# Isoxazole‐Based Compounds Targeting the Taxane‐Binding Site of Tubulin

## TL;DR

A new compound, 2j, targets the same site on tubulin as taxanes and shows promise in treating taxane-resistant cancers.

## Contribution

A novel steroidal isoxazole compound (2j) is developed that binds to the taxane site on tubulin and overcomes resistance in prostate cancer cells.

## Key findings

- Compound 2j binds to the taxane site on tubulin with a nanomolar K_D and stabilizes polymerized tubulin.
- 2j induces G2/M cell cycle arrest and apoptosis in docetaxel-resistant prostate cancer cells.
- The compound circumvents resistance pathways associated with taxane-based therapies.

## Abstract

Taxanes and other tubulin‐targeting medications are essential for treating advanced malignancies, especially in patients undergoing less aggressive chemotherapy. However, their clinical efficacy is often limited by significant off‐target toxicity and adverse side effects. In this study, the synthesis and characterisation of novel steroidal A‐ring‐fused isoxazoles, which were obtained through iodine‐mediated oxidative cyclization of dihydrotestosterone (DHT)‐derived α,β‐unsaturated oximes, are reported. According to mechanistic studies, the most potent compounds induced mitotic arrest and disrupted cytoskeletal integrity at low micromolar concentrations. The lead compound, 2j, notably increased the rate of tubulin polymerisation in vitro and stabilised polymerised tubulin in the cells, leading to a G2/M block of the cell cycle. Molecular docking studies indicated that 2j is bound preferably to the taxane site on tubulin, forming conserved interactions. MicroScale Thermophoresis was used to further study this binding and showed a nanomolar K
D for 2j. The fact that 2j maintained its activity in docetaxel‐resistant prostate cancer cells, demonstrating its ability to circumvent resistance pathways linked to existing therapies with taxane‐like drugs, supports its clinical relevance. Therefore, our results encourage additional research and development for its potential therapeutic use in cancer treatment, particularly in resistant cases.

Lead compound 2j targets the taxane site of tubulin with a nanomolar K
D and induces G2/M block by mitotic arrest at low micromolar doses. Prolonged mitotic arrest led to the induction of apoptosis in cancer cells, also in docetaxel‐resistant prostate cancer cells, suggesting its potential in taxane‐resistant cancer therapy.