Natural organic compounds that affect to microtubule functions

Area of Science:

• Biochemistry and Molecular Biology
• Cell Biology
• Pharmacology

Background:

• Microtubules (MTs), essential for cell division and function, are composed of tubulin (TN) and associated proteins.
• Antimitotic agents, which interfere with MT function, are crucial for cancer therapy and biochemical research.
• Many antimitotic agents bind to beta-TN at specific sites, including the colchicine (CLC) and vinblastine (VLB) sites.

Purpose of the Study:

• To investigate the binding interactions of various VLB-site ligands with tubulin.
• To identify and characterize novel binding sites on tubulin for antimitotic agents.
• To understand the mechanisms of drug resistance related to tubulin-binding agents.

Main Methods:

• Studied a variety of natural antimitotic agents, including rhizoxin (RZX), ansamitocin P-3 (ASMP3), phomopsin A (PMSA), dolastatin 10 (DLS10), ustiloxins (USL), and arenastation A (ARSA).
• Identified a distinct RZX/MAY-binding site on beta-tubulin, partially overlapping with the VLB-site.
• Generated and analyzed RZX-resistant beta-tubulin gene mutants in Aspergillus nidulans to elucidate drug-target interactions.

Main Results:

• PMSA, DLS10, USLs, and ARSA bind to the newly identified RZX/MAY-binding site on beta-tubulin.
• A single amino acid alteration (Asn-to-Ile at position 100) in beta-tubulin conferred resistance to RZX, ASMP3, and ARSA.
• These natural ligands exhibit potent cytotoxicity against tumor cells, with varying activity against fungal strains.

Conclusions:

• A distinct RZX/MAY-binding site on beta-tubulin exists, offering new targets for drug development.
• Understanding tubulin-drug interactions at this site is crucial for developing effective antimitotic agents.
• The identified resistance mechanism provides insights into overcoming drug resistance in cancer and fungal infections.