Two New Classes of Drugs to Target Chemotherapy Resistant and High Risk B-ALL

Abstract 2590

Survival remains less than 50% for children and young adults with relapsing acute lymphoblastic leukemia (ALL). Increases in ALL survival over the last 50 years have been due largely to modifications in the use of existing therapies rather than the development of new drugs. B-cell ALL (B-ALL) is the most common childhood malignancy. New therapies are needed to target B-ALL that is resistant to conventional therapies and/or harbors driver molecular lesions (such as IKZF deletion or dysregulated CRLF2 expression) that have been linked with high-risk B-ALL. Here we evaluate the ability of two new classes of drugs to target B-ALL that is resistant to vincristine and/or doxorubicin, as well as B-ALL with IKZF or CRLF2 lesions.

NovoMedix has recently developed two new classes of drugs with nanomolar efficacy in cell models of high-risk B-ALL (drug resistant Nalm-6, SupB15 [Ikaros deletion], and MHH-CALL-4 [CRLF-2d]) and demonstrated safety in animals. Both classes of drugs consist of novel drug-like molecules with molecular weights <400. IC_50s for representatives of each class of drugs are shown in Table I. Note that the resistant cell lines are 650 times more resistant to vincristine and 15 times more resistant to doxorubicin with little to no change in efficacy for NM814 and NM869. This indicates that these drugs could be used in combination with current standard of care therapies as well as salvage therapy for relapsed, refractory disease. Standard combination therapy is associated with systemic toxicities that have long term consequences. New drugs that enhance standard multidrug combinations without overlapping toxicities would be of great benefit. Drugs described here have been tested in animals and are safe and effective in another cancer model, resulting in significant decrease in tumor volumes with no significant decrease in animal weights and no other signs of toxicity over the course of the 40 day study.

Both NM814 and NM869 induce strong caspase activity at 16 hours that is inhibited by pan-3/7, 8, and 9 caspase inhibitors. This suggests that apoptosis is the major mechanism of cell death (confirmed by flow cytometry) and that a signaling cascade and/or multiple pathways are targeted by these drugs. Both drugs also inhibit cyclin D3 expression (assessed by Western blot) in Nalm-6 and SupB15 (and cyclin D1 in other cell lines), indicating that they induce cell cycle arrest. Furthermore, in a HeLa cell extract in vitro translation assay, both compounds inhibit protein translation, a major mechanism for regulation of cell cycle proteins, such as the cyclins. Additional mechanisms of action are divergent: B-ALL treated with NM869 continued to synthesize DNA but failed to undergo mitosis as indicated by the accumulation of hyperdiploid (4N) cells suggesting that it can act as a mitotic inhibitor; while NM814 strongly upregulated several tumor suppressor genes, including p21 and histone H2A.x in B-ALL cell lines. Ongoing studies are evaluating efficacy in high-risk primary B-ALL models. Data presented here establish these two classes of drugs as strong candidates for combination therapies to target high-risk and relapsing B-ALL with the potential for less toxic multi-drug combinations.