of X-ray dose for this cell line. The strong cytocidal effects of the decay of 125I correlate with localized irradiation of the DNA by the low energy Auger electrons.

Animals↗

PubMed1986

The in vitro radiobiology of astatine-211 decay.

Chinese hamster V79 cells in culture were exposed to astatine-211, an alpha-particle-emitting radiohalogen. The dose-log survival response was linear with no detectable shoulder. Cells in monolayers had a D0 of 1.0 microCi/ml. Suspended cells had a D0 of 0.60 microCi/ml with a cellular uptake of 2.5 fCi/cell; this is equal to approximately 1.5 alpha-particle traversals per cell nucleus. The frequencies of chromosome and chromatid breaks were linear with dose, but the number declined rapidly with time. These data are discussed in relation to published alpha-particle beam studies and the potential use of 211At in radionuclide therapy.

Alpha Particles↗

PubMed1985

Chemotoxicity of indium-111 oxine in mammalian cells.

We have studied the uptake and toxicity of [111In]oxine in Chinese hamster V79 lung fibroblasts. The incorporation of the radionuclide into these cells reached a plateau within 2 hr. Uptake was proportional to the extracellular radioactive concentration. Both radioactive and "decayed" [111In]oxine exhibited similar toxicities, indicating that the observed toxicity was chemical in nature. These results are discussed in terms of the present status of this radiolabeling agent.

Animals↗

PubMed1985

Intracellular distribution and radiotoxicity of chromium-51 in mammalian cells: Auger-electron dosimetry.

The kinetics of uptake and of radiotoxicity of chromium-51, an Auger-electron emitter, have been studied in V79 lung fibroblasts of the Chinese hamster. Intracellular radioactivity was directly proportional to the incubation period and to the extracellular concentration of the Cr-51. About 14% of the cellular activity was associated with the nucleus, whereas approximately 2% was guanidine-precipitable and therefore bound to DNA. The growth rate of V79 cells was slowed following intracellular incorporation of Cr-51. The cell-survival curve, in terms of colony-forming ability, was of the low-LET type, with a D37 of 6.2 pCi/cell. Theoretical dosimetric estimates indicate that, under the given experimental conditions, the mean lethal dose to the cell nucleus was 870 rad. Although this value is somewhat larger than the x-ray D37 dose of 580 rad for this cell line, it is more realistic than the gross underestimate obtained by classical MIRD calculations (2-3 rad/cell).

Animals↗

PubMed1984

Biological studies of a new class of technetium complexes: the hexakis(alkylisonitrile)technetium(I) cations.

This study describes the preparation and synthesis of a new class of cationic technetium compounds, the hexakis(alkylisonitrile)technetium(+ 1) complexes, at both carrier added and no carrier added concentrations in aqueous media from pertechnetate. Biological distribution and imaging data in animals indicate that certain members of this class may be effective for cardiac imaging in man. The usefulness of these lipophilic water-soluble species for labeling mammalian cells is also reported.

Animals↗