Previously, a series of CPT-SSA conjugates were tested for their stability in phosphate buffer/rat plasma and in vitro inhibitory activity in tumor cell growth (data not shown). Two of these conjugates, JF-10-71 and JF-10-81, displaying higher and lower stability, respectively, were chosen for further experiments in serial tumor cell lines. Also, free CPT and SSA itself were tested as controls. The results (Table 1) show that the IC50 values increased compared with CPT to JF-10-81 and further to JF-10-71 with the exception of the CA20948 cells. CPT and both conjugates were particularly effective in SSTR2-overexpressing IMR32 cells displaying IC50 values 3.1, 64.13, and 282.50 nM, respectively. SSTR2-overexpressing CA20948 cells were poorly responsive to CPT itself (IC50, 3077 nM); however, its somatostatin conjugates were actually more potent (IC50: JF-10-81, 1790 nM; JF-10-71, 1363 nM). SSA itself exhibited little effect on growth of all tested cell lines even at doses up to 10^-5 M.