Prostaglandin and thromboxane synthesis by M5076 ovarian reticulosarcoma during growth: effects of a thromboxane synthetase inhibitor.

The five stable metabolites [prostaglandin F2 alpha (PGF2 alpha), prostaglandin D2 (PGD2), prostaglandin E2 (PGE2), thromboxane B2 (TXB2), and 6-ketoprostaglandin F1 alpha (6-keto-PGF1 alpha)] of arachidonic acid (AA) via the cyclooxygenase pathway were measured by high-resolution gas chromatography-mass spectrometry in M5076 ovarian reticulosarcoma (M5) homogenates at various times after tumor implantation (Days 15, 18, 21, and 24). Vegetating tumor showed an active AA overall metabolism, which significantly increased during tumor growth. Synthesis of selected products (TXB2, PGD2, and PGE2) increased markedly over time (up to 10.6, 3.5, and 0.9 micrograms/g, respectively). The overall metabolic profile was TXB2 much greater than PGD2 greater than PGF2 alpha greater than 6-keto-PGF1 alpha greater than PGE2 on Day 15 and TXB2 much greater than PGD2 much greater than PGF2 alpha greater than 6-keto-PGF1 alpha on Day 24. TXB2 was also by far the most abundant product of in vitro-cultured M5 cells. Chronic treatment of M5-bearing mice with dazmegrel (UK-38,485), a selective thromboxane synthetase inhibitor (100 mg/kg p.o. daily, from Day 7 to killing), resulted in incomplete TXB2 synthesis inhibition, AA metabolism diversion toward the other prostaglandins, and no effects of tumor growth and metastasis. More frequent dazmegrel treatment (100 mg/kg p.o. every 8 h from Day 1 to killing) resulted in complete TXB2 synthetase inhibition, AA metabolism diversion, and increased tumor growth and metastasis. These data do not support the hypothesis of thromboxane synthetase inhibitors reducing tumor growth. However, since TXB2 suppression was accompanied by the production of other products possibly interfering in tumor growth, no conclusions on the effective role of TXA2 in malignancy can be drawn.

Prostaglandin and thromboxane synthesis by Lewis lung carcinoma during growth.

The five stable metabolites [prostaglandin F2 alpha, prostaglandin D2, prostaglandin E2 (PGE2), thromboxane B2, and 6-keto-prostaglandin F1 alpha] of arachidonic acid (AA) via the cyclooxygenase pathway were measured by high-resolution gas chromatography-mass spectrometry in Lewis lung carcinoma homogenates at various times after tumor implantation (11 to 25 days). Vegetating and necrotic sections of the primary tumor and lung metastases were examined. Vegetating tumor showed a very active AA metabolism. Synthesis of PGE2, the most abundant product, markedly increased during tumor growth (up to 30 micrograms/g). A high and increasing synthetic capacity was also noted for prostaglandin D2 (up to 9 micrograms/g). Minor time differences and lower levels (up to 1.4 micrograms/g) were found for the other AA metabolites. PGE2 and prostaglandin D2 were the major products in necrotic tumor, too, but synthesis was markedly less than in vegetating tumor, and no increase was noted over time. Metastatic tissue showed a different AA metabolic profile, as compared to primary tumor and surrounding lung tissue, with PGE2 and 6-keto-prostaglandin F1 alpha being the main metabolites.

Pharmacokinetics of anticancer agents in patients with impaired liver function.

This report reviews published information on the clinical pharmacokinetics of antitumour agents in patients with liver dysfunction, associated with primary liver disease or liver metastases. Information was available for anthracyclines and their related compounds, antimetabolites, cyclophosphamide, vinca alkaloids, taxanes and epipodophyllotoxins. Changes in the pharmacokinetic profile or metabolism in patients with mild or severe hepatobiliary dysfunction are described and the relationships between serum levels, parameters employed for measuring hepatic function and toxic or therapeutic effects are examined. Current knowledge of the pharmacokinetics of antineoplastic agents in liver disease is far from complete, mostly obtained in small numbers of non-homogeneous patients often presenting only moderate liver dysfunction, and empirical guidelines for dose assessment are still largely applied in clinical practice. Because of the complex pathophysiological mechanisms of liver insufficiency in cancer patients, there is still doubt whether endogenous markers are useful. Although caution in treating cancer patients with liver insufficiency is compulsory, for most compounds there seems no need to recommend dose reductions for moderate impairment. However, for the tubulin acting agents, vincristine, vinblastine and possibly for paclitaxel and docetaxel, there is strong evidence that dose adjustment is mandatory in order to avoid excessive neutropenia and neurotoxicity.

Doxorubicin toxicity and pharmacokinetics in old and young rats.

Doxorubicin (Dx) toxicity was compared in old (24 months) and young (6 weeks) Crl:CD(SD) BR male rats, and a clear age-related increase was found. The mortality of all animals receiving a single i.v. Dx dose was followed for 270 days. Old rats died after doses of 2.5 mg/kg, while young animals died after doses two times higher, 5 mg/kg. In old rats body weight loss started 10 to 15 days after Dx, compared to 50 to 80 days for young animals. In young and old rats pharmacokinetic and metabolic studies of Dx were conducted in vivo and in the liver perfusion model. Peak levels of Dx and areas under the time/concentration curves (AUC) in serum and in several tissues of old rats were 1.5 to 2 times higher than in young rats. Concentrations of Dx metabolites in serum and tissues (doxorubicinol, Dxol, and doxorubicinone, Dxone) in young and old rats were not noteworthy. However, higher percentages of Dxone than Dxol were found in both groups in vivo and in vitro. Old livers appeared to produce more Dxone as a percentage, particularly in the bile, which was higher. Urinary elimination of Dx markedly slowed with age; only small amounts of the metabolites were eliminated in urine. In vivo and in vitro availability of Dx and its metabolites is discussed in view of their possible role in the greater toxicity observed in 24-month-old rats.

Distribution and antitumoral activity of adriamycin combined with warfarin in mice.

The distribution of adriamycin (AM) in C57Bl/6 mice bearing intramuscular Lewis lung carcinoma under the influence of combined treatment with warfarin (W) was investigated by a fluorimetric procedure. AM was injected IV at the dose of 7.5 mg/kg 14 days after tumor transplantation and W was given in the drinking water for 96 h, starting 24 h before AM.. No substantial modifications in the serum and tissue distribution of AM fluorescence were observed under combined short-term treatment with W.

Do anticancer agents reach the tumor target in the human brain?

The development of effective chemotherapy for tumors of the central nervous system (CNS) is complicated in that the blood-brain barrier (BBB) hampers the penetration of most drugs into the brain and cerebrospinal fluid (CSF). This review summarizes the main reports on the distribution to CNS tumors and peritumoral normal brain of antitumor agents such as epipodophyllotoxins, cis-diamminedichloroplatinum(II), some nitrosoureas, bleomycin, vinblastine, and other clinically used antitumor agents as well as that of some experimental compounds with specific physicochemical properties. Drug levels were measured at surgical resection or in autopsy samples taken from patients who presented with different primary brain tumors or with brain metastases from extracerebral tumors. The observations made in each study were summarized in some detail, and the main points were then evaluated comparatively so as to highlight common aspects in the pharmacokinetic patterns of antitumor agents in human CNS tumors. Independently of their physicochemical properties, most antitumor agents appear to accumulate to a greater extent and to persist longer in intracerebral tumors than in the normal peritumoral brain. From in vitro cytotoxicity assays, it appears that epipodophyllotoxins, platinum compounds, bleomycin, and nitrosoureas reach potentially active therapeutic concentrations at the tumor target. However, all drugs have difficulty in reaching brain tissue adjacent to the tumor, as the intact BBB hampers their penetration. Plasma and CSF drug concentrations usually give little useful indication of the absolute quantity of drugs in brain tumors. To obtain a clear understanding of the CNS distribution of antitumor agents, one must determine whether the compound being measured is actually responsible for the observed activity and must consider the role of metabolites in the effect of the parent drug.

Distribution, metabolism, and irreversible binding of hexamethylmelamine in mice bearing ovarian carcinoma.

The covalent binding of hexamethylmelamine (HMM) and its metabolites was studied in liver, tumor, blood, kidney, spleen, lung, brain, heart, and small intestine after a single IP injection of 2,4,6-14C-hexamethylmelamine (50 mg/kg) to C57Bl/6J female mice bearing 20-day-old M5076/73A ovarian cancer. Covalent binding to tissue macromolecules was measured 2, 10, and 40 h after injection of the drug. At 2 h liver and small intestine showed the highest levels of irreversibly bound metabolites, the lowest being found in brain and heart. Except in the small intestine, where a decrease was observed between 2 and 10 h, the level of covalent binding was constant up to 40 h. HMM metabolism was also studied. Tissue distribution of pentamethylmelamine (PMM), 2,2,4,6-tetramethylmelamine (TMM), and 2,4,6-trimethylmelamine (TriMM) was determined at the three times considered. At 2 h the drug was already extensively metabolized, TriMM being the major metabolite among those determined.

Hepatobiliary metabolism and urinary excretion of 4-demethoxydaunorubicin as compared to daunorubicin in rats.

The hepatic metabolism and biliary excretion of 4-demethoxydaunorubicin (4DDM) was studied in Crl: CD(SD) BR rats by the liver perfusion technique. In the same strains of rats urinary excretion was investigated in vivo. Daunorubicin (DM) was always included for comparison. The drugs and their metabolites were determined in the perfusion medium, in the bile and liver and in the urine by high-performance liquid chromatography with fluorimetric detection. Compared to its analogue DM, 4DDM markedly differed in the metabolic and excretory profile. The cumulative biliary and urinary excretion of 4DDM and the metabolites was quantitatively lower than that of DM (18% vs 36% of the dose) and was consistent with prolonged persistence of 4DDM in plasma in vivo. The extensive carbonyl reduction of 4DDM and DM observed in previous in vivo pharmacokinetic studies was also evident in this study. 13-hydroxy metabolites, daunorubicinol (DMol) and 4-demethoxydaunorubicinol (4DDMol), either as such or after glycosidic cleavage, i.e. 4DDMol aglycone, were present in appreciable amounts in the perfusion medium, bile, liver and urine. In the hepatobiliary system, however, the 13-hydroxy derivative of DM amounted to a much lower fraction than the DM aglycone (17% vs 50% of the total dose), 80% of the total 4DDM dose was accounted for by 4DDMol aglycone. In urine uncleaved DMol or 4DDMol represented more than 75% of the total amount excreted for both drugs. Conjugation, a major step in the excretion of aglycones, seems to play a minor role in the biliary and urinary excretion of 4DDM and 4DDMol.

Intact rat liver nuclei catalyze adriamycin irreversible interactions with DNA and nuclear proteins.

Male rat liver intact nuclear preparations are able to metabolize adriamycin to reactive species that irreversibly interact with nuclear DNA and proteins in the presence of reduced NADPH. This process was not inhibited by 1 mM SKF-525A, suggesting that a nuclear monooxygenase enzymatic system was not involved.

Antitumoral activity of the oxazaphosphorine derivative, mafosfamide-cyclohexylamine salt (ASTA 7557) on a murine ovarian reticular cell sarcoma and its subline resistant to cyclophosphamide.

The antitumor activity of mafosfamide (MFA), and its parent compound cyclophosphamide (CTX), was investigated against an ovarian reticular cell sarcoma growing i.m. in C57BI/6 mice (M5), which is very sensitive to CTX, and against a subline of this tumor (R16) resistant to CTX. MFA is the prototype of a class of oxazaphosphorines which do not require metabolic activation since under physiologic conditions they undergo rapid spontaneous hydrolyzation to the activated 4-hydroxyoxazaphosphorine and retain a spectrum of activity very similar to the parent compound. After a single dose (300 mg/kg X 1) or repeated low doses (100 mg/kg X 6) the antitumoral activity of MFA on the M5 tumor appeared comparable to or only slightly lower than CTX; the highest T/C value for median survival times was 167% in MFA-treated mice vs. 176% in the CTX group. MFA showed no activity against the R16 subline, thus indicating cross-resistance between the two drugs. Marked thickening of the glissonian capsule with compression of the lobular area of the liver, observed on i.p. administration of MFA, did not result in histopathologic abnormalities of the hepatic parenchyma. The therapeutic efficacy of MFA was similar with i.p. and the i.v. route. MFA may represent a good candidate to replace CTX in cases in which a compound acting per se, and not through metabolites, is preferred.

Effect of phenobarbital on cyclophosphamide cytotoxic activity and pharmacokinetics in mice.

The interaction between cyclophosphamide (CPA) and phenobarbital (PB) was investigated in B6D2F1 mice, checking both the antileukemic and immunosuppressive activity together with the serum levels of CPA and its metabolites. A reduced cytotoxic activity of CPA has been observed when PB is given for 2 days before CPA and an interval of at least 6 hours elapses between the last treatment of PB and the administration of CPA. On the contrary, when PB is given simultaneously with CPA for 2 or 4 consecutive days, an increased antileukemic activity of CPA occurs. In the experimental condition where PB decreases the activity of CPA, serum levels of CPA, assayed by means of a new specific gas-chromatographic method, and of its NBP-alkylating metabolites, indicate that this effect may be explained on a pure pharmacokinetic basis. However, for the situation where an increased effect of CPA was observed under the influence of PB, pharmacokinetic data did not provide a clear explanation.

Differential adriamycin distribution to blood components.

The differential distribution of doxorubicin (Adriamycin = AM) and daunorubicin (Daunomycin = DM) within the blood components, after an i.v. injection of 10 or 15 mg/kg of body weight, was investigated from its metabolites and quantified by means of the TLC scanning fluorescence technique. AM accumulated in the following order (of decreasing percentages): plasma and red cells (RBC), white cells (WBC), and platelets (PT), but the absolute amount of drug that reached each cell type was related to its relative volume. In the presence of higher blood concentrations (after injection of 15 mg/kg of body weight) the RBCs accumulated much more AM than the plasma, WBC, and PT; suggesting that the RBC fraction has a greater capacity to concentrate the drug. However, if the concentration of AM is expressed per unit volume of each component, a markedly higher value was observed for PT, and this was confirmed by in vitro results obtained by incubating blood in the presence of AM. DM seemed to be distributed on a percent basis to a greater extent than AM in the RBC fraction. Both compounds were taken up by blood cells, particularly platelets, to levels in excess of the extracellular concentration.