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

BackgroundThis first-in-human study evaluated AMG 208, a small-molecule MET inhibitor, in patients with advanced solid tumors.MethodsThree 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.ResultsFifty-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.ConclusionsIn this study, AMG 208 had manageable toxicities and showed evidence of antitumor activity, particularly in prostate cancer

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

Targeting BTK with Ibrutinib in Relapsed or Refractory Mantle-Cell Lymphoma – Results of an International, Multicenter, Phase 2 Study of Ibrutinib (PCI-32765) – EHA Encore

Bruton's tyrosine kinase (BTK) is a central mediator of B-cell receptor (BCR) signaling essential for normal B-cell development. Ibrutinib is an oral BTK inhibitor that induces apoptosis and inhibits migration and adhesion of malignant B-cells. Updated results of this international, multicenter, phase 2 study of single agent ibrutinib in relapsed or refractory MCL will be presented.Ibrutinib 560mg PO QD was administered continuously until disease progression. Tumor response was assessed every 2 cycles (one cycle=28 days). The study enrolled 115 patients (65 bortezomib-naïve, 50 bortezomib-exposed); 111 patients were treated; 110 were evaluable for response. Baseline characteristics included: median age 68 years, time since diagnosis 42 months, number of prior treatments 3; bulky disease (>10cm) 13%, prior stem cell transplant 10%, high risk MIPI 49%.Median time on treatment was 9.2 months; 53% of patients remain on therapy. Median PFS was 13.9 months and DOR has not yet been reached. Responses increased with longer treatment: comparing to previous data described at ASH 2011, the CR rate increased from 16% to 39%, and the ORR increased from 69% to 75%

RAS is required for the expression of interleukin-1(beta) in two diverse leukemic cell lines

Under normal physiological conditions, cells of the hematopoietic system produce Interleukin-1$\beta$(IL-1$\beta)$ only when a stimulus is present. Leukemic cells, however, can constitutively produce this cytokine without an exogenous source of activation. In addition, IL-1$\beta$ can operate as an autocrine and/or paracrine growth factor for leukemic blasts. In order to study the cellular basis for this aberrant production, we analyzed two leukemic cell lines (B1 and W1) which express high levels of IL-1$\beta$ and use IL-1$\beta$ as an autocrine growth factor. Initial studies demonstrated: (1) lack of rearrangement and/or amplification in the IL-1$\beta$ gene and its promoter; and (2) intact responsiveness to regulators such as cycloheximide and dexamethasone, implying that the molecular defect was upstream. Analysis of the Ras inducible transcription factors by gel shift assay demonstrated constitutive transcription factor binding in the IL-1$\beta$ promoter. Furthermore, RAS mutations were found at codon 12 in the K-RAS and N-RAS genes in the B1 and W1 cells, respectively. To deduce the effects of activated Ras on IL-1$\beta$ expression, two classes of farnesyltransferase inhibitors and an adenoviral vector expressing antisense targeted to K-RAS were utilized. The farnesyltransferase inhibitors perillyl alcohol and B581 were able to reduce IL-1$\beta$ levels by 80% and 50% in the B1 cells, respectively. In W1 cells, IL-1$\beta$ was reduced by 60% with 1mM perillyl alcohol. Antisense RNA targeted to K-RAS confirmed the results demonstrating a 50% reduction in IL-1$\beta$ expression in the B1 cells. In addition, decreased binding at the crucial NF-IL6/CREB binding site correlated with decreased IL-1$\beta$ production and cellular proliferation implying that this site was a downstream effector of Ras signaling. Our data suggest that mutated RAS genes may be responsible for autocrine IL-1$\beta$ production in some leukemias by stimulating signal transduction pathways that activate the IL-1$\beta$ promoter

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

Tipifarnib-Induced Apoptosis in Acute Myeloid Leukemia and Multiple Myeloma Cells Depends on Ca2+ Influx through Plasma Membrane Ca2+ ChannelsS⃞

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 ([Ca2+]i) in both cell lines. These elevations in [Ca2+]i were accompanied by highly dynamic plasmalemmal blebbing and frequently resulted in membrane lysis. The tipifarnib-induced elevations in [Ca2+]i were not blocked by thapsigargin or ruthenium red, but were inhibited by application of Ca2+-free extracellular solution and by the Ca2+ channel blockers Gd3+ and La3+. Conversely, 2-aminoethoxydiphenyl borate (2-APB) potentiated the tipifarnib-evoked [Ca2+]i overload. Preventing Ca2+ influx diminished tipifarnib-evoked cell death, whereas 2-APB potentiated this effect, demonstrating a link between tipifarnib-induced Ca2+ 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 Ca2+ channel and intracellular Ca2+ overload

Characterization of a R115777 Resistant Human Multiple Myeloma Cell Line with Cross-Resistance to PS-341

Abstract Multiple myeloma is an incurable disease where new treatment strategies are required to improve on current treatment standards. Based on this knowledge we have performed a phase II clinical trial testing the farnesyltransferase inhibitor R115777 in patients with relapsed myeloma (Alsina M. et al, Blood 2004). R115777 was found to have a favorable toxicity profile and 64% of patients achieved disease stabilization. RAS mutation and inhibition of farnesyltransferase did not correlate with clinical efficacy; findings consistent with our prior observation that R115777 induces apoptosis via a Ras independent mechanism (Beaupre D.M. et al, Mol. Cancer Ther. 2004). In order to further characterize the mechanisms by which R115777 induces apoptosis in myeloma cells and to investigate drug resistance, we have identified and characterized a R115777 resistant human myeloma cell line. 8226/S cells were cultured continuously in increasing concentrations of R115777 for over 6 months. 8226/R5 cells were found to be nearly 50 times more resistant to R115777 compared to the parent cell line. K-Ras remained prenylated in both resistant and sensitive cells after R115777 treatment; however, HDJ-2 farnesylation was inhibited in both lines implying that farnesyltranseferase (the drug target) is not modified. 8226/R5 cells were also resistant to a diverse group of anti-tumor agents including PS-341. 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 furthermore influx and efflux of R115777 was similar in both parent and resistant cells. Expression of the drug resistance proteins hsp27, 70, and 90 were also not increased. Comparison of 8226/S and 8226/R5 gene expression profiles revealed increased expression of JAK2 in resistant cells. Interestingly, STAT3 phosphorylation was significantly increased in the 8226/R5 line consistent with its reported role in myeloma drug resistance. Experiments are underway to delineate the contribution of JAK2 to the multidrug resistant phenotype. Characterization of aberrant JAK2 activation is relevant since constitutive STAT3 activity is frequently observed in primary myeloma isolates