The phosphatidylinositol 3-kinase (PI3K)/AKT and RAS oncogenic signalling modules are frequently mutated in sporadic human cancer. Although each of these pathways has been shown to play critical roles in driving tumour growth and proliferation, their activation in normal human cells can also promote cell senescence. Although the mechanisms mediating RAS-induced senescence have been well characterised, those controlling PI3K/AKT-induced senescence are poorly understood. Here we show that PI3K/AKT pathway activation in response to phosphatase and tensin homolog (PTEN) knockdown, mutant PI3K, catalytic, α polypeptide (PIK3CA) or activated AKT expression, promotes accumulation of p53 and p21, increases cell size and induces senescence-associated β-galactosidase activity. We demonstrate that AKT-induced senescence is p53-dependent and is characterised by mTORC1-dependent regulation of p53 translation and stabilisation of p53 protein following nucleolar localisation and inactivation of MDM2. The underlying mechanisms of RAS and AKT-induced senescence appear to be distinct, demonstrating that different mediators of senescence may be deregulated during transformation by specific oncogenes. Unlike RAS, AKT promotes rapid proliferative arrest in the absence of a hyperproliferative phase or DNA damage, indicating that inactivation of the senescence response is critical at the early stages of PI3K/AKT-driven tumourigenesis. Furthermore, our data imply that chronic activation of AKT signalling provides selective pressure for the loss of p53 function, consistent with observations that PTEN or PIK3CA mutations are significantly associated with p53 mutation in a number of human tumour types. Importantly, the demonstration that mTORC1 is an essential mediator of AKT-induced senescence raises the possibility that targeting mTORC1 in tumours with activated PI3K/AKT signalling may exert unexpected detrimental effects due to inactivation of a senescence brake on potential cancer-initiating cells.

Lenalidomide combined with dexamethasone is an effective treatment for refractory/ relapsed multiple myeloma (MM). Lenalidomide stimulates natural killer (NK) cells and enhances antitumor responses.We assessed NK cell number and function in 25 patients with MM participating in a clinical trial of lenalidomide and dexamethasone. NK cell numbers increased from a mean of 2.20 ؎ 0.05 ؋ 10 5 /mL (baseline) to a mean of 3.90 ؎ 0.03 ؋ 10 5 /mL (cycle 6; P ‫؍‬ .05); however, in vitro NKcell-mediated cytotoxicity decreased from 48.9% ؎ 6.8% to 27.6% ؎ 5.1% (P ‫؍‬ .0028) and could not be rescued by lenalidomide retreatment. Lenalidomide increased normal donor NK-cell cytotoxicity in vitro from 38.5% to 53.3%, but this was completely abrogated by dexamethasone. Dexamethasone suppression of NK cellmediated cytotoxicity was partially reversed by a 3-day washout, but these cells remained refractory to lenalidomideinduced enhanced function. Lymphocyte subset depletion experiments revealed that lenalidomide's enhancement of NK cell-mediated cytotoxicity was mediated by CD4 ؉ T-cell production of interleukin 2 and that dexamethasone acted by suppressing interleukin-2 production. Similarly, the reduced ability of NK cells from patients with MM to respond to lenalidomide was also due to impaired CD4 T-cell function. IntroductionMultiple myeloma (MM) is characterized by the uncontrolled proliferation of monoclonal plasma cells in the bone marrow (BM) and accumulation of monoclonal paraprotein in the serum of the majority of affected patients. 1 There is evidence that MM, at least in its early stages, is under the control of innate and adaptive immune responses, 2-9 which are ultimately subverted by the production of plasma cell and BMderived immunosuppressive cytokines including interleukin 6 (IL-6), transforming growth factor ␤ (TGF-␤), insulin-like growth factor 1 (IGF-1), vascular endothelial growth factor (VEGF), and tumor necrosis factor ␣ (TNF-␣). 10 The disease-associated immunoparesis of MM is further compounded by the immunosuppressive effects of anti-MM therapy. 10 Conventional MM therapy has used alkylator or anthracyclinebased chemotherapy in combination with the corticosteroids dexamethasone or prednisolone. Increasingly, nonchemotherapy agents such as the immunomodulatory (IMiD) drugs thalidomide and lenalidomide or the proteasome inhibitor Bortezomib have been incorporated into induction regimens commonly to replace chemotherapy agents, but are still used in combination with high-dose corticosteroids such as dexamethasone. 11,12 The anti-MM effect of immunomodulatory drugs is thought to be mediated by the combined effects of tumor necrosis factor ␣ inhibition, direct inhibition of plasma cell proliferation, suppression of angiogenesis, and promotion of T-cell costimulation, [13][14][15][16] and disruption of adhesion between malignant plasma cells and BM stroma. [17][18][19] Lenalidomide also shows substantial capacity to activate natural killer (NK) cell cytotoxicity and NK cell-driven antibodydependent cell-mediat...

Thalidomide and its analogues (lenalidomide and pomalidomide) are small molecule glutamic acid derivatives of the immunomodulatory drug (IMiD) class. In addition to the immuno-adjuvant and anti-inflammatory properties that define an IMiD, the thalidomide analogues demonstrate an overlapping and diverse range of biological activities, including anti-angiogenic, teratogenic and epigenetic effects. Importantly, the IMiDs possess anti-cancer activity with selectivity for molecularly defined subgroups of hematological malignancies, specifically mature B-cell neoplasms and myelodysplasia with deletion of chromosome 5q. Emerging insight into the pathophysiological drivers of these IMiD-responsive disease states can now be synthesized using previously disclosed IMiD activities and recently discovered thalidomide targets to build unifying models of IMiD mechanism of action. Attention to mechanisms of IMiD-induced clinical toxicities, in particular the recently identified association of lenalidomide with second primary malignancies, provides an additional tool for determination of drug mechanism. This review seeks to define the molecular IMiD targets and biological outputs that underpin their anti-neoplastic activity. It is anticipated that elucidation of important IMiD targets will allow the rational development of new-generation therapeutics with the potential to separate thalidomide-analogue efficacy from clinical toxicity.

N-methyl-2-pyrrolidone (NMP) is a common solvent and drug vehicle. We discovered unexpected antineoplastic and immunomodulatory activity of NMP in a cMYC-driven myeloma model. Coincident to this, NMP was identified as an acetyllysine mimetic and candidate bromodomain ligand. Accordingly, NMP-treated cells demonstrated transcriptional overlap with BET-bromodomain inhibition, including downregulation of cMYC and IRF4. NMP's immunomodulatory activity occurred at sub-BET inhibitory concentrations, and, despite phenotypic similarities to lenalidomide, its antimyeloma activity was independent of the IMiD targets cereblon and Ikaros-1/3. Thus, low-affinity yet broad-spectrum bromodomain inhibition by NMP mediates biologically potent, cereblon-independent immunomodulation and at higher doses targets malignant cells directly via BET antagonism. These data reveal that NMP is a functional acetyllysine mimetic with pleotropic antimyeloma and immunomodulatory activities. Our studies highlight the potential therapeutic benefits of NMP, the consequences of current human NMP exposures, and the need for reassessment of scientific literature where NMP was used as an "inert" drug-delivery vehicle.