Ibrutinib plus lenalidomide and rituximab has promising activity in relapsed/refractory non-germinal center B-cell-like DLBCL.

The outcome of patients with relapsed/refractory diffuse large B-cell lymphoma (DLBCL) is poor, particularly in patients ineligible for stem cell transplantation or who fail induction therapy or salvage therapy. The phase 1b portion of this open-label, dose-escalation (3+3+3 design) study examined the maximum tolerated dose (MTD) and preliminary safety and activity of the regimen in transplant-ineligible adults with histologically confirmed relapsed/refractory DLBCL after at least 1 prior therapy. Patients received once-daily 560 mg ibrutinib, 375 mg/m2 intravenous rituximab day 1 of cycles 1 to 6, and 10, 15, 20, or 25 mg lenalidomide days 1 to 21 of each 28-day cycle. Forty-five patients were treated; median time since diagnosis was 14.1 months, and 51% of the patients had non-germinal center B-cell-like (non-GCB) DLBCL, 33% had transformed DLBCL, 60% were refractory, and 27% were primary refractory. Because of dose-limiting toxicities, a de-escalation cohort (10 mg lenalidomide) was initiated, and with subsequent re-escalation up to 25 mg lenalidomide, the MTD was not reached. In response-evaluable patients, the overall response rate (ORR) was 44% (complete response [CR], 28%); among them, the ORR was 65% (CR, 41%) in non-GCB and 69% and 56% in relapsed (n = 16) and secondary refractory (n = 27) disease, respectively. Overall and for non-GCB, median response duration was 15.9 months, with 2 patients receiving therapy beyond 3 years. Phase 2 was initiated with 20 mg lenalidomide in relapsed/refractory non-GCB, whereas the phase 1b 25-mg lenalidomide cohort was being completed; an additional 25-mg cohort in phase 2 is currently ongoing. This study was registered at www.clinicaltrials.gov as #NCT02077166.

The combination of ibrutinib and rituximab demonstrates activity in first-line follicular lymphoma.

This phase 2 study evaluated the activity and safety of ibrutinib, a Bruton's tyrosine kinase inhibitor, plus rituximab in adults with previously untreated follicular lymphoma. Patients received once-daily ibrutinib 560 mg continuously plus once-weekly rituximab 375 mg/m2 for 4 weeks beginning Week 1 (Arm 1, n = 60) or Week 9 (following an 8-week ibrutinib lead-in) to explore biomarkers (Arm 2, n = 20). The primary endpoint was the best overall response rate (ORR). The median age was 58 years; most had an Eastern Cooperative Oncology Group Performance Status of 0 (74%) and Stage III/IV disease (84%). At a median study follow-up of 34 months in Arm 1 and 29 months in Arm 2, ORRs were 85% [95% confidence interval (CI) 73-93] and 75% (95% CI 51-91), respectively, with complete responses in 40% and 50%. The median duration of response was not reached in either arm; 30-month progression-free and overall survival rates were 67% and 97% (Arm 1) and 65% and 100% (Arm 2). The most common adverse events were fatigue, diarrhoea and nausea. Higher grade (Grade 3/4) haematological, haemorrhagic and cardiac events occurred infrequently. Ibrutinib plus rituximab was active and tolerable in first-line follicular lymphoma.

Targeting Bruton tyrosine kinase with ibrutinib in relapsed/refractory marginal zone lymphoma.

Marginal zone lymphoma (MZL) is a heterogeneous B-cell malignancy for which no standard treatment exists. MZL is frequently linked to chronic infection, which may induce B-cell receptor (BCR) signaling, resulting in aberrant B-cell survival and proliferation. We conducted a multicenter, open-label, phase 2 study to evaluate the efficacy and safety of ibrutinib in previously treated MZL. Patients with histologically confirmed MZL of all subtypes who received ≥1 prior therapy with an anti-CD20 antibody-containing regimen were treated with 560 mg ibrutinib orally once daily until progression or unacceptable toxicity. The primary end point was independent review committee-assessed overall response rate (ORR) by 2007 International Working Group criteria. Among 63 enrolled patients, median age was 66 years (range, 30-92). Median number of prior systemic therapies was 2 (range, 1-9), and 63% received ≥1 prior chemoimmunotherapy. In 60 evaluable patients, ORR was 48% (95% confidence interval [CI], 35-62). With median follow-up of 19.4 months, median duration of response was not reached (95% CI, 16.7 to not estimable), and median progression-free survival was 14.2 months (95% CI, 8.3 to not estimable). Grade ≥3 adverse events (AEs; >5%) included anemia, pneumonia, and fatigue. Serious AEs of any grade occurred in 44%, with grade 3-4 pneumonia being the most common (8%). Rates of discontinuation and dose reductions due to AEs were 17% and 10%, respectively. Single-agent ibrutinib induced durable responses with a favorable benefit-risk profile in patients with previously treated MZL, confirming the role of BCR signaling in this malignancy. As the only approved therapy, ibrutinib provides a treatment option without chemotherapy for MZL. This study is registered at www.clinicaltrials.gov as #NCT01980628.

Outcomes in 370 patients with mantle cell lymphoma treated with ibrutinib: a pooled analysis from three open-label studies.

Ibrutinib is highly active in treating mantle cell lymphoma (MCL), an aggressive B-cell lymphoma. We pooled data from three ibrutinib studies to explore the impact of baseline patient characteristics on treatment response. Patients with relapsed/refractory MCL (n = 370) treated with ibrutinib had an objective response rate (ORR) of 66% (20% complete response; 46% partial response); median duration of response (DOR), progression-free survival (PFS) and overall survival (OS) were 18·6, 12·8 and 25·0 months, respectively. Univariate analyses showed patients with one versus >one prior line of therapy had longer OS. Multivariate analyses identified that one prior line of therapy affected PFS; Eastern Cooperative Oncology Group (ECOG) performance status, simplified MCL international prognostic index (sMIPI) score, bulky disease, and blastoid histology affected OS and PFS. Patients with blastoid versus non-blastoid histology had similar time to best response, but lower ORR, DOR, PFS and OS. OS and PFS were longer in patients with better sMIPI, patients with ECOG performance status 0-1, non-bulky disease and non-blastoid histology. Additionally, the proportion of patients with poor prognostic factors increased with increasing lines of therapy. Together, results suggest that patient outcomes following treatment failure with ibrutinib are related to the natural biological evolution of the disease.

Long-term follow-up of MCL patients treated with single-agent ibrutinib: updated safety and efficacy results.

Ibrutinib, an oral inhibitor of Bruton tyrosine kinase, is approved for patients with mantle cell lymphoma (MCL) who have received one prior therapy. We report the updated safety and efficacy results from the multicenter, open-label phase 2 registration trial of ibrutinib (median 26.7-month follow-up). Patients (N = 111) received oral ibrutinib 560 mg once daily, and those with stable disease or better could enter a long-term extension study. The primary end point was overall response rate (ORR). The median patient age was 68 years (range, 40-84), with a median of 3 prior therapies (range, 1-5). The median treatment duration was 8.3 months; 46% of patients were treated for >12 months, and 22% were treated for ≥2 years. The ORR was 67% (23% complete response), with a median duration of response of 17.5 months. The 24-month progression-free survival and overall survival rates were 31% (95% confidence interval [CI], 22.3-40.4) and 47% (95% CI, 37.1-56.9), respectively. The most common adverse events (AEs) in >30% of patients included diarrhea (54%), fatigue (50%), nausea (33%), and dyspnea (32%). The most frequent grade ≥3 infections included pneumonia (8%), urinary tract infection (4%), and cellulitis (3%). Grade ≥3 bleeding events in ≥2% of patients were hematuria (2%) and subdural hematoma (2%). Common all-grade hematologic AEs were thrombocytopenia (22%), neutropenia (19%), and anemia (18%). The prevalence of infection, diarrhea, and bleeding was highest for the first 6 months of therapy and less thereafter. With longer follow-up, ibrutinib continues to demonstrate durable responses and favorable safety in relapsed/refractory MCL. The trial is registered to www.ClinicalTrials.gov as #NCT01236391.

Targeting BTK with ibrutinib in relapsed or refractory mantle-cell lymphoma.

BACKGROUND: Bruton's tyrosine kinase (BTK) is a mediator of the B-cell-receptor signaling pathway implicated in the pathogenesis of B-cell cancers. In a phase 1 study, ibrutinib, a BTK inhibitor, showed antitumor activity in several types of non-Hodgkin's lymphoma, including mantle-cell lymphoma. METHODS: In this phase 2 study, we investigated oral ibrutinib, at a daily dose of 560 mg, in 111 patients with relapsed or refractory mantle-cell lymphoma. Patients were enrolled into two groups: those who had previously received at least 2 cycles of bortezomib therapy and those who had received less than 2 complete cycles of bortezomib or had received no prior bortezomib therapy. The primary end point was the overall response rate. Secondary end points were duration of response, progression-free survival, overall survival, and safety. RESULTS: The median age was 68 years, and 86% of patients had intermediate-risk or high-risk mantle-cell lymphoma according to clinical prognostic factors. Patients had received a median of three prior therapies. The most common treatment-related adverse events were mild or moderate diarrhea, fatigue, and nausea. Grade 3 or higher hematologic events were infrequent and included neutropenia (in 16% of patients), thrombocytopenia (in 11%), and anemia (in 10%). A response rate of 68% (75 patients) was observed, with a complete response rate of 21% and a partial response rate of 47%; prior treatment with bortezomib had no effect on the response rate. With an estimated median follow-up of 15.3 months, the estimated median response duration was 17.5 months (95% confidence interval [CI], 15.8 to not reached), the estimated median progression-free survival was 13.9 months (95% CI, 7.0 to not reached), and the median overall survival was not reached. The estimated rate of overall survival was 58% at 18 months. CONCLUSIONS: Ibrutinib shows durable single-agent efficacy in relapsed or refractory mantle-cell lymphoma. (Funded by Pharmacyclics and others; ClinicalTrials.gov number, NCT01236391.)

Modulation of RNA splicing enhances response to BCL2 inhibition in leukemia.

Therapy resistance is a major challenge in the treatment of cancer. Here, we performed CRISPR-Cas9 screens across a broad range of therapies used in acute myeloid leukemia to identify genomic determinants of drug response. Our screens uncover a selective dependency on RNA splicing factors whose loss preferentially enhances response to the BCL2 inhibitor venetoclax. Loss of the splicing factor RBM10 augments response to venetoclax in leukemia yet is completely dispensable for normal hematopoiesis. Combined RBM10 and BCL2 inhibition leads to mis-splicing and inactivation of the inhibitor of apoptosis XIAP and downregulation of BCL2A1, an anti-apoptotic protein implicated in venetoclax resistance. Inhibition of splicing kinase families CLKs (CDC-like kinases) and DYRKs (dual-specificity tyrosine-regulated kinases) leads to aberrant splicing of key splicing and apoptotic factors that synergize with venetoclax, and overcomes resistance to BCL2 inhibition. Our findings underscore the importance of splicing in modulating response to therapies and provide a strategy to improve venetoclax-based treatments.

Tipifarnib-induced apoptosis in acute myeloid leukemia and multiple myeloma cells depends on Ca2+ influx through plasma membrane Ca2+ channels.

A major contributing factor to the high mortality rate associated with acute myeloid leukemia and multiple myeloma is the development of resistance to chemotherapy. We have shown that the combination of tipifarnib, a nonpeptidomimetic farnesyltransferase inhibitor (FTI), with bortezomib, a proteosome inhibitor, promotes synergistic death and overcomes de novo drug resistance in acute myeloid leukemia cell lines. Experiments were undertaken to identify the molecular mechanisms by which tipifarnib produces cell death in acute myeloid leukemia and multiple myeloma cell lines (U937 and 8226, respectively). Tipifarnib, but not other FTIs tested [N-[4-[2(R)-amino-3-mercaptopropyl]amino-2-phenylbenzoyl]methionine methyl ester trifluoroacetate salt (FTI-277) and 2'-methyl-5-((((1-trityl-1H-imidazol-4-yl)methyl)amino)methyl)-[1,1'-biphenyl]-2-carboxylic acid (FTI-2153), promotes elevations in intracellular free-calcium concentrations ([Ca(2+)](i)) in both cell lines. These elevations in [Ca(2+)](i) were accompanied by highly dynamic plasmalemmal blebbing and frequently resulted in membrane lysis. The tipifarnib-induced elevations in [Ca(2+)](i) were not blocked by thapsigargin or ruthenium red, but were inhibited by application of Ca(2+)-free extracellular solution and by the Ca(2+) channel blockers Gd(3+) and La(3+). Conversely, 2-aminoethoxydiphenyl borate (2-APB) potentiated the tipifarnib-evoked [Ca(2+)](i) overload. Preventing Ca(2+) influx diminished tipifarnib-evoked cell death, whereas 2-APB potentiated this effect, demonstrating a link between tipifarnib-induced Ca(2+) influx and apoptosis. These data suggest that tipifarnib exerts its effects by acting on a membrane channel with pharmacological properties consistent with store-operated channels containing the Orai3 subunit. It is noteworthy that Orai3 transcripts were found to be expressed at lower levels in tipifarnib-resistant 8226/R5 cells. Our results indicate tipifarnib causes cell death via a novel mechanism involving activation of a plasma membrane Ca(2+) channel and intracellular Ca(2+) overload.

Starting dose selection and dose escalation for oncology small molecule first-in-patient trials: learnings from a survey of FDA-approved drugs.

The ideal starting dose for an oncology first-in-patient (FIP) trial should be low enough to be safe but not too far removed from therapeutically relevant doses. A low starting dose combined with small dose increments could lead to a lengthy dose escalation and could expose patients unnecessarily to sub-therapeutic dosing. In the current analyses, we reviewed 59 approved small molecule oncology drugs (SMOD) with the overarching goals to assess the current approaches of FIP starting dose selection and dose escalation, and to identify potential opportunities for improving trial efficiency and minimizing number of patients receiving sub-therapeutic dose levels. Of 59 SMODs, the majority (~ 66%) were kinase inhibitors and ~ 73% were approved for solid tumor indications. Most of the trials used a 3 + 3 design for dose escalation and had a median (range) of 4 cohorts (0-11) to reach MTD from the starting dose. The maximum tolerated dose (MTD) or recommended phase 2 dose (RP2D) to starting dose ratio was highly variable with a median (range) of 8 (0.25-125). About 71% of the FIP trials had < 6 dose escalation steps to reach MTD or RP2D (with 15% ≤ 2 dose escalations), but the remaining 29% of trials had ≥ 6 dose escalation steps to reach MTD or RP2D suggesting that there is still room for increasing efficiency by reducing the number of dose escalation steps, reducing the variability in MTD to starting dose ratio, and consequently reducing significant number of patients exposed at sub-therapeutic doses in the dose escalation phase of FIP study.

Application of Real-World Data to External Control Groups in Oncology Clinical Trial Drug Development.

Randomized controlled trials (RCTs) that assess overall survival are considered the "gold standard" when evaluating the efficacy and safety of a new oncology intervention. However, single-arm trials that use surrogate endpoints (e.g., objective response rate or duration of response) to evaluate clinical benefit have become the basis for accelerated or breakthrough regulatory approval of precision oncology drugs for cases where the target and research populations are relatively small. Interpretation of efficacy in single-arm trials can be challenging because such studies lack a standard-of-care comparator arm. Although an external control group can be based on data from other clinical trials, using an external control group based on data collected outside of a trial may not only offer an alternative to both RCTs and uncontrolled single-arm trials, but it may also help improve decision-making by study sponsors or regulatory authorities. Hence, leveraging real-world data (RWD) to construct external control arms in clinical trials that investigate the efficacy and safety of drug interventions in oncology has become a topic of interest. Herein, we review the benefits and challenges associated with the use of RWD to construct external control groups, and the relevance of RWD to early oncology drug development.

Navigating the Regulatory Landscape to Develop Pediatric Oncology Drugs: Expert Opinion Recommendations.

Regulatory changes have been enacted in the United States (US) and European Union (EU) to encourage the development of new treatments for pediatric cancer. Here, we review some of the factors that have hampered the development of pediatric cancer treatments and provide a comparison of the US and EU regulations implemented to address this clinical need. We then provide some recommendations for each stage of the oncology drug development pathway to help researchers maximize their chance of successful drug development while complying with regulations. A key recommendation is the engagement of key stakeholders such as regulatory authorities, pediatric oncologists, academic researchers, patient advocacy groups, and a Pediatric Expert Group early in the drug development process. During drug target selection, sponsors are encouraged to consult the Food and Drug Administration (FDA), European Medicines Agency (EMA), and the FDA target list, in addition to relevant US and European consortia that have been established to characterize and prioritize oncology drug targets. Sponsors also need to carefully consider the resourcing requirements for preclinical testing, which include ensuring appropriate access to the most relevant databases, clinical samples, and preclinical models (cell lines and animal models). During clinical development, sponsors can account for the pharmacodynamic (PD)/pharmacokinetic (PK) considerations specific to a pediatric population by developing pediatric formulations, selecting suitable PD endpoints, and employing sparse PK sampling or modeling/simulation of drug exposures where appropriate. Additional clinical considerations include the specific design of the clinical trial, the potential inclusion of children in adult trials, and the value of cooperative group trials.

In the last few decades, great progress has been made in developing new treatments for adult cancers. However, development of new treatments for childhood cancers has been much slower. To encourage drug companies (sponsors) to develop effective treatments for childhood cancer, authorities in the United States (US) and Europe have made new rules for drug development. Under these new rules, sponsors developing drugs for specific cancers in adults have to consider whether the target of that drug also causes cancers in children. If this is the case, sponsors have to carry out clinical studies of their drug in children who have cancer that is caused by the same drug target. In this article, we describe some reasons for why drug development for childhood cancers has been slow and the rules created to address this problem in the US and Europe. We share some recommendations to help sponsors maximize their chances of developing an effective drug in children while satisfying the new rules. Specifically, sponsors need to be aware of the differences between studying drugs in adults versus children and how these influence the way the drug is tested. We make several recommendations for each stage of the development process, beginning with what is needed even before human studies begin. Finally, we highlight some issues that sponsors need to think about during drug development, from the preclinical stage (testing drugs in cells and animals) through to clinical testing in adults and pediatric patients with cancer.

Phase 1b/2 study of ibrutinib and lenalidomide with dose-adjusted EPOCH-R in patients with relapsed/refractory diffuse large B-cell lymphoma.

Relapsed/refractory diffuse large B-cell lymphoma (DLBCL) is difficult to cure; non-germinal center B-cell-like (non-GCB) and activated B-cell-like (ABC) DLBCL have worse outcomes than GCB DLBCL. Ibrutinib and lenalidomide are synergistic in vitro in ABC DLBCL and may augment salvage chemotherapy. In part 1 of this phase 1b/2 study (NCT02142049), patients with relapsed/refractory DLBCL received ibrutinib 560 mg and escalating doses of lenalidomide on Days 1-7 with DA-EPOCH-R (Days 1-5) in 21-day cycles. In part 1 (N = 15), the maximum tolerated dose was not reached with lenalidomide 25 mg (recommended part 2 dose [RP2D]); most common grade ≥3 adverse events were anemia (73%) and febrile neutropenia (47%); the overall response rate (ORR) was 40%. At the RP2D (n = 26), ORR was 71% in non-GCB and 64% in ABC. Ibrutinib and lenalidomide with DA-EPOCH-R had a manageable safety profile and antitumor activity in relapsed/refractory DLBCL, especially the non-GCB subtype.

Tipifarnib and bortezomib are synergistic and overcome cell adhesion-mediated drug resistance in multiple myeloma and acute myeloid leukemia.

It has been established in preclinical models of multiple myeloma and acute myeloid leukemia (AML) that the bone marrow microenvironment provides protection from chemotherapy- and death receptor-mediated apoptosis. This form of resistance, termed de novo drug resistance, occurs independent of chronic exposure to cancer-related therapies and likely promotes the development of multidrug resistance. Consequently, it is of major interest to identify compounds or drug combinations that can overcome environment-mediated resistance. In this study, we investigated the activity of tipifarnib (Zarnestra, formerly R115777) combined with bortezomib (Velcade, formerly PS-341) in microenvironment models of multiple myeloma and AML. The combination proved to be synergistic in multiple myeloma and AML cell lines treated in suspension culture. Even in tumor cells relatively resistant to tipifarnib, combined activity was maintained. Tipifarnib and bortezomib were also effective when multiple myeloma and AML cells were adhered to fibronectin, providing evidence that the combination overcomes cell adhesion-mediated drug resistance (CAM-DR). Of importance, activation of the endoplasmic reticulum stress response was enhanced and correlated with apoptosis and reversal of CAM-DR. Multiple myeloma and AML cells cocultured with bone marrow stromal cells also remained sensitive, although stromal-adhered tumor cells were partially protected (relative to cells in suspension or fibronectin adhered). Evaluation of the combination using a transwell apparatus revealed that stromal cells produce a protective soluble factor. Investigations are under way to identify the cytokines and/or growth factors involved. In summary, our study provides the preclinical rationale for trials testing the tipifarnib and bortezomib combination in patients with multiple myeloma and AML.

Combination of Ibrutinib and ABT-199 in Diffuse Large B-Cell Lymphoma and Follicular Lymphoma.

Diffuse large B-cell lymphoma (DLBCL) and follicular lymphoma are the most prevalent B-lymphocyte neoplasms in which abnormal activation of the Bruton tyrosine kinase (BTK)-mediated B-cell receptor signaling pathway contributes to pathogenesis. Ibrutinib is an oral covalent BTK inhibitor that has shown some efficacy in both indications. To improve ibrutinib efficacy through combination therapy, we first investigated differential gene expression in parental and ibrutinib-resistant cell lines to better understand the mechanisms of resistance. Ibrutinib-resistant TMD8 cells had higher BCL2 gene expression and increased sensitivity to ABT-199, a BCL-2 inhibitor. Consistently, clinical samples from ABC-DLBCL patients who experienced poorer response to ibrutinib had higher BCL2 gene expression. We further demonstrated synergistic growth suppression by ibrutinib and ABT-199 in multiple ABC-DLBCL, GCB-DLBCL, and follicular lymphoma cell lines. The combination of both drugs also reduced colony formation, increased apoptosis, and inhibited tumor growth in a TMD8 xenograft model. A synergistic combination effect was also found in ibrutinib-resistant cells generated by either genetic mutation or drug treatment. Together, these findings suggest a potential clinical benefit from ibrutinib and ABT-199 combination therapy. Mol Cancer Ther; 16(7); 1246-56. ©2017 AACR.

Characterization of a R115777-resistant human multiple myeloma cell line with cross-resistance to PS-341.

The farnesyl transferase inhibitor R115777 has been found to have clinical activity in diverse hematopoietic tumors. Clinical efficacy, however, does not correlate with Ras mutation status or inhibition of farnesyl transferase. To further elucidate the mechanisms by which R115777 induces apoptosis and to investigate drug resistance, we have identified and characterized a R115777-resistant human myeloma cell line. 8226/R5 cells were found to be at least 50 times more resistant to R115777 compared with the parent cell line 8226/S. K-Ras remained prenylated in both resistant and sensitive cells after R115777 treatment; however, HDJ-2 farnesylation was inhibited in both lines, implying that farnesyl transferase (the drug target) has not been mutated. Whereas many 8226 lines that acquire drug resistance have elevated expression of P-glycoprotein, we found that P-glycoprotein expression is not increased in the 8226/R5 line and intracellular accumulation of R115777 was not reduced. In fact, 8226/R5 cells were insensitive to a diverse group of antitumor agents including PS-341, and multidrug resistance did not correlate with the expression of heat shock proteins. Comparison of gene expression profiles between resistant and sensitive cells revealed expression changes in several genes involved in myeloma survival and drug resistance. Future experiments will attempt to identify genes that are directly linked to the resistant phenotype. Identification of molecules associated with R115777 and PS-341 resistance is clinically relevant because both compounds are being tested in solid tumors and hematopoietic malignancies.

The role of PIM1 in the ibrutinib-resistant ABC subtype of diffuse large B-cell lymphoma.

Diffuse large B cell lymphoma (DLBCL) is a heterogeneous lymphoma and the most common subtype of non-Hodgkin lymphoma, accounting for roughly 30% of newly diagnosed cases in the United States. DLBCL can be separated into the activated B cell-like (ABC) and germinal center B cell-like (GCB) subtypes, with distinct gene expression profiles, oncogenic aberrations, and clinical outcomes. ABC-DLBCL is characterized by chronically active B-cell receptor (BCR) signaling that can be modulated by Bruton's tyrosine kinase (BTK) activity. Thus, BTK serves as an attractive therapeutic target in this type of B-cell malignancy. Ibrutinib, a first-in-class, orally available covalent BTK inhibitor, has demonstrated clinical activity in several B-cell leukemias and lymphomas. A phase 1/2 clinical trial of single-agent ibrutinib in relapsed and refractory DLBCL patients revealed an overall response rate of 37% in ABC-DLBCL patients. However, responses to kinase-directed therapies are often limited by emerging resistance mechanisms that bypass the therapeutic target. Here we report the discovery of point mutations within the kinase PIM1 that reduce sensitivity to ibrutinib in ABC-DLBCL. These mutations stabilize PIM1 and affect upstream regulators and downstream targets of NF-κB signaling. The introduction of mutant PIM1 into an ABC-DLBCL cell line, TMD8, increased colony formation and decreased sensitivity to ibrutinib. In addition, ibrutinib-resistant cell lines generated by prolonged ibrutinib exposure in vitro upregulated PIM1 expression, consistent with a role for PIM1 in antagonizing ibrutinib activity. The combination of a pan-PIM inhibitor with ibrutinib synergistically inhibited proliferation in vitro and tumor growth in vivo. Together, these data provide a rationale for combining BTK and PIM1 inhibition in the treatment of ABC-DLBCL.

R115777 induces Ras-independent apoptosis of myeloma cells via multiple intrinsic pathways.

Ras activation is frequently observed in multiple myeloma either by mutation or through interleukin-6 receptor signaling. Recently, drugs designed to inhibit Ras have shown promise in preclinical myeloma models and in clinical trials. In this report, we characterize the pathways by which the clinically tested farnesyl transferase inhibitor (FTI) R115777 induces apoptosis in multiple myeloma cells. Contrary to the proposed mechanistic action of FTIs, we found that R115777 induces cell death despite Ras prenylation implying participation of Ras-independent mechanism(s). Apoptosis proceeded via an intrinsic cascade and was associated with an increase in the expression and activity of Bax. Bax activation correlated with a loss of mitochondrial membrane integrity and activation of the endoplasmic reticulum (ER) stress response. These pathways activate caspase-9 and consistent with this, cell death was prevented by caspase-9 blockade. Interestingly, cells overexpressing Bcl-X(L) remained partially sensitive to R115777 despite suppression of mitochondrial membrane dysfunction and ER-related stress. Taken together, these results indicate that R115777 induces apoptosis in a Ras-independent fashion via multiple intrinsic pathways.

A first-in-human study of AMG 208, an oral MET inhibitor, in adult patients with advanced solid tumors.

BACKGROUND: This first-in-human study evaluated AMG 208, a small-molecule MET inhibitor, in patients with advanced solid tumors. METHODS: Three to nine patients were enrolled into one of seven AMG 208 dose cohorts (25, 50, 100, 150, 200, 300, and 400 mg). Patients received AMG 208 orally on days 1 and days 4-28 once daily. The primary objectives were to evaluate the safety, tolerability, pharmacokinetics, and maximum tolerated dose (MTD) of AMG 208. RESULTS: Fifty-four patients were enrolled. Six dose-limiting toxicities were observed: grade 3 increased aspartate aminotransferase (200 mg), grade 3 thrombocytopenia (200 mg), grade 4 acute myocardial infarction (300 mg), grade 3 prolonged QT (300 mg), and two cases of grade 3 hypertension (400 mg). The MTD was not reached. The most frequent grade ≥3 treatment-related adverse event was anemia (n = 3) followed by hypertension, prolonged QT, and thrombocytopenia (two patients each). AMG 208 exposure increased linearly with dose; mean plasma half-life estimates were 21.4-68.7 hours. One complete response (prostate cancer) and three partial responses (two in prostate cancer, one in kidney cancer) were observed. CONCLUSIONS: In this study, AMG 208 had manageable toxicities and showed evidence of antitumor activity, particularly in prostate cancer.

Targeting B cell receptor signaling with ibrutinib in diffuse large B cell lymphoma.

The two major subtypes of diffuse large B cell lymphoma (DLBCL)--activated B cell-like (ABC) and germinal center B cell-like (GCB)--arise by distinct mechanisms, with ABC selectively acquiring mutations that target the B cell receptor (BCR), fostering chronic active BCR signaling. The ABC subtype has a ∼40% cure rate with currently available therapies, which is worse than the rate for GCB DLBCL, and highlights the need for ABC subtype-specific treatment strategies. We hypothesized that ABC, but not GCB, DLBCL tumors would respond to ibrutinib, an inhibitor of BCR signaling. In a phase 1/2 clinical trial that involved 80 subjects with relapsed or refractory DLBCL, ibrutinib produced complete or partial responses in 37% (14/38) of those with ABC DLBCL, but in only 5% (1/20) of subjects with GCB DLBCL (P = 0.0106). ABC tumors with BCR mutations responded to ibrutinib frequently (5/9; 55.5%), especially those with concomitant myeloid differentiation primary response 88 (MYD88) mutations (4/5; 80%), a result that is consistent with in vitro cooperation between the BCR and MYD88 pathways. However, the highest number of responses occurred in ABC tumors that lacked BCR mutations (9/29; 31%), suggesting that oncogenic BCR signaling in ABC does not require BCR mutations and might be initiated by non-genetic mechanisms. These results support the selective development of ibrutinib for the treatment of ABC DLBCL.