In patients non-proliferative disseminated tumour cells (DTCs) can persist in the bone marrow (BM) while other organs (i.e. lung) present growing metastasis. This suggested that the BM might be a metastasis “restrictive soil” by encoding dormancy-inducing cues in DTCs. Here we show in a HNSCC model that strong and specific TGFβ2 signalling in the BM activates p38α/β, inducing a [ERK/p38]low signalling ratio. This results in induction of DEC2/SHARP1 and p27, downregulation of CDK4 and dormancy of malignant DTCs. TGFβ2-induced dormancy required TGFβ-receptor-I, TGFβ-receptor-III and SMAD1/5 activation to induce p27. In lungs, a metastasis “permissive soil” with low TGFβ2 levels, DTC dormancy was short lived and followed by metastatic growth. Importantly, systemic inhibition of TGFβ-receptor-I or p38α/β activities awakened dormant DTCs fueling multi-organ metastasis. Our work reveals a “seed and soil” mechanism where TGFβ2 and TGFβRIII signalling through p38α/β regulates DTC dormancy and defines restrictive (BM) and -permissive (lung) microenvironments for HNSCC metastasis.

Purpose Somatic deletions that affect the lymphoid transcription factor–coding gene IKZF1 have previously been reported as independently associated with a poor prognosis in pediatric B-cell precursor (BCP) acute lymphoblastic leukemia (ALL). We have now refined the prognostic strength of IKZF1 deletions by analyzing the effect of co-occurring deletions. Patients and Methods The analysis involved 991 patients with BCP ALL treated in the Associazione Italiana Ematologia ed Oncologia Pediatrica–Berlin-Frankfurt-Muenster (AIEOP-BFM) ALL 2000 trial with complete information for copy number alterations of IKZF1, PAX5, ETV6, RB1, BTG1, EBF1, CDKN2A, CDKN2B, Xp22.33/Yp11.31 (PAR1 region; CRLF2, CSF2RA, and IL3RA), and ERG; replication of findings involved 417 patients from the same trial. Results IKZF1 deletions that co-occurred with deletions in CDKN2A, CDKN2B, PAX5, or PAR1 in the absence of ERG deletion conferred the worst outcome and, consequently, were grouped as IKZF1plus. The IKZF1plus group comprised 6% of patients with BCP ALL, with a 5-year event-free survival of 53 ± 6% compared with 79 ± 5% in patients with IKZF1 deletion who did not fulfill the IKZF1plus definition and 87 ± 1% in patients who lacked an IKZF1 deletion ( P ≤ .001). Respective 5-year cumulative relapse incidence rates were 44 ± 6%, 11 ± 4%, and 10 ± 1% ( P ≤ .001). Results were confirmed in the replication cohort, and multivariable analyses demonstrated independence of IKZF1plus. The IKZF1plus prognostic effect differed dramatically in analyses stratified by minimal residual disease (MRD) levels after induction treatment: 5-year event-free survival for MRD standard-risk IKZF1plus patients was 94 ± 5% versus 40 ± 10% in MRD intermediate- and 30 ± 14% in high-risk IKZF1plus patients ( P ≤ .001). Corresponding 5-year cumulative incidence of relapse rates were 6 ± 6%, 60 ± 10%, and 60 ± 17% ( P ≤ .001). Conclusion IKZF1plus describes a new MRD-dependent very-poor prognostic profile in BCP ALL. Because current AIEOP-BFM treatment is largely ineffective for MRD-positive IKZF1plus patients, new experimental treatment approaches will be evaluated in our upcoming trial AIEOP-BFM ALL 2017.

The pathways that allow quiescent disseminated cancer cells to survive during prolonged dormancy periods are unknown. Here, we identify the transcription factor ATF6␣ as a pivotal survival factor for quiescent but not proliferative squamous carcinoma cells. ATF6␣ is essential for the adaptation of dormant cells to chemotherapy, nutritional stress, and, most importantly, the in vivo microenvironment. Mechanism analysis showed that MKK6 and p38␣/␤ contribute to regulating nuclear translocation and transcriptional activation of ATF6␣ in dormant cancer cells. Downstream, ATF6␣ induces survival through the up-regulation of Rheb and activation of mTOR signaling independent of Akt. Down-regulation of ATF6␣ or Rheb reverted dormant tumor cell resistance to rapamycin and induced pronounced killing only of dormant cancer cells in vivo. Knocking down ATF6␣ also prolonged the survival of nude mice bearing dormant tumor cells. Targeting survival signaling by the ATF6␣-Rheb-mTOR pathway in dormant tumor cells may favor the eradication of residual disease during dormancy periods.dormancy ͉ endoplasmic reticulum stress ͉ quiescence ͉ p38 ͉ MKK6 M inimal residual disease caused by solitary disseminated tumor cells (DTC) is a well recognized event associated with unfavorable patient prognosis (1, 2). These cells, which usually stain negative for proliferation markers (e.g., Ki67) (3, 4), may be the source of tumor recurrence that can develop up to decades after treatment of the primary tumor (3, 4). These findings suggest that tumor cells may be able to reprogram into a quiescent behavior upon specific cues from the microenvironment (5). This may result from growth arrest and survival programs that allow dormant tumor cells to resist therapy and survive for long periods of time. Understanding how dormant DTCs survive dissemination and therapy and persist in a viable state for prolonged periods is of fundamental clinical interest.Despite clinical evidence that dormancy may arise from tumor cell quiescence, models that recapitulate such a behavior are scarce (5, 6). We hypothesized that tumor cells able to reversibly acquire a nontumorigenic phenotype may recapitulate the programs of stress resistance that result in tumor cell quiescence. We previously identified a highly tumorigenic and metastatic human squamous carcinoma cell line (T-HEp3) that, when passaged in culture for Ͼ40 generations, reprograms into a reversible dormant phenotype (D-HEp3). This behavior is revealed upon inoculation of the cells in vivo and is durable for months (7-9). Mechanistic studies showed that dormancy is due to a G 0 -G 1 arrest triggered in part by a low ERK/p38 signaling ratio and activation of the endoplasmic reticulum (ER) stress kinase PERK (10). However, the signals responsible for the prolonged survival of these quiescent tumor cells in vivo had remained unknown.The transcription factor ATF6 is an important survival mediator upon ER stress. Although D-HEp3 cells display an ER stress response characterized by PERK activation and chaperone upre...

Key Points Axl inhibition by BGB324 is active in FLT3-mutated and FLT3 wild-type AML, and presence of Axl and Gas6 are required for therapeutic efficacy. AML cells educate BMDSCs to secrete Gas6, which mediates leukemia cell proliferation and therapy resistance.

IKZF1 gene deletions have been associated with a poor outcome in pediatric precursor B-cell acute lymphoblastic leukemia. To assess the prognostic relevance of IKZF1 deletions for patients treated on Berlin-Frankfurt-Münster Study Group trial ALL-BFM 2000, we screened 694 diagnostic acute lymphoblastic leukemia samples by Multiplex Ligation-dependent Probe Amplification. Patients whose leukemic cells bore IKZF1 deletions had a lower 5-year event-free survival (0.69±0.05 vs. 0.85±0.01; P<0.0001) compared to those without, mainly due to a higher cumulative incidence of relapses (0.21±0.04 vs. 0.10±0.01; P=0.001). Although IKZF1 deletions were significantly associated with the P2RY8-CRLF2 rearrangement, their prognostic value was found to be independent from this association. Thus, IKZF1 deletion is an independent predictor of treatment outcome and a strong candidate marker for integration in future treatment stratification strategies on ALL-BFM protocols. Clinicaltrials.gov identifier: NCT00430118 ABSTRACTConsecutively enrolled patients from the ALL-BFM 2000 study population with sufficient spare leukemic DNA available were included in our present study (Online Supplementary Table S1). BM or peripheral blood specimens had to contain more than 80% blasts, as assessed morphologically before gradient centrifugation.

The stress-activated kinase p38 plays key roles in tumor suppression and induction of tumor cell dormancy. However, the mechanisms behind these functions remain poorly understood. Using computational tools, we identified a transcription factor (TF) network regulated by p38A/B and required for human squamous carcinoma cell quiescence in vivo. We found that p38 transcriptionally regulates a core network of 46 genes that includes 16 TFs. Activation of p38 induced the expression of the TFs p53 and BHLHB3, while inhibiting c-Jun and FoxM1 expression. Furthermore, induction of p53 by p38 was dependent on c-Jun down-regulation. Accordingly, RNAi down-regulation of BHLHB3 or p53 interrupted tumor cell quiescence, while down-regulation of c-Jun or FoxM1 or overexpression of BHLHB3 in malignant cells mimicked the onset of quiescence. Our results identify components of the regulatory mechanisms driving p38-induced cancer cell quiescence. These may regulate dormancy of residual disease that usually precedes the onset of metastasis in many cancers.

The proteasome inhibitor bortezomib (Velcade) effectively eradicates multiple myeloma (MM) cells, partly by activating endoplasmic reticulum (ER) stress apoptotic signaling. However, MM recurrences in bortezomib-treated patients are invariable. We have shown that ER stress signaling can also induce growth arrest and survival in cancer cells. Thus, we hypothesized that bortezomib therapy could induce quiescence and survival of residual MM cells, contributing to disease recurrence. Here, we report that in MM cells, proteasome inhibition with MG-132 or bortezomib results in a surviving cell fraction that enters a prolonged quiescent state (G 0 -G 1 arrest). Mechanism analysis revealed that bortezomibsurviving quiescent cells attenuate eIF2A phosphorylation and induction of the ER stress proapoptotic gene GADD153. This occurs independently of the eIF2A upstream kinases PERK, GCN2, and PKR. In contrast, the prosurvival ERchaperone BiP/Grp78 was persistently induced. The bortezomib-surviving quiescent fraction could be eradicated by a simultaneous or sequential combination therapy with salubrinal, an inhibitor of GADD34-PP1C phosphatase complex, and, in consequence, eIF2A dephosphorylation. This effect was mimicked by expression of a phosphorylated mimetic eIF2A-S51D mutant. Our data indicate that bortezomib can induce growth arrest in therapy-surviving MM cells and that attenuation of eIF2A phosphorylation contributes to this survival. Most importantly, this survival mechanism can be blocked by inhibiting eIF2A dephosphorylation. Thus, strategies that maintain eIF2A in a hyperphosphorylated state may be a novel therapeutic approach to maximize bortezomib-induced apoptosis and reduce residual disease and recurrences in this type of cancer. [Cancer Res 2009;69(4):1545-52]

Acute lymphoblastic leukemia (ALL) is the most common childhood cancer. One of the major clinical challenges is adequate diagnosis and treatment of central nervous system (CNS) involvement in this disease. Intriguingly, there is little solid evidence on the mechanisms sustaining CNS disease in ALL. Here, we present and discuss recent data on this topic, which are mainly derived from preclinical model systems. We thereby highlight sites and routes of leukemic CNS infiltration, cellular features promoting infiltration and survival of leukemic cells in a presumably hostile niche, and dormancy as a potential mechanism of survival and relapse in CNS leukemia. We also focus on the impact of ALL cytogenetic subtypes on features associated with a particular CNS tropism. Finally, we speculate on new perspectives in the treatment of ALL in the CNS, including ideas on the impact of novel immunotherapies.