Question

Ciprofloxacin inhibits the following enzyme in eukaryotic cells

• A. Topoisomerase II
• B. Topoisomerase IV
• C. Alkaline phosphatase
• D. Acetyl choline esterase

Hint:

Fluoroquinolone Targets:
Bacterial cells $\rightarrow$ DNA Gyrase (G-ve) & Topoisomerase IV (G+ve).
Eukaryotic Mammalian cells $\rightarrow$ Weak off-target inhibition of TOPOISOMERASE II.

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
Comparative molecular pharmacology of fluoroquinolones: high-affinity selective inhibition of prokaryotic type II topoisomerases (DNA gyrase) with weak off-target cross-inhibition of mammalian Topoisomerase II.

Step 2: Detailed Explanation:
Molecular target selectivity of Ciprofloxacin (Fluoroquinolone):
1. Prokaryotic Targets (High Affinity): Selectively binds and inhibits bacterial DNA Gyrase (bacterial Type II topoisomerase) and Topoisomerase IV at low nanomolar concentrations ($IC_{50} < 1\;\mu\text{M}$).
2. Eukaryotic (Mammalian) Cross-Reactivity: At substantially higher supratherapeutic concentrations ($100 - 1000\times$ higher), fluoroquinolones weakly inhibit the mammalian/eukaryotic structural ortholog Topoisomerase II (DNA Topoisomerase II), which is responsible for potential mitochondrial toxicity and chondrotoxicity in young animals.
- (Topoisomerase IV is purely prokaryotic; Alkaline phosphatase and AChE are unrelated).

Step 3: Final Answer:
Therefore, ciprofloxacin inhibits Topoisomerase II in eukaryotic cells, corresponding to option (A).