The Eph-receptor A7 is a soluble tumor suppressor for follicular lymphoma.

Insights into cancer genetics can lead to therapeutic opportunities. By cross-referencing chromosomal changes with an unbiased genetic screen we identify the ephrin receptor A7 (EPHA7) as a tumor suppressor in follicular lymphoma (FL). EPHA7 is a target of 6q deletions and inactivated in 72% of FLs. Knockdown of EPHA7 drives lymphoma development in a murine FL model. In analogy to its physiological function in brain development, a soluble splice variant of EPHA7 (EPHA7(TR)) interferes with another Eph-receptor and blocks oncogenic signals in lymphoma cells. Consistent with this drug-like activity, administration of the purified EPHA7(TR) protein produces antitumor effects against xenografted human lymphomas. Further, by fusing EPHA7(TR) to the anti-CD20 antibody (rituximab) we can directly target this tumor suppressor to lymphomas in vivo. Our study attests to the power of combining descriptive tumor genomics with functional screens and reveals EPHA7(TR) as tumor suppressor with immediate therapeutic potential.

Jekyll and Hyde: Activating the Hypoxic Translational Machinery.

Global translational remodeling has emerged as a principal mechanism of biological adaptation. Oxygen deficiency (hypoxia) disables the basal protein synthesis machinery ('Jekyll') and activates a hypoxic translational architecture ('Hyde') to drive translatome remodeling. Independent from mRNA-level fluctuations, this newer paradigm modernizes a field traditionally dominated by the hypoxia-inducible factor (HIF) transcriptional program.

Whole-genome sequencing reveals complex genomic features underlying anti-CD19 CAR T-cell treatment failures in lymphoma.

CD19-directed chimeric antigen receptor (CAR-19) T cells are groundbreaking immunotherapies approved for use against large B-cell lymphomas. Although host inflammatory and tumor microenvironmental markers associate with efficacy and resistance, the tumor-intrinsic alterations underlying these phenomena remain undefined. CD19 mutations associate with resistance but are uncommon, and most patients with relapsed disease retain expression of the wild-type receptor, implicating other genomic mechanisms. We therefore leveraged the comprehensive resolution of whole-genome sequencing to assess 51 tumor samples from 49 patients with CAR-19-treated large B-cell lymphoma. We found that the pretreatment presence of complex structural variants, APOBEC mutational signatures, and genomic damage from reactive oxygen species predict CAR-19 resistance. In addition, the recurrent 3p21.31 chromosomal deletion containing the RHOA tumor suppressor was strongly enriched in patients for whom CAR T-cell therapy failed. Pretreatment reduced expression or monoallelic loss of CD19 did not affect responses, suggesting CAR-19 therapy success and resistance are related to multiple mechanisms. Our study showed that tumor-intrinsic genomic alterations are key among the complex interplay of factors that underlie CAR-19 efficacy and resistance for large B-cell lymphomas.

A phase 2 biomarker-driven study of ruxolitinib demonstrates effectiveness of JAK/STAT targeting in T-cell lymphomas.

Signaling through JAK1 and/or JAK2 is common among tumor and nontumor cells within peripheral T-cell lymphoma (PTCL). No oral therapies are approved for PTCL, and better treatments for relapsed/refractory disease are urgently needed. We conducted a phase 2 study of the JAK1/2 inhibitor ruxolitinib for patients with relapsed/refractory PTCL (n = 45) or mycosis fungoides (MF) (n = 7). Patients enrolled onto 1 of 3 biomarker-defined cohorts: (1) activating JAK and/or STAT mutations, (2) ≥30% pSTAT3 expression among tumor cells by immunohistochemistry, or (3) neither or insufficient tissue to assess. Patients received ruxolitinib 20 mg PO twice daily until progression and were assessed for response after cycles 2 and 5 and every 3 cycles thereafter. The primary endpoint was clinical benefit rate (CBR), defined as the combination of complete response, partial response (PR), and stable disease lasting at least 6 months. Only 1 of 7 patients with MF had CBR (ongoing PR > 18 months). CBR among the PTCL cases (n = 45) in cohorts 1, 2, and 3 were 53%, 45%, and 13% (cohorts 1 & 2 vs 3, P = .02), respectively. Eight patients had CBR > 12 months (5 ongoing), including 4 of 5 patients with T-cell large granular lymphocytic leukemia. In an exploratory analysis using multiplex immunofluorescence, expression of phosphorylated S6, a marker of PI3 kinase or mitogen-activated protein kinase activation, in <25% of tumor cells was associated with response to ruxolitinib (P = .05). Our findings indicate that ruxolitinib is active across various PTCL subtypes and support a precision therapy approach to JAK/STAT inhibition in patients with PTCL. This trial was registered at www.clincialtrials.gov as #NCT02974647.

T Cell-Activating Bispecific Antibodies in Cancer Therapy.

Effector lymphocytes are multifunctional cells of the immune system that promote cytolysis of pathogen-infected cells and nascent tumors. Tumors must learn to evade effectors and employ a wide variety of mechanisms to do so. Bispecific Abs (BsAbs) are an emerging cancer immunotherapy approach seeking to re-engage either T effectors or NK cells with malignant cells. Possessing specificity for effector cells on one end and a tumor Ag on the other, these molecules work by attracting effectors to the target cell to build an immunologic synapse and induce tumor cell killing. The BsAb blinatumomab, for example, has specificity for the T cell-activating cell surface protein CD3 and the B cell Ag CD19. The only BsAb with regulatory approval currently, blinatumomab is used in the treatment of relapsed or refractory B cell acute lymphoblastic leukemia. Many additional BsAbs are in preclinical development, however, targeting many different tumor types. The variety of potential effector cells and cancer Ags, along with potential combination therapies, make BsAbs an active area of drug development. In this review, we discuss cancer recognition by the immune system and structural and mechanistic aspects of BsAbs. We summarize key steps in preclinical development and subsequent translation to medical practice. Future directions for BsAbs include combinations with a wide variety of both immunologic and nonimmunologic therapies. Defining their optimum clinical use is at early stages.

RNA G-quadruplexes cause eIF4A-dependent oncogene translation in cancer.

The translational control of oncoprotein expression is implicated in many cancers. Here we report an eIF4A RNA helicase-dependent mechanism of translational control that contributes to oncogenesis and underlies the anticancer effects of silvestrol and related compounds. For example, eIF4A promotes T-cell acute lymphoblastic leukaemia development in vivo and is required for leukaemia maintenance. Accordingly, inhibition of eIF4A with silvestrol has powerful therapeutic effects against murine and human leukaemic cells in vitro and in vivo. We use transcriptome-scale ribosome footprinting to identify the hallmarks of eIF4A-dependent transcripts. These include 5' untranslated region (UTR) sequences such as the 12-nucleotide guanine quartet (CGG)4 motif that can form RNA G-quadruplex structures. Notably, among the most eIF4A-dependent and silvestrol-sensitive transcripts are a number of oncogenes, superenhancer-associated transcription factors, and epigenetic regulators. Hence, the 5' UTRs of select cancer genes harbour a targetable requirement for the eIF4A RNA helicase.

Short survival and frequent transformation in extranodal marginal zone lymphoma with multiple mucosal sites presentation.

Between 11 and 37% of extranodal marginal zone lymphoma (EMZL) patients present with disease involvement in multiple mucosal sites (MMS). We analyzed 405 EMZL patients seen between 1995 and 2017: 265 (65.4%) patients presented with stage I disease, 49 of 309 (15.8%) patients with bone marrow involvement, and 35 of 328 (10.7%) patients with monoclonal gammopathy (MG). Forty-three (10.6%) patients had MMS presentation, which was more frequently seen in patients aged >60 years (55.8%). Five (17.9%) of 28 MMS patients had MG. MMS patients commonly exhibited the International Prognostic Index (IPI) >2 (79.1%), Follicular Lymphoma International Prognostic Index (FLIPI) >2 (39.5%), and Mucosa-Associated Lymphoid Tissue Lymphoma International Prognostic Index (MALT-IPI) 2-3 (60.5%). Both MMS presentation and MG were associated with shorter survival univariately. In multivariable Cox regression models, shorter progression-free survival (PFS) and overall survival (OS) were observed in patients with MMS (hazard ratio [HR] = 3.08 and 2.92, respectively), age ≥60 years (HR = 1.52 and 2.45, respectively), and in patients who failed to attain a complete remission following initial therapy (HR = 3.27 and 2.13, respectively). Elevated lactate dehydrogenase was associated with shorter PFS (HR = 1.92), while anemia (HR = 2.46) was associated with shortened OS. MALT-IPI ≥2 (HR = 2.47 and 4.75), FLIPI >2 (HR = 1.65 and 2.09), and IPI >2 (HR = 2.09 and 1.73) were associated with shorter PFS and OS, respectively. Higher grade transformation (HGT) occurred in 11 (25.6%) MMS patients with a 5-year cumulative incidence of 13.2% (95% CI 4.7-26.1%). EMZL patients with MMS presentation represent a novel clinical subset associated with shorter PFS, OS, and higher incidence of HGT that needs novel therapeutic approaches.

Yttrium-90-Ibritumomab Tiuxetan (Zevalin®) Radioimmunotherapy after Cytoreduction with ESHAP Chemotherapy in Patients with Relapsed Follicular Non-Hodgkin Lymphoma: Final Results of a Phase II Study.

BACKGROUND: Radioimmunotherapy (RIT) is effective in treating relapsed/refractory follicular lymphoma (FL), with durable remissions in first-line consolidation. We hypothesized that RIT with ibritumomab tiuxetan (Zevalin®) would result in durable remissions by eliminating minimal residual disease after cytoreduction. METHODS: Patients with FL received 2 cycles of ESHAP (etoposide, methylprednisolone, cytarabine, cisplatin) every 28 days, followed by Zevalin 4-6 weeks later if there was no disease progression and bone marrow biopsy showed < 25% involvement. RESULTS: Twenty-eight patients were treated, with a median age of 61 years, median of 3 prior therapies, 49% high-risk disease (Follicular Lymphoma International Prognostic Index, FLIPI), and 39% progressive disease. Three patients did not receive Zevalin due to residual bone marrow involvement. The main toxicities were cytopenias, with 11% febrile neutropenia. The overall response rate (ORR) was 72%, with 45% achieving complete response. With a median follow-up of 73 months, 1-year progression-free survival (PFS) was 38%, and median PFS was 10 months, but median overall survival (OS) was not reached. CONCLUSION: The study did not reach its primary endpoint of a 1-year PFS of 67.3%. Reasons for this could include low accrual, high-risk disease, and inadequate debulking provided by 2 cycles of ESHAP. However, this protocol was associated with tolerable toxicity, high ORR, and high OS. Further studies would optimize debulking and focus on high-risk FL patients.

A Phase II Exploratory Study of PXD-101 (Belinostat) Followed by Zevalin in Patients with Relapsed Aggressive High-Risk Lymphoma.

OBJECTIVE: Aggressive lymphomas (aNHL) including diffuse large B-cell lymphoma (DLBCL) have poor outcomes in relapsed refractory patients. Prior studies have demonstrated that loss of major histocompatibility complex class II (MHCII) expression in DLBCL is associated with poor survival. The objective of this single-arm phase II study was to evaluate if PXD-101 would increase MHCII expression, synergize with Zevalin, and improve clinical outcomes. METHODS: This was a single-center open-label phase II trial (NCT01686165) geared toward heavily pretreated patients with CD20-positive aNHL. The primary endpoint was overall response rate (ORR) in aNHL patients treated with 2 cycles of PXD-101 followed by restaging CT and 1 cycle of Zevalin. RESULTS: Five patients were enrolled, and all were heavily pretreated. Therapy was well tolerated, with nausea and vomiting being the most frequent adverse events. All patients progressed after receiving therapy; the study did not achieve the required ORR to proceed to the next stage. CONCLUSION: The pleotropic effects of histone deacetylase inhibition and lack of clinical biomarkers have precluded a priori identification of responding patients. Thus, while we report a negative trial of PXD-101 in combination with Zevalin, this study highlights the importance of a clinically feasible biomarker.

ATP-competitive, marine derived natural products that target the DEAD box helicase, eIF4A.

Activation of translation initiation is a common trait of cancer cells. Formation of the heterotrimeric eukaryotic initiation factor F (eIF4F) complex is the rate-limiting step in 5' m7GpppN cap-dependent translation. This trimeric complex includes the eIF4E cap binding protein, the eIF4G scaffolding protein, and the DEAD box RNA helicase eIF4A. eIF4A is an ATP-dependent helicase and because it is the only enzyme in the eIF4F complex, it has been shown to be a potential therapeutic target for a variety of malignancies. To this end, we have used a simple ATPase biochemical screen to survey several hundred marine and terrestrial derived natural products. Herein, we report the discovery of two natural products from marine sources, elisabatin A (1) and allolaurinterol (2), which show low µM inhibition of eIF4A ATPase activity. Enzymological analyses revealed 1 and 2 to be ATP-competitive, and cellular evaluations showed reasonable cytotoxicity against A549 (lung cancer) and MDA-MA-468 (breast cancer) cell lines. However, only compound 2 showed potent inhibition of helicase activity congruent with its ATPase inhibitory activity.

A targeted mutational landscape of angioimmunoblastic T-cell lymphoma.

The genetics of angioimmunoblastic T-cell lymphoma (AITL) are very poorly understood. We defined the mutational landscape of AITL across 219 genes in 85 cases from the United States and Europe. We identified ≥2 mutations in 34 genes, nearly all of which were not previously implicated in AITL. These included loss-of-function mutations in TP53 (n = 4), ETV6 (n = 3), CCND3 (n = 2), and EP300 (n = 5), as well as gain-of-function mutations in JAK2 (n = 2) and STAT3 (n = 4). TET2 was mutated in 65 (76%) AITLs, including 43 that harbored 2 or 3 TET2 mutations. DNMT3A mutations occurred in 28 (33%) AITLs; 100% of these also harbored TET2 mutations (P < .0001). Seventeen AITLs harbored IDH2 R172 substitutions, including 15 with TET2 mutations. In summary, AITL is characterized by high frequencies of overlapping mutations in epigenetic modifiers and targetable mutations in a subset of cases.

Progress against follicular lymphoma.

PURPOSE OF REVIEW: To share the recent progress in research and new therapies against follicular lymphoma and highlight the exciting opportunities to improve the treatment of follicular lymphoma. RECENT FINDINGS: Follicular lymphoma has been somewhat neglected by the research community, but recent genomic studies have identified key genetic lesions in follicular lymphoma. In addition, a new murine model is available to explore the function of these lesions in the development, progression, and treatment of follicular lymphoma. Moreover, new small-molecule inhibitors are now available that target key pathways in follicular lymphoma including B-cell receptor signaling and histone modifiers. SUMMARY: Follicular lymphoma is a very common and still incurable form of lymphoma. However, recent genomic and in-vivo biological studies are beginning to unveil the molecular drivers of follicular lymphoma. This coincides with the development of effective small-molecule inhibitors against key targets. Together these developments suggest that we are at a long overdue watershed moment in the treatment of follicular lymphoma.

Bispecific antibodies and CAR-T cells: dueling immunotherapies for large B-cell lymphomas.

Despite recent advances in frontline therapy for diffuse large B-cell lymphoma (DLBCL), at least a third of those diagnosed still will require second or further lines for relapsed or refractory (rel/ref) disease. A small minority of these can be cured with standard chemoimmunotherapy/stem-cell transplant salvage approaches. CD19-directed chimeric antigen receptor T-cell (CAR-19) therapies are increasingly altering the prognostic landscape for rel/ref patients with DLBCL and related aggressive B-cell non-Hodgkin lymphomas. Long-term follow up data show ongoing disease-free outcomes consistent with cure in 30-40% after CAR-19, including high-risk patients primary refractory to or relapsing within 1 year of frontline treatment. This has made CAR-19 a preferred option for these difficult-to-treat populations. Widespread adoption, however, remains challenged by logistical and patient-related hurdles, including a requirement for certified tertiary care centers concentrated in urban centers, production times of at least 3-4 weeks, and high per-patients costs similar to allogeneic bone-marrow transplantation. Bispecific antibodies (BsAbs) are molecular biotherapies designed to bind and activate effector T-cells and drive them to B-cell antigens, leading to a similar cellular-dependent cytotoxicity as CAR-19. May and June of 2023 saw initial approvals of next-generation BsAbs glofitamab and epcoritamab in DLBCL as third or higher-line therapy, or for patients ineligible for CAR-19. BsAbs have similar spectrum but generally reduced severity of immune related side effects as CAR-19 and can be administered in community settings without need to manufacture patient-specific cellular products. To date and in contrast to CAR-19, however, there is no convincing evidence of cure after BsAbs monotherapy, though follow up is limited. The role of BsAbs in DLBCL treatment is rapidly evolving with trials investigating use in both relapsed and frontline curative-intent combinations. The future of DLBCL treatment is bound increasingly to include effector cell mediated immunotherapies, but further optimization of both cellular and BsAb approaches is needed.

NRF2 translation block by inhibition of cap-dependent initiation sensitizes lymphoma cells to ferroptosis and CAR-T immunotherapy.

Cancers coopt stress-response pathways to drive oncogenesis, dodge immune surveillance, and resist cytotoxic therapies. Several of these provide protection from ferroptosis, iron-mediated oxidative cell death. Here, we found dramatic sensitization to ferroptosis upon disruption of cap-dependent translation in diffuse large B-cell lymphoma (DLBCL). Specifically, rocaglate inhibitors of the eIF4A1 RNA helicase synergized with pharmacologic ferroptosis inducers, driven by a collapse of glutathione production that protects polyunsaturated fatty acids from ferroptotic oxidation. These effects occur despite initial up-regulation of specific protective factors. We find lost translation of NRF2, oncogenic master regulator of antioxidant gene-expression, is a key consequence of eIF4A1 inhibition. In vivo, combination of the clinical rocaglate zotatifin with a pharmacologically optimized ferroptosis inducer eradicated DLBCL patient derived xenografts. Moreover, we found zotatifin pre-exposure sensitized DLBCL to CD19-directed chimeric antigen receptor (CAR-19) T cells. Translational disruption therefore provides new opportunities to leverage therapeutic impacts of ferroptosis inducers including cytotoxic immunotherapies.

The cyclin-G associated kinase (GAK) is a novel mitotic kinase and therapeutic target in diffuse large B-cell lymphoma.

Diffuse large B cell lymphoma (DLBCL) is an aggressive non-Hodgkin lymphoma and the most frequently diagnosed hematologic malignancy in the United States. DLBCL exhibits significant molecular and clinical heterogeneity, and at least a third of patients are left uncured with standard frontline chemoimmunotherapy. As such, there is a critical need to identify novel targeted therapies to improve outcomes. We conducted a phenotypic screen of kinase inhibitors against DLBCL cell lines and non-malignant controls. We identified the cyclin G-associated kinase (GAK) as a tumor-selective, readily druggable target whose inhibition killed DLBCL cell lines, while sparing non-malignant blood cells. Upon investigation of GAK's cellular function, we discovered that inhibition results in G2/M-phase cell cycle arrest. Immunofluorescent confocal microscopy revealed significant chromosome misalignment and spindle distortion in DLBCL cells following GAK-inhibition, disrupting progression through mitosis. Analysis of RNA-seq data from clinical samples showed increased GAK expression associates strongly with RB1 deficiency in DLBCL cases, suggesting dependency on GAK for proper mitotic progression linked to retinoblastoma associated protein (RB) loss of function, a common DLBCL driver. In cell-cycle analyses and under microscopy, RB-deficient DLBCL cells treated with an exquisitely selective GAK inhibitor showed complete arrest at G2/M, pronounced distortion of mitotic spindles, and widespread chromosomal damage. Finally, in vivo studies of DLBCL xenograft-bearing NSG mice achieved a dramatic tumor-burden reduction in response to targeted GAK inhibition. These results reveal a novel cell cycle kinase suitable for therapeutic exploitation in DLBCL patients and linked to the common, undruggable biomarker of RB loss of function.

Functional drivers of resistance to anti-CD19 CAR-T cell therapy in diffuse large B cell lymphoma.

Chimeric antigen receptor T-cell therapy targeting CD19 (CAR-19) promotes impressive durable remissions for relapsed or refractory (rel/ref) large B-cell lymphoma (LBCL) patients with historically poor prognoses. Despite this, over half of patients still fail to respond or eventually progress. Studies to reveal mechanisms of resistance have examined host clinical parameters, CAR-19 product composition, and tumor microenvironment (TME) alterations, while a relative paucity of studies has analyzed contributions by genomic alterations in tumor cells. Factors associated with outcome include increased tumor volume, specific characteristics of infused CAR-T products, infiltration by myeloid cells in tumor microenvironments, and markers of complexity in LBCL genomes. Functional laboratory studies of resistance are largely absent in the current literature, illustrating a need for experiments in genetically accurate immunocompetent systems to confirm candidate alterations' roles in resistance and inform future improvements. In this review, we highlight key studies that have elucidated biomarkers of resistance in hosts, CAR products, TMEs, and comparatively understudied tumor-intrinsic mediators encoded by tumor genomes. We conclude with an experimental framework suitable for CAR-19 resistance biomarker identification and laboratory functional validation.

Efficacy of checkpoint inhibition after CAR-T failure in aggressive B-cell lymphomas: outcomes from 15 US institutions.

Checkpoint inhibitor (CPI) therapy with anti-PD-1 antibodies has been associated with mixed outcomes in small cohorts of patients with relapsed aggressive B-cell lymphomas after CAR-T failure. To define CPI therapy efficacy more definitively in this population, we retrospectively evaluated clinical outcomes in a large cohort of 96 patients with aggressive B-cell lymphomas receiving CPI therapy after CAR-T failure across 15 US academic centers. Most patients (53%) had diffuse large B-cell lymphoma, were treated with axicabtagene ciloleucel (53%), relapsed early (≤180 days) after CAR-T (83%), and received pembrolizumab (49%) or nivolumab (43%). CPI therapy was associated with an overall response rate of 19% and a complete response rate of 10%. Median duration of response was 221 days. Median progression-free survival (PFS) and overall survival (OS) were 54 and 159 days, respectively. Outcomes to CPI therapy were significantly improved in patients with primary mediastinal B-cell lymphoma. PFS (128 vs 51 days) and OS (387 vs 131 days) were significantly longer in patients with late (>180 days) vs early (≤180 days) relapse after CAR-T. Grade ≥3 adverse events occurred in 19% of patients treated with CPI. Most patients (83%) died, commonly because of progressive disease. Only 5% had durable responses to CPI therapy. In the largest cohort of patients with aggressive B-cell lymphoma treated with CPI therapy after CAR-T relapse, our results reveal poor outcomes, particularly among those relapsing early after CAR-T. In conclusion, CPI therapy is not an effective salvage strategy for most patients after CAR-T, where alternative approaches are needed to improve post-CAR-T outcomes.

Cooperation between deficiencies of IRF-4 and IRF-8 promotes both myeloid and lymphoid tumorigenesis.

Interferon regulatory factor 4 (IRF-4) plays important functions in B- and T-cell development and immune response regulation and was originally identified as the product of a proto-oncogene involved in chromosomal translocations in multiple myeloma. Although IRF-4 is expressed in myeloid cells, its function in that lineage is not known. The closely related family member IRF-8 is a critical regulator of myelopoiesis, which when deleted in mice results in a syndrome highly similar to human chronic myelogenous leukemia. In early lymphoid development, we have shown previously that IRF-4 and IRF-8 can function redundantly. We therefore investigated the effects of a combined loss of IRF-4 and IRF-8 on hematologic tumorigenesis. We found that mice deficient in both IRF-4 and IRF-8 develop from a very early age a more aggressive chronic myelogenous leukemia-like disease than mice deficient in IRF-8 alone, correlating with a greater expansion of granulocyte-monocyte progenitors. Although these results demonstrate, for the first time, that IRF-4 can function as tumor suppressor in myeloid cells, interestingly, all mice deficient in both IRF-4 and IRF-8 eventually develop and die of a B-lymphoblastic leukemia/lymphoma. Combined losses of IRF-4 and IRF-8 therefore can cooperate in the development of both myeloid and lymphoid tumors.

MATRIX platform to analyze translation machinery remodeling in glioblastoma cells.

Here, we present a protocol using MATRIX (mass spectrometry analysis of active translation factors using ribosome density fractionation and isotopic labeling experiments) platform to investigate changes of the protein synthesis machinery in U87MG glioblastoma cells in response to the rocaglate silvestrol. This protocol describes steps to perform SILAC (stable isotope labeling by amino acids in cell culture), ribosome density fractionation, protein isolation, and mass spectrometry analysis. This approach can be applied to study any adaptive remodeling of protein synthesis machineries. For complete details on the use and execution of this protocol, please refer to Ho et al. (2021).1.

Targeting the PI3K/AKT/mTOR pathway in non-Hodgkin's lymphoma: results, biology, and development strategies.

Signaling by the PI3K/AKT/mTOR pathway is frequently deregulated in non-Hodgkin's lymphoma (NHL), prompting evaluation of the rapamycin-analog (rapalog) mTOR inhibitors in multiple clinical trials. The drugs show activity as single agents, and the rapalog temsirolimus is now accepted as a therapeutic option in relapsed/refractory mantle cell lymphoma. Response rates, however, are typically below 50%, resulting in remissions that are neither complete nor durable. Results of preclinical studies shed important new light on resistance mechanisms that may explain results. Looking ahead, it is likely PI3K/AKT/mTOR inhibition will find expanded roles in NHL therapy due to 1) assessments of the rapalogs in combination with other therapies and in less heavily pretreated patients, 2) the development and evaluation of multiple novel inhibitors of the pathway that may increase specificity and potency, 3) alternative treatment strategies able to bypass particular resistance mechanisms, and 4) increased efforts to identify biomarkers for better pretreatment patient stratification.