Letters to the Editor 1197 Acknowledgements patient subgroup characterized by very poor prognosis. J Clin Oncol 1989; 7: 119–125. This study is supported in part by the grants CA 62242, CA 107476 3 San Miguel JF, Garcia-Sanz R, Gonzalez M, Moro MJ, Hernandez JM, and CA 62242 from the National Cancer Institute, National Ortega F et al. A new staging system for multiple myeloma based on the number of S-phase plasma cells. Blood 1995; 85: Institutes of Health, Bethesda, MD and the Eastern Cooperative 448–455. Oncology Group, Boston, MA (SVR). 4 Rajkumar SV, Fonseca R, Dewald GW, Therneau TM, Lacy MQ, Kyle RA et al. Cytogenetic abnormalities correlate with the plasma P Kapoor1, S Kumar1, SJ Mandrekar2, KM Laumann2, 1 1 1 1 cell labeling index and extent of bone marrow involvement in A Dispenzieri , MQ Lacy , D Dingli , MA Gertz , myeloma. Cancer Genet Cytogenet 1999; 113: 73–77. 1 1 1 1 RA Kyle , PR Greipp , SV Rajkumar and TE Witzig 5 Garcia-Sanz R, Gonzalez-Fraile MI, Mateo G, Hernandez JM, 1 Division of Hematology, Mayo Clinic, Lopez-Berges MC, de las Heras N et al. Proliferative activity of Rochester, MN, USA and plasma cells is the most relevant prognostic factor in elderly 2Division of Biomedical Statistics and Informatics, multiple myeloma patients. Int J Cancer 2004; 112: 884–889. Mayo Clinic, Rochester, MN, USA 6 Lacy MQ, Gertz MA, Dispenzieri A, Hayman SR, Geyer S, E-mail: [email protected] Kabat B et al. Long-term results of response to therapy, time to progression, and survival with lenalidomide plus dexametha- sone in newly diagnosed myeloma. Mayo Clin Proc 2007; 82: 1179–1184. References 7 Rajkumar SV, Hayman S, Gertz MA, Dispenzieri A, Lacy MQ, Greipp PR et al. Combination therapy with thalidomide plus 1 Greipp PR, Lust JA, O’Fallon WM, Katzmann JA, Witzig TE, Kyle RA. dexamethasone for newly diagnosed myeloma. J Clin Oncol Plasma cell labeling index and beta 2-microglobulin predict survival 2002; 20: 4319–4323. independent of thymidine kinase and C-reactive protein in multiple 8 Kapoor P, Kumar S, Fonseca R, Lacy MQ, Witzig TE, Hayman SR myeloma. Blood 1993; 81: 3382–3387. et al. Impact of risk stratification on outcome among patients with 2 Boccadoro M, Marmont F, Tribalto M, Fossati G, Redoglia V, multiple myeloma receiving initial therapy with lenalidomide and Battaglio S et al. Early responder myeloma: kinetic studies identify a dexamethasone. Blood 2009; 114: 518–521. Inhibition of eIF4E with ribavirin cooperates with common chemotherapies in primary acute myeloid leukemia specimens Leukemia (2011) 25, 1197–1200; doi:10.1038/leu.2011.57; In preclinical studies, it was shown that M4/M5 AML published online 1 April 2011 specimens were more sensitive to ribavirin than normal controls or M1/M2 AML specimens with normal eIF4E levels.6 This strongly suggests that cells with elevated eIF4E have developed an oncogene addiction to this protein.2,6 Acute myeloid leukemia (AML) is the most common type of acute In a Phase II trial, ribavirin monotherapy led to clinical leukemia in adults and it is associated with poor outcomes. Typical responses including remissions in poor prognosis M4 and M5 induction strategies involve treatment with cytarabine (Ara-C) AML patients.7 Further, molecular studies showed that ribavirin along with an anthracycline, either idarubicin or daunorubicin, inhibited eIF4E activity in patients.7 Importantly, there was no andisreferredtoas7þ 3 therapy.1 This strategy can result in an therapy-related toxicity observed in these patients.7 These approximately 70% complete remission rate, but of these, about clinical studies suggested that ribavirin could be a new tool 70% will relapse.1 Further confounding the difficulty in inducing for AML treatment. Thus, we set out to investigate whether remissions is the morbidity associated with this treatment regimen. ribavirin treatment enhances the activity of anti-cancer agents Many patients over the age of 60, who are the majority of AML commonly used in the treatment of AML, including Ara-C, patients, cannot tolerate this treatment modality.1 Thus, it is idarubicin, sorafenib and azacytidine. imperative to develop novel strategies to treat AML. The effects of drug combinations were assessed using primary The eukaryotic translation initiation factor eIF4E is over- specimens from AML patients (obtained from the BCLQ tissue expressed in many cancers, including the M4 and M5 FAB bank with ethics committee approval) or healthy volunteers 2,3 subtypes of AML. Elevated eIF4E levels are generally correlated (Supplementary Table 1). We examined whether 1 mM ribavirin 2,3 with poor prognosis in these cancers. eIF4E affects gene expres- potentiated the effects of Ara-C (0.5 nM), idarubicin (0.3 nM)or sion post-transcriptionally by enhancing the mRNA export and/or Ara-C þ idarubicin, using colony growth assays in methylcellu- translation of specific growth promoting transcripts.2–5 Both of lose. Results from AML specimens derived from seven indivi- these activities contribute to the oncogenic potential of eIF4E and duals diagnosed with M4/M5 AML were assessed and these both require the ability of eIF4E to associate with the 50 7-methyl results are amalgamated in Table 1. Although both ribavirin and guanosine cap (m7G) structure found on mRNAs.4,5 Ara-C alone reduced colony number to about 40% of the Ribavirin acts as a competitive inhibitor of the cap, thereby untreated samples, the combination further reduced colonies to inhibiting the mRNA export and translation functions of about 20%. Similarly, idarubicin alone slightly reduced colony eIF4E.2,6 The ability of ribavirin to directly bind eIF4E and number to about 80%, but in combination with ribavirin to inhibit cap binding is based on a battery of biochemical studies 20–30%. Idarubicin with Ara-C reduced colony numbers to including NMR, mass spectrometry, fluorescence, cap chromato- about 20–30%, with the exception of the M4 AML Flt3-WT graphy and 3H ribavirin eIF4E immunoprecipitation.2,6 specimen (see below). Strikingly, the triple combination Leukemia Letters to the Editor 1198 Table 1 Effects of drugs on colony formation of primary AML specimens Drug AML-M4 AML-M4 AML-M5 AML-M5 AML-M1 AML-M1 AML-M2 Normal Normal FLT3 MUT FLT3 WT FLT3 MUT FLT3 WT High 4E PBMC CD34+ %Av±s.d. %Av ± s.d. %Av±s.d. %Av±s.d. %Av±s.d. %Av±s.d. %Av±s.d. %Av±s.d. %Av±s.d. Untreated 100±8a 100±10 100±9b 100±8 100±7 100±8 100±3 100±12a 100±3 Rib 41±8a 41±548±6b 53±445±477±569±580±14a 87±3 Ara-C 49±5a 63±12 39±7b 42±454±559±971±568±11b 82±3 Ara-C+Rib 18±3a 20±726±9b 17±719±453±753±575±8b 70±5 Ida 70±6a 99±13 75±6b 76±684±492±584±386±10a 94±3 Ida+Rib 19±3a 16±10 34±6b 33±529±475±679±362±10a 88±5 Ida+Ara-C 24±3a 60±723±4b 20±421±456±664±363±13b 82±3 Ida+Ara-C+Rib 10±3a 7±513±36±214±247±656±661±10b 74±4 Sor 50±955±10 64±7b 57±667±478±11 70±11 77±5NA Sor+Rib 21±416±323±4b 31±425±365±11 73±362±7NA Aza 77±778±963±867±677±572±478±360±766±7 Aza+Rib 30±67±432±524±628±559±767±349±570±3 Abbreviations: Av, average as a percent of the relevant untreated control; FLT3 MUT, specimens with internal tandem duplication; FLT3 WT, no mutation detected; NA, not available; s.d., standard deviation. Specimens are treated as described in the materials and methods. All experiments were carried out in replicates of five and repeated at least three independent times. Drug abbreviations and dosages were as follows: Rib ¼ ribavirin (1 mM), Ara-C ¼ cytarabine (0.5 nM), Ida ¼ idarubicin (0.3 nM), Sor ¼ sorafenib (2 mM), Aza ¼ azacytidine (3 mM). Note that cross comparison indicated that there was no correlation between NPM status and ribavirin dependent colony inhibition consistent with results in the clinical trial.6 aIndicates results amalgamated from three specimens. bIndicates results amalgamated from two specimens. (ribavirin/Ara-C/idarubicin) reduced colonies to 5–10% in all (Supplementary Table 2), modestly reduced colony number (to M4/M5 specimens examined. The triple combination, at these 70%) in M4/M5 and M1 high-4E specimens (Table 1). The concentrations, only slightly affected specimens from healthy addition of ribavirin strikingly reduced this (to 10–30%). M1/M2 volunteers (Table 1, Supplementary Table 2). specimens, or those from healthy volunteers, were sensitive to Our studies show that ribavirin was active in both Flt3 wild treatment with azacytidine (60–70%), but ribavirin did not type and mutant specimens (Table 1), reducing colony numbers substantially augment this. Thus, M4/M5 AML and M1-high4E to about 40% for both Flt3 mutant and wild-type specimens in specimens are more sensitive to the azacytidine-ribavirin the M4 or M5 setting. This suggests, in this limited number of combination than the other groups. specimens, that ribavirin sensitivity is independent of Flt3 status, Our studies indicate that a wide variety of agents cooperate as we observed in our Phase II clinical trial. The only major with ribavirin to reduce colony growth. Thus, we examined difference observed in this context was the lack of sensitivity of the effects of these agents on eIF4E activity in primary AML the M4 AML Flt3-WT for idarubicin alone, or combined with specimens treated for 48 h. We confirmed that ribavirin targeted Ara-C.