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Structure-activity studies of cerulenin analogues as protein palmitoylation inhibitors
D S Lawrence1, J T Zilfou, C D Smith
1Department of Pharmacology, Pennsylvania State University, Hershey, Pennsylvania 17033, USA.
Abstract:
Activation of ras oncogenes occurs in a high percentage of tumors, making the enzymes involved in the posttranslational processing of their encoded proteins (p21s) attractive targets for the development of new drugs. Although most effort has focused on farnesyl transferase, which catalyzes the first processing step, attachment of palmitate to p21 is required for optimal transformation by H-ras and N-ras. We have demonstrated that the natural product cerulenin ([2R,3S]-2,3-epoxy-4-oxo-7,10-trans,trans-dodecadienamide) inhibits the palmitoylation of H-ras- and N-ras-encoded p21s in parallel with inhibition of cell proliferation. More than 30 analogues of cerulenin, both aromatic and aliphatic, with various chain lengths and amide substitutions, have been synthesized for use in SAR studies. Studies on the inhibition of T24 cell proliferation indicate that the alpha-keto-epoxy moiety is critical for cytotoxicity, while alkyl chain length had only modest effects on potency. Several compounds inhibited the incorporation of [(3)H]palmitate into p21 in intact T24 cells, with the unsubstituted carboxamides being more active than N,N-dimethyl compounds. In contrast to the effects on palmitoylation, the only compounds which inhibited fatty acid synthase contained alkyl side chains of 12 carbons or fewer. Regression analyses indicated that inhibition of palmitoylation is more closely related to inhibition of proliferation than is inhibition of fatty acid synthase. Further characterization of the molecular pharmacology of these and analogous compounds may define a new class of drugs with antitumor activity.
Insights
The natural product cerulenin and its analogues inhibit the palmitoylation of ras proteins, crucial for tumor cell growth. This inhibition of palmitoylation, rather than fatty acid synthase, correlates with reduced cancer cell proliferation, suggesting a new drug development strategy.
Area of Science:
- Oncology
- Medicinal Chemistry
- Molecular Biology
Background:
- Ras oncogene activation is common in tumors, making its posttranslational processing enzymes drug targets.
- Palmitoylation of p21 proteins is essential for optimal transformation by H-ras and N-ras.
- Farnesyl transferase has been a primary focus, but palmitoylation is also critical.
Purpose of the Study:
- To investigate the natural product cerulenin and its analogues as inhibitors of p21 palmitoylation.
- To explore the structure-activity relationships (SAR) of cerulenin analogues for potential anticancer drug development.
- To determine the correlation between inhibition of palmitoylation, fatty acid synthase, and cell proliferation.
Main Methods:
- Synthesis and testing of over 30 cerulenin analogues with varied structures.
- Assay of p21 palmitoylation inhibition in intact T24 cells using radiolabeled palmitate.
- Measurement of T24 cell proliferation and fatty acid synthase inhibition.
Main Results:
- Cerulenin and its analogues inhibited H-ras and N-ras p21 palmitoylation and T24 cell proliferation.
- The alpha-keto-epoxy moiety of cerulenin was critical for cytotoxicity; alkyl chain length had minor effects.
- Unsubstituted carboxamides were more potent inhibitors of palmitoylation than N,N-dimethyl analogues.
- Inhibition of palmitoylation correlated better with antiproliferative effects than fatty acid synthase inhibition.
Conclusions:
- Cerulenin analogues represent a promising new class of anticancer agents targeting p21 palmitoylation.
- Inhibition of protein palmitoylation is a viable strategy for developing drugs against ras-driven tumors.
- Further research into the molecular pharmacology of these compounds could lead to novel therapeutics.