Frequent 4EBP1 Amplification Induces Synthetic Dependence on FGFR Signaling in Cancer

Simple Summary Our work establishes that amplification of 4EBP1, as a part of Chr. 8p11, creates a synthetic dependency on FGFR1 signaling in cancer. 4EBP1 is phosphorylated by FGFR1 and PI3K signaling, and accordingly cancer with 4EBP1-FGFR1 amplification is more sensitive to FGFR1 and PI3K inhibition due to inhibition of 4EBP1 phosphorylation. Moreover, we characterize the translational targets of 4EBP1 and identify that 4EBP1 specifically regulates the translation of genes involved in insulin signaling, glucose metabolism, and the inositol pathway that plays a role in cancer progression. The eIF4E translation initiation factor has oncogenic properties and concordantly, the inhibitory eIF4E-binding protein (4EBP1) is considered a tumor suppressor. The exact molecular effects of 4EBP1 activation in cancer are still unknown. Surprisingly, 4EBP1 is a target of genomic copy number gains (Chr. 8p11) in breast and lung cancer. We noticed that 4EBP1 gains are genetically linked to gains in neighboring genes, including WHSC1L1 and FGFR1. Our results show that FGFR1 gains act to attenuate the function of 4EBP1 via PI3K-mediated phosphorylation at Thr37/46, Ser65, and Thr70 sites. This implies that not 4EBP1 but instead FGFR1 is the genetic target of Chr. 8p11 gains in breast and lung cancer. Accordingly, these tumors show increased sensitivity to FGFR1 and PI3K inhibition, and this is a therapeutic vulnerability through restoring the tumor-suppressive function of 4EBP1. Ribosome profiling reveals genes involved in insulin signaling, glucose metabolism, and the inositol pathway to be the relevant translational targets of 4EBP1. These mRNAs are among the top 200 translation targets and are highly enriched for structure and sequence motifs in their 5 ' UTR, which depends on the 4EBP1-EIF4E activity. In summary, we identified the translational targets of 4EBP1-EIF4E that facilitate the tumor suppressor function of 4EBP1 in cancer

Targeting cap-dependent translation blocks converging survival signals by AKT and PIM kinases in lymphoma

PIM kinase expression in human lymphomas can influence the outcome of chemotherapy, and blocking cap-dependent translation can reverse PIM-mediated rapamycin resistance in murine lymphomas

Functional genomics lead to new therapies in follicular lymphoma

Recent technological advances allow analysis of genomic changes in cancer in unprecedented detail. The next challenge is to prioritize the multitude of genetic aberrations found and identify therapeutic opportunities. We recently completed a study that illustrates the use of unbiased genetic screens and murine cancer models to find therapeutic targets among complex genomic data. We genetically dissected the common deletion of chromosome 6q and identified the ephrin receptor A7 (EPHA7) as a tumor suppressor in lymphoma. Notably, EPHA7 encodes a soluble splice variant that acts as an extrinsic tumor suppressor. Accordingly, we developed an antibody-based strategy to specifically deliver EPHA7 back to tumors that have lost this gene. Recent sequencing studies have implicated EPHA7 in lung cancer and other tumors, suggesting a broader therapeutic potential for antibody-mediated delivery of this tumor suppressor for cancer therapy. Together, our comprehensive approach provides new insights into cancer biology and may directly lead to the development of new cancer therapies

Genomic studies indicate a novel combination therapy for follicular lymphoma

Follicular lymphoma (FL) is an incurable form of B-cell lymphoma. Genomic alterations that inactivate RB signaling are surprisingly common in indolent FL. We show that FLs that are positive for phosphorylated RB respond to dual CDK4/BCL2 inhibition. Our results imply that RB phosphorylation identifies patients likely to benefit from such dual intervention

Targeted cancer therapy What if the driver is just a messenger?

“Shoot the driver” is the paradigm of targeted cancer therapy. However, resistance to targeted inhibitors of signaling pathways is a major problem. In part, the redundancy of signaling networks can bypass targeted inhibitors and thereby reduce their biological effect. In this case, the driver turns out to be one of several potential messengers and is easily replaced. Cocktails of multiple targeted inhibitors are an obvious solution. This is limited, however, by the lack of potent inhibitors and may also produce increased toxicity. Therefore, we explored the direct blockade of a key biological activity downstream from multiple converging oncogenic signals. Specifically, several oncogenic signaling pathways, including AKT, MAPK and PIM kinase signals, converge on the activation of cap-dependent translation. In cancer cells, aberrant activation of cap-dependent translation favors the increased expression of short-lived oncoproteins like c-MYC, MCL1, CYCLIND1 and the PIM kinases. Intriguingly, cancer cells are especially sensitive to even temporary reductions in these proteins. We will discuss our findings concerning translational inhibitor therapy in cancer

Targeted cancer therapy

“Shoot the driver” is the paradigm of targeted cancer therapy. However, resistance to targeted inhibitors of signaling pathways is a major problem. In part, the redundancy of signaling networks can bypass targeted inhibitors and thereby reduce their biological effect. In this case, the driver turns out to be one of several potential messengers and is easily replaced. Cocktails of multiple targeted inhibitors are an obvious solution. This is limited, however, by the lack of potent inhibitors and may also produce increased toxicity. Therefore, we explored the direct blockade of a key biological activity downstream from multiple converging oncogenic signals. Specifically, several oncogenic signaling pathways, including AKT, MAPK and PIM kinase signals, converge on the activation of cap-dependent translation. In cancer cells, aberrant activation of cap-dependent translation favors the increased expression of short-lived oncoproteins like c-MYC, MCL1, CYCLIND1 and the PIM kinases. Intriguingly, cancer cells are especially sensitive to even temporary reductions in these proteins. We will discuss our findings concerning translational inhibitor therapy in cancer

MicroRNAs Mediate Resistance to Tyrosine Kinase Inhibitors in Philadelphia-Positive B-ALL by Down-Regulating Key Tumor Suppressors

Abstract Abstract 2553 The Philadelphia (Ph) chromosome (t(9;22)(q34;q11)) is the most common recurrent cytogenetic abnormality in adult B-cell acute lymphoblastic leukemia (B-ALL). Resulting expression of the BCR-ABL fusion gene product, a constitutively active tyrosine kinase, leads to an extremely poor prognosis when the disease is treated with chemotherapy alone. In recent years targeted therapy with tyrosine kinase inhibitors (TKIs) in combination with chemotherapy has improved outcomes. Therapeutic resistance remains a major clinical problem, however, with less than half of patients surviving three years from initial therapy in most series even with up-front TKI-chemotherapy regimens. TKI resistance in B-ALL may result from acquired mutations of the BRC-ABL protein or from BCR-ABL-independent causes, including feedback activation of BCL6 or activation of other oncogenic signaling pathways through poorly understood mechanisms. In this study, we screened a whole-genome library of microRNAs for ability to produce resistance to TKI therapy in murine pro-B cells transformed with BCR-ABL. Several initial candidates from the screen were individually confirmed to confer TKI resistance, including miR 148/152 and 19, known oncomirs in T-ALL. Computational analysis of the gene targets of validated miRs shows significant overlap at several tumor-suppressor pathways, including down-regulation of PTEN, a known mechanism of TKI resistance in Ph+ B-ALL cell lines. In sum, we have identified a novel mechanism of TKI resistance in Ph+ B-ALL mediated by miRs and leading to down-regulation of specific tumor suppressive intermediates. These findings will allow development of new therapeutic combinations to improve outcomes for B-ALL patients. Disclosures: No relevant conflicts of interest to declare

Targeting Translation Bypasses Pim Kinase Activity, a Common and Adverse Prognostic Marker In Lymphoma

Abstract Abstract 119 The PI3K/AKT/mTOR pathway is frequently activated in lymphoma, but rapamycin-analog (rapalog) mTOR inhibitors have shown only modest benefits in clinical trials on lymphoma patients. To better understand the resistance of lymphomas to rapalogs, we have undertaken a study of the Pim family kinases, which signal in parallel to PI3K/AKT/mTOR and whose expression has been detected in multiple subtypes of non-Hodgkin lymphoma (NHL). The two pathways converge on activation of cap-dependent translation, suggesting new treatment possibilities by targeting this common downstream output. To assess the clinical relevance of Pim activity, we have quantified Pim1 and Pim2 expression in multiple NHL subtypes using tissue microarray (TMA) technology. We find common expression of Pim1, Pim2, or both proteins in diffuse large B-cell lymphoma (DLBCL, 65.5%), follicular lymphoma (58%), small lymphocytic lymphoma (76.5%) and mantel cell lymphoma (89.7%). Importantly, Kaplan-Meier survival analysis of clinical data linked to our DLBCL TMAs show a strong trend toward a worse overall survival when Pim expression is present in diagnostic tumor samples compared to Pim-negative tumors (p=0.0965). Studies in vivo demonstrate Pim's ability to accelerate oncogenesis in a manner similar to AKT in model systems specific to Burkitt's lymphoma (Eμ -Myc) and follicular lymphoma (VavP-Bcl2). Treatment studies in secondary recipient animals show that Pim promotes resistance to anthracycline chemotherapy like AKT. However, Pim tumors completely resist rapamycin in stark contrast to AKT tumors. To elaborate on these findings, we have employed a genetically defined system of rapamycin sensitivity lacking mTOR's upstream repressor TSC2. These studies show that Pim's ability to mediate rapamycin resistance is dependent on its ability to maintain inhibitory phosphorylation of the translation repressor 4EBP1. Specifically, a phosphorylation-site deficient mutant of 4EBP1 completely abrogates Pim's ability to maintain the viability of the TSC2 −/− cells. We have expanded on this finding using the drug silvestrol, which inhibits cap-dependent translation by targeting eIF4A. Silvestrol shows high potency against Pim-expressing TSC2 −/− cells (IC50 < 1 nM) and also against a panel of Pim-expressing lymphoma cell lines (IC50 1–10 nM). Indeed, targeting cap-dependent translation appeared more effective than the Pim kinase inhibitor SGI-1776 (IC50 1–10 μ M against lymphoma cell lines), which has significantly higher potency against Pim1 than Pim2. In conclusion, we have more clearly defined Pim kinase activity as a major mediator of oncogenesis in multiple NHL subtypes and as a likely negative prognostic marker in DLBCL. Our mechanistic and treatment studies provide a strong rational basis for targeting cap-dependent translation as a treatment strategy to bypass Pim activity and improve lymphoma patients' responses to both cytotoxic and rapalog therapies. Disclosures: No relevant conflicts of interest to declare