Farnesyltransferase inhibitor R115777 inhibits cell growth and induces apoptosis in mantle cell lymphoma

Mechanisms of Chromosome Congression during Mitosis

Chromosome congression during prometaphase culminates with the establishment of a metaphase plate, a hallmark of mitosis in metazoans. Classical views resulting from more than 100 years of research on this topic have attempted to explain chromosome congression based on the balance between opposing pulling and/or pushing forces that reach an equilibrium near the spindle equator. However, in mammalian cells, chromosome bi-orientation and force balance at kinetochores are not required for chromosome congression, whereas the mechanisms of chromosome congression are not necessarily involved in the maintenance of chromosome alignment after congression. Thus, chromosome congression and maintenance of alignment are determined by different principles. Moreover, it is now clear that not all chromosomes use the same mechanism for congressing to the spindle equator. Those chromosomes that are favorably positioned between both poles when the nuclear envelope breaks down use the so-called "direct congression" pathway in which chromosomes align after bi-orientation and the establishment of end-on kinetochore-microtubule attachments. This favors the balanced action of kinetochore pulling forces and polar ejection forces along chromosome arms that drive chromosome oscillatory movements during and after congression. The other pathway, which we call "peripheral congression", is independent of end-on kinetochore microtubule-attachments and relies on the dominant and coordinated action of the kinetochore motors Dynein and Centromere Protein E (CENP-E) that mediate the lateral transport of peripheral chromosomes along microtubules, first towards the poles and subsequently towards the equator. How the opposite polarities of kinetochore motors are regulated in space and time to drive congression of peripheral chromosomes only now starts to be understood. This appears to be regulated by position-dependent phosphorylation of both Dynein and CENP-E and by spindle microtubule diversity by means of tubulin post-translational modifications. This so-called "tubulin code" might work as a navigation system that selectively guides kinetochore motors with opposite polarities along specific spindle microtubule populations, ultimately leading to the congression of peripheral chromosomes. We propose an integrated model of chromosome congression in mammalian cells that depends essentially on the following parameters: (1) chromosome position relative to the spindle poles after nuclear envelope breakdown; (2) establishment of stable end-on kinetochore-microtubule attachments and bi-orientation; (3) coordination between kinetochore- and arm-associated motors; and (4) spatial signatures associated with post-translational modifications of specific spindle microtubule populations. The physiological consequences of abnormal chromosome congression, as well as the therapeutic potential of inhibiting chromosome congression are also discussed.

B-cell receptor signaling in the pathogenesis of lymphoid malignancies

B-cell receptor (BCR) signaling pathway plays a central role in B-lymphocyte development and initiation of humoral immunity. Recently, BCR signaling pathway has been shown as a major driver in the pathogenesis of B-cell malignancies. As a result, a vast array of BCR-associated kinases has emerged as rational therapeutic targets changing treatment paradigms in B cell malignancies. Based on high efficacy in early-stage clinical trials, there is rapid clinical development of inhibitors targeting BCR signaling pathway. Here, we describe the essential components of BCR signaling, their function in normal and pathogenic signaling and molecular effects of their inhibition in vitro and in vivo.

Mouse models of mantle cell lymphoma, complex changes in gene expression and phenotype of engrafted MCL cells: implications for preclinical research

Mantle cell lymphoma (MCL) is an aggressive type of B-cell non-Hodgkin lymphoma (NHL) associated with poor prognosis. Animal models of MCL are scarce. We established and characterized various in vivo models of metastatic human MCL by tail vein injection of either primary cells isolated from patients with MCL or established MCL cell lines (Jeko-1, Mino, Rec-1, Hbl-2, and Granta-519) into immunodeficient NOD.Cg-Prkdc(scid) Il2rg(tm1Wjl)/SzJ mice. MCL infiltration was assessed with immunohistochemistry (tissues) and flow cytometry (peripheral blood). Engraftment of primary MCL cells was observed in 7 out of 12 patient samples. The pattern of engraftment of primary MCL cells varied from isolated involvement of the spleen to multiorgan infiltration. On the other hand, tumor engraftment was achieved in all five MCL cell lines used and lymphoma involvement of murine bone marrow, spleen, liver, and brain was observed. Overall survival of xenografted mice ranged from 22 ± 1 to 54 ± 3 days depending on the cell line used. Subsequently, we compared the gene expression profile (GEP) and phenotype of the engrafted MCL cells compared with the original in vitro growing cell lines (controls). We demonstrated that engrafted MCL cells displayed complex changes of GEP, protein expression, and sensitivity to cytotoxic agents when compared with controls. We further demonstrated that our MCL mouse models could be used to test the therapeutic activity of systemic chemotherapy, monoclonal antibodies, or angiogenesis inhibitors. The characterization of MCL murine models is likely to aid in improving our knowledge in the disease biology and to assist scientists in the preclinical and clinical development of novel agents in relapsed/refractory MCL patients.

Nuclear assembly as a target for anti-cancer therapies

Current anti-cancer therapies have a great deal of undesirable side effects; therefore, there is a need to develop efficient and cancer cell-specific new drugs without strong dose-limiting side effects. In my opinion, mechanisms of nuclear assembly and organization represent a novel platform for drug targets, which might fulfill these criteria. The nuclear stiffness and organization of some cancer types are often compromised, making them more vulnerable for further targeting the mechanisms of nuclear integrity than their normal counterparts. Here I will discuss the nuclear organization of normal cells and cancer cells, the molecular mechanisms that govern nuclear assembly with emphasis on those that, in my view, might be considered as targets for future anti-cancer therapies.

The role of the nuclear lamina in cancer and apoptosis

Not long after the discovery of lamin proteins, it became clear that not all lamin subtypes are ubiquitously expressed in cells and tissues. Especially, A-type lamins showed an inverse correlation with proliferation and were thus initially called statins. Here we compare the findings of both A- and B-type lamin expression in various normal tissues and their neoplastic counterparts. Based on immunocytochemistry it becomes clear that lamin expression patterns are much more complicated than initially assumed: while normally proliferative cells are devoid of A-type lamin expression, many neoplastic tissues do show prominent A-type lamin expression. Conversely, cells that do not proliferate can be devoid of lamin expression. Yet, within the different types of tissues and tumors, lamins can be used to distinguish between tumor subtypes. The link between the appearance of A-type lamins in differentiation and the appearance of A-type lamins in a tumor likely relates the proliferative capacity of the tumor to its differentiation state.While lamins are targets for degradation in the apoptotic process, and accordingly are often used as markers for apoptosis, intriguing studies on an active role of lamins in the initiation or the prevention of apoptosis have been published recently and give rise to a renewed interest in the role of lamins in cancer.

Murine models in mantle cell lymphoma

Mantle cell lymphoma (MCL), an aggressive, heterogeneous B-cell lymphoma associated with a relatively short survival has been challenging to study in the laboratory due to the lack of in vitro and in vivo models that accurately recapitulate the disease. Advancement has been made in the characterization of MCL cell lines through the generation of the ATCC MCL bank, enabling their use in xenograft murine models. These models provide valuable but limited information for the preclinical evaluation and development of targeted therapies for MCL despite their deficiencies of a functioning immune system and correct micro-environment. Currently, there is only one double transgenic murine model known to develop spontaneous MCL. There is an urgency to develop innovative transgenic murine models that could be used to better predict therapeutic responses and precisely decipher mechanisms of action, to foster refinement of novel therapeutics for mantle cell lymphoma.

The proteasome inhibitor bortezomib targets cell cycle and apoptosis and acts synergistically in a sequence-dependent way with chemotherapeutic agents in mantle cell lymphoma

Single-agent bortezomib, a potent, selective, and reversible inhibitor of the 26S proteasome, has demonstrated clinical efficacy in relapsed and refractory mantle cell lymphoma (MCL). Objective response is achieved in up to 45% of the MCL patients; however, complete remission rates are low and duration of response proved to be relatively short. These limitations may be overcome by combining proteasome inhibition with conventional chemotherapy. Rational combination treatment and schedules require profound knowledge of underlying molecular mechanisms. Here we show that single-agent bortezomib treatment of MCL cell lines leads to G2/M arrest and induction of apoptosis accompanied by downregulation of EIF4E and CCND1 mRNA but upregulation of p15(INK4B) and p21 mRNA. We further present synergistic efficacy of bortezomib combined with cytarabine in MCL cell lines. Interestingly this sequence-dependent synergistic effect was seen almost exclusively in combination with AraC, indicating that pretreatment with cytarabine, followed by proteasome inhibition, may be the preferred approach.

Tipifarnib and tanespimycin show synergic proapoptotic activity in U937 cells

BACKGROUND

Farnesyltransferase inhibitor tipifarnib (R115777) has been used for treatment of hematological malignancies; however, its observed anticancer effect was limited. This prompted us to search for inhibitors that would show synergic, proapoptotic effect when combined with R115777. We decided to study LY294002, which inhibits PI-3 kinase, and tanespimycin (17AAG), which inhibits Hsp90--a chaperone for a number of proteins, including Akt kinase.

METHODS

The effect of drugs, used alone or in combination, was tested in U937 cells (human leukemic monocyte lymphoma), which are often used as a model for liquid tumor. The number of viable cells was evaluated with trypan blue staining, while apoptosis was assessed by presence of active caspase-3 and terminal dUTP nick-end labeling of DNA (TUNEL).

RESULTS

At concentrations in which R115777, LY294002 and 17AAG were only slowing down the proliferation rate, when used separately, the combination of R115777 + LY294002 and R115777 + 17AAG significantly reduced the number of cells and induced cellular apoptosis.

CONCLUSIONS

Our results suggest that the combination of R115777 + 17AAG could be useful in treating some of the hematological malignancies.

Multi-institutional phase 2 study of the farnesyltransferase inhibitor tipifarnib (R115777) in patients with relapsed and refractory lymphomas

A phase 2 study of the oral farnesyltransferase inhibitor tipifarnib was conducted in 93 adult patients with relapsed or refractory lymphoma. Patients received tipifarnib 300 mg twice daily on days 1-21 of each 28-day cycle. The median number of prior therapies was 5 (range, 1-17). For the aggressive B-cell, indolent B-cell, and T-cell and Hodgkin lymphoma (HL/T) groups, the response rates were 17% (7/42), 7% (1/15), and 31% (11/36), respectively. Of the 19 responders, 7 were diffuse large B-cell non-Hodgkin lymphoma (NHL), 7 T-cell NHL, 1 follicular grade 2, and 4 HL. The median response duration for the 19 responders was 7.2 months (mean, 15.8 months; range, 1.8-62), and 5 patients in the HL/T group are still receiving treatment at 29-64+ months. The grade 3/4 toxicities observed were fatigue and reversible myelosuppression. Correlative studies suggest that Bim and Bcl-2 should be examined as potential predictors of response in future studies. These results indicate that tipifarnib has activity in lymphoma, particularly in heavily pretreated HL/T types, with little activity in follicular NHL. In view of its excellent toxicity profile and novel mechanism of action, further studies in combination with other agents appear warranted. This trial is registered at www.clinicaltrials.gov as #NCT00082888.

Combination therapy of bortezomib with novel targeted agents: an emerging treatment strategy

Clinical trials evaluating combinations of targeted agents with bortezomib, the first-in-class proteasome inhibitor, have been initiated, with the objective of enhancing its single agent activity in hematologic malignancies (myeloma, mantle cell lymphoma), as well as expanding its efficacy in solid tumors. In most cases, preclinical studies have provided a supportive rationale for designing these doublet combination studies. Novel, small molecule-targeted agents being investigated with bortezomib in clinical trials include protein deacetylase inhibitors, kinase inhibitors, farnesyltransferase inhibitors, heat-shock protein 90 inhibitors, pan-Bcl-2 family inhibitors, and other classes of targeted inhibitors. Preliminary clinical data, available from a number of ongoing trials, suggest that most of these combinations are well tolerated and some have promising clinical efficacy that will require subsequent confirmation. Translational studies, conducted as part of the trials, may provide important insights into the putative mechanism of action delineated by preclinical studies of the combinations. The emergence of novel proteasome inhibitors may also expand the opportunities for optimizing these combination therapies. There is potential for an increasingly broad clinical trials program to investigate this therapeutic approach in a range of tumor types, as well as to consider additional agents in sequence or in combination.

2-D PAGE-based comparison of proteasome inhibitor bortezomib in sensitive and resistant mantle cell lymphoma

Although gene expression following bortezomib treatment has been previously explored, direct effects of bortezomib-induced proteasome inhibition on protein level has not been analyzed so far. Using 2-D PAGE in five mantle cell lymphoma cell lines, we screened for cellular protein level alterations following treatment with 25 nM bortezomib for up to 4 h. Using MS, we identified 38 of the 41 most prominent reliably detected protein spots. Twenty-one were affected in all cell lines, whereas the remaining 20 protein spots were exclusively altered in sensitive cell lines. Western blot analysis was performed for 17 of the 38 identified proteins and 70.6% of the observed protein level alterations in 2-D gels was verified. All cell lines exhibited alterations of the cellular protein levels of heat shock-induced protein species (HSPA9, HSP7C, HSPA5, HSPD1), whereas sensitive cell lines also displayed altered cellular protein levels of energy metabolism (ATP5B, AK5, TPI1, ENO-1, ALDOC, GAPDH), RNA and transcriptional regulation (HNRPL, SFRS12) and cell division (NEBL, ACTB, SMC1A, C20orf23) as well as tumor suppressor genes (ENO-1, FH). These proteins clustered in a tight interaction network centered on the major cellular checkpoints TP53. The results were confirmed in primary mantle cell lymphoma, thus confirming the critical role of these candidate proteins of proteasome inhibition.

Imidazole-containing farnesyltransferase inhibitors: 3D quantitative structure-activity relationships and molecular docking

One of the most promising anticancer and recent antimalarial targets is the heterodimeric zinc-containing protein farnesyltransferase (FT). In this work, we studied a highly diverse series of 192 Abbott-initiated imidazole-containing compounds and their FT inhibitory activities using 3D-QSAR and docking, in order to gain understanding of the interaction of these inhibitors with FT to aid development of a rational strategy for further lead optimization. We report several highly significant and predictive CoMFA and CoMSIA models. The best model, composed of CoMFA steric and electrostatic fields combined with CoMSIA hydrophobic and H-bond acceptor fields, had r (2) = 0.878, q (2) = 0.630, and r (pred) (2) = 0.614. Docking studies on the statistical outliers revealed that some of them had a different binding mode in the FT active site based on steric bulk and available active site space, explaining why the predicted activities differed from the experimental activities.