**2.1 DNA intercalators as helix destabilizing agents**

#### **2.1.1 Mono-intercalators**

Historically, the first DNA intercalating compound evidencing DNA destabilization properties was acridine orange (Figure 1), a well-known dsDNA intercalating compound and a strong single-stranded DNA (ssDNA) binder. It emitted green fluorescence emission from dsDNA binding and red luminescence from ssDNA interaction. Acridine orange enhances the global helix stability but exerts local denaturation of DNA (Kapuscinski & Darzynkiewicz, 1983; 1984; Darzynkiewicz et al, 1983). Ellipticine and adriamycin (Figure 1) also induce local unzipping of the DNA and bind ssDNA (Zunino et al., 1972), in contrast with ethidium bromide (BET), highly specific to dsDNA and stabilizing DNA. Intercalation of acridine orange, ellipticine and adriamycin progressively unzip the DNA helix preferentially in heterochromatin, ribosomes and polysomes (Darzynkiewicz et al., 1983).
