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P08.47 Dianhydrogalactitol (VAL-083) causes bifunctional alkylation leading to irreparable DNA double-strand breaks, S/G2 phase cell-cycle arrest and tumor cell death in an MGMT independent manner offering a unique treatment paradigm for GBM


ABSTRACT: Abstract Glioblastoma (GBM) is the most common brain cancer. Systemic therapy with temozolomide or nitrosoureas is often ineffective due to the activity of the DNA repair enzyme O6-methylguanine-DNA-methyltransferase (MGMT). Patients with recurrent GBM have limited treatment options and very poor prognosis. Dianhydrogalactitol (VAL-083) is a first-in-class bifunctional alkylating agent that rapidly induces interstrand DNA cross-links targeting N7 of guanine leading to cell cycle arrest and apoptosis due to DNA double-strand breaks. VAL-083 readily crosses the blood-brain barrier, accumulates in brain tumor tissue and has shown activity in prior NCI-sponsored clinical trials against CNS tumors, including GBM and medulloblastoma. We have previously shown that VAL-083´s cytotoxic activity is independent of MGMT in contrast to temozolomide and nitrosoureas. We have also demonstrated VAL-083 is active against GBM cancer stem cells (CSCs) and acts as a radiosensitizer in GBM CSCs, in vitro. We have also previously shown that VAL-083 circumvents cisplatin-resistance and is less dependent on p53 activity than cisplatin suggesting a distinct mechanism of action for VAL-083. We recently completed enrollment of a Phase I/II clinical trial in the United States for recurrent GBM in patients who have failed temozolomide and bevacizumab (clinicaltrials.gov identifier: NCT01478178). Separate clinical trials are planned in GBM patients with high expression of MGMT both in recurrent bevacizumab-naive GBM patients (clinicaltrials.gov identifier: NCT02717962) and in newly diagnosed GBM patients utilizing MGMT promoter methylation as a validated biomarker for patient selection. Here we report new insights into VAL-083 mechanism of action by showing that VAL-083 rapidly induces interstrand DNA cross-links leading to irreversible S/G2 cell-cycle arrest and cell death caused by replication-dependent DNA damage. VAL-083 pulse-treatment leads to persistent phosphorylation of DNA double-strand break (DSB) sensors ATM, single-strand DNA-binding Replication Protein A (RPA32), and histone variant H2A.X. After 10 months in culture, following a standard protocol for inducing chemo-resistance, cancer cells remained sensitive to VAL-083 at low M concentrations. Taken together, these results support a unique molecular mechanism for VAL-083 that differs from both temozolomide, nitrosoureas or cisplatin. Our data further suggest that the mechanism of VAL-083 is impervious to important DNA-repair strategies employed by cancer cells to escape effects of alkylating agents commonly used in the treatment of GBM and that efficient resistance mechanisms against VAL-083 treatment are not easily acquired by cancer cells.

SUBMITTER: Zhai B 

PROVIDER: S-EPMC5782675 | biostudies-literature | 2016 Sep

REPOSITORIES: biostudies-literature

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