Effects of cell density on drug-induced cell kill kinetics in vitro (inoculum effect)

Imetelstat-mediated alterations in fatty acid metabolism to induce ferroptosis as a therapeutic strategy for acute myeloid leukemia

Telomerase enables replicative immortality in most cancers including acute myeloid leukemia (AML). Imetelstat is a first-in-class telomerase inhibitor with clinical efficacy in myelofibrosis and myelodysplastic syndromes. Here, we develop an AML patient-derived xenograft resource and perform integrated genomics, transcriptomics and lipidomics analyses combined with functional genetics to identify key mediators of imetelstat efficacy. In a randomized phase II-like preclinical trial in patient-derived xenografts, imetelstat effectively diminishes AML burden and preferentially targets subgroups containing mutant NRAS and oxidative stress-associated gene expression signatures. Unbiased, genome-wide CRISPR/Cas9 editing identifies ferroptosis regulators as key mediators of imetelstat efficacy. Imetelstat promotes the formation of polyunsaturated fatty acid-containing phospholipids, causing excessive levels of lipid peroxidation and oxidative stress. Pharmacological inhibition of ferroptosis diminishes imetelstat efficacy. We leverage these mechanistic insights to develop an optimized therapeutic strategy using oxidative stress-inducing chemotherapy to sensitize patient samples to imetelstat causing substantial disease control in AML.

Fenbendazole Suppresses Growth and Induces Apoptosis of Actively Growing H4IIE Hepatocellular Carcinoma Cells via p21-Mediated Cell-Cycle Arrest

Bendimidazole anthelmintics (BAs) have gained interest for their anticancer activity. The anticancer activity is mediated via multiple intracellular changes, which are not consistent under different conditions even in the same cells. We investigated the anticancer activity of fenbendazole (FZ, one of BAs) under two different growth conditions. The growth rate of H4IIE cells was dose-dependently decreased by FZ only in actively growing cells but not in fully confluent quiescent cells. Apoptosis-associated changes were also induced by FZ in actively growing cells. Markers of autophagy were not changed by FZ. The number of cells was markedly increased in sub-G1 phase but decreased in S- and G2/M phases by FZ. FZ up-regulated p21 (an inhibitor of cyclin-CDK) but suppressed the expression of cell cycle-promoting proteins (cyclin D1 and cyclin B1). FZ did not affect integrin αV or n-cadherin expression as well as cell migration. Glycolytic changes (glucose consumption and lactate production) and the generation of reactive oxygen species (ROS) were not affected by FZ. Although the activity of mitogen-activated protein kinases (MAPKs) was altered by FZ, the inhibition of MAPKs did not affect the pro-apoptotic activity of FZ. Taken together, FZ selectively suppressed the growth of cells via p21-mediated cell cycle arrest at G1/S and G2/M, and resulted in apoptosis only in actively growing cells but not in quiescent cells. Glucose metabolism, ROS generation, and MAPKs are unlikely targets of FZ at least in H4IIE rat hepatocellular carcinoma cells used in this study.

Superparamagnetic Iron Oxide Nanoparticles Carrying Chemotherapeutics Improve Drug Efficacy in Monolayer and Spheroid Cell Culture by Enabling Active Accumulation

Cytotoxic and cytostatic chemotherapeutics act by attacking rapidly dividing tumor cells, predominantly affecting malignant tissue and to a certain degree preserving healthy cells. Nonetheless, severe side effects are caused as quickly proliferating healthy cells such as hematopoietic precursors and mucous membranes are impaired as well. This limits the administered dose and eventually allows tumor cells to escape treatment. In order to increase intratumoral drug concentration and simultaneously reduce systemic side effects, nanoparticles have come into focus as drug carriers. The functionalization of superparamagnetic iron oxide nanoparticles (SPIONs) with chemotherapeutics such as mitoxantrone (MTO) enables targeted drug transport by using magnetic forces. Here, we investigate SPIONs consisting of individual iron oxide cores of 10 nm in diameter and a total hydrodynamic diameter of 53 ± 0.8 nm as a transporting system for MTO. Comparing the killing efficacy in monolayer cell culture and multicellular tumor spheroids of HT-29 cells, we show that spheroids tolerate considerably higher doses of nanoparticle-loaded MTO. Therefore, dose predictions from conventional monolayer cell cultures are often misleading for in vivo applications. This was true for both soluble and nanoparticle-bound MTO. Using flow chambers mimicking in vivo blood flow, we furthermore demonstrate that SPIONs can magnetically accumulate MTO. We conclude that SPIONs can function as an effective delivery platform to increase local drug concentrations, thereby potentially overcoming chemotherapy resistance of cells.

In Vitro Research Reproducibility: Keeping Up High Standards

Concern regarding the reproducibility of observations in life science research has emerged in recent years, particularly in view of unfavorable experiences with preclinical in vivo research. The use of cell-based systems has increasingly replaced in vivo research and the application of in vitro models enjoys an ever-growing popularity. To avoid repeating past mistakes, high standards of reproducibility and reliability must be established and maintained in the field of in vitro biomedical research. Detailed guidance documenting the appropriate handling of cells has been authored, but was received with quite disparate perception by different branches in biomedical research. In that regard, we intend to raise awareness of the reproducibility issue among scientists in all branches of contemporary life science research and their individual responsibility in this matter. We have herein compiled a selection of the most susceptible steps of everyday in vitro cell culture routines that have the potential to influence cell quality and recommend practices to minimize the likelihood of poor cell quality impairing reproducibility with modest investment of time and resources.

Engineering a Cell Home for Stem Cell Homing and Accommodation

Distilling complexity to advance regenerative medicine from laboratory animals to humans, in situ regeneration will continue to evolve using biomaterial strategies to drive endogenous cells within the human body for therapeutic purposes; this approach avoids the need for delivering ex vivo-expanded cellular materials. Ensuring the recruitment of a significant number of reparative cells from an endogenous source to the site of interest is the first step toward achieving success. Subsequently, making the "cell home" cell-friendly by recapitulating the natural extracellular matrix (ECM) in terms of its chemistry, structure, dynamics, and function, and targeting specific aspects of the native stem cell niche (e.g., cell-ECM and cell-cell interactions) to program and steer the fates of those recruited stem cells play equally crucial roles in yielding a therapeutically regenerative solution. This review addresses the key aspects of material-guided cell homing and the engineering of novel biomaterials with desirable ECM composition, surface topography, biochemistry, and mechanical properties that can present both biochemical and physical cues required for in situ tissue regeneration. This growing body of knowledge will likely become a design basis for the development of regenerative biomaterials for, but not limited to, future in situ tissue engineering and regeneration.

Engineered Breast Cancer Cell Spheroids Reproduce Biologic Properties of Solid Tumors

Solid tumors develop as 3D tissue constructs. As tumors grow larger, spatial gradients of nutrients and oxygen and inadequate diffusive supply to cells distant from vasculature develops. Hypoxia initiates signaling and transcriptional alterations to promote survival of cancer cells and generation of cancer stem cells (CSCs) that have self-renewal and tumor-initiation capabilities. Both hypoxia and CSCs are associated with resistance to therapies and tumor relapse. This study demonstrates that 3D cancer cell models, known as tumor spheroids, generated with a polymeric aqueous two-phase system (ATPS) technology capture these important biological processes. Similar to solid tumors, spheroids of triple negative breast cancer cells deposit major extracellular matrix proteins. The molecular analysis establishes presence of hypoxic cells in the core region and expression of CSC gene and protein markers including CD24, CD133, and Nanog. Importantly, these spheroids resist treatment with chemotherapy drugs. A combination treatment approach using a hypoxia-activated prodrug, TH-302, and a chemotherapy drug, doxorubicin, successfully targets drug resistant spheroids. This study demonstrates that ATPS spheroids recapitulate important biological and functional properties of solid tumors and provide a unique model for studies in cancer research.

Aggregation Effects and Population-Based Dynamics as a Source of Therapy Resistance in Cancer

OBJECTIVE

Evolution of resistance allows cancer cells to adapt and continue proliferating even when therapy is initially very effective. Most investigations of treatment resistance focus on the adaptive phenotypic properties of individual cells. We propose that the resistance of a single cell to therapy may extend beyond its own phenotypic and molecular properties and be influenced by the phenotypic properties of surrounding cells and variations in cell density. Similar variation exists in population densities of animals living in groups and can significantly affect the outcome of an external threat.

METHODS

We investigate aggregation effects in cancer therapy using Darwinian models that integrate phenotypic properties of individual cells and common population effects found in nature to simulate the dynamics of resistance and sensitivity in the diverse cellular environments within cancers.

RESULTS

We demonstrate that the density of cancer cell populations can profoundly influence response to chemotherapy independent of the properties of individual cells. Most commonly, these aggregation effects benefit the tumor allowing cells to survive even with phenotypic properties that would render them highly vulnerable to therapy in the absence of population effects.

CONCLUSION

We demonstrate aggregation effects likely play a significant role in conferring resistance to therapy on tumor cells that would otherwise be sensitive to treatment.

SIGNIFICANCE

The potential role of aggregation in outcomes from cancer therapy has not been previously investigated. Our results demonstrate these dynamics may play a key role in resistance to therapy and could be used to design evolutionarily-enlightened therapies that exploit aggregation effects to improve treatment outcomes.

Life in 3D is never flat: 3D models to optimise drug delivery

The development of safe, effective and patient-acceptable drug products is an expensive and lengthy process and the risk of failure at different stages of the development life-cycle is high. Improved biopharmaceutical tools which are robust, easy to use and accurately predict the in vivo response are urgently required to help address these issues. In this review the advantages and challenges of in vitro 3D versus 2D cell culture models will be discussed in terms of evaluating new drug products at the pre-clinical development stage. Examples of models with a 3D architecture including scaffolds, cell-derived matrices, multicellular spheroids and biochips will be described. The ability to simulate the microenvironment of tumours and vital organs including the liver, kidney, heart and intestine which have major impact on drug absorption, distribution, metabolism and toxicity will be evaluated. Examples of the application of 3D models including a role in formulation development, pharmacokinetic profiling and toxicity testing will be critically assessed. Although utilisation of 3D cell culture models in the field of drug delivery is still in its infancy, the area is attracting high levels of interest and is likely to become a significant in vitro tool to assist in drug product development thus reducing the requirement for unnecessary animal studies.

Interdependence of initial cell density, drug concentration and exposure time revealed by real-time impedance spectroscopic cytotoxicity assay

We investigated the combined effect of the initial cell density (12,500, 35,000, 75,000, and 100,000 cells cm(-2)) and concentration of the anti-cancer drug doxorubicin on HeLa cells by performing time-dependent cytotoxicity assays using real-time electrochemical impedance spectroscopy. A correlation between the rate of cell death and the initial cell seeding density was found at 2.5 μM doxorubicin concentration, whereas this was not observed at 5 or 100 μM. By sensing the changes in the cell-substrate interaction using impedance spectroscopy under static conditions, the onset of cytotoxicity was observed 5 h earlier than when using a standard colorimetric end-point assay (MTS) which measures changes in the mitochondrial metabolism. Furthermore, with the MTS assay no cytotoxicity was observed after 15 h of incubation with 2.5 μM doxorubicin, whereas the impedance showed at this time point cell viability that was below 25%. These results indicate that impedance detection reveals cytotoxic events undetectable when using the MTS assay, highlighting the importance of combining impedance detection with traditional drug toxicity assays towards a more in depth understanding of the effect of anti-cancer drugs on in vitro assays. Moreover, the detection of doxorubicin induced toxicity determined with impedance under static conditions proved to be 6 times faster than in perfusion culture.

High cell density attenuates reactive oxygen species: implications for in vitro assays

In vitro cell-based assays are an essential and universally used step in elucidation of biological processes as well as in drug development. However, results obtained depend on the validity of protocols used. This statement certainly pertains to in vitro assays of oxidative stress. The holy grail of in vitro models is reliability and predictability of outcomes that relate to a single variable like addition of hydrogen peroxide or xanthine oxidase. Without such validated outcomes, comparison of results among different laboratories is not possible. Achieving this goal requires a thorough understanding of the complex interplay between the cells, their environment, and the experimental assays. Furthermore, as this knowledge is attained, it must be disseminated and used to update and standardize existing protocols. Here, we confirm and extend the effect of pyruvate and cell density on in vitro oxidative stress assays. Cell viability was assessed using a colorimetric assay measuring the reduction of a tetrazolium salt (XTT) into a colored formazan dye. Extracellular hydrogen peroxide concentrations were measured using the foxp3 assay. We confirmed a previously reported finding that pyruvate, a common ingredient in cell culture media, acts as an extracellular scavenger of reactive oxygen species. We also demonstrated that cell density directly correlates with resistance to oxidative stress in tissue culture. It is theorized that the protective effect due to cell density predominantly relates to intracellular factors such as reduced glutathione and extracellular factors such as catalase.

Erybraedin C and bitucarpin A, two structurally related pterocarpans purified from Bituminaria bituminosa, induced apoptosis in human colon adenocarcinoma cell lines MMR- and p53-proficient and -deficient in a dose-, time-, and structure-dependent fashion

Pterocarpans, the second group of natural isoflavonoids, have received considerable interest on account of their medicinal properties. These drugs are employed as antitoxins, but display antifungal, antiviral and antibacterial properties as well. Erybraedin C and bitucarpin A are two new structurally related pterocarpans recently purified and characterized. Bitucarpin A differs from erybraedin C for the absence of a prenyl group in 5' position and the presence of a methoxylate hydroxyl group in 7, 4' positions. These compounds proved not to be clastogens in human lymphocytes per se but displayed anticlastogenic activity against mytomicin C and bleomycin C. Here we extended the study of their antiproliferative and apoptosis-inducing mechanism on human cell lines. Two human adenocarcinoma cell lines, LoVo and HT29, as examples of slow-growing solid tumors, proficient and deficient in mismatch repair system (MMR), p53 and Bcl-2, were used to evaluate the cytotoxicity of the drugs and their effects on the cell cycle, measured by flow cytometry. Erybraedin C similarly affects the survival of HT29 (MMR +/+, p53 -/- and Bcl-2 +/+) and LoVo (MMR -/-, p53 +/+ and Bcl-2 -/-) cells (LD(50): 1.94 and 1.73 microg/ml, respectively). By contrast, bitucarpin A exhibits a differential cytotoxicity in the cell lines (LD(50): 6.00 microg/ml, HT29, and 1.84 microg/ml, LoVo). The cell cycle distributions of the LoVo and HT29 cells treated with erybraedin C lacked a specific checkpoint arrest, whereas they underwent a characteristic sub-G(1) peak, time- and drug-concentration dependent. So that apoptotic process induced by erybraedin C in both adenocarcinoma cell lines is independent of cell cycle arrest and of phenotypic status of the cells as well. By contrast, bitucarpin A affects cell cycle progression on both cell lines, inducing a transient block in G(0)/G(1) along 24-96 h, and induces apoptosis with a cell density and treatment time dependency. Similar results were obtained with the positive control drug etoposide. The programmed cellular death on human adenocarcinoma cell lines may be efficiently activated, via a topoisomerase II poison pattern, by erybraedin C, the drug containing regio-specific hydroxyl and prenyl groups. The apoptotic effect induced by the methoxylated bitucarpin A proved to be conditioned by cell density and required higher dose (5-fold-LD(50)) and longer treatment time. The present study provides evidences that erybraedin C may act as a potent growth inhibitory compound, at low and high cell density, comparable to other clinically important antineoplastic natural drugs including etoposide, on human colon adenocarcinoma cells. Bitucarpin A proved less active because it was conditioned by cell density effect, but this finding may represent a clinical advantage against early micrometastatic diseases.

Flow cytometric assay for evaluation of the effects of cell density on cytotoxicity and induction of apoptosis

BACKGROUND

We used a flow cytometric assay, which allows us to perform precise measurements within a wide range of cell concentrations to study the effect of the density of cultured cells on their sensitivity to cytotoxic compounds.

METHODS

To measure cytotoxic action, cells are plated in a 96-well plate at a density ranging from 700 to 100,000 cells/ml and are allowed to grow for 72 h in the presence of various concentrations of a cytotoxic agent. To quantitate the number of surviving cells, each sample is analyzed in a flow cytometer with equal acquisition time. Viable cells are identified by light scattering characteristics identical to those for untreated cells. To estimate the amount of viable, apoptotic, or necrotic (late apoptotic) cells, the samples are stained with Annexin V and propidium iodide.

RESULTS

Using this method, we found that the cytotoxicity of ascorbic acid for malignant lymphoid CEM-C7 cells can be increased significantly when cell density decreases, reaching a value that is typically lower than the normal physiological concentration of ascorbic acid in blood.

CONCLUSION

The flow cytometric analysis described in this study can be useful in comparing the effects of cell density on the cytotoxic action of various compounds.

Vincristine saturation of cellular binding sites and its cytotoxic activity in human lymphoblastic leukemia cells: mechanism of inoculum effect

Vincristine (VCR) is an active agent in the treatment of acute lymphoblastic leukemia (ALL). We evaluated the relationship between the cytotoxic activity of VCR and the degree of VCR saturation of cellular drug binding sites, using the MOLT-3 ALL cell line. When MOLT-3 cells at a density of 1 x 10(6) or 1 x 10(8) cells/mL of pH-controlled medium were exposed to VCR for 1 hr, its cytotoxic activity on cells at high density was 10-fold less than on cells at low density (inoculum effect). The number of VCR binding sites measured by Scatchard analysis was 9.25 x 10(6)/cell. At high cell density, the saturation of VCR binding sites was one log order less than that at low density. Irrespective of cell density, curves of cell-kill versus the degree of VCR saturation of the cellular binding sites overlapped each other. Minimal cytotoxic activity was observed at 0.3% VCR saturation, and nearly maximal cytotoxic activity occurred at about 25% saturation, with the Ic50 at about 4% saturation. These data show that the VCR-induced cell-kill effect is dependent on the degree of saturation of VCR binding sites rather than on the extracellular VCR concentration. The lesser cell-kill on cells at high density can be explained by the lack of drug molecules to sufficiently saturate cellular binding sites. This phenomenon may be responsible, at least in part, for the poor chemotherapeutic outcome of ALL patients with high leukocyte counts at presentation.

Mechanisms of resistance to combinations of vincristine, etoposide and doxorubicin in Chinese hamster ovary cells

We have isolated from Chinese hamster ovary cells, 30 sublines resistant to vincristine, doxorubicin or etoposide and 43 sublines evading treatment with a pair of these drugs. Isolated in one step and under low selective pressure, sublines were 3- to 25-fold more resistant to their selecting drug(s) than the parental cells. Possible P-glycoprotein-associated multidrug resistance was investigated through pgp gene copy number and mRNA expression level. DNA topoisomerase II alteration was evaluated from the ability of nuclear extracts to form cleavable complexes. Vincristine (all sublines) and doxorubicin (6/7 sublines) preferentially selected for pgp gene amplification and mRNA overexpression, whereas selection with etoposide resulted in a decrease of cleavable complex formation in 11 out of 13 sublines. A common pgp gene-mediated resistance was found in the 13 doxorubicin plus vincristine-selected sublines, whereas all but one of the 12 etoposide plus vincristine-resistant sublines displayed both pgp mRNA overexpression and decreased ability to form cleavable complexes. Among the 18 doxorubicin plus etoposide selected sublines, five exhibited a decreased ability to form cleavable complexes only, six exhibited pgp mRNA overexpression only and six exhibited both alterations. Overall, drug resistance could not be attributed to either mechanism in three of the 73 sublines. We conclude that under low selective pressure it is possible to find a combination of drugs which require simultaneous selection of more than one resistance mechanism; such cells emerge with very low frequency.

Cloning of human tumor cell lines in porous glass capillary tubes: a further development of the human tumor stem cell assay

The conventional human tumor stem cell assay for cloning tumor cells for drug sensitivity testing is limited by its inability to test drug combinations. In an attempt to overcome this limitation, we cloned tumor cell lines within porous glass capillary tubes. In contrast to plastic porous tubes, the porous glass membranes were transparent, and colony formation could be judged on an inverted microscope. Human as well as animal cell lines showed sufficient colony growth. Colonies formed within these porous tubes were homogeneously distributed, and their morphology was similar to those formed in the common stem cell assay. Cloning efficiency and colony size depended on the mean pore diameter of the glass membrane, with best colony growth within tubes with a pore diameter ranging from 8.5 nm to 14 nm. A linear relationship between number of cells seeded and number of grown colonies could be demonstrated for the cell lines MDA-231 and Colo 201. Colony growth achieved within porous glass capillary tubes is comparable to that achieved in Petri dishes and in nonporous tubes. We conclude that the porous capillary cloning system meets the basic suppositions for a quantitative cloning assay. Moreover, the porosity of the glass membrane offers the possibility of variable perfusion of medium and drugs. Further investigations will focus on various perfusion modalities and chemosensitivity testing.

High cell density-dependent resistance and P-glycoprotein-mediated multidrug resistance in mitoxantrone-selected Chinese hamster cells

Mitoxantrone (MIT) resistance has been studied in a colony selected from the CHO AA8 parental line in one step under a low degree of selective pressure (9 nM). The cells of the clonal isolate AA8/MIT C1(0) were sensitive to 9 nM MIT at low cell density but able to grow at high density. Parental AA8 cells were not able to grow under the latter condition. Decreased MIT accumulation (-20%) was observed at this step (step 0) in the absence of overexpression of mdr RNA coding for the drug efflux pump P-glycoprotein. Furthermore, AA8/MIT C1(0) did not exhibit cross resistance to vincristine, Adriamycin and etoposide at low cell density. During subsequent controlled growth for 2 months at high cell density in the presence of 9 nM drug, an additional selection occurred leading to a 4-fold MIT-resistant subline AA8/MIT C1(+). This subline was characterized at this step (step I) and after an additional 4 months of culture in the presence of 9 nM MIT (step II). Analysis of mdr gene expression and gene copy number showed an increase in mdr RNA and a pattern of mdr gene amplification which changed between step I and II. AA8/MIT C1(+)II exhibited a classical multidrug resistance phenotype with decreased accumulation of [14C]MIT and cross-resistance to vincristine, Adriamycin and etoposide. The ability to form the cleavable complex in the presence of etoposide in DNA topoisomerase II-containing nuclear extracts was identical in AA8/MIT C1(+)II and AA8 cell lines. These results demonstrate a new sequence of events in MIT resistance: low level of drug resistance at high cell density followed by mdr gene amplification.

Increased drug resistance of cultured human cancer cell lines in three-dimensional cellular growth assay using collagen gel matrix

We have conducted a three-dimensional cellular growth assay using collagen gel matrix with an endpoint of the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-2H tetrazolium bromide (MTT) assay, on four human gastric and colonic cancer cell lines. Three-dimensionally growing cells in collagen gel matrix were 2- to 180-fold more resistant to mitomycin C, doxorubicin, 5-fluorouracil, and cisplatin than those in monolayer culture, and these resistances were increased further when the cells increased their three-dimensionality. Furthermore, the influence of fibroblasts in the collagen gel matrix on the chemosensitivity of cancer cells was less than that in monolayer culture. Since this new assay using collagen gel matrix with an endpoint of the MTT assay was able to detect the increase of drug resistance of human cancer cell lines by three-dimensional cellular growth using a simple and convenient procedure, it was considered to be more useful than conventional monolayer cultures for evaluating the chemosensitivity of cancer cells.

Relationship between tumor cell density and drug concentration and the cytotoxic effects of doxorubicin or vincristine: mechanism of inoculum effects

When tumor cell density increases, the cytotoxic activity of certain anticancer agents, such as vincristine (VCR) and doxorubicin (DXR), progressively decreases. This phenomenon is termed the inoculum effect. Since VCR and DXR are less active in an acidic environment, we questioned whether the inoculum effects could have resulted from acidification of the medium that may have developed due to the high cell density. However, measurements of the cytotoxic activity of these agents in a pH-controlled medium revealed only a minor correction of the inoculum effects. Second, we wondered whether the inoculum effects that occurred at the high cell density might have been attributable to insufficient amounts of drugs to bind all the binding sites of the cells. To test this hypothesis, we used drug-resistant sublines, which required higher VCR or DXR concentrations for cell killing than did the parent cell line. When higher drug concentrations were used, the dose-response curves generated for low- and high-density cell populations became closer and overlapped each other, resulting in virtual disappearance of the inoculum effects. Measurements of cellular drug levels revealed that at a high cell density, cells accumulated much smaller amounts of both VCR and DXR in parallel with the positive inoculum effect. In contrast, when high concentrations of the drugs were used in drug-resistant cells, differences in the cellular drug contents between low and high cell densities became narrow. Cisplatin (DDP) belongs to a group of drugs that do not produce inoculum effects, and DDP's cytotoxic effects were not influenced by the pH-controlled medium or by the use of drug-resistant cell lines. These observations indicate that the inoculum effects are the result of the unavailability of VCR or DXR molecules to all cellular binding sites when cells at high densities are exposed to drugs. The drug concentration relative to cell density was apparently the major determinant for the inoculum effects seen in VCR- or DXR-induced cell killing.

Antitumor activities of new platinum compounds, DWA2114R, NK121 and 254-S, against human leukemia cells sensitive or resistant to cisplatin

(R)-(-)-1,1-(2-amino-methylpyrrorodine)-platinum(II) (DWA2114R), cis-1,1-cyclobutanedicarboxylato(2R)-2-methyl-1,4-butanediammin eplatinum(II) (NK121; CI-973) and glycolate-o,-o'-diammine platinum(II) (254-S; NSC375101D) are new platinum compounds developed in Japan. We studied the antitumor effects of these compounds on the cisplatin (cis-diamminedichloroplatinum, DDP)-resistant human leukemia cell line, K562/DDP. K562/DDP cells were 10-fold resistant to DDP, while the cells showed minimal cross-resistance to carboplatin (2.1-fold) and DWA2114R (3.3-fold), and were as sensitive to NK121 (1.6-fold) and 254-S (1.0-fold) as the parent cells. Increases in exposure time of K562 cells to DWA2114R resulted in progressive shifting of the dose-response curve to the left, or more effective cell growth inhibition of the cells. Time dependency indices (ID80 obtained from dose-response curve after 1 hr-exposure of K562 cells to drug followed by 72 hr-culture without drug/ID80 after 24 hr-exposure) of DDP, NK121 and 254-S were 10, 8 and 20, respectively. A multidrug resistant cell-line, MOLT-3/TMQ200, was as sensitive to platinum compounds as the parent MOLT-3 cells. Little or no influence of tumor cell density was observed in the growth inhibition of MOLT-3 or K562 cells induced by these new compounds even if cells were concentrated to a density of 10(8) cells/ml. These results indicate that NK121 and 254-S may overcome the drug resistance developed in the patients after treatment with DDP. The antitumor effect of DWA2114R is more dependent not only on drug-concentration but also on exposure time than that of DDP, suggesting that continuous infusion rather than bolus administration appears the favorable schedule in clinical trials.

Mitoxantrone. A review of its pharmacodynamic and pharmacokinetic properties, and therapeutic potential in the chemotherapy of cancer

Mitoxantrone is a dihydroxyanthracenedione derivative which as intravenous mono- and combination therapy has demonstrated therapeutic efficacy similar to that of standard induction and salvage treatment regimens in advanced breast cancer, non-Hodgkin's lymphoma, acute nonlymphoblastic leukaemia and chronic myelogenous leukaemia in blast crisis; it appears to be an effective alternative to the anthracycline component of standard treatment regimens in these indications. Mitoxantrone is also effective as a component of predominantly palliative treatment regimens for hepatic and advanced ovarian carcinoma. Limited studies suggest useful therapeutic activity in multiple myeloma and acute lymphoblastic leukaemia. Regional therapy of malignant effusions, hepatic and ovarian carcinomas has also been very effective, with a reduction in systemic adverse effects. Mitoxantrone inhibits DNA synthesis by intercalating DNA, inducing DNA strand breaks, and causing DNA aggregation and compaction, and delays cell cycle progression, particularly in late S phase. In vitro antitumour activity is concentration- and exposure time-proportional, and synergy with other antineoplastic drugs has been demonstrated in murine tumour models. Leucopenia may be dose-limiting in patients with solid tumours, whereas stomatitis may be dose-limiting in patients with leukaemia. Other adverse effects are usually of mild or moderate severity although cardiac effects, particularly congestive heart failure, may be of concern, especially in patients with a history of anthracycline therapy, mediastinal irradiation or cardiovascular disease. Mitoxantrone displays an improved tolerability profile compared with doxorubicin and other anthracyclines, although myelosuppression may occur more frequently. Thus, mitoxantrone is an effective and better tolerated alternative to the anthracyclines in most haematological malignancies, in breast cancer and in advanced hepatic or ovarian carcinoma. Further studies may consolidate its role in the treatment of these and other malignancies.

Chemosensitivity testing of small cell lung cancer using the MTT assay

A simple colorimetric test, the MTT assay, has been adapted for chemosensitivity testing of human small cell lung cancer cell lines, and fresh tumour samples. Optimal conditions for clinical chemosensitivity testing were determined using established SCLC lines. Nineteen different chemotherapeutic agents were tested, and sixteen of them were found to be cytotoxic in this assay system. The drug sensitivity of a panel of 16 SCLC cell lines was measured and compared. There was very little intraexperiment variation, but the interexperiment variation was significant. Cell lines which were derived from patients who had not received chemotherapy at the time the cell line was established were more sensitive (to all but one of the drugs) than lines derived from treated patients, and the differences were statistically significant for two of the drugs. One cell line, NCI-H209, which was derived from an untreated patient, stood out as being the most sensitive or among the most sensitive to all of the drugs tested. Another cell line, H69AR, which is a multidrug resistant subline of the cell line NCI-H69, was the most resistant to many of the natural product drugs tested. Multiple drug chemosensitivity testing was performed on eight fresh tumour samples from SCLC patients (five pleural effusions, one lymph node, and two primary tumours). It was possible to perform chemosensitivity testing on all of the clinical samples in which sufficient tumour cells were available. The drug sensitivity of the clinical samples was, in most cases, within the same range as for the cell lines. Since this assay is very rapid and simple to perform, it may have practical applications in clinical drug sensitivity testing of human tumours.

The influence of tumor cell density on cellular accumulation of doxorubicin or cisplatin in vitro

The effect of tumor cell density on the cellular pharmacokinetics of doxorubicin (DXR) and cisplatin (CDDP) was studied using MOLT-3 human acute lymphoblastic leukemia cells. As determined by the MTT assay, the growth-inhibitory effect of DXR was approx. 40 times lower when cell density was increased from 10(6) to 10(8) cells/ml (positive inoculum effect), whereas little or no influence of cell density was observed in CDDP-induced cell-growth inhibition. As measured by high-performance liquid chromatography using a fluorescence detector, the cellular accumulation of DXR showed 6- and 18-fold decreases after 1 h incubation when the cells were concentrated from 10(6) to 10(7) and 10(8) cells/ml, respectively. Only at low cell density (10(6) cells/ml) did the amount of DXR in the cells increase with increasing exposure times of up to 6 h. The DXR concentration in the supernatant that was separated from a cell suspension showing a density of 10(8) cells/ml fell to 20% of that obtained at 10(6) cells/ml. The metabolites of DXR, including Adriamycinol and Adriamycinone, were not detectable in the cell extracts or supernatants at any cell density examined. In contrast, the cellular accumulation of CDDP calculated from the platinum concentration, which was measured with a flameless atomic absorption spectrophotometer, was essentially identical at all cell densities examined; moreover, extension of the exposure period resulted in a linear increase in the amount of CDDP in the cells. CDDP concentrations in the supernatants were equally retained, irrespective of cell densities. These observations indicate that the positive inoculum effect shown in DXR-induced cell-growth inhibition results from the decreased cellular accumulation of the drug at high cell densities. We found no influence for cell density on the cellular accumulation of CDDP that might be relevant to the therapeutic potentiation of this drug at high tumor-cell density.

Pharmacokinetics and metabolism of mitoxantrone. A review

Mitoxantrone, a cytotoxic anthracenedione derivative, has given clinical evidence of beneficial activity in breast cancer, lymphoma and leukaemia. Several different mechanisms of action have been suggested to account for this. In addition to intercalation, biological effects such as electrostatic interactions with DNA, DNA-protein cross-links, immunosuppressive activities, inhibition of topoisomerase II, prostaglandin biosynthesis and calcium release have been described. Various methods of drug monitoring in biological fluids and tissues are available: the highest sensitivity has been achieved with high performance liquid chromatography with electrochemical detection, radioimmunoassay and enzyme linked immunosorbent assay. Early pharmacokinetic studies of mitoxantrone in experimental animals using radioactive material showed an extensive tissue distribution and a long terminal plasma half-life. The best fit for the plasma concentration-time curve in humans is achieved in a 3-compartment model. All studies reported a short absorption half-life of between 4.1 and 10.7 minutes, with the distribution phase being between 0.3 and 3.1 hours. In contrast, the values of the terminal half-life are quite variable, ranging from 8.9 hours to 9 days. Differences might be attributed to assay sensitivity, number and weighting of data points beyond 24 hours and coadministration drugs. Many studies showed a very large volume of distribution with sequestration of mitoxantrone in a deep tissue compartment. In autopsy studies, relatively high tissue concentrations have been measured in liver, bone marrow, heart, lung, spleen and kidney. Bile is the major route for the elimination of mitoxantrone, with lesser amounts excreted in the urine. Several metabolites have been separated, 2 of which were identified as the monocarboxylic and dicarboxylic acid derivatives. Mitoxantrone is usually administered by rapid intravenous infusion at 3-weekly intervals; other regimens include continuous infusion, daily repeated doses or weekly administration. In peritoneal carcinosis, the pharmacological advantage of intraperitoneal administration is clear. The optimal regimen for different disease categories with respect to efficacy and side-effects remains to be determined in future clinical trials.

Differential sensitivity to (dl)-5-methyltetrahydrofolate of normal CFU-GM and HL-60 cells

We studied the effect of (dl)-5-methyltetrahydrofolate on clonogenic growth of HL-60 cells in comparison with human normal CFU-GM. Seven normal bone marrow samples were tested for CFU-GM assay with or without (dl)-mTHF at concentrations ranging from 1.25 X 10(-4) to 5 X 10(-4) M. (dl)-mTHF only slightly affected CFU-GM formation, while, at the same concentrations, it showed a dose related inhibition of HL-60 colony formation, up to a complete arrest of growth at the doses of 5 X 10(-4) and 1 X 10(-3) M. The same impairment of proliferation was observed in liquid culture. These results are in keeping with reported observations, describing a different membrane system mediating "folate" transport in normal and leukemic cells.

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.

Interactions of doxorubicin and cis-platin in squamous carcinoma cells in culture

Doxorubicin (DXR) has a positive inoculum effect and penetrates poorly into the core of multicellular tumour spheroids (MTS). Cis-platin (DDP) displays neither of these characteristics. We evaluated whether combining these 2 agents would influence the cell kill effect at a tumour mass level. MTS were produced from a PC-10 squamous lung carcinoma cell line. MTS were exposed to either drug first for 1 h with different intervals between exposure. Cells were then trypsinized to a single cell suspension and subjected to clonogenic assay. Combination effects were analyzed by median effect plot analysis. The more MTS ml-1 medium, the lower the cell kill effect of DXR. Simultaneous exposure to the 2 drugs was synergistic. DXR exposure first followed by DDP was less efficacious than, or the same as, the simultaneous exposure. In contrast, DDP followed by DXR was more efficacious with the best cell kill at a 1 h interval between each drug. This phenomenon was observed even at non-toxic doses of DDP. The fluorescent microscopic study of DXR indicated that prior exposure of MTS to DDP resulted in increased DXR penetration into the MTS core leading to heightened synergism with this sequence. These data suggest that the proper combination of DXR plus DDP should be in sequence with DDP first. Clinical, toxicological and pharmacological trials of DDP administration first, followed by DXR, are warranted.

An in vitro study comparing the cytotoxicity of three platinum complexes with regard to the effect of thiol depletion

The cytotoxicity of three platinum complexes, cis-diamminedichloroplatinum(II) (cis-platin), cis-dichloro-trans-dihydroxy-cis-bis (isopropylamine) platinum(IV), (CHIP) and diammine (1, 1-cyclobutane-dicarboxylato) platinum(II) (carboplatin) on Chinese Hamster ovary (CHO) and mouse sarcoma RIF-1 cells cultured in vitro has been compared. The tumour cell line was much more sensitive to the cytotoxic action of the three agents compared to the CHO cell line. CHIP and carboplatin gave similar dose-response curves, both being much less toxic than cis-platin. The effect of thiol modification on platinum toxicity was also investigated. Substantial reduction in the intracellular non-protein sulphydryl content markedly enhanced the cytotoxicity of CHIP but had much less effect on carboplatin and cis-platin. Thiol depletion by diethylmaleate had a negligible effect on cis-platin toxicity.