20-O-acylcamptothecin derivatives: evidence for lactone stabilization

Area of Science:

• Medicinal Chemistry
• Organic Chemistry
• Pharmacology

Background:

• Camptothecin (CPT) is a potent anticancer agent, but its clinical use is limited by poor solubility and lactone ring instability.
• Modifications at the 20-position are crucial for improving CPT's pharmacological properties.
• Understanding the stability of CPT derivatives under physiological and varying pH conditions is vital for drug development.

Purpose of the Study:

• To investigate the stability of 20-O-acyl and 20-O-ether camptothecin (CPT) derivatives in aqueous solutions.
• To compare the stability of these derivatives with the parent 20-hydroxy CPT (20-OH CPT) at physiological pH.
• To elucidate the mechanisms of lactone ring opening and CPT release under different pH conditions.

Main Methods:

• UV and NMR spectrophotometry were employed to assess the structural integrity and stability of CPT derivatives.
• High-Performance Liquid Chromatography (HPLC) was used to analyze the ring opening and degradation products.
• Studies were conducted across a range of pH values, including physiological pH (7.4) and alkaline conditions (≥8.5 and >9.5).

Main Results:

• At physiological pH (7.4), 20-O-acyl CPT derivatives exhibited significantly greater stability in their lactone form compared to 20-OH CPT.
• The lactone ring of 20-O-ether CPT derivatives opened at pH ≥ 8.5, whereas 20-O-acyl CPT derivatives remained stable.
• PEGylated and alkylated 20-O-acyl-CPT derivatives released native CPT at pH > 9.5 through exocyclic cleavage, preventing the isolation of open-chain carboxylate forms.

Conclusions:

• 20-O-acyl modification enhances the stability of the camptothecin lactone ring at physiological pH.
• 20-O-acyl CPT derivatives offer improved stability over 20-O-ether derivatives and parent CPT in relevant biological pH ranges.
• The findings provide critical insights into the chemical stability of CPT derivatives, informing the design of more stable and effective CPT-based drugs.