Hematological effects of the alkylating agents

Analysis of CD34+ cell collection using two mobilization regimens for newly diagnosed multiple myeloma patients reveals the separate impact of mobilization and collection variables

Mobilization regimens for CD34+ cells have generally been judged successful based on the number of cells collected without evaluating mobilization separately from collection. Using retrospective data for patients who collected CD34+ cells on Total Therapy protocols 3a/3b (VTD-PACE) and Total Therapy 4/5 using a novel regimen that added low dose melphalan to VTD-PACE (MVTD-PACE), we analyzed mobilization and collection variables separately. A significant difference favoring MVDT-PACE was found in mean CD34+ cells/µL on day 2 of collection and in mean ratio of CD34+ cells/µL on day 2 to day 1. However, because apheresis variables and growth factor dose during collection were manipulated to optimize individual collections, the two regimens were not significantly different when the mean total CD34+ cells ×10(6) /kg collected was compared. Thus, when evaluating a chemotherapy regimen or new growth factor for mobilization, it is important to realize that total CD34+ cells collected is dependent on both mobilization and collection variables.

Inhibition of CFU-E/BFU-E and CFU-GM colony growth by Cyclophosphamide, 5-Fluorouracil and Taxol: development of a high-throughput in vitro method

The major side effect of anticancer drugs is damage to the hematopoietic system. These compounds may interfere with cell proliferation and differentiation in different blood lineages causing many diseases such as neutropenia, aplastic anaemia or trombocytopenia. The clonogenic assays are useful in vitro tools for evaluating and predicting acute xenobiotics myelotoxicity. A miniaturisation of these assays, in order to reduce costs and increase the number of compounds that could be tested, is under investigation. The in vitro sensitivity of human burst-forming unit erythroid (BFU-E) and colony-forming unit granulocyte-macrophage (CFU-GM) to three anticancer drugs: cyclophosphamide (CTX), 5-fluorouracil (5-FU) and taxol (TAX) was evaluated both in 35 mm plate and 96-well plate systems and the dose-response curves, IC50 values and IC90 values were compared. The correlation between in vitro data and clinical plasma levels confirms that severe hematotoxicity is the primary adverse effect of these drugs with an evident selectivity on erythroid progenitors for cyclophosphamide. IC50 and IC90 values, calculated on the basis of results obtained with the traditional assay, correlate with those obtained in microplate, as well as the dose-response curves, indicating that the 96 well plate assay could be a useful and reliable tool for high-throughput screening in early stages of drug development.

N-acetyl-L-cysteine does not affect the pharmacokinetics or myelosuppressive effect of busulfan during conditioning prior to allogeneic stem cell transplantation

Busulfan is currently used as a main component in the conditioning regimen prior to allogeneic stem cell transplantation (SCT). Several studies have shown a correlation between exposure to busulfan and transplantation-related liver toxicity, such as venoocclusive disease (VOD) in patients undergoing SCT. Busulfan is metabolized mainly through glutathione (GSH). During high-dose therapy, busulfan may deplete hepatocellular levels of GSH. As part of the conditioning therapy, busulfan is usually followed by high doses of cyclophosphamide. The activation of cyclophosphamide yields a cytotoxic metabolite, 4-hydroxy cyclophosphamide, which is highly reactive and detoxified through GSH. According to recent studies using cell lines and animal models N-acetyl-L-cysteine (NAC), a GSH precursor, does not hamper the myeloablative effect of busulfan during conditioning. In the present study, we administered NAC during conditioning to 10 patients at risk of VOD due to pretransplant liver disorders or elevated liver enzymes. No side effects related to the NAC infusions were observed and busulfan concentrations were not affected. All patients became pancytopenic and engrafted with 100% donor cells. None of the patients developed VOD or liver failure. Increased liver enzymes during conditioning decreased or normalized in all patients. We suggest that NAC therapy is safe and does not impair the myeloablative effect of busulfan during conditioning prior to SCT.

The comparative toxicity of chlorambucil and chlorambucil-spermidine conjugate to BALB/c mice

The acute intraperitoneal toxicities of chlorambucil and chlorambucil-spermidine conjugate have been compared, in mice. Both compounds were neurotoxic and also caused a prolonged fall in bodyweight and a depletion of lymphocyte numbers associated with a fall in the total leukocyte count and loss of spleen and thymus weight. Alanine aminotransferase and aspartate aminotransferase activities and blood urea nitrogen concentration were increased at 24 h after conjugate administration, but had returned to normal at 72 h. Chlorambucil significantly decreased blood urea nitrogen concentration for 72 h, but did not affect transferase activity. Tissue concentrations of conjugate were measurable in liver and kidney for 12 days and lung for 5 days after dosing. The toxicity of both compounds was cumulative. In mol/kg, the chlorambucil-spermidine conjugate was 10-fold more toxic than chlorambucil, on the basis of their neurotoxicity, but only 2- to 3-fold more toxic on the basis of their effects on lymphocyte depression. The increased toxicity of the conjugate does not improve its therapeutic index relative to chlorambucil.

Toxicological review of busulfan (Myleran)

Busulfan is a bifunctional alkylating agent that appears to be cytotoxic to slowly proliferating or non-proliferating stem cell compartments, although its specific molecular and cellular mechanisms are unknown. It is the drug of preference in treatment of chronic myelogenous or granulocytic leukemia because its cytotoxic activity results in primary damage or destruction of hematopoietic cells. Additional effects resulting from the cytotoxicity of busulfan in hematological and other tissues, as documented by both human and animal model studies, include lethality, sterility, teratogenicity, and alteration of immune function. Busulfan has been shown to be mutagenic to microorganisms, mammalian cells in culture, Drosophila, and rodents. This agent is also considered potentially carcinogenic to humans. Various tissue hyperplasia and preneoplastic cells have been observed in animal model studies with busulfan, and case reports on human patients implicate busulfan as the causative agent in induction of secondary malignancies. Reports from human and animal studies of busulfan's cytotoxicity, teratogenicity, carcinogenicity, and mutagenicity have been reviewed. This information may be useful in a quantitative assessment of the effects of this agent and the identification of significant deficiencies in the data base. Demonstration that busulfan induces mutations in both somatic and germ cells suggests the need to assess its risk to humans.

The effects of methotrexate and melphalan in sheep

1 Sheep were injected with either methotrexate or melphalan in an attempt to lower the numbers of neutrophil granulocytes in peripheral blood. 2 Methotrexate, 5.0 mg/kg intravenously, on three consecutive days, produced no noticeable clinical or haematological changes. 3 A single dose of melphalan, 1.0 mg/kg intravenously, depleted lymphocytes and granulocytes, but the numbers of the latter then rose to values exceeding the levels before melphalan treatment. Doubling the dose of melphalan proved fatal. 4 The failure of methotrexate to produce changes can be explained in terms of ruminant metabolism.

COMPARATIVE EFFECTS OF NITROGEN MUSTARD (HN2), CHLORAMBUCIL (CB 1348), AND BUSULPHAN (MYLERAN) ON THE PERIPHERAL BLOOD AND THE FERROKINETIC PATTERNS IN DOGS

Three alkylating agents, HN2 (methyl-bis(betachlorethyl)amine), chlorambucil (p-(di-2-chlorethylamino)-phenylbutyric acid), and busulphan (1,4-dimethanesulphonoxybutane) were studied with regard to their effects on leukocyte and red cell production in dogs. This was assessed by estimation of the peripheral blood leukocyte and reticulocyte changes as well as alterations in the plasma iron, Fe59 disappearance rate, plasma iron turnover, and red cell incorporation of radioactive iron. The two chlorethylamines had a similar effect on both leukocyte and red cell production. The effect on peripheral leukocyte counts was evident in 24 hours and the reticulocyte response indicated maximum interference with erythropoiesis on the third to seventh day following the drug. The effect of busulphan on both granulocytes and lymphocytes was slower to appear and slowly progressive. A difference in ferrokinetic pattern between the chlorethylamines and busulphan was also noted. The dissimilarity in ferrokinetic patterns may indicate a difference not only in mechanism of these agents on proliferating normoblasts but also in the inhibitory effects on the acceptance of iron by the red cell precursors and other body iron pools.