Stability of solutions of antineoplastic agents during preparation and storage for in vitro assays. General considerations, the nitrosoureas and alkylating agents

Microphysiological Drug-Testing Platform for Identifying Responses to Prodrug Treatment in Primary Leukemia

Despite increasing survival rates of pediatric leukemia patients over the past decades, the outcome of some leukemia subtypes has remained dismal. Drug sensitivity and resistance testing on patient-derived leukemia samples provide important information to tailor treatments for high-risk patients. However, currently used well-based drug screening platforms have limitations in predicting the effects of prodrugs, a class of therapeutics that require metabolic activation to become effective. To address this issue, a microphysiological drug-testing platform is developed that enables co-culturing of patient-derived leukemia cells, human bone marrow mesenchymal stromal cells, and human liver microtissues within the same microfluidic platform. This platform also enables to control the physical interaction between the diverse cell types. Herein, it is made possible to recapitulate hepatic prodrug activation of ifosfamide in their platform, which is very difficult in traditional well-based assays. By testing the susceptibility of primary patient-derived leukemia samples to the prodrug ifosfamide, sample-specific sensitivities to ifosfamide in primary leukemia samples are identified. The microfluidic platform is found to enable the recapitulation of physiologically relevant conditions and the testing of prodrugs including short-lived and unstable metabolites. The platform holds great potential for clinical translation and precision chemotherapy selection.

Inhibition of thioredoxin reductase but not of glutathione reductase by the major classes of alkylating and platinum-containing anticancer compounds

Mammalian thioredoxin reductase (TrxR) is important for cell proliferation, antioxidant defense, and redox signaling. Together with glutathione reductase (GR) it is the main enzyme providing reducing equivalents to many cellular processes. GR and TrxR are flavoproteins of the same enzyme family, but only the latter is a selenoprotein. With the active site containing selenocysteine, TrxR may catalyze reduction of a wide range of substrates, but can at the same time easily be targeted by electrophilic compounds due to the extraordinarily high reactivity of a selenolate moiety. Here we addressed the inhibition of the enzyme by major anticancer alkylating agents and platinum-containing compounds and we compared it to that of GR. We confirmed prior studies suggesting that the nitrosourea carmustine can inhibit both GR and TrxR. We next found, however, that nitrogen mustards (chlorambucil and melphalan) and alkyl sulfonates (busulfan) efficiently inhibited TrxR while these compounds, surprisingly, did not inhibit GR. Inhibitions were concentration and time dependent and apparently irreversible. Anticancer anthracyclines (daunorubicin and doxorubicin) were, in contrast to the alkylating agents, not inhibitors but poor substrates of TrxR. We also found that TrxR, but not GR, was efficiently inhibited by both cisplatin, its monohydrated complex, and oxaliplatin. Carboplatin, in contrast, could not inhibit any of the two enzymes. These findings lead us to conclude that representative compounds of the major classes of clinically used anticancer alkylating agents and most platinum compounds may easily target TrxR, but not GR. The TrxR inhibition should thereby be considered as a factor that may contribute to the cytotoxicity seen upon clinical use of these drugs.

Mucocutaneous cholinergic system is targeted in mustard-induced vesication

The purpose of this research is to elucidate the pharmacological mechanism mediating vesicating effects of sulfur mustard (HD) and identify an antidote to its action. HD causes blisters because epithelial cells lose their attachments. Epithelial cell adhesion is under control of the local cytotransmitter acetylcholine (ACh) working through the muscarinic and nicotinic receptor, mAChR and nAChR, classes expressed by epithelial cells. In this study, nitrogen mustard (NM)-a structural analog of HD-was used to elucidate the mechanism of vesicating effects of mustards in mucocutaneous tissues. NM caused cell detachment and cholinergic agents antagonized its effect. Radioligand binding inhibition experiments showed that NM binds to the ligand-binding site of ACh receptors (AChRs) of both classes. Ligation of AChRs on the cell membrane of keratinocytes (KC) and bronchial epithelial cells (BEC) with NM increased total esterolytic activity of serine proteinases (TEASP). Antagonists of both classes of AChRs, atropine and mecamylamine, diminished NM-induced changes, suggesting that the pathobiological effects of NM on KC and BEC result from an agonist-like degradation of ligated AChRs, predominantly of the muscarinic class. Thus, biological effects of NM on cell adhesion were antagonist-like, whereas its pharmacological effect on TEASP was agonist-like. These findings support a hypothesis that pharmacologic protection from the vesicating action of HD can be achieved by using cholinergic drugs.

Stabilization and preformulation of anticancer drug--SarCNU

The stability of SarCNU (NSC364432), 1-(2-chloroethyl)-3-sarcosinamide-1-nitrosourea in several pharmaceutically acceptable solvents was investigated by high pressure liquid chromatography (HPLC). The influences of light, ionic strength, pH, buffer concentration, and the following excipients: benzyl alcohol, ascorbic acid, sodium bisulfite, and disodium EDTA were studied at room temperature. The stability of the drug was also determined in water, EtOH, PG, Capmul PG, DMSO, and in different combinations of these cosolvents at four different temperatures. The degradation of the drug, which is catalyzed not only by general but also by specific acid and base, follows first order kinetics. Antioxidants, EDTA, and light have no effect on the degradation rate, suggesting oxidation is not a major degradation pathway. The t(90) in pure cosolvent is 25-50 times higher than that in water or semi-aqueous vehicles. Neat EtOH can be used to store the drug in a nonaqueous concentrate that is diluted with aqueous solvent prior to injection.

Modulation of growth and radiochemosensitivity of human malignant glioma cells by acidosis

BACKGROUND

Glioblastoma commonly is characterized by hypoxia and acidosis and the histologic features of tissue necrosis and neovascularization. Current approaches of adjuvant radiochemotherapy for patients with glioblastoma have only a modest impact on the natural course of this disease.

METHODS

The authors examined the effects of acidosis on growth and response to irradiation and chemotherapy in cultured human malignant glioma cells.

RESULTS

The authors found that mild acidosis (pH 7.0) inhibited the growth of cell lines that retained wild type p53 activity but did not inhibit the growth of cell lines that were devoid of p53 function. Transfer of a dominant-negative p53 gene into p53 wild type cells failed to override the acidosis-conferred growth arrest, suggesting that loss of p53 activity per se does not mediate escape from acidosis-induced growth inhibition. Moderate acidosis (pH 6.6) inhibited the growth of all cell lines. Acidosis-mediated growth arrest was not associated with a specific type of cell cycle arrest, e.g., in G0/G1 or G2/M phase. Acidosis did not result in consistent changes in radiosensitivity; however, it enhanced the cytotoxic effects of lomustine but conferred protection from topotecan, vincristine, teniposide, and cisplatin cytotoxicity. Lomustine exhibited enhanced stability at low pH, providing a putative mechanism for the enhanced cytotoxic effects of lomustine in acidotic conditions. Decreased sensitivity to the other drugs did not result from altered multidrug resistance drug transport activity.

CONCLUSIONS

Taken together, the current results suggest that tissue acidosis may be an important determinant of glioma cell responses to adjuvant radiochemotherapy. The superior activity of nitrosoureas, such as lomustine, compared with other agents in patients with glioblastoma may result in part from prolonged drug stability in an acidotic microenvironment.

Use of pure t-butanol as a solvent for freeze-drying: a case study

1-(2-Chloroethyl)-3-sarcosinamide-1-nitrosourea, (SarCNU) (NSC-364432) is a new antitumor drug that is of interest to the National Cancer Institute. It is intended for use as an intravenous injection. Although SarCNU is sufficiently soluble in water to obtain the desired dosage, it is highly unstable. Its T(90) in aqueous solution at room temperature is less than 6 h. Neat tertiary butyl alcohol (TBA), a low toxicity, high vapor pressure and low melting solvent, was determined to be an excellent freeze-drying medium. Lyophilization of SarCNU from pure TBA produces a uniform cake composed of needle-shaped crystals. Thermal analysis and gas chromatography indicate that the cake contains less than 0.001% residual solvent. The SarCNU cake can be readily reconstituted with either water or an aqueous solution of 40% propylene glycol and 10% ethanol. The reconstituted solutions are stable for 4 and 13 h, respectively.

In vitro concentration response studies and in vitro phase II tests as the experimental basis for regional chemotherapeutic protocols

The theoretical pharmacologic benefit of regional vs. systemic chemotherapy is defined and the concentration response behavior of cytostatic drugs and their optimal exposure times are described with human cancer cell lines (HT29, NMG64/84) and fresh human tumor cell suspensions in the human tumor colony assay (HTCA). The theoretical pharmacological advantages are 5.8 to 6 for adriamycin (ADM), 8 for cisplatinum (CDDP), 6.3 for epidoxorubicin (EPI), 22 to 58 for 5-fluorouracil (5FU), 4.6 for mitomycin C (MMC), and 6.3 for mitoxantrone (NOV). The drugs differed in their cytotoxic potency in vitro and thus also potential efficacy for regional chemotherapy; however, all but 5-fluorodeoxyuridine (5FUDR) exerted cytotoxicity dependent on exposure time and concentration. On average, elevation of the test concentrations by 1 lg doubled responses in fresh human tumor cell suspensions. From these results and clinical considerations, optimal times were defined for the regional chemotherapy strategies of hepatic artery infusion, intraperitoneal instillation, and chemoembolisation as performed at our institution.

Internal morphology of poly(D,L-lactide-co-glycolide) BCNU-loaded microspheres. Influence on drug stability

The solvent extraction/evaporation process has been used to form poly(D,L-lactide-co-glycolide) (PLAGA) BCNU-loaded microspheres designed for use as intracranial controlled-release implants. Their actual payload could reach 25% with a 20-50 microns size distribution. Scanning electron microscopy showed that such carriers had a smooth surface and a spherical geometry. Differential scanning calorimetry analyses carried out on drug-loaded microspheres established that the PLAGA Tg was markedly shifted towards the low temperatures along with the disappearance of the BCNU melting endotherm. Annealing experiments performed at room temperature did not induce any change of the loaded microsphere DSC profiles. These features indicated that the BCNU acted as a plasticizer for the coating material and formed with it a solid solution. Similarly, stability of encapsulated BCNU was assessed in different conditions of storage. It appeared that drug degradation increased with temperature increase: 5.4, 8.8, 32.4 and 51.2% of decomposition after 3 month storage at -18, 4, room temperature (RT) and 37 degrees C respectively. Since the free drug was stable at 4 degrees C and experienced only 10.6% decomposition at RT during the same storage time, the state of solid solution involving the intimate mixing of the drug and the polyester in the matrix favors a progressive decomposition of BCNU. However, keeping the microspheres 6 months at -18 degrees C or 3 months at 4 degrees C prevents a loss of drug superior to 10%.

A randomised study of bolus vs continuous pump infusion of ifosfamide and doxorubicin with oral etoposide for small cell lung cancer

One hundred and fifty-nine previously untreated patients with small cell lung cancer (SCLC), who were not eligible for intensive chemotherapy, were entered into a randomised study of intravenous (i.v.) doxorubicin and ifosfamide (with mesna) and oral etoposide. The i.v. drugs were given either by bolus therapy or by a continuous infusion (CI) pump over 7 days via a central venous line. Therapy was given for 6 weeks only. On weeks 1, 3 and 5 IV doxorubicin 35 mg m-2 was given with 5 days of oral etoposide 100 mg m-2 daily. On weeks 2, 4 and 6 IV ifosfamide 5 g m-2 was given with equidose mesna. The overall median survival was 25 weeks for patients in the bolus arm and 30 weeks for the CI therapy (P = 0.45). The overall response rate was 64% (18% complete response-CR) and 69% (30% CR) respectively (P = 0.13). The median WHO score for haematological toxicity was 4 for bolus therapy and 3 for CI therapy (P = 0.0007). Despite a trend for less supportive care for patients on CI therapy there were no significant differences in the use of i.v. antibodies and blood or platelet transfusions. There were fewer treatment delays due to myelotoxicity in the CI arm (P = 0.04). The median WHO score for non-haematological toxicity was 2 in both treatment groups. There was significantly less nausea (P = 0.037) but more mucositis (P = 0.01) in the CI arm. Weekly chemotherapy using CI treatment was as effective as bolus therapy. It was well accepted by patients. The assessment of quality of life in a subgroup of patients showed a statistically significant reduction in anxiety and depression for both groups of patients during therapy.

2 chlorodeoxyadenosine activity and cross resistance patterns in primary cultures of human hematologic neoplasms

2-Chlorodeoxyadenosine (2-CDA) is an adenosine deaminase resistant analogue of deoxyadenosine which has shown clinical activity in human hematologic neoplasms. The exact mode of action of this drug remains the subject of investigation. We applied the Differential Staining Cytotoxicity (DiSC) assay to 50 human tumour specimens obtained from patients with a variety of hematologic malignancies to characterise the activity spectrum of 2-CDA. We evaluated the disease-specific activity of this agent in vitro and compared its relative cytotoxicity with that of other antineoplastic agents in current clinical use. Comparisons were conducted against nitrogen mustard, doxorubicin, vincristine and cytosine arabinoside. Our results indicate that 2-CDA has activity in myeloid and many lymphoid neoplasms but that multiple myeloma specimens reveal significant resistance. Cross resistance studies reveal a correlation between 2-CDA and the alkylator nitrogen mustard but no correlation between 2-CDA and doxorubicin, vincristine nor cytosine arabinoside. The results suggest 2-CDA activity in many human hematologic neoplasms with the clear exception of multiple myeloma and further suggest a relationship between this agent and alkylators of the mustard class. The DiSC assay may provide useful insights in the pre-clinical evaluation of new antineoplastic drugs and may help to elucidate drug activities and mechanisms of action.

Pharmacokinetics and cytotoxicity of B.3839, a molecular combination of 5-fluorouracil and N-(2-chloroethyl)-N-nitrosourea, in a mouse model

B.3839 is the prototype compound in a series of novel molecular combinations of chloroethylnitrosoureas and 5-fluorouracil(5-FU) and has been tested against MAC tumours in mice. Previous studies have shown it is moderately active against MAC15A and highly active against MAC13 though this activity is dependent on route of administration. The aim of this study was to determine whether bioavailability could explain this difference in anti-tumour activity. Plasma levels of B.3839 and 5-FU after i.p. and oral administration were measured using HPLC. Non tumour-bearing and MAC26 bearing mice gave almost identical plasma profiles after i.p. administration with the Cmax being 29.8 and 30.4 micrograms ml-1 and t1/2 16 and 15 min. The AUCs were 15.3 and 13.9 micrograms h ml-1 suggesting tumour load had no influence over plasma levels. Oral administration gave a much lower Cmax of 8.0 micrograms ml-1 but an AUC of 15.2 micrograms h ml-1 due to a longer terminal t1/2 (94 min) giving 99% bioavailability. Levels of 5-FU release from B.3839 by either route were considered too small to influence anti-tumour activity. Cytotoxicity assays in vitro against the MAC lines gave IC70 values of 5.3, 13.8 and 8.6 micrograms ml-1 for MAC 26, 13 and 15A respectively after a one hour exposure. Bone marrow toxicity was shown to be less severe than that of TCNU which is currently in clinical trials. The results show bioavailability alone is not enough to explain tumour response. There appears to be a need for a threshold concentration (C) to be maintained for a period of time (t).

The inhibition of DNA synthesis in chronic lymphocytic leukaemia cells by chlorambucil in vitro

The inhibition of 3H-thymidine incorporation into the DNA of mitogen-stimulated lymphocytes from patients with chronic lymphocytic leukaemia by chlorambucil was measured in vitro and the results related to clinical drug resistance. The assay proved to be both sensitive and specific showing a clear separation of those patients with responsive disease from those with disease resistant to treatment. There was evidence of primary drug resistance in untreated patients. In almost all patients who received treatment this led to increasing resistance to chlorambucil in vitro. The assay is predictive of clinical responsiveness and provides a potential means whereby new therapeutic agents and treatment modifiers may be investigated.

Cytotoxic effect of 1,3 bis (2-chloroethyl)-N-nitrosourea at elevated temperatures: Arrhenius plot analysis and tumour response

The effect of hyperthermia on the cytotoxicity of 1,3-bis-(2-chloroethyl)-N-nitrosourea (BCNU) was investigated in vitro and in vivo. Tumour cells were early-generation isotransplants of a spontaneous C3Hf/Sed mouse fibrosarcoma, FSa-II. For in vitro studies, single cell suspensions containing 1.0 x 10(6) cells/ml were treated in a water bath where a desired temperature was maintained by a constant-temperature circulator. Cell survival was determined by lung colony assay immediately thereafter. For in vivo studies the tumour cell suspensions were transplanted into the dorsal site of the C3Hf/Sed mouse foot. Tumours were treated by immersing animal feet into a constant-temperature water bath when tumours reached an average diameter of 4 mm (35 mm3). The tumour growth (TG) time or the time for one-half of the treated tumours to reach 1000 mm3 from initial treatment day was used as an endpoint. BCNU dose-cell survival curve at 37 degrees C was exponential with a D0 of 1.1 microgram/ml. Dose-cell survival curves at 37-43 degrees C were determined as a function of treatment time at pH 6.7 and 7.4. BCNU of 1 microgram/ml was added immediately before treatment. The slope of the survival curve became steeper with increasing temperature, indicating that the cytotoxic effect of BCNU was enhanced by hyperthermia. The Arrhenius plot analysis showed that activation energies at pH 6.7 and 7.4 were 53 and 51 kcal/M, respectively (no significant difference). Of interest in this analysis was that the Arrhenius plot did not show a breaking point which has been observed for other agents. Further investigation demonstrated that the decomposition of BCNU, which has been reported to be essential for production of reactive intermediates, occurred in aqueous medium at elevated temperatures. The magnitude of this decomposition depended on treatment temperature. As a result, preheated BCNU became less cytotoxic with an increase in preheating temperatures. The activation energy for this decomposition was about one-half of the activation energy for BCNU cytotoxicity. Studies in vivo indicated that the effect of BCNU was enhanced with increasing temperatures, and the enhancement was greatest when BCNU was administered i.p. immediately before hyperthermia. A glucose dose of 5 g/kg administered i.p. 60 min before hyperthermia further enhanced the antitumour effect of BCNU.

A systematic study on the chemical stability of ifosfamide

The degradation kinetics of ifosfamide in aqueous solution have been investigated over the pH region 1-13 at 70 degrees C. A stability indicating high-performance liquid chromatographic assay with UV detection was used to separate degradation products from the parent compound. The degradation kinetics were studied as related to pH, buffer composition, ionic strength, temperature and drug concentration. A pH-rate profile at 70 degrees C, obtained from (pseudo) first-order kinetic plots, was constructed after corrections for buffer effects were made. The degradation reactions of ifosfamide were found to be largely independent of pH, although proton or hydroxyl catalysis occurs at extreme pH values. Ifosfamide shows maximum stability in the pH region 4-9, corresponding to a half-life of 20 h.

Solasodine glycosides. In vitro preferential cytotoxicity for human cancer cells

Solamargine [(22R,25R)-spiro-5-en-3 beta-yl-alpha-L-rhamnopyranosyl- (1----2glu)-O-alpha-L-rhamnopyranozyl (1----4glu)-beta-D-glucopyranoze], a glycoside of solasodine preferentially inhibits the uptake of tritiated thymidine by cancer cells. In contrast, solamargine at equivalent concentration, and the mono- and diglycosides of solasodine have a limited effect on the uptake of tritiated thymidine for other cell types, including unstimulated lymphocytes and lymphocytes stimulated with Con A. In contrast the solasodine glycosides do not inhibit the uptake of tritiated thymidine by lymphocytes stimulated with PHA or PWM. The inhibition of tritiated thymidine uptake by solamargine and the mono- and di-glycosides of solasodine are dependent upon their cellular uptake by endogenous endocytic lectins (EELs). The mode of action of the solasodine glycosides, in particular solamargine, appears to be the induction of cell lysis, as determined by morphological examination.

Determination of tauromustine and its demethylated metabolites in plasma and urine

A sensitive, selective and precise high-performance liquid chromatographic method for simultaneous determination of tauromustine and its demethylated metabolites in plasma and urine has been developed. It is based on solid-phase extraction on C18 sorbent and separation on a semipolar column. The analytical procedure is described in detail. The method has been validated with respect to linearity, recovery, selectivity, precision and detection limit. The stability of the determined substances in various media has also been studied.

Sensitivity of human malignant intracranial tumors against MCNU in vitro in comparison to ACNU and BCNU

An in vitro chemosensitivity test was carried out in 50 specimen of human malignant intracranial tumors. Aim of the study was to evaluate the proportion of sensitivity against MCNU (Ranomustine) in comparison to ACNU and BCNU. 47 tests were evaluable. Mean viability of the specimen was 83.3 +/- 18.7%, mean plating efficiency was 0.068 +/- 0.051%. 9/47 settings revealed sensitivity against MCNU in vitro (ACNU: 10/47; BCNU: 16/46). There was no advantage of MCNU concerning age or sex of the patients. Brain metastases seemed to be slightly more frequent sensitive against MCNU than primary brain tumors. Cross resistance between ACNU, BCNU and MCNU was rather high. The results of this in vitro series do not encourage a clinical trial of MCNU as an alternative to the commonly used nitrosoureas.

Preanalytical considerations in drug assays in clinical pharmacokinetic studies

Many hospital pharmacy laboratories undertake drug analysis in biological fluids for the production of pharmacokinetic data. The success of such an undertaking very much depends on the selection of a suitable analytical method and a proper approach to sample collection and handling. This paper surveys the main types of biological specimens taken from the patients for pharmacokinetic drug analysis and discusses factors that affect them during or subsequent to their removal. Guidelines are provided in specimen handling and dealing with many problems which could arise prior to actual analysis. By its very nature this paper brings in many disciplines, the full details of which are well beyond its scope, however, some discussion on pharmacokinetic and bioavailability methods in relation to sampling procedures is included to put the matter into a proper perspective.

Stability of solutions of antineoplastic agents during preparation and storage for in vitro assays. III. Antimetabolites, tubulin-binding agents, platinum drugs, amsacrine, L-asparaginase, interferons, steroids and other miscellaneous antitumor agents

The stability of solutions of the antitumour antimetabolites, vinca alkaloids, podophyllotoxins, interferons, steroids and platinum drugs as well as maytansine, asparaginase, amsacrine, flavone-8-acetic acid, mitoguazone, and N-phosphonoacetyl-L-aspartate (PALA) is reviewed. Much of the published work has been done with biological, not stability-indicating, assays; thus, the relevant results should be used with caution. With this proviso, almost all of these drugs can be stored in solution for several days at room temperature or 4 degrees C. Most reports also suggest that the drugs that have been tested are stable when frozen in solution. For a number of the drugs, particular precautions are required; for instance, amsacrine should not be mixed with chloride-containing solutions, whereas cisplatin is most stable in solutions containing greater than 0.1 M chloride.

Use of the MTT assay for rapid determination of chemosensitivity of human leukemic blast cells

A microcytotoxicity assay employing a tetrazolium salt has been adapted for testing the response of human leukemic blast cells to a variety of chemotherapeutic agents. After exposure to various concentrations of drugs, the viability of fresh leukemic blast cells was measured using a tetrazolium salt, MTT, which is converted to blue formazan crystals by living cells. The amount of formazan produced was quantitated using a microtitre plate spectrophotometer. In the present study, optimal conditions for chemosensitivity testing of human leukemia samples were determined, and the relative chemosensitivity of five patient samples was tested.

Sensitivity of normal human bone marrow myeloid progenitor cells to anthracycline, cisplatin, anthracene and flavone acetic acid derivatives, and its relevance for the prediction of human plasma concentrations of anticancer drugs

Many in vitro investigations with anticancer agents are performed at concentrations equal to the peak concentrations or fractions of the peak concentrations achieved in human plasma after administration of these agents. In an effort to develop an in vitro test capable of predicting these peak plasma concentrations prior to the completion of pharmacokinetic studies, the effect of several classes of anticancer agents against normal human bone marrow myeloid progenitor cells (CFU-GM) was studied. The investigated agents included anthracycline antibiotics, cisplatin and its analogs, anthracene derivatives and two flavone acetic acid derivatives. The CFU-GM were exposed to these agents for 30-60 min. An exponential relationship between drug concentration and CFU-GM growth was observed for all compounds with the exception of the flavone acetic acid derivatives which were inactive. For the latter two compounds, an inhibition of CFU-GM growth was observed after continuous exposure. When compared to the plasma concentrations after parenteral administration of these agents, there was a very good agreement between 1/10 of the peak plasma concentration and the concentration inducing a 90% inhibition of the CFU-GM growth for the anthracycline antibiotics and anthracene derivatives. In contrast, for cisplatin and its analogs, there was a better agreement between 1/10 of the peak plasma concentration and the concentration inducing a 10% inhibition of CFU-GM growth. The combination of concentrations inducing inhibitions of 10 and 90% of the CFU-GM growth provides a range of concentrations that predict reasonably well the peak plasma concentrations of several anticancer agents and that could be used as guides for other in vitro investigations.

The relationship between membrane permeability to adriamycin and adriamycin cytotoxicity in CHO cells at elevated temperatures

The cytotoxicity of adriamycin at elevated temperatures was studied in CHO cells in vitro using a clonogenic assay. There is a significant increase in the cytotoxicity of adriamycin at temperatures which are not lethal to mammalian cells (38 degrees C-42 degrees C). The uptake of [14C]adriamycin was studied in similar conditions to determine whether the thermal enhancement of adriamycin cytotoxicity was due to an increase in membrane permeability. Although measurable increases in adriamycin uptake occur in the elevated but non-lethal temperature range, they are insufficient to explain the observed increase in cytotoxicity.

The effect of hyperthermia on the cytotoxicity of melphalan in Chinese hamster ovary cells

The heat stability of melphalan during incubation at temperatures from 37 degrees C to 45 degrees C was determined by spectrophotometric and HPLC analyses and by direct measurement of melphalan cytotoxicity using a colonogenic assay Although OD 250 changed little during exposure to temperatures up to 45 degrees C for periods of up to 1 h, the melphalan HPLC peak decreased as function of incubation time and temperature. Loss of cytotoxicity following heating paralleled the decay of the melphalan HPLC peak. Despite the inactivation of melphalan by heat, the cytotoxic effects of melphalan were enhanced at elevated temperatures from 38 degrees C to 42 degrees C and synergism was observed at lethal temperatures above 42 degrees C.

Stability of solutions of antineoplastic agents during preparation and storage for in vitro assays. II. Assay methods, adriamycin and the other antitumour antibiotics

The methods used to test drug stability are discussed in the light of two recent publications using biological assays. It is concluded that, as far as possible, stability-indicating assays should be used so that possible false results do not lead to erroneous conclusions. Many of the results of the stability studies with adriamycin were found to be at variance with each other, with a 20-fold difference in stability being reported in one case by different groups from virtually identical experiments. Definitive statements about adriamycin stability are therefore impossible, but it is clear that it is sensitive to light, adsorbs to membrane filters and containers (except polypropylene and siliconised glass), chelates metal ions and probably degrades rapidly in medium. Adriamycin's analogues may well have the same spectrum of sensitivity. Bleomycin, actinomycin D and neocarzinostatin were found to be stable for greater than or equal to 2 weeks at room temperature. All the other antitumour antibiotics investigated (except rubidazone) are stable for greater than or equal to 24 h at room temperature and longer at 5 degrees C. Almost all of them are sensitive to light and are most stable in neutral or slightly acid media, and many of them adsorb to membrane filters. They can probably all be stored frozen in solution.

In vitro growth and chemosensitivity studies of childhood cancers using clonogenic assay

We evaluated the usefulness of the recently developed Human Tumor Clonogenic Assay (HTCA) for chemosensitivity studies in childhood cancers. A total of 20 childhood cancer specimens containing 8 neuroblastomas, 4 malignant lymphomas, three hepatoblastomas, two rhabdomyosarcomas, two germinomas and one adrenal carcinoma were assayed. Overall, 65 per cent (13/20) of tumor cell specimens showed adequate colony forming ability to yield the sensitivity of anticancer drugs. The pattern of in vitro sensitivity of a particular tumor to most anticancer drugs tested was not dissimilar to the clinical experiences of these agents. The overall in vitro response rate of childhood cancers to anticancer agents was 51 per cent. A retrospective analysis of this assay revealed a true positive rate of 57 per cent and a true negative rate of 100 per cent.