Maria Grazia Donelli

Do anticancer agents reach the tumor target in the human brain

SummaryThe 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.

Evidence for covalent binding of adriamycin to rat liver microsomal proteins.

Abstract Adriamycin (NSC-123, 127) is an anticancer drug of the anthracycline type widely used in the clinical practice for the treatment of different malignancies (1). Intercalation with DNA has been suggested as having a role in the mechanism of action of this drug (2, 3, 4). Recently, reports by Sinha (5) and Lucacchini et al. (6) suggested a covalent interaction of Adriamycin (AM) with DNA and proteins. These studies, however, were not conclusive since they were carried out by spectrophotometric and Chromatographie procedures. In the present study a covalent interaction between AM and microsomal proteins was demonstrated in a more “classical” covalent binding study with the 14 C-labelled compound.

Influence of tumor on adriamycin concentration in blood cells

SummaryThe relative distribution of adriamycin to plasma and blood cells after IV injection of 10 mg/kg was investigated in CD rats bearing intramuscular 256 Walker carcinosarcomas 15 days old. The drug was measured by a fluorimetric procedure and the amount of unchanged compound was separated from metabolites and quantitated by means of a TLC scanning fluorescence technique. In the presence of a tumor much lower hematocrit values are found, with marked anemia and thrombocytopenia associated with leukocytosis. These modified hematologic parameters account for an altered pattern of drug distribution. The low number of blood cells per milliliter results in a smaller amount of drug being present in the cellular fraction, so that more of the compound (even twice as much) is made available in plasma. Changes in adriamycin concentrations per unit volume or cell of each cell type are inversely related to changes in their relative number per milliliter. The only cell fraction where the drug increase per cell or cubic micrometer does not compensate the marked reduction in cell count observed in the presence of tumor is the platelet fraction, in which adriamycin amounts are 25% or less of those observed in the blood of normal rats, indicating that these blood cells become saturated in tumor-bearing animals.

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

SummaryThe 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.

Diferential adriamycin® istribution to blood components

SummaryThe 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 in Cd-COBS rats. AM and DM were measured by a fluorimetric procedure, and the unchanged compound was separated 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 byin 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. This work was supported by NCI (Contract No. NOI CM 67064) and CNR (Progetto Finalizzato: Control of Cancer Growth).

Effects of three new anthracyclines and doxorubicin on the rat isolated heart

The acute cardiac toxicity of three second‐generation anthracycline analogues and doxorubicin was compared in a model of the rat isolated Langendorff perfused heart. The drugs, doxorubicin (DX), 4‐epi‐doxorubicin (4′EDX), 4‐demethoxy‐daunorubicin (4DMDR) and 4′‐deoxy‐doxorubicin (4′dxDX) were infused for 40 min at a concentration of 26 μM into the isolated hearts. All four compounds significantly reduced cardiac work and its first derivative. The time to 50% decrease in work (TW50) was respectively 36, 23, 9 and 7 min for DX, 4′EDX, 4′dxDx and 4DMDR. The three anthracycline derivatives, but not DX, significantly increased coronary resistance. Heart rate was reduced by all compounds compared with baseline, but not compared with controls. Rhythm disturbances were seen with all five hearts perfused with 4DMDR, which stopped beating before 40 min; 2/5 hearts in the 4′EDX group and 1/5 hearts in the 4′dxDX group also stopped before the end of perfusion. All the compounds reached concentrations in the myocardium 8 to 50 times higher than in the perfusing medium. The more cardiotoxic the compound, the higher was its myocardial concentration; a significant correlation was found for all four agents. Noradrenaline was never measurable in the perfusate of control and DX hearts; perfusion with the three anthracycline derivatives caused some release, but the pattern was not clearcut and the maximum concentrations attained in the perfusate were relatively low (< 1ṁ6 times 10−9 M). In conclusion, in the rat isolated perfused heart, the early cardiotoxicity induced by equimolar concentrations of the three anthracycline compounds was greater than that induced by DX and was directly related to drug accumulation in the myocardium. Catecholamines do not seem to have a major role in the development of toxicity in this model.

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.

Is better drug availability in secondary neoplasms responsible for better response to chemotherapy

Abstract The response of intramuscular Lewis Lung carcinoma (3LL) and its pulmonary metastases to graded doses of adriamycin (AM) was investigated in C57B1/6 mice given the drug i.v. 11 days after tumor implantation and the effect was quantitated by recording tumor or metastases weight at various intervals after treatment. In the same experimental tumor model the distribution of AM in primary and secondary neoplasms was studied by a fluorimetric procedure. The results indicate that, compared to the primary 3LL implant, AM has a much more pronounced effect on a percentage basis on the lung nodules, where the drug reaches 3–5 times the levels in the intramuscular tumor. In order to clarify the role of this better drug availability in determining the higher response at the metastic site, the experimental correlation law between AM amount (peak level or area under the concentration versus time curve, AUC) and the drug effect (the smallest ratio of mean tumor or metastases weights in treated to untreated animals) was investigated for both primary and secondary tumors, and the concentration-response curves thus constructed were compared with the dose-response curves. If the effect is related to drug concentration, there is definitely less difference between the response of intramuscular 3LL and its metastases to AM and it even disappears at certain concentrations. The ed 50 for the primary tumor is 10 times higher than for the lung nodules if derived from the dose-response curve, and only 2–3 times higher if derived from the concentration-response curve. Moreover, the lack of linear relationship and the biexponential correlation between the variables of effect and dose or peak concentration or AUC, either for the intramuscular or pulmonary 3LL, indicates that the effect does not increase proportionally to the drug amounts, suggesting that other factors beside AM concentration may contribute to the better drug response at the metastatic site.

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

The interaction between cyclophosphamide (CPA) and phenobarbital (PB) was investigated in B6D2F, 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.

Importance of the presence of necrosis in studying drug distribution within tumor tissue

SummaryThe differential distribution of antitumoral agents such as adriamycin, methylnitrosourea, cyclophosphamide and methotrexate in the vegetating and necrotic part of the intramuscular Lewis Lung carcinoma of C57B1 mice is investigated.As expected, these drugs are found to be mostly absent in the necrotic, while accumulating in the viable part of the tumor. Our findings suggest that measurement of antitumoral agents at the tumor level should be performed in the viable part of the tumor in order to get a proper estimate of the actual drug concentrations reached.