Activity of the Hypoxia-Activated Prodrug, TH-302, in Preclinical Human Acute Myeloid Leukemia Models

Abstract

Purpose: Acute myeloid leukemia (AML) is an aggressive hematologic neoplasm. Recent evidence has shown the bone marrow microenvironment in patients with AML to be intrinsically hypoxic. Adaptive cellular responses by leukemia cells to survive under low oxygenation also confer chemoresistance. We therefore asked whether therapeutic exploitation of marrow hypoxia via the hypoxia-activated nitrogen mustard prodrug, TH-302, could effectively inhibit AML growth.Experimental Design: We assessed the effects of hypoxia and TH-302 on human AML cells, primary samples, and systemic xenograft models.Results: We observed that human AML cells and primary AML colonies cultured under chronic hypoxia (1% O 2 , 72 hours) exhibited reduced sensitivity to cytarabine-induced apoptosis as compared with normoxic controls. TH-302 treatment resulted in dose-and hypoxia-dependent apoptosis and cell death in diverse AML cells. TH-302 preferentially decreased proliferation, reduced HIF-1a expression, induced cell-cycle arrest, and enhanced double-stranded DNA breaks in hypoxic AML cells. Hypoxia-induced reactive oxygen species by AML cells were also diminished. In systemic human AML xenografts (HEL, HL60), TH-302 [50 mg/kg intraperitoneally (i.p.) 5 times per week] inhibited disease progression and prolonged overall survival. TH-302 treatment reduced the number of hypoxic cells within leukemic bone marrows and was not associated with hematologic toxicities in nonleukemic or leukemic mice. Later initiation of TH-302 treatment in advanced AML disease was as effective as earlier TH-302 treatment in xenograft models.Conclusions: Our results establish the preclinical activity of TH-302 in AML and provide the rationale for further clinical studies of this and other hypoxia-activated agents for leukemia therapy.

Hypoxia Promotes Dissemination and Colonization in New Bone Marrow Niches in Waldenström Macroglobulinemia

“…Antitumor activity of the hypoxiaactivated pro-drug (TH-302) was demonstrated in combination with bortezomib which improved survival of mice with myeloma (14). TH-302 also delayed onset and progression of acute myeloid leukemia (AML) xenograft model (23). Moreover, blocking HIF1a signaling, which is constitutively expressed in mouse lymphoma and human AML stem cells, preferentially eliminated cancer stem cells abrogating colony-forming unit activity and tumor initiation (24).…”

Therapeutically targeting SELF‐reinforcing leukemic niches in acute myeloid leukemia: A worthy endeavor?

“…Since gluataminase inhibitors also cause mitochondrial apoptosis through an increase in glutamine level, an additional strategy to hinder mitochondrial oxidative phosphorylation might take advantage of the synergy between these drugs and ABT compounds [117]. Another intriguing possibility is to exploit hypoxia-activated prodrugs [81,118]. It has been demonstrated that after exposure to hypoxia and TH-302, a hypoxia-activated prodrug which under hypoxic conditions releases the DNA alkylating agent bromoisophohoramide mustard, chemoresistant AML cells became sensitive to cytarabine and undergo apoptosis; thus this represents the rational for phase I clinical trials in refractory AML [118].…”

“…Another intriguing possibility is to exploit hypoxia-activated prodrugs [81,118]. It has been demonstrated that after exposure to hypoxia and TH-302, a hypoxia-activated prodrug which under hypoxic conditions releases the DNA alkylating agent bromoisophohoramide mustard, chemoresistant AML cells became sensitive to cytarabine and undergo apoptosis; thus this represents the rational for phase I clinical trials in refractory AML [118]. Leukemic cell-induced changes in stromal cell activities and the intrinsic alterations adopted by the BM microenvironment to promote AML development and progression might be additional treatment targets to hinder leukemic niches.…”

The Role of Hypoxia and Exploitation of the Hypoxic Environment in Hematologic Malignancies

“…TH-302 also effectively inhibited onset, progression of AML, and extended the overall survival, both in systemic AML xenograft models and mice with advanced AML disease. In vitro, TH-302 decreased HIF1a protein expression and reduced ROS production, which resulted in decreased proliferation, increased cellcycle arrest, and induced double-stranded DNA breaks (80). TH-302 is currently evaluated in phase I/II study in patients with relapsed/refractory multiple myeloma combination with dexamethasone, with or without bortezomib (NCT01522872).…”