Better treatments are needed for patients with diffuse large B-cell lymphoma (DLBCL) at high risk of failing standard therapy. Avoiding apoptosis is a hallmark of cancer, and in DLBCL the redundantly functioning anti-apoptotic proteins BCL2 and MCL1 are frequently expressed. Here, we explore drugs that cause loss of MCL1, particularly the potent new cyclin-dependent kinase inhibitor dinaciclib, which knocks down MCL1 by inhibiting CDK9. Dinaciclib induces apoptosis in DLBCL cells but is completely overcome by increased activity of BCL2. We find clinical samples have frequent co-expression of MCL1 and BCL2, suggesting therapeutic strategies targeting only one will lead to treatment failures due to activity of the other. The BH3 mimetic ABT-199 potently and specifically targets BCL2. Single-agent ABT-199 had modest anti-tumor activity against most DLBCL lines and resulted in compensatory up-regulation of MCL1 expression. ABT-199 synergized strongly, however, when combined with dinaciclib and with other drugs affecting MCL1, including standard DLBCL chemotherapy drugs. We show potent anti-tumor activities of these combinations in xenografts and in a genetically accurate murine model of MYC-BCL2 double-hit lymphoma. In sum, we reveal a rational treatment paradigm to strip DLBCL of its protection from apoptosis and improve outcomes for high-risk patients.

The anaplastic lymphoma kinase ALK is chromosomally rearranged in a subset of certain cancers, including 2–7% non-small cell lung cancers (NSCLC) and ~70% of anaplastic large cell lymphomas (ALCL). The ALK kinase inhibitors crizotinib and ceritinib are approved for relapsed ALK+ NSCLC, but acquired resistance to these drugs limits median progression-free survival on average to ~10 months. Kinase domain mutations are detectable in 25–37% of resistant NSCLC samples, with activation of bypass signaling pathways detected frequently with or without concurrent ALK mutations. Here we report that, in contrast to NSCLC cells, drug resistant ALCL cells show no evidence of bypassing ALK by activating alternate signaling pathways. Instead, drug resistance selected in this setting reflects upregulation of ALK itself. Notably, in the absence of crizotinib or ceritinib, we found that increased ALK signaling rapidly arrested or killed cells, allowing a prolonged control of drug-resistant tumors in vivo with the administration of discontinuous rather than continuous regimens of drug dosing. Furthermore, even when drug resistance mutations were detected in the kinase domain, overexpression of the mutant ALK was toxic to tumor cells. We confirmed these findings derived from human ALCL cells in murine pro-B cells that were transformed to cytokine independence by ectopic expression of an activated NPM-ALK fusion oncoprotein. In summary, our results show how ALK activation functions as a double-edged sword for tumor cell viability, with potential therapeutic implications.

The DEAD-box RNA helicase eIF4A1 carries out the key enzymatic step of cap-dependent translation initiation and is a well-established target for cancer therapy, but no drug against it has entered evaluation in patients. We identified and characterized a natural compound with broad antitumor activities that emerged from the first target-based screen to identify novel eIF4A1 inhibitors. We tested potency and specificity of the marine compound elatol versus eIF4A1 ATPase activity. We also assessed eIF4A1 helicase inhibition, binding between the compound and the target including binding site mutagenesis, and extensive mechanistic studies in cells. Finally, we determined maximum tolerated dosing and assessed activity against xenografted tumors. We found elatol is a specific inhibitor of ATP hydrolysis by eIF4A1 with broad activity against multiple tumor types. The compound inhibits eIF4A1 helicase activity and binds the target with unexpected 2:1 stoichiometry at key sites in its helicase core. Sensitive tumor cells suffer acute loss of translationally regulated proteins, leading to growth arrest and apoptosis. In contrast to other eIF4A1 inhibitors, elatol induces markers of an integrated stress response, likely an off-target effect, but these effects do not mediate its cytotoxic activities. Elatol is less potent than the well-studied eIF4A1 inhibitor silvestrol but is tolerated at approximately 100× relative dosing, leading to significant activity against lymphoma xenografts. Elatol's identification as an eIF4A1 inhibitor with antitumor activities provides proof of principle for target-based screening against this highly promising target for cancer therapy..

Acquired resistance to targeted inhibitors remains a major, and inevitable, obstacle in the treatment of oncogene-addicted cancers. Newer-generation inhibitors may help overcome resistance mutations, and inhibitor combinations can target parallel pathways, but durable benefit to patients remains elusive in most clinical scenarios. Now, recent studies suggest a third approach may be available in some cases—exploitation of oncogene overexpression that may arise to promote resistance. Here, we discuss the importance of maintaining oncogenic signaling at “just-right” levels in cells, with too much signaling, or oncogene overdose, being potentially as detrimental as too little. This is highlighted in particular by recent studies of mutant-BRAF in melanoma and the fusion kinase nucleophosmin–anaplastic lymphoma kinase (NPM–ALK) in anaplastic large cell lymphoma. Oncogene overdose may be exploitable to prolong tumor control through intermittent dosing in some cases, and studies of acute lymphoid leukemias suggest that it may be specifically pharmacologically inducible.

The PIM family kinases promote growth and survival of tumor cells and are expressed in a wide variety of human cancers. Their potential as therapeutic targets, however, is complicated by overlapping activities with multiple other pathways and remains poorly defined in most clinical scenarios. Here we explore activity of the new pan-PIM inhibitor PIM447 in a variety of lymphoid-derived tumors. We find strong activity in cell lines derived from the activated B-cell subtype of diffuse large B-cell lymphoma (ABC-DLBCL). Sensitive lines show lost activation of the mTORC1 signaling complex and subsequent lost activation of cap-dependent protein translation. In addition, we characterize recurrent PIM1 protein-coding mutations found in DLBCL clinical samples and find most preserve the wild-type protein's ability to protect cells from apoptosis but do not bypass activity of PIM447. Pan-PIM inhibition therefore may have an important role to play in the therapy of selected ABC-DLBCL cases.