The use of site-selective cAMP analogs greatly advanced our understanding of the mechanism of cAMP action in growth control. It was discovered that site-selective cAMP analogs can act as novel biological agents capable of inducing growth inhibition and differentiation in a broad spectrum of human cancer cell lines, including carcinomas, sarcomas, and leukemias, without causing cytotoxicity. 8-Cl-cAMP, the most potent site-selective cAMP analog, was selected as a preclinical Phase I antineoplastic agent of the National Cancer Institute (January 27, 1988). It was the first introduction of a cAMP analog into clinical testing in over 30 years of cAMP research. Significantly, this was the first demonstration that a cAMP analog can induce its biological effect at micromolar concentrations-the physiological concentration of cAMP, as opposed to the millimolar pharmacological or cytotoxic concentrations of cAMP analogs reported in all previous literature. The discovery rendered a critical assessment that the potency of a cAMP analog in growth inhibition depends on the analog's ability to selectively modulate the RI and RII regulatory subunits of cAMP-dependent protein kinase precisely, down-regulation of RI alpha with up-regulation of RIIbeta leading to the restoration of the normal balance of these cAMP transducing proteins in cancer cells. The use of antisense strategy and retroviral vector-mediated gene transfer technology provided direct evidence that two isoforms, the RIalpha and RIIbeta regulatory subunits of cAMP-dependent protein kinase, have opposite roles in cell growth and differentiation; RIalpha being growth stimulatory while RIIbeta is a growth-inhibitory and differentiation-inducing protein. As RIalpha expression is enhanced during chemical or viral carcinogenesis, in human cancer cell lines, in primary human tumors, and in multidrug-resistant (MDR) cancer cells as opposed to non-MDR parental cells, it is a target for cancer diagnosis and therapy. 8- Cl-cAMP and RIalpha antisense oligodeoxynucleotide, those that effectively down-regulate RI and up-regulate RIIbeta provide new approaches toward differentiation therapy and chemoprevention of cancer. A Phase I clinical study of 8-Cl-cAMP has now been completed.

Agency
National Institute of Health (NIH)
Institute
National Cancer Institute (NCI)
Type
Intramural Research (Z01)
Project #
1Z01CB005216-24
Application #
5200922
Study Section
Project Start
Project End
Budget Start
Budget End
Support Year
24
Fiscal Year
1995
Total Cost
Indirect Cost
Name
Division of Cancer Biology and Diagnosis
Department
Type
DUNS #
City
State
Country
United States
Zip Code