Clofarabine inhibits Ewing sarcoma growth through a novel molecular mechanism involving direct binding to CD99

Area of Science:

• Oncology
• Molecular Biology
• Pharmacology

Background:

• Ewing sarcoma (ES) is an aggressive pediatric bone and soft tissue cancer.
• CD99, a cell surface protein, is crucial for ES cell malignancy.
• Targeting CD99 presents a potential therapeutic strategy for ES.

Purpose of the Study:

• To identify small molecules that bind to CD99 and inhibit ES cell growth.
• To elucidate the mechanism of action of identified compounds.
• To evaluate the efficacy of these compounds in preclinical ES models.

Main Methods:

• Screening of small molecule libraries for CD99 binding.
• In vitro assays using ES and non-ES cell lines.
• Assessment of drug effects on CD99 dimerization and signaling.
• In vivo studies using ES xenografts.

Main Results:

• Two FDA-approved drugs, clofarabine and cladribine, selectively inhibited ES cell growth.
• Both drugs inhibited CD99 dimerization and downstream signaling.
• A clofarabine analog demonstrated CD99-dependent cytotoxicity independent of DNA metabolism.
• Clofarabine showed superior efficacy in inhibiting ES xenograft growth.

Conclusions:

• Clofarabine and cladribine represent a novel therapeutic approach for Ewing sarcoma by targeting CD99.
• This mechanism of action for clofarabine is distinct from its known DNA-targeting effects.
• Targeting cell surface CD99 offers a promising strategy for treating this challenging pediatric malignancy.