S834 PEGCRISANTASPASE AND VENETOCLAX COMBINATION IS HIGHLY EFFECTIVE AGAINST ACUTE MYELOID LEUKEMIA (AML), MECHANISTICALLY DRIVEN SYNERGISM BETWEEN GLUTAMINE DEPLETION AND BCL‐2 INHIBITION
Authors: A. Emadi, R. Gartenhaus, B. Bhandary, H. Kaizer, E. Chang, E.Y. Choi, B. Carter‐Cooper, A. Shetty, A. Mahurkar, B. Kapadia, R. Lapidus
Journal: HemaSphere (2019)

Background: We reported that Erwinaze could effectively deplete plasma glutamine (Gln) to undetectable levels in patients (pts) with relapsed/refractory (R/R) AML and these pts had higher probability of clinical response. We hypothesized that Gln depletion (pegcrisantaspase, a recombinant pegylated Erwinia crisantaspase, PegC [Jazz Pharmaceuticals]) leads to activation of mitochondrial apoptotic pathways and synergizes with Bcl‐2 inhibition (venetoclax, Ven). In vitro , we demonstrated that anti‐AML activity of Ven was potentiated 10–44 fold by PegC; presence of PegC (0.01 IU/mL) decreased Ven's IC 50 (5.3→0.12 μM in MOLM‐14 &amp; 7.5→0.76 μM in MonoMac‐6 cells). Ven‐PegC demonstrated synergy in killing AML cells. Here, we report the mechanism of action (MOA), and in vivo safety and efficacy of Ven‐PegC in AML. Aims: (1) To determine toxicity profile of Ven‐PegC in mice (2) To analyze effect of Ven‐PegC on plasma Gln in vivo (3) To determine efficacy of Ven‐PegC in orthotopic pt‐derived xenograft (PDX), and (4) To assess changes in the transcriptome/translatome of AML cells treated with Ven‐PegC. Methods: Toxicity profile of Ven‐PegC was investigated in immune competent (CD1) and incompetent (NRG/NSG) mice. To measure pharmacodynamic (PD) effect of PegC, NSG mice were dosed once IV at 3 different doses [125, 250 and 500 IU/kg (n = 4 mice/dose)]. We euthanized 2 mice on days 3 and 10 and measured plasma amino acids by LCMS. Efficacy of Ven‐PegC was assessed in an AML pt‐derived xenograft model (AML‐45) that expresses luciferase. We injected 1x10 6 AML‐45‐luc cells IV into NRG mice, and after engraftment mice were treated with vehicle, Ven (75 mg/kg, PO, 5x/week), PegC (200 IU/kg, IV, 1x/week), or Ven‐PegC for 2 weeks (wks), 1 wk off, then 2 more wks. Mice were imaged weekly and survival monitored. For MOA, MOLM‐14 cells were treated with each agent alone and combined followed by RNA isolation, RNA‐seq and transcriptome analysis. For translatome, cells were treated similarly and subjected to western blotting, cap enrichment and polysomal fractionation. Results: For safety, Ven‐PegC resulted in mild weight loss with full recovery at PD active doses. Amylase, lipase, creatinine, and transaminases were unchanged after 3 wks of Ven‐PegC treatment. Ven‐PegC induced myelosuppression as expected (7.4 ± 1.0x10 3 /μL control vs 1.9 ± 0.3x10 3 /μL combination, p&lt;0.003). For PD, asparagine was not detectable on days 3 &amp; 10 post dosing. No plasma Gln was detected on day 3 and on day 10 was undetectable at the highest dose. For efficacy, Ven‐PegC significantly lowered leukemia burden compared to monotherapies (p &lt; 0.03). On Day 36, AML was virtually undetectable in mice treated with Ven‐PegC (Fig. 1A‐1B). For MOA, immunoblot analysis showed decreased phosphorylation of mTOR substrates (p70S6K &amp; 4E‐BP1) with Ven‐PegC. A significant decrease in cap driven translation complexes and in eIF4E phosphorylation at Ser‐209 followed by enhanced interaction with 4E‐BP1 were observed with Ven‐PegC (Fig. 1C). Transcriptome analysis showed differential gene expression pattern between groups (RT‐qPCR validated; Fig. 1D). p90RSK, a key gene in ribosomal biogenesis and cell proliferation, was reduced upon Ven‐PegC treatment in MOLM‐14 transcriptome profiling (RNA‐qPCR/immunoblot analysis confirmed). Analysis of altered translational profile is ongoing. Summary/Conclusion: Ven‐PegC is a mechanistically‐driven, highly active treatment against AML in the PDX model. Ven‐PegC appears to broadly regulate the ribosomal biosynthetic pathway, a major driver for chemo‐resistance. The Phase 1 clinical trial in pts with R/R AML is planned. image