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Using JM and MOLT3, two human T-cell acute lymphoblastic leukemia cell lines, we investigated the ability of 24-h thymidine exposures to enhance the cytotoxicity of cis-diammine-1,1-cyclobutane dicarboxylate platinum (II) (carboplatin). Clinically achievable thymidine concentrations (for 24 h) significantly enhanced carboplatin killing. Unexpectedly, thymidine-carboplatin enhancement was as great at a relatively low 200-micrograms thymidine/ml as at the clinically much more toxic range of 1000 micrograms/ml. For a constant thymidine concentration (500 micrograms/ml), thymidine-carboplatin interaction increased with longer thymidine exposures until about 16 to 24 h. Thymidine and 41.8 degrees C hyperthermia (for 1 h) together enhanced carboplatin killing significantly more than did hyperthermia-carboplatin or thymidine-carboplatin combinations. These results show that relatively brief, presumptively nonmyelosuppressive thymidine exposures can significantly increase carboplatin killing. Carboplatin-thymidine killing can then be further augmented by 41.8 degrees C hyperthermia.

This report describes the preparation of polylysine-diethylene triamine pentaacetic acid (DTPA)-metal ion complexes and of iodinated polylysine derivatives and the preferential binding of these polymers to glioblastomas in culture. Synthetic polylysines (DP88 and DP299) were modified covalently either with the chelator DTPA or with 125I-Bolton Hunter reagent. The polylysine (DP88) was modified initially with fluorescein to permit fluorescence cytological studies and quantitative measurements of polylysine concentrations. The polylysines contained an average of one DTPA per 16 lysyl moieties. The polylysine-DTPA derivatives were then modified with a mixture of 153Gd and stable Gd. A copolymer (DP120) of lysine and tyrosine (4:1) was modified with 125I using chloramine T as catalyst. C6 (rat) and U87 MG (human) glioblastoma cells, in culture, bound six to seven times more polylysine-DTPA-Gd than endothelial cells from either aorta or brain. Each of the tumor cell types bound 10(8) molecules of the modified polylysine per cell when 2.5 x 10(5) cells were reacted with 50 micrograms or greater of the polylysine-DTPA-nuclide complex. The higher molecular weight polylysines delivered more radionuclide to the cells in culture. Although the tumor cells bound more [125I]polylysine and [125I]poly(lysine HBr,tyrosine) than they bound polylysyl-DTPA-Gd, the endothelial cells and the plastic culture dish also bound more of the iodinated polymers. The stoichiometry of polylysine bound per cell suggests that the sialic acid moieties on the cell surface are the primary binding sites for polylysine derivatives. Fluorescence microscopy studies revealed that the fluorescein polylysine (DP88) and the fluorescein polylysine-DTPA nuclide complex bound the tumor cells primarily at branch points along the neuritic processes, at the edge of the perikaryon and at the terminal regions of the outgrowth process. The polylysyl-DTPA-Gd can be used, with magnetic resonance imaging, to provide measurable contrast of the margin between C6 glioblastomas and normal brain in vivo in Wistar Furth rats.

Thermal radiosensitization was studied in two human T-cell acute lymphoblastic leukemia cell lines (JM and MOLT3) with regard to heat-irradiation sequence and heating duration. In MOLT3 thermal radiosensitization was maximal when 43.5 degrees C hyperthermia immediately preceded or followed irradiation; at 41.5 degrees C, radiosensitization was maximal with hyperthermia immediately before or up to 3 h after irradiation. In JM, enhancement of radiation killing was unexpectedly maximal when 41.5 or 43.5 degrees C hyperthermia preceded irradiation by 2 to 4 h. Thermal radiosensitization increased exponentially with increasing duration of heating at 41.5 degrees C for at least 3 h in MOLT3. In contrast, in JM, radiosensitization increased exponentially for 1.6 h but additional heating (up to 3 h net heating) had no appreciable further effect on radiation killing. For JM, repair of single and double stranded DNA breaks was investigated using alkaline and neutral elution techniques to determine whether the unusual results regarding heat-irradiation sequencing were related to effects of heat on repair of DNA damage. These studies were unable to detect significant differences in repair of single or double stranded DNA breaks between unheated control cells and cells heated at 41.5 degrees C for 1 h ending 4 h before irradiation. The direct cytotoxicity of hyperthermia was also studied in both cell lines.

Localized hyperthermia (43 degrees) in single or multiple fractions was applied to mouse mammary adenocarcinoma TA3Ha implanted into the s.c. tail tissue of strain A mice. The effects of heat on the growth of local tumors, on the pattern of metastasis, and on the survival periods of the hosts were studied. Hyperthermia was administered by heating the tumor-bearing tails in a water bath. Multiple 30-min hyperthermia treatments at 5- or 7-day intervals controlled local tumor growth better than did a single 30-min treatment or multiple 30-min treatments at 3-day intervals or at intervals longer than 7 days. Heat treatments that produced cytostatic effects on tumors, sparing the normal tissue, had no effect on either the survival of the hosts or the extent of metastasis to the lungs and the lumbar lymph nodes. However, local treatments reduced the frequency of renal lymph node metastasis, indicating that concurrent metastases in different sites may exhibit differential heat sensitivities.

Hyperthermic enhancement of cis-diammine-1,1-cyclobutane dicarboxylate platinum(II) (carboplatin) cytotoxicity was studied in vitro in JM, a human acute lymphoblastic leukemia cell line. Corrected for direct heat toxicity, hyperthermia enhanced carboplatin killing at the clinically relevant temperatures of 40.5 degrees and 41.8 degrees C. The thermal enhancement ratios at these temperatures were 1.89 and 3.32, respectively. Cell killing increased exponentially with increasing duration of combined treatment (41.8 degrees C, carboplatin 30 micrograms/ml) for at least 3.5 h. Hyperthermic enhancement was maximal when heat was given during or immediately before carboplatin; enhancement was diminished when heat preceded carboplatin by more than an hour and was not apparent when heat followed drug treatment. As carboplatin is associated with different clinical toxicity than is cis-diamminedichloroplatinum(II), carboplatin may represent an ideal drug in its class of anticancer agents to use in clinical whole body hyperthermia trials.