Abstract
Background: Germinal center B-cell like (GCB) diffuse large B-cell lymphoma (DLBCL), a type of non-Hodgkin lymphoma (NHL), arises from malignant transformation of B-cells within the germinal center (GC). GC cells exhibit stem cell-like qualities and GCB DLBCL cells have increased NAD dependence to sustain rapid cell proliferation. NAD biosynthesis is carried out largely through nicotinamide phosphoribosyltransferase (NAMPT), highlighting the critical role NAMPT plays in cancer metabolism. However, NAD is also required in healthy cells and drugs targeting NAMPT have been plagued by on-target toxicities.
RPT1G is a first-in-class hyperbolic NAMPT inhibitor that eliminates NAD in cancer cells while allowing NAD production in healthy tissues (Crimmins, ASH 2023). We previously demonstrated RPT1G efficacy in acute leukemias (Crimmins, ASH 2024) and the safety, tolerability, and NAMPT inhibition of RPT1G was recently exhibited in a first-in-human Phase 1 study (NCT06667765). Here we show that RPT1G achieves significant in vitro and in vivo efficacy in NHL cancers, particularly in GCB DLBCL.
Methods: NHL cell lines were incubated with RPT1G alone or in combination with other drugs for 72 or 96 hours. Cell viability was assessed using CellTiter Glo. Synergy scores were calculated using SynergyFinder Plus. DLBCL xenograft mouse studies were initiated when the average tumor size reached 150-200 mm3 and tumor volume was assessed at various timepoints.
Results: RPT1G exhibited sensitivity differences across the spectrum of NHL cells. Approximately 50% of GCB DLBCL cell lines showed RPT1G sensitivity while activating B-cell origin (ABC) DLBCL cell lines were largely insensitive. This in vitro result was confirmed in vivo using xenograft mouse models with the GCB DLBCL line, OCI-LY7, and the ABC DLBCL line, OCI-LY3. RPT1G treatment for 13 days significantly inhibited tumor growth in the OCI-LY7 model (83% tumor growth inhibition, p=0.0012), but not the OCI-LY3 model, confirming that NAMPT inhibition with RPT1G is most efficacious in NHL of GC origin. A follow up OCI-LY7 xenograft study showed that a 3.5-fold acute increase in plasma in the NAMPT substrate nicotinamide (NAM) correlated to a reduction in tumor growth. In humans, RPT1G induces NAM >3.5-fold at multiple dose levels, indicating that these doses will be efficacious against hematological malignancies.
Potential biomarkers were evaluated to determine prognostic value for RPT1G efficacy. We hypothesized that NAMPT expression would impact the efficacy of RPT1G. Indeed, NHL cells with lower NAMPT expression were more vulnerable to RPT1G inhibition, with GCB DLBCL expressing less NAMPT compared to ABC DLBCL cells. Expression analysis of common oncogenes identified a positive correlation between sensitivity to RPT1G and c-Myc expression. The c-Myc oncogene rearrangement is found in 10% of DLBCL and has a negative prognostic impact on patients. Thus, NAMPT and c-Myc can serve as prognostic biomarkers for RPT1G sensitivity in lymphoma patients.
Combination treatments with RPT1G and other drugs can provide increased efficacy to relapsed patients while reducing monotherapy-associated dose-limiting toxicities with these other drugs. Evaluation of RPT1G and in GCB DLBCL cells showed moderate synergy. Lymphomas are characterized by high expression of poly(ADP-ribose) polymerase (PARP) and ongoing clinical studies with PARP inhibitors are showing promising efficacy. We observed strong synergy between RPT1G and the PARP inhibitor olaparib.
Conclusion: RPT1G is efficacious in several hematological cancers, including acute leukemias and lymphomas. RPT1G is an effective treatment for NHL cancers of GC origin as a monotherapy and in combination with SOC and targeted therapies like olaparib. RPT1G was safe and well-tolerated in a first-in-human Phase 1 trial (NCT06667765) and is currently being evaluated in R/R AML and HR-MDS patients (NCT07107126). These results provide the basis for expansion of hyperbolic NAMPT inhibition for lymphomas, particularly those of GC origin.
