Valproic acid enhances fludarabine-induced apoptosis mediated by ROS and involving decreased AKT and ATM activation in B-cell-lymphoid neoplastic cells

Histone deacetylase (HDAC) inhibitors have been shown synergize with a number of cytotoxic drugs in leukemic cells. In chronic lymphocytic leukemia (CLL), the first line therapy is based on the combination of fludarabine, a nucleoside analogue, and rituximab, an anti-CD20 monoclonal antibody, and there are presently no HDAC inhibitors are used to manage CLL. In the present study, we found that the addition of valproic acid (VPA), a HDAC inhibitor, increases cell death in B-cell-neoplasm-derived cell lines, BJAB, NALM-6 and I-83. This increased apoptosis caused release of mitochondrial cytochrome c, activation of caspases, and increased reactive oxygen species (ROS). The addition of a ROS scavenger inhibited cell death induced by the VPA-fludarabine combination. In contrast, blocking the death receptor pathway failed to inhibit VPA increased fludarabine induced apoptosis. Combination of VPA and fludarabine treatment decreased both total and phosphorylated levels of AKT, an important anti-apoptotic protein, and ATM, a pivotal protein in DNA damage response. Chemical inhibition of AKT or ATM was sufficient to enhance fludarabine-induced apoptosis. We next examined patient samples from a local clinical trial where relapsed CLL patients were treated with VPA and examined the effects of VPA on AKT and ATM in vivo. After 30 days, there was a reduction in ATM levels in three out of the four patients treated, while AKT phosphorylation was reduced only in one patient. Taken together, VPA reduces ATM levels, thereby increasing ROS-dependent cell death via the mitochondrial apoptotic pathway when combined with fludarabine.

The role of the ubiquitin proteasome system in lymphoma

The ubiquitin-proteasome system (UPS) maintains the integrity of cellular processes by controlling protein degradation pathways. The role of the UPS in proliferation, cell cycle, differentiation, DNA repair, protein folding, and apoptosis is well documented, and a wide range of protein activities in these signaling pathways can be manipulated by UPS inhibitors, which include many anti-cancer agents. Naturally occurring and synthetic drugs designed to target the UPS are currently used for hematological cancers, including lymphoma. These drugs largely interfere with the E1 and E2 regions of the 26S proteasome, blocking proteasomal activity and promoting apoptosis by enhancing activities of the extrinsic (death receptors, Trail, Fas) and intrinsic (caspases, Bax, Bcl2, p53, nuclear factor-kappa B, p27) cell death programs. This review focuses on recent clinical developments concerning UPS inhibitors, signaling pathways that are affected by down-regulation of UPS activities, and apoptotic mechanisms promoted by drugs in this class that are used to treat lymphoma.

Initial management strategies for follicular lymphoma

Follicular lymphoma (FL) can vary markedly in its initial presentation, and no single standard approach for its initial management has been adopted. Available options for the initial management of FL include watchful waiting, radiation, single-agent rituximab and combination of rituximab and chemotherapy with strategies segregated for patients who have low and high tumor burden disease based on established criteria. However, marked debate occurs regarding the role of watchful waiting in the modern era for low tumor burden, asymptomatic patients, the optimal timing of rituximab, the selection of chemotherapy regimen to partner with rituximab in high tumor burden patients, and strategies for the management of relapsed disease. We provide an evidence-based discussion on these and other issues regarding the management of FL, and propose a mathematical modeling approach for addressing some of these questions.

Treatment Strategies for Patients with Diffuse Large B-Cell Lymphoma: Past, Present, and Future

Diffuse large B-cell lymphoma (DLBCL) is the most commonly occurring lymphoma in the Western world. DLBCL is a clinically, biologically, and pathologically heterogeneous entity with biologically distinct subtypes that have different expected treatment outcomes. The addition of rituximab to combination chemotherapy has improved outcomes for all patients with DLBCL and can produce cure for many individuals. Relapsed DLBCL is generally managed with salvage chemo-immunotherapy followed by high dose therapy and autologous stem cell transplantation which can cure additional patients. However, outcomes for patients who relapse early after upfront rituximab and chemotherapy have a poorer prognosis. Novel therapies and strategies are desperately needed for these patients and several emerging treatments hold promise for improving DLBCL treatment outcomes in the future.

Bone marrow CFU-GM and human tumor xenograft efficacy of three tubulin binding agents

PURPOSE

The dynamic instability of microtubules in cells is one of the key targets of anticancer therapeutics. Microtubule-disrupting agents such as vinca alkaloids and microtubule-stabilizing agents such as taxanes are important antitumor agents. The bone marrow toxicity and human tumor xenograft activity of three tubulin-binding compounds, vincristine, paclitaxel, and tasidotin were compared.

METHODS

Mouse and human bone marrow were subjected to colony-forming (CFU-GM) assays over a 5-log concentration range in culture. In vivo, a range of tasidotin doses was compared with vincristine, paclitaxel, and docetaxel for efficacy in several human tumor xenografts.

RESULTS

The IC(90) concentrations for vincristine and paclitaxel for mouse CFU-GM were 30 and 27 nM, and for human CFU-GM were 3 and 9 nM, giving mouse to human differentials of ten- and threefold. Tasidotin produced IC(90)s of >300 nM in mouse and 65 nM in human CFU-GM, thus a >4.6-fold differential between species. In vivo, tasidotin resulted in a dose-dependent increase in tumor growth delay in the RL lymphoma, the RPMI 8226 multiple myeloma, and MX-1 breast carcinoma models. Vincristine and tasidotin were also very effective against these tumors. The PC-3 prostate carcinoma was very responsive to full-dose paclitaxel and docetaxel while tasidotin generated a dose dependent effect.

CONCLUSIONS

Bringing together bone marrow toxicity data, pharmacokinetic parameters, and human tumor xenograft efficacy provides valuable information for the translation of preclinical findings to the clinic.

Idiotype vaccine strategies for improving outcomes in follicular lymphoma

BACKGROUND

Follicular lymphoma (FL) is a common indolent lymphoma associated with a relapsing course. Preclinical models and clinical studies demonstrate that immunizing FL patients against their own tumor idiotype induces humoral and cellular immunity and supresses tumor growth.

METHODS

We review idiotype vaccine strategies that have been tested in FL patients in frontline and relapsed settings to examine the safety and efficacy of this approach.

RESULTS

Several Phase II trials of recombinant or hybridoma-produced vaccines or vaccines combined with other immunotherapy demonstrate cellular and humoral anti-idiotype responses and clinical responses, indicating that idiotype vaccines provide promise for improving FL outcomes.

CONCLUSION

These strategies are now being evaluated in Phase III trials but have yet to demonstrate clear advantages in progression-free survival.