*3.1. Isolation and Screening of an Antitumor Compound Producing Strains*

Thirty-nine strains belonging to actinomycetes were isolated from the soil samples. The crude extracts of these isolates were examined for their cytotoxic activity at dilution concentrations of 100 μg/mL and 20 μg/mL. As a result of primary screening, fourteen strains showed cytotoxic activity to human colon tumor cell line HCT-116 (Figure 1). Due to the superior cytotoxic activity of strain NEAU-wh3-1, which inhibition rate was greater than 80% at both concentrations, further chemical investigations were performed on this strain.

**Figure 1.** Antitumor activities of extracts obtained from fourteen isolates against human colon tumor cell line HCT-116.
