Biodistribution and scintigraphy of [111In]DTPA-adriamycin in mammary tumor-bearing rats.

The aim of this study was to develop an 111In-labeled diethylenetriamine pentaacetic acid-adriamycin (DTPA-ADR) conjugate to image breast cancer. DTPA-ADR was synthesized by reacting adriamycin with DTPA anhydride in the presence of carbonyldiimidazole. After dialysis (MW cut off was 500), the product was freeze-dried (yield 40-50%). An in vitro cell culture study was performed using cells from the 13,762 Fischer rat mammary tumor line. Drug concentrations tested were 0.1-100 microM. Biodistribution studies were conducted at 0.5, 2, 24 and 48 h in mammary tumor-bearing rats (n = 3/time interval, 10 microCi/rat, i.v.) with 13,762 cells (10(5) cells/rat, s.c.). Planar imaging and autoradiograms were obtained at the same intervals. In vitro cell culture assays showed an IC50 of 0.1 +/- 0.01 microM for ADR and 7.2 +/- 0.29 microM for DTPA-ADR, respectively. In biodistribution studies, tumor/blood uptake ratios of [111In]DTPA-ADR at 0.5, 2, 24 and 48 h were 0.55 +/- 0.17, 0.94 +/- 0.17, 3.06 +/- 0.53 and 3.66 +/- 0.35, respectively, whereas those for [111In]DTPA (control) were 1.19 +/- 0.69, 0.84 +/- 0.07, 0.56 +/- 0.10 and 0.60 +/- 0.03, respectively. The tumor uptake value (%ID/g) of [111In]DTPA-ADR at 0.5 h was 0.20 +/- 0.06. Planar images and autoradiograms showed good visability of tumors. Biodistribution, autoradiography and radionuclide imaging of [111In]DTPA-ADR in breast tumor-bearing rats showed that tumor-to-blood ratios increased steadily between 30 min and 48 h. These results indicate that DTPA-ADR, a new cancer imaging agent, might be useful in the diagnosis of breast cancer and may predict a therapeutic effect prior to treatment.

Neurochemical basis of interleukin 2-modified discrimination behaviour.

We trained one group of rats to discriminate 0.8 mg/kg intraperitoneal (i.p.) d-amphetamine from 1 ml/kg saline and the other to discriminate 0.3 mg/kg i.p. (+/-)-ethylketocyclazocine (EKC) from saline. Recombinant human interleukin 2 (rIL-2), 2 x 10(6) U/kg (or 8.2 nmol/kg) given i.p. 1 h prior to tests, potentiated responses elicited by 0.4 mg/kg d-amphetamine. This potentiation of d-amphetamine responses was suppressed by the opioid receptor antagonist naloxone (1 mg/kg) when administered i.p. together with IL-2. IL-2 (4 x 10(6) U/kg) alone produced EKC-like responses in the EKC-trained animals. The cytokine also potentiated 0.1 mg/kg EKC responses at 2 x 10(6) U/kg, an action that was suppressed by 1 mg/kg naloxone. Data from the present study show that IL-2 exerts the same neurochemical action as that previously observed with IFN-alpha for both d-amphetamine and EKC discrimination in rats.

The opioid mechanism of interferon-alpha action.

Rats were trained to discriminate the opioid receptor agonist ethylketocyclazocine (EKC) (0.3 mg/kg body weight, intraperitoneally) from saline. Interferon-alpha (IFN-alpha), when substituted for EKC, elicited a dose-related increase in EKC-like responses. This generalization of EKC responses was blocked by the opioid antagonist naloxone (1 mg/kg). Potentiation of responses to a low dose (0.1 mg/kg) of EKC by IFN-alpha (1 x 10(6) U/kg or 0.22 nmol/kg) was also observed. Data thus indicate the involvement of opioid neurons on the action of IFN-alpha. d-Amphetamine (0.8 mg/kg) was shown to potentiate both EKC (0.1 mg/kg) and IFN-alpha (1 x 10(6) U/kg). The present study confirms our previously proposed opioid-mediated dopaminergic mechanism of IFN-alpha.

Opioid-dopaminergic mechanisms in the potentiation of d-amphetamine discrimination by interferon-alpha.

In rats trained to discriminate 0.8 mg/kg IP d-amphetamine from 1 ml/kg saline, 4 x 10(6) U/kg of recombinant human interferon-alpha (rIFN-alpha) given intramuscularly 1 h prior to tests potentiated responses elicited by 0.4 mg/kg d-amphetamine. Coadministration of the opioid receptor antagonist naloxone (1 mg/kg IP) with rIFN-alpha suppressed the potentiation of d-amphetamine by the cytokine. Opioid-dopaminergic mechanisms are proposed to explain the action of rIFN-alpha.

Beta-adrenoceptor binding studies with LY195448 and metabolites.

LY195448(R) (a phenethanolamine derivative that has demonstrated cytotoxic activity against cell cultures in vitro but that exhibited a hypotensive side effect during phase I trials), its p-hydroxy and acid metabolites, and a noncytotoxic S-stereoisomer were evaluated with respect to competitive binding against the beta-adrenergic antagonist [3H]dihydroalprenolol in rat brain cortex and human cardiac tissues. When IC50 and Ki values were compared, the R-isomer of LY195448 in general was more potent than the S-stereoisomer. While LY195448(R) was about 10-fold more active than the p-hydroxy metabolite in cardiac tissues, the two compounds were nearly equipotent both in blocking the binding of radioligand to the brain and in reducing blood pressure in rats. In the cerebral preparation, the binding of the acid metabolite was weak, with its activity being equal to that of the S-stereoisomer.

The effect of the experimental antitumor agent caracemide on brain choline acetyltransferase.

Caracemide was found to inhibit choline acetyltransferase (CAT) from rat brain. A concentration of 0.5 mM caracemide inhibited the enzyme by 93%, whereas a degradation product from caracemide, N-(methylcarbamoyloxy)acetamide, produced only a 50% inhibition. Two other degradation products, N-(methyl-carbamoyloxy)-N'-methylurea and N-hydroxy-N'-methylurea, lacked any inhibitory activity. With bovine brain CAT, caracemide showed noncompetitive inhibition with the substrate choline, Km 337 microM, Ki240 microM, Vmax 2.83 nmol acetylcholine formed/min/mg protein and mixed inhibition with the substrate acetyl-CoA, Km 21 microM, Ki 146 microM, Vmax 3.85 nmol acetylcholine formed/min/mg protein.

Inhibition of brain choline acetyltransferase by tetraplatin.

Tetraplatin inhibited choline acetyltransferase (CAT) from rat and bovine brain with I50 values of 13.5 and 40 microM, respectively. At 0.5 mM concentration, tetraplatin exhibited inhibition of the rat brain enzyme by 89%, whereas cisplatin yielded only 18% inhibition. With bovine CAT, tetraplatin showed noncompetitive inhibition with the substrate choline, Km 337 microM, Ki 29 microM, Vmax 2.83 nmoles acetylcholine formed/min/mg protein, and competitive inhibition with the substrate acetyl-CoA, Km 21 microM, Ki 16 microM, Vmax 3.85 nmoles acetylcholine formed/min/mg protein.