Table 1. Relative in vitro inhibition of Top1 by CPT, hCPT, and derivatives.

Ligand	Position			Inhibition
	10	11	20
CPT	H	H	OH	0.9*
hCPT	H	H	OH	1.0*
± 20-deoxy CPT	H	H	H	0.03**
± 20-Cl CPT	H	H	Cl	0.29**
10-OH CPT	OH	H	OH	3.5*
10,11-diF hCPT	F	F	OH	12.0*

Modified A-ring ring positions (10, 11) and E-ring position (20) are indicated for CPT/hCPT derivatives; modifications shown in italics (see Fig. 1 for CPT and hCPT structures).

*As reported by Laco et al. [15], [16].

**As reported by Wang et al. for racemic CPT derivatives [20]. All Top1 inhibition assays were performed using an end-labeled dsDNA oligonucleotide.