Potent Inhibition of the Growth and Induction of Apoptosis of Mantle Cell Lymphoma By the Novel Anthracycline Berubicin in Vitro and in Vivo

Rituximab in combination with hyperfractionated cyclophosphamide, vincristine, doxorubicin (DOX), and dexamethasone has been a successful frontline therapy for aggressive mantle cell lymphoma (MCL), a distinct and heterogeneous subtype of non-Hodgkin lymphoma, with complete remission rates as high as 87% in patients at or below 65 years of age. However, the efficacy of rituximab in combination with hyperfractionated cyclophosphamide, vincristine, DOX, and dexamethasone comes at the expense of severe grade III-IV toxic effects, and its use is limited by de novo or acquired multidrug resistance. Berubicin (WP744; BRN) is a clinically evaluated analog of DOX that, like DOX, stabilizes cleavable complexes between DNA and topoisomerase II, leading to irreversible double-strand DNA breaks and abrogation of DNA religation. In contrast to DOX, BRN overcomes multidrug resistance by circumventing efflux mediated by ATP-binding cassette proteins like P-glycoprotein and MRP-1. BRN is also the first anthracycline derivative to effectively cross the blood-brain barrier, with demonstrated phase 1 responses in brain cancer patients. Our MCL studies demonstrated that treatment with BRN decreased cell growth threefold to sixfold more potently than DOX in all tested MCL cell lines (Mino, Jeko-1, SP53, and Granta 519) and four MCL patient samples by arresting MCL cell-cycle progression at the G2/M phase and inducing extensive apoptosis. Moreover, in a Western blot assay, Jeko-1 and Mino cells exhibited activation of caspase-3 and caspase-9 and cleavage of poly(ADP-ribose) polymerase over time, pointing to the presence of a mitochondria-mediated apoptosis pathway in BRN-treated MCL cell lines. We then assessed the in vivo activity of BRN, using DOX as a control, in MCL-bearing severe combined immunodeficient (SCID) and SCID-hu mice. Our results indicated that SCID mice given 10 mg/kg DOX survived no more than 15 days after treatment, whereas all mice given 10 mg/kg BRN survived up to 63 days after treatment. On the other hand, when BRN and DOX were administered at lower doses of 5 mg/kg in a SCID-hu MCL mouse model, similar survival durations for BRN and DOX were observed. In summary, our studies demonstrate that BRN is highly potent against MCL in vitro and displays a wider therapeutic window than DOX, delivering very promising in vivo activity in both SCID and SCID-hu MCL models. These results indicate that BRN should be evaluated in the treatment of other lymphomas and seriously considered as an effective replacement for DOX in MCL treatment. BRN’s success in Phase 1 studies in glioma patients and observed safety and effectiveness in MCL models warrant further investigation of its clinical use and combination with existing therapies in MCL patients. Disclosures Priebe: MD Anderson: Waldemar Priebe holds patents and has a financial interest in the development of berubicin. Patents & Royalties.