The mammalian target of rapamycin inhibitor RAD001 (everolimus) synergizes with chemotherapeutic agents, ionizing radiation and proteasome inhibitors in pre-B acute lymphocytic leukemia.
BACKGROUND
Despite incremental improvements in outcomes for patients with acute lymphoblastic leukemia, significant numbers of patients still die from this disease. Mammalian target of rapamycin inhibitors have shown potential in vitro and in vivo as therapeutic agents against a range of tumors including acute lymphoblastic leukemia.


METHODS
Flow cytometry was used to evaluate drug-induced cell death in acute lymphoblastic leukemia cell lines and patients' samples. Human xenografts in immunocompromised mice were used to assess the in vivo effects of selected combinations. Pharmacological inhibitors and lentiviral small interfering ribonucleic acid knock-down of p53 were used to investigate the mechanism of cell killing involved.


RESULTS
Synergistic interactions between RAD001 and cytotoxic agents were demonstrated in vitro and in vivo, with increased caspase-dependent killing. RAD001 suppressed p53 and p21 responses, while suppression of p53 did not prevent killing, indicating p53 independence. RAD001 and cytotoxic agents activated the JUN N-terminal kinase pathway and the combination further increased JUN N-terminal kinase activation. JUN N-terminal kinase inhibition reduced synergistic cell killing by cytotoxic agents and RAD001 in pre-B acute lymphoblastic leukemia cell lines and patients' samples. Bortezomib and MG132, which activate the JUN N-terminal kinase pathway, also synergized with RAD001 in killing pre-B acute lymphoblastic leukemia cells. Killing was greater when RAD001 was combined with proteasome inhibitors than with cytotoxic drugs.


CONCLUSIONS
These observations suggest that combining mammalian target of rapamycin inhibitors with conventional chemotherapy or selected novel agents has the potential to improve clinical responses in patients with pre-B acute lymphoblastic leukemia.
Westmead Institute for Cancer Research, Westmead Millennium Institute, Westmead, NSW, 2145, Australia.
Philip
P
Saunders
Adam
A
Cisterne
Jocelyn
J
Weiss
Kenneth F
KF
Bradstock
Linda J
LJ
Bendall
D000818:Animals; D000971:Antineoplastic Combined Chemotherapy Protocols; D001897:Boronic Acids / Q000627:therapeutic use*; D000069286:Bortezomib; D045744:Cell Line, Tumor; D003131:Combined Modality Therapy; D000068338:Everolimus; D006801:Humans; D007166:Immunosuppressive Agents / Q000627:therapeutic use; D007976:Leupeptins / Q000627:therapeutic use*; D051379:Mice; D016688:Mice, Inbred NOD; D016513:Mice, SCID; D015452:Precursor B-Cell Lymphoblastic Leukemia-Lymphoma / Q000188:drug therapy / Q000473:pathology / Q000532:radiotherapy / Q000628:therapy*; D011379:Prognosis; D011480:Protease Inhibitors / Q000627:therapeutic use*; D011719:Pyrazines / Q000627:therapeutic use*; D011839:Radiation, Ionizing; D020123:Sirolimus / Q000031:analogs & derivatives* / Q000627:therapeutic use; D015996:Survival Rate; D058570:TOR Serine-Threonine Kinases / Q000037:antagonists & inhibitors*; D014916:Whole-Body Irradiation
D001897:Boronic Acids; D007166:Immunosuppressive Agents; D007976:Leupeptins; D011480:Protease Inhibitors; D011719:Pyrazines; D000069286:Bortezomib; D000068338:Everolimus; C546843:mTOR protein, mouse; D058570:TOR Serine-Threonine Kinases; C072553:benzyloxycarbonylleucyl-leucyl-leucine aldehyde; D020123:Sirolimus