Chemo-Resistance in Diffuse Large Cell Lymphoma: Novel Drug Combinations Targeting NFAT/NF-Kb Growth/Survival/Chemo-Resistance Signaling Pathways in Validated Novel Experimental Systems

Abstract 1428

Acquired chemo-resistance (ACR) is currently the most important cause of treatment failure and early mortality in DLBCL, arguably the most important unmet need in lymphoma therapy today. Diffuse Large B cell Lymphoma (DLBCL), the most common human lymphoma, comprises a genetically and clinically diverse group of aggressive B cell non-Hodgkin lymphomas (NHL-B), among a small group of important human cancers increasing in incidence in the US over the last four decades. NHL-B are the fifth most common cancers in the USA (>62,000 new cases/20,000 deaths) expected in 2011. The molecular biologic and genetic basis of the patho-physiology of these important lymphoid tumors is still mostly unresolved. This is due primarily to the lack of valid patho-biologic experimental models allowing for identification of the key patho-physiologic molecular/genetic mechanisms involved in chemo-resistance, resulting in mostly unsuccessful empiric new drug salvage trials, rather than efficient drug-targeting key growth/survival/chemo-resistance (GSC) pathways essential for effective salvage therapies. We have been developing such novel translational experimental DLBCL systems (>25 DLBCL cell lines derived from relapsed DLBCL patients) and novel agents as the conceptual basis of this model. We have distinguished a set of cell lines that are more resistant to chemo-therapy and identified that the transcription factor p52 component of the alternative NF-kB pathway is highly expressed in DLBCL cell lines that show the highest chemo-resistance characteristics. Down-regulation of p52 sensitizes resistant cells to chemotherapy. This is of particular interest since previous studies have not as yet established definitive role(s) for the alternative NF-kB pathway, particularly p52, in chemo-resistance development. We have discovered that the second generation proteasome inhibitor, Carfilzomib can target the alternative NF-kB-p52 pathway by down-regulating the TNF-receptor family BAFF-R, resulting in lymphoma cell growth inhibition and apoptosis induction. NFATc1, another important multifunctional regulatory molecule (transcription factor (TF), chromatin remodeler, etc), that we have shown to be intrinsically involved with NF-kBs in most DLBCL, and whose involvement in DLBCL is becoming increasingly important on multiple levels, that was recently confirmed genetically, identifying NFATc1 expression as a candidate oncogene in ABC DLBCLs. We have also discovered that GSK3b, a key upstream natural inhibitor of NFATc1, is constitutively phosphorylated in DLBCL cells and can negatively regulate NFATc1 activation. The PKC beta II inhibitor Enzastaurin, affectively inhibits pGSK3b, leading to NFATc1 inactivation and inhibiting cell growth/survival in a broad range of DLBCL cell lines, both GCB and ABC subtypes, with IC: 50 values in the low uM ranges. Enzastaurin strongly synergizes with Carfilzomib to inhibit DLBCL cell growth and induce apoptosis, particularly in chemo-resistant DLBCL cells. Carfilzomib alone enhances pGSK3b and NFATc1 activation, while Enzastaurin abolishes CFZ-induced pGSK3b and NFATc1, suggesting a mechanism for the synergistic activity of the drugs. Novel drug combinations with agents that target multiple growth, survival, and chemo-resistance pathways, such as Carfilzomib and Enzastaurin, represent promising, emerging therapeutic options for reversing chemo-resistance in relapsed/refractory DLBCL patients.