Synergistic Leukemia Eradication by Combined Treatment with Retinoic Acid and HIF Inhibition by EZN-2208 (PEG-SN38) in Preclinical Models of PML-RARα and PLZF-RARα–Driven Leukemia

Abstract

Purpose: Retinoic acid-arsenic trioxide (ATRA-ATO) combination therapy is the current standard of care for patients with acute promyelocytic leukemia (APL) carrying the oncogenic fusion protein PML-RARa. Despite the high cure rates obtained with this drug combination, resistance to arsenic is recently emerging. Moreover, patients with APL carrying the PLZF-RARa fusion protein are partially resistant to ATRA treatment. Hypoxia-inducible factor-1a (HIF-1a) activation has been recently reported in APL, and EZN-2208 (PEG-SN38) is a compound with HIF-1a inhibitory function currently tested in clinical trials. This study investigates the effect of EZN-2208 in different preclinical APL models, either alone or in combination with ATRA.Experimental Design: Efficacy of EZN-2208 in APL was measured in vitro by assessing expression of HIF-1a target genes, cell migration, clonogenicity, and differentiation, vis a vis the cytotoxic and cytostatic effects of this compound. In vivo, EZN-2208 was used in mouse models of APL driven by PML-RARa or PLZFRARa, either alone or in combination with ATRA.Results: Treatment of APL cell lines with noncytotoxic doses of EZN-2208 causes dose-dependent downregulation of HIF-1a bona fide target genes and affects cell migration and clonogenicity in methylcellulose. In vivo, EZN-2208 impairs leukemia progression and prolongs mice survival in APL mouse models. More importantly, when used in combination with ATRA, EZN-2208 synergizes in debulking leukemia and eradicating leukemia-initiating cells.Conclusions: Our preclinical data suggest that the combination ATRA-EZN-2208 may be tested to treat patients with APL who develop resistance to ATO or patients carrying the PLZF-RARa fusion protein.

Development of Inhibitors Targeting Hypoxia-Inducible Factor 1 and 2 for Cancer Therapy

“…However, the classification may not be accurate, because some agents target more than one mechanism and it may be inappropriate to include them in a definite category. The targets and mechanisms of HIF inhibitors (Table 1) and some evaluated in clinical trials [Data were obtained from National Clinical Trial (https://clinicaltrials.gov)] are summarized 3031323334353637383940414243444546474849505152535455…”

The hypoxia signalling pathway in haematological malignancies

“…L-ascorbic acid was also able to specifically inhibit the proliferation of human CML cells via downregulation of HIF-1α transcription [135]. EZN-2968, a small 3 rd generation antisense oligonucleotide against HIF1A mRNA, delayed acute promyelocytic leukaemia (APL) and MM progression [160, 161]. EZN-2968 has also been reported to block the interaction between MM cells and BM stromal cells through HIF-1α inhibition [161].…”

“…EZN-2968 has also been reported to block the interaction between MM cells and BM stromal cells through HIF-1α inhibition [161]. Furthermore, the combination of EZN-2088, a polyethylene glycol conjugate of irinotecan (PEG-SN38), with all-trans retinoic acid (ATRA) synergized to eradicate preclinical models of PML-RARα (promyelocytic leukaemia protein-retinoic receptor antagonist alpha) and PLZF (promyelocytic leukaemia zinc finger)-RARα-driven leukaemia [160]. More recently, it has been shown that chetomin, a small molecule able to disrupt HIF-1α binding to the p300 coactivator, exhibited antitumor activity in primary MM cells from patients [162].…”

The role of hypoxia-inducible factors in leukemias

“…EZN-2208 (pegylated SN38) has also been shown to inhibit the expression and transcriptional activity of HIF-1α in APL. 59 None of these molecules target HSCs. Another molecule, TH-302, is a hypoxia-activated prodrug that has been reported to preferentially decrease proliferation, reduce HIF-1α expression and induce cell-cycle arrest in AML cells.…”