fludarabine + cladribine + busulfan

A combination chemotherapy regimen consisting of fludarabine, cladribine, and busulfan used primarily as a conditioning regimen before hematopoietic stem cell transplantation (HSCT) for patients with hematologic malignancies. The combination works through synergistic cytotoxic effects where fludarabine and cladribine (purine nucleoside analogs) inhibit DNA synthesis and repair, creating DNA strand breaks and chromatin remodeling, while busulfan (DNA alkylating agent) creates DNA cross-links. This combination creates a "loop of death" where attempts to repair DNA damage lead to additional damage and ultimately cell death.