A Screening Method for Identification of Heterochromatin-Promoting Drugs Using Drosophila

Summary

Drosophila is a widely used experimental model suitable for screening drugs with potential applications for cancer therapy. Here, we describe the use of Drosophila variegated eye color phenotypes as a method for screening small-molecule compounds that promote heterochromatin formation.

Abstract

Drosophila is an excellent model organism that can be used to screen compounds that might be useful for cancer therapy. The method described here is a cost-effective in vivo method to identify heterochromatin-promoting compounds by using Drosophila. The Drosophila's DX1 strain, having a variegated eye color phenotype that reflects the extents of heterochromatin formation, thereby providing a tool for a heterochromatin-promoting drug screen. In this screening method, eye variegation is quantified based on the surface area of red pigmentation occupying parts of the eye and is scored on a scale from 1 to 5. The screening method is straightforward and sensitive and allows for testing compounds in vivo. Drug screening using this method provides a fast and inexpensive way for identifying heterochromatin-promoting drugs that could have beneficial effects in cancer therapeutics. Identifying compounds that promote the formation of heterochromatin could also lead to the discovery of epigenetic mechanisms of cancer development.

Introduction

Heterochromatin is a condensed form of DNA that plays a central role in gene expression, in regulating chromosome segregation during cell division, and in protecting against genome instability¹. Heterochromatin has been considered to be a gene repression regulator and to protect chromosome integrity during cell mitosis^2,3. It is associated with the di- and tri-methylation of histone H3 lysine 9 (H3K9me) during lineage commitment^4,5. Moreover, recruitment of Heterochromatin Protein 1 (HP1) chromodomain proteins is also considered....

Protocol

1. Drug library preparation

1. Identify and prepare a drug library to be screened using appropriate solvent at a desired concentration (e.g., 10 mM in DMSO).
   NOTE: A specific example for a drug library is the Oncology Set III from National Cancer Institute (NCI) Developmental Therapeutics Program (DTP). Compounds in this set are provided as 20 µL at 10 mM in 100% DMSO in two 96-well PP U-bottom plates and stored at -20 °C. The NCI Plate maps, and the basic chemical data of each drug could be found at the following websites:
   

Results

This protocol was successfully used to screen compounds that promote heterochromatin formation in Drosophila, which is an efficient and low-cost in vivo system for drug development (Figure 1). We screened a small-molecule drug library, Oncology Set III, which is composed of 97 FDA authorized oncology drugs, using the DX1 strain of Drosophila melanogaster (Figure 1B). The results for a significant drug were represented .......

Discussion

Heterochromatin is a condensed form of DNA that plays a central role in regulating gene expression. It is becoming increasingly more recognized in cancer and may serve as a potential target for cancer therapy^15,16,17,18. Small-molecule compounds are commonly used in drug development due to advantages in manufacture, preservation, and metabolism in human bodies. To identify heterochromatin-promo.......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
Drosophila		DX1 strain	DX1 flies were kindly provided by James Birchler (University of Missouri)
Drosophila food media	UCSD fly kitchen
Methotrexate	NCI drug library
Dimethyl sulfoxide (DMSO)	Sigma	D2650
Ethyl alcohol	Sigma	E7023-500ML