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Summary

The article reports important biophysical DNA targeting information for a group of medicinal natural product compounds and has implications in ethnomedical research.

Abstract

A group of four structurally related abietane diterpenes (including royleanone and 7-acetoxy-horminone) were investigated for their DNA binding capabilities using isothermal titration calorimetry (ITC), circular dichroism (CD) and fluorescence displacement spectroscopy, and a topoisomerase DNA-unwinding assay. Both ITC and CD spectroscopy data indicate that the abietane diterpenes of this study exhibit strong binding to DNA, likely preferring a DNA-groove binding mode. Binding constants (K) were found to be in the order of 106-8 M-1 and were strongly enthalpically driven. The binding of all compounds to DNA was accompanied by large negative enthalpy changes (more than -20 kcal/mol) and negative entropy changes. The substituent at the 7th position of the abietane ring system was important in determining both the magnitude of binding and the propensity to stack within their DNA binding sites, with derivatives 7-one/ene > 7-OAc/H. This is significant given the reports that the identity of the substituent at position-7 is a strong determinant for bioactivity. Although the specific CD data observed was compound-dependent, most showed strong signal perturbations around one or both of the DNA signature wavelengths (245 and 280 nm). However, we do not attribute these perturbations to DNA intercalation. Compounds that were capable of self-stacking (i.e., 7-ene and 7-one) were also able to elicit very strong positively induced CD signal (ICD) around 330 nm, as well as perturbations at higher wavelengths. Additionally, topoisomerase DNA-unwinding and ethidium fluorescence displacement assays were used to corroborate the DNA binding mode, which was found to be consistent with the abietane diterpene compounds adopting a non-intercalative DNA binding mode. These findings are significant given that other researchers have found that the identity of the substituent at position-7 is a strong determinant for bioactivity. These early findings are very promising and have far reaching implications in the field of ethnomedicine.

Research questions

1. Do the abietane diterpenes in this study bind to DNA
2. If so, how do the bind to DNA, i.e., what is the mode/mechanism of binding 
3. If they bind DNA, is there a correlation between their structures and how they bind/how strongly they bind. This relates to SAR (Structure-Activity-Relationships)

What was already known 

Plant from which the compounds were isolated has a long history of traditional usage in many Central American and Caribbean folklore cultures and is known for its medicinal benefits, including anti-microbial, anti-oxidants, anti-inflammatory as well as anti-cancer activities. That is, has been used as ethnomedicines.

What the research adds to the discussion

The research study was able to: 
1. Confirm that these abietane diterpene natural product compounds bind to (target) DNA, binding very strongly in some cases. 2. Determine how they bind to DNA 
3. Show a correlation between the structure of the compounds and their ability to bind/target DNA. 
4. Show a correlations between the structure of the compounds and their known bioactivity. This is related to term known as SAR (Structure Activity Relationship) 
5. Provide a fundamental understanding of how structural differences or changes in these compounds could potentially enhance their bioactivity and medicinal potency. 
6. Provide a potential avenue for the advancement of abietane diterpene natural products in the field of ethnomedicinal research.

Implications for society

Has implications in the field of ethnomedicine and natural products. That is, using natural sources (especially those from ethnic groups or folklore cultures) to solve and develop treatments and cures for many diseases and disorders existing in our society.

Funding 

Â鶹´«Ã½ÍÅ¶Ó Foundation