Combining RAD001 (Everolimus) with Proteasome Inhibitors Bortezomib (Velcade) or MG132 Significantly Enhances Pre-B ALL Cell Death in Vitro.

Abstract 2743

Poster Board II-719

Mammalian target of rapamycin (mTOR) inhibitors have shown potential as novel therapeutic agents with efficacy against a wide range of tumors including precursor-B acute lymphoblastic leukemia (pre-B ALL). We have previously reported RAD001 (16μM) induces JNK pathway activation in pre-B ALL cells and that combining RAD001 with DNA damaging agents in vitro significantly enhanced JNK dependent death, via a caspase dependent mechanism. We sought to evaluate agents, which may favor JNK activation and promote JNK dependent cell death in pre-B ALL cells. Bortezomib and MG132 have both been reported to activate the JNK pathway via death receptor activation, with reported efficacy in pre-B ALL. Consistent with the literature we observed enhanced JNK pathway activation in pre-B ALL cells treated with bortezomib. Analysis of annexin V and 7AAD expression by flow cytometry utilizing JNK inhibitor SP600125 (5μM) showed that a significant proportion of pre-B ALL cell death observed with bortezomib was JNK dependent.

Combining RAD001 (4–16μM) with bortezomib in vitro (10–20nM) significantly enhanced cell death in pre-B ALL cell lines and patient cases at 24 hours. This observation was supported by equivalent observations combining MG132 (250–500nM) with RAD001 (8–16μM). The degree of enhanced killing was greater than that achieved combining RAD001 (16μM) with DNA damaging agents. Enhanced killing was also achieved at a significantly lower dose of RAD001 relative to combination therapy with DNA damage. Utilizing JNK inhibitor SP600125 (5μM) we determined that a significant proportion of enhanced killing was JNK dependent.

In conclusion we have identified two novel and clinically available agents which when combined can significantly enhance pre-B ALL cell death. Our observations suggest combining agents which induce JNK activation has the potential to enhance clinical responses in pre-B ALL, particularly for patients with advanced or relapsed disease, for whom treatment with cytotoxic chemotherapy offers little hope of improved survival. In vivo studies will provide further insight into this promising strategy.