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Structure-activity studies of aplysiatoxin-type tumor promoters
Abstract:
The cellular activities and responses of aplysiatoxin in vitro and in vivo are very similar to those of the diterpene 12-O-tetradecanoylphorbol-13-acetate (TPA) and the indole aklaloids teleocidin B and lyngbyatoxin A. Even though aplysiatoxin, TPA, and teleocidin B are chemically and structurally quite distinct from one another, all three compounds produce essentially the same plethora of biological effects by apparently binding to the same receptor on the cell membrane, the so-called phorboid receptor. Several aplysiatoxin-type compounds have been studied in three test systems for evaluating potential tumor-promoting activity, viz. mouse ear skin for irritation, murine dorsal skin for the induction of ornithine decarboxylase (ODC) activity, and an epidermal particulate fraction of dorsal mouse skin for the inhibition of specific binding of [3H]-TPA. Some of the compounds were tested in a 30-week two-step carcinogenesis experiment in mice. In most cases the results of the 30-week test correlated with the activities of the three preliminary tests. The overall study indicated that the hydroxyl groups on C-3, C-20, and C-30 are essential for maximum activity. Inspection of Dreiding models showed that the oxygens on C-27, C-3, and C-30 of aplysiatoxin are aligned with the oxygens on C-3, C-4, and C-20 of TPA, respectively. The latter oxygens are in functional groups that are known to be necessary for the high activity of TPA.
Insights
Aplysiatoxin and related compounds exhibit tumor-promoting activity by binding to the phorboid receptor, similar to TPA. Specific hydroxyl groups are crucial for this activity, influencing cellular responses and tumor promotion.
Area of Science:
- Marine natural products chemistry
- Chemical biology
- Toxicology
Background:
- Aplysiatoxin, 12-O-tetradecanoylphorbol-13-acetate (TPA), teleocidin B, and lyngbyatoxin A share similar cellular activities.
- These compounds, despite structural differences, bind to the phorboid receptor, mediating comparable biological effects.
Purpose of the Study:
- To evaluate the tumor-promoting potential of aplysiatoxin-type compounds.
- To identify structural features essential for the biological activity of aplysiatoxin.
Main Methods:
- In vitro and in vivo assays for tumor promotion, including mouse ear irritation and ornithine decarboxylase (ODC) induction.
- Inhibition of [3H]-TPA binding to epidermal fractions.
- Long-term (30-week) two-step carcinogenesis experiments in mice.
Main Results:
- Aplysiatoxin-type compounds demonstrated tumor-promoting activity across multiple test systems.
- Results from preliminary tests correlated well with the long-term carcinogenesis experiment.
- Hydroxyl groups at positions C-3, C-20, and C-30 were identified as essential for maximal activity.
Conclusions:
- Aplysiatoxin and its analogs possess significant tumor-promoting capabilities.
- Structural analysis suggests a specific alignment of oxygen atoms is critical for receptor binding and activity, analogous to TPA.
- The findings provide insights into the structure-activity relationships of phorboid receptor ligands.