Novel photo-active labeled diagnostic and therapeutic peptides which are
conformationally constrained backbone cyclized somatostatin analogs,
having improved somatostatin receptor subtype affinity and selectivity
are disclosed. The backbone cyclized peptide analogs disclosed possess
unique and superior properties over other analogs, such as chemical and
metabolic stability, selectivity, increased bioavailability and improved
pharmacokinetics. Furthermore, the unique patterns of receptor subtype
selectivity provide compounds having improved diagnostic and therapeutic
utilities. Pharmaceutical compositions comprising the photo-active
backbone cyclized somatostatin analogs, reagents for synthesizing same,
and methods of using such compositions for diagnostic and therapeutic
purposes including optical imaging and photodynamic therapy are also
disclosed.