In vitro bone marrow granulocyte-macrophage progenitor cultures in the assessment of hematotoxic potential of the new drugs

Immunotoxicity, genotoxicity and epigenetic toxicity of nanomaterials: New strategies for toxicity testing?

The unique properties of nanomaterials (NMs) are beneficial in numerous industrial and medical applications. However, they could also induce unintended effects. Thus, a proper strategy for toxicity testing is essential in human hazard and risk assessment. Toxicity can be tested in vivo and in vitro; in compliance with the 3Rs, alternative strategies for in vitro testing should be further developed for NMs. Robust, standardized methods are of great importance in nanotoxicology, with comprehensive material characterization and uptake as an integral part of the testing strategy. Oxidative stress has been shown to be an underlying mechanism of possible toxicity of NMs, causing both immunotoxicity and genotoxicity. For testing NMs in vitro, a battery of tests should be performed on cells of human origin, either cell lines or primary cells, in conditions as close as possible to an in vivo situation. Novel toxicity pathways, particularly epigenetic modification, should be assessed along with conventional toxicity testing methods. However, to initiate epigenetic toxicity screens for NM exposure, there is a need to better understand their adverse effects on the epigenome, to identify robust and reproducible causal links between exposure, epigenetic changes and adverse phenotypic endpoints, and to develop improved assays to monitor epigenetic toxicity.

Alternative methods in toxicology: CFU assays application, limitation and future prospective

Blood is a fluid connective tissue which plays a vital role for normal body function. It consist different type of blood cells which is continuously reproduce inside the bone marrow from hematopoietic system. Xenobiotics could be specifically toxic to the hematopoietic system and they can cause hematological disorders by disturbing the normal functions. In vitro hematopoietic colony-forming cell assays play a crucial role to evaluate potential toxic effects of new xenobiotics and also helpful in bridging the gap between preclinical toxicology studies in animal models and clinical investigations. Use of these assays in conjunction with, high-throughput screening reduces the cost and time associated with these assays. This article provides a critical view over in vitro hematopoietic colony-forming cell assays in assessment of hematotoxicity.

Paclitaxel and CYC3, an aurora kinase A inhibitor, synergise in pancreatic cancer cells but not bone marrow precursor cells

BACKGROUND

Amplification of aurora kinase A (AK-A) overrides the mitotic spindle assembly checkpoint, inducing resistance to taxanes. RNA interference targeting AK-A in human pancreatic cancer cell lines enhanced taxane chemosensitivity. In this study, a novel AK-A inhibitor, CYC3, was investigated in pancreatic cancer cell lines, in combination with paclitaxel.

METHODS

Western blot, flow cytometry and immunostaining were used to investigate the specificity of CYC3. Sulforhodamine B staining, time-lapse microscopy and colony-formation assays were employed to evaluate the cytotoxic effect of CYC3 and paclitaxel. Human colony-forming unit of granulocyte and macrophage (CFU-GM) cells were used to compare the effect in tumour and normal tissue.

RESULTS

CYC3 was shown to be a specific AK-A inhibitor. Three nanomolar paclitaxel (growth inhibition 50% (GI(50)) 3 nM in PANC-1, 5.1 nM in MIA PaCa-2) in combination with 1 μM CYC3 (GI(50) 1.1 μM in MIA PaCa2 and 2 μM in PANC-1) was synergistic in inhibiting pancreatic cell growth and causing mitotic arrest, achieving similar effects to 10-fold higher concentrations of paclitaxel (30 nM). In CFU-GM cells, the effect of the combination was simply additive, displaying significantly less myelotoxicity compared with high concentrations of paclitaxel (30 nM; 60-70% vs 100% inhibition).

CONCLUSION

The combination of lower doses of paclitaxel and CYC3 merits further investigation with the potential for an improved therapeutic index in vivo.

In vitro comparison of O4-benzylfolate modulated, BCNU-induced toxicity in human bone marrow using CFU-GM and tumor cell lines

2-Amino-O4-benzylpteridine derivatives inactivate the human DNA repair protein O6-alkylguanine-DNA alkyltransferase and have been tested as modulators of alkylating agent chemotherapy. Recently, the therapeutic potential of O4-benzylfolate (O4BF) in modulating bis-chloroethylnitrosourea (BCNU) toxicity was demonstrated in vitro using human HT29 and KB tumor lines. The current studies replicated the previous findings in HT29 and KB cells using ATP as an endpoint. However, the effective treatment conditions were severely toxic to human neutrophil progenitors called CFU-granulocyte/macrophage (CFU-GM), which could not tolerate > or =40 microM BCNU at any O4BF concentration. A lower BCNU concentration (10 microM) in combination with O4BF (2-100 microM) was only moderately tumoricidal. To screen for conditions tolerated by CFU-GM, bone marrow (BM) cells were pre-incubated (5 h) with O4BF, co-treated with O4BF and BCNU (42 h), washed, and plated to quantify CFU-GM survival. O4BF at 2 or 5 microM progressively lowered the inhibitory concentrations (ICs) for BCNU, but further increases in O4BF concentrations did not. Increasing O4BF concentrations with constant BCNU (10 microM) under the same prolonged exposure as in the human marrow study achieved only modest tumoricidal effects. In summary, the unexpected finding that normal BM cells are impacted by an agent developed to target malignant tissue refutes speculation that normal beta-folate receptor expressing hematopoietic cells will be spared. Further, the validated IC90 endpoint from the huCFU-GM assay has provided a reference point for judging the potential therapeutic effectiveness of this investigational combination in man using in vitro assays.

In vitro and animal models of drug-induced blood dyscrasias

Drug-induced blood dyscrasias can be either acute and predictable or delayed and unpredictable (idiosyncratic). The predictable toxicity is relatively easy to reproduce with in vitro models, although they may not work for drugs that require bioactivation. It is very unlikely that idiosyncratic blood dyscrasias can be modeled in vitro, although some drugs (or their reactive metabolites) that cause idiosyncratic reaction are toxic to bone marrow cells in vitro. Although the mechanisms of idiosyncratic reactions are poorly understood, there is evidence that most are due to reactive metabolites and some are immune-mediated. Therefore screening drugs for their bioactivation by myeloperoxidase, the major oxidative enzyme in bone marrow, may provide some measure of the risk that a drug will cause blood dyscrasias. Several examples of drug-induced idiosyncratic agranulocytosis, aplastic anemia and thrombocytopenia are presented, but better in vivo models are clearly needed to gain a clearer understanding of these adverse reactions.