<p>ABSTRACT</p><p>Chemotherapy is a common method used for cancer treatment. Especially when it concerns cancers that have grown invasively it seems to be the only efficient treatment due to the substances ability to reach and affect almost the entire body. One major obstacle regarding chemotherapy is that the patients often develop resistance to the cytotoxic substances used. Fluorometric microculture cytotoxicity assay (FMCA) is a method developed to measure sensitivity of tumor cells to different cytotoxic substances in vitro. The assay is based on hydrolysis of fluorescein diacetate to fluorescein by cells with intact cell membranes after incubation with drugs for 72 hours. This study investigated the impact of two methodological factors that may cause errors in the achieved results; namely the possible occurrence of drug decay during incubation and the use of an inappropriate amount of cells. These factors were tested by exposing the cytotoxic drugs to pre-incubation in absence of tumor cells for different times and to use suspensions with different concentrations of cells. The results indicated occurrence of drug decay in 3 of the 18 substances tested and that the amount of cells affected the results for most of the drugs tested but to different extent.</p>

ABSTRACT Chemotherapy is a common method used for cancer treatment. Especially when it concerns cancers that have grown invasively it seems to be the only efficient treatment due to the substances ability to reach and affect almost the entire body. One major obstacle regarding chemotherapy is that the patients often develop resistance to the cytotoxic substances used. Fluorometric microculture cytotoxicity assay (FMCA) is a method developed to measure sensitivity of tumor cells to different cytotoxic substances in vitro. The assay is based on hydrolysis of fluorescein diacetate to fluorescein by cells with intact cell membranes after incubation with drugs for 72 hours. This study investigated the impact of two methodological factors that may cause errors in the achieved results; namely the possible occurrence of drug decay during incubation and the use of an inappropriate amount of cells. These factors were tested by exposing the cytotoxic drugs to pre-incubation in absence of tumor cells for different times and to use suspensions with different concentrations of cells. The results indicated occurrence of drug decay in 3 of the 18 substances tested and that the amount of cells affected the results for most of the drugs tested but to different extent.