Proton relaxation enhancement by manganese(III)TPPS4 in a model tumor system.

Managanese(III)tetraphenylporphine sulfonate [Mn(III)TPPS4] has been investigated as a tumor specific paramagnetic contrast agent for magnetic resonance imaging (MRI) of L1210 solid tumors in mice. Mn(III)TPPS4 was found to clear rapidly from the blood and concentrate in the kidneys, tumor and liver. Although relatively high ratios of tumor to normal tissues could be obtained (e.g., greater than 90 for tumor/muscle), the kidneys were found to have the highest concentration of the metalloporphyrin at all doses and time periods tested. A significant decrease in the longitudinal relaxation time was measured for excised tissues (kidney, tumor, liver, muscle) from mice that were treated with Mn(III)TPPS4. A linear correlation was observed between the longitudinal relaxation rate determined for L1210 tumor and the corresponding concentration of Mn(III)TPPS4 found at various injected doses and time intervals between the injection and analysis. A small animal radiofrequency receiver coil designed for use with a 0.15-T clinical imager was employed to evaluate the ability of Mn(III)TPPS4 to selectively increase the signal intensity of the implanted L1210 tumor. The images show a conspicuous enhancement in the contrast between the tumor and adjacent tissue upon treatment with this agent. The results indicate that Mn(III)TPPS4 is a useful prototype paramagnetic metalloporphyrin MRI contrast agent with a significant affinity for the L1210 tumor.

Dynamics of antifolate transport via the reduced folate carrier and the membrane folate receptor in murine leukaemia cells in vitro and in vivo.

Murine L1210 leukaemia cells expressing either the reduced folate carrier (RFC) or the membrane folate receptor (MFR) were studied in vitro and in vivo to assess the dynamics of membrane transport of two categories antifolates; folate-based inhibitors of dihydrofolate reductase (methotrexate, edatrexate, aminopterin, PT523, and PT644) and thymidylate synthase (TS) [CB3717, raltitrexed, plevitrexed (BGC9331), pemetrexed and GW1843]. The potency of in situ inhibition of TS was used as an endpoint to analyze the in vitro dynamics of RFC/MFR-membrane transport of these antifolates. Both for L1210-RFC and L1210-MFR cells, the potency of in situ TS inhibition was closely correlated with increasing affinities of these transporters for the antifolates (r = 0.64, P < 0.05 and r = -0.65, P < 0.05, respectively). Within the group of antifolates for which MFR had a low binding affinity, those that had the ability to become polyglutamylated, were more potent inhibitors of TS in situ activity than non-polyglutamatable antifolates. In vivo activity of methotrexate, edatrexate, raltitrexed and pemetrexed was assessed in L1210-RFC and L1210-MFR bearing mice that were fed either a standard or a folate-deficient chow. Dietary folate depletion significantly reduced the MTD for methotrexate (sevenfold), edatrexate (sevenfold), raltitrexed (50-fold) and pemetrexed (150-fold). Based on increased life spans, antitumor effects of methotrexate and edatrexate were markedly better in L1210-RFC bearing mice on the folate-deficient chow (ILS: 455 and 544%, respectively) than on standard chow (ILS: 213 and 263%, respectively). No therapeutic effects of methotrexate and edatrexate were observed for L1210-MFR bearing mice on either chow condition, which may be consistent with the low binding affinity for MFR. Irrespective of the folate diet status, pemetrexed and raltitrexed were inactive against both L1210-RFC and L1210-MFR bearing mice, which may be due to high circulating plasma thymidine levels. Collectively, this study underscores that modulation of dietary folate status can provide a basis within which the therapeutic effect of antifolates may be further improved.

Tetra-p-aminophenylporphyrin conjugated with Gd-DTPA: tumor-specific contrast agent for MR imaging.

Tetra-p-aminophenylporphyrin (TPP) was conjugated with gadolinium diethylenetriaminepentaacetic acid (DTPA) and used as a contrast agent in magnetic resonance (MR) imaging to achieve tumor selectivity in nude mice. A substantial decrease in T1 was measured in excised tissues (kidneys, tumor, and liver) from mice that received the porphyrin derivative Gd2(DTPA)4 TPP. Toxicity and phototoxicity were less than those obtained with hematoporphyrin derivative in both L1210 lymphoblastic leukemia cells and HT 29 human colonic cancer cells, as determined with in vitro assays. MR images showed an enhancement of contrast between the tumor and adjacent tissue after injection of this agent. The results indicate that Gd2(DTPA)4TPP could be a useful prototype paramagnetic porphyrin MR imaging contrast agent with an affinity for tumors.

Biophysical aspects of the integrated combination of cytostatic drugs with radiotherapy. Part 2: Dose-effect relationships and 31P NMR spectroscopy of L 1210 cells (monolayers) and 9L glioma cells (monolayers and tumor spheroids) treated with activated isophosphamide, adriamycin, epirubicin and 6 MeV electrons.

Dose-effect relations have been evaluated by the treatment of cell cultures (9L glioma cells of rat as monolayers and tumor spheroids, L 1210 cells of mice) with activated isophosphamide, adriamycin, epirubicin and 6 MeV electrons. The magnitude of synergistic effects obtained by combined treatment modalities is strictly pH-dependent, but even for tumor spheroids it appears that there exists an optimum time-interval between drug administration and consecutive irradiation. The determination of the intracellular pH value with the help of pH sensor microelectrodes and 31P NMR spectroscopy indicates that 31P spectroscopy only provides the global pH of the complete culture (average value), whereas the local pH can only be determined by sensors. The ATP-concentration before and after irradiation depends significantly on the glucose supply of the culture medium.