Cytotoxicity evaluation procedure

As 1,2,5-thiadiazole analogues, potent HlV-1 reverse transcriptase inhibitors, some simple 1,2,5-oxadiazoles, compounds 4-6 (Fig. 9), have been synthesized using the traditional Wieland procedure as key for the heterocycle formation [121]. Such as thiadiazole parent compounds, derivative with chlorine atoms on the phenyl ring, i.e., 5, showed the best anti-viral activity. Selectivity index (ratio of cytotoxic concentration to effective concentration) ranked in the order of 5 > 6 > 4. The activity of Fz derivative 6 proved the N-oxide lack of relevance in the studied bioactivity. These products have been claimed in an invention patent [122]. On the other hand, compound 7 (Fig. 9) was evaluated for its nitric oxide (NO)-releasing property (see below) as modulator of the catalytic activity of HlV-1 reverse transcriptase. It was found that NO inhibited dose-dependently the enzyme activity, which is hkely due to oxidation of Cys residues [123]. 

Preliminary Cytotoxicity Testing. An essential first step is to carry out a preliminary study to evaluate the toxicity of the test material to the indicator cells, under the conditions of the main mutagenicity test. When selecting dose levels, the solubility of the test compound, the resulting pH of the media, and the osmolality of the test solutions all need to be considered. The latter two parameters have been known to induce false positive effects in in vitro mammalian tests (Brusick, 1986). The experimental procedure is carried out as follows. 

Various standards and procedures exist for the evaluation of the biological and immunotoxicity response of an implant [81] from the point of view of biocompatibility. Acute toxicity screening and in vivo implantation tests are fundamental in this respect. Cytotoxicity testing to detect the biological activity of the material on a mammalian cell monolayer is often the first step in assessing biocompatibility of a device. An international standard on the biological evaluation... 

An important immune function to evaluate in the context of immuno-deficiency, and one that represents a form of nonspecific immunity/host resistance, is the function of natural killer (NK) cells. NK cells are lymphocytes distinct from either B-cells or T-cells, which contribute to immunocompetence by mediating major histocompatibility complex-independent cytotoxicity (Lotzova 1993). For the purposes of these studies, a combined measurement of both basal and augmented NK cell function was used. In this assay, murine splenoc5des were exposed for 24 hours to various concentrations of drugs in the presence or absence of an optimum concentration of recombinant IL-2 (Thomas et al. 1993). The cells were then washed and cocultured for 4 hours with radiolabeled YAC-1 tumor cells (a murine NK-sensitive cell line). Tumor cell lysis was quantitated as described above for the CTL procedure. 

There are a growing number of studies evaluating the combination of antiangiogenic therapy with cytotoxic procedures such as chemotherapy and radiation therapy... 

Experimental controls namely, negative contfols, blanks, and positive controls should be used in all biological evaluations to accurately validate a certain procedure and compare the results between materials. Some examples of materials that may be used as positive and negative controls for cytotoxicity assays are listed in Table 7.5. 

For the direct contact tests, materials with at least one flat surface need to be nsed, although the materials can have various shapes, sizes, or physical states (eg, liquid, solid, and gel). An important factor to consider is that the sterility of the sample mnst be maintained throughout the test procedure as, for example, bacterial contamination can lead to false evaluation of cytotoxicity. In this regard, the effect of sterilization on... 

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