A Phase I Trial of DFMO Targeting Polyamine Addiction in Patients with Relapsed/Refractory Neuroblastoma

Abstract

Background: Neuroblastoma (NB) is the most common cancer in infancy and most frequent cause of death from extracranial solid tumors in children. Ornithine decarboxylase (ODC) expression is an independent indicator of poor prognosis in NB patients. This study investigated safety, response, pharmacokinetics, genetic and metabolic factors associated with ODC in a clinical trial of the ODC inhibitor difluoromethylornithine (DFMO) ± etoposide for patients with relapsed or refractory NB.

Methods and findings: Twenty-one patients participated in a phase I study of daily oral DFMO alone for three weeks, followed by additional three-week cycles of DFMO plus daily oral etoposide. No dose limiting toxicities (DLTs) were identified in patients taking doses of DFMO between 500-1500 mg/m2 orally twice a day. DFMO pharmacokinetics, single nucleotide polymorphisms (SNPs) in the ODC gene and urinary levels of substrates for the tissue polyamine exporter were measured. Urinary polyamine levels varied among patients at baseline. Patients with the minor T-allele at rs2302616 of the ODC gene had higher baseline levels (p=0.02) of, and larger decreases in, total urinary polyamines during the first cycle of DFMO therapy (p=0.003) and had median progression free survival (PFS) that was over three times longer, compared to patients with the major G allele at this locus although this last result was not statistically significant (p=0.07). Six of 18 evaluable patients were progression free during the trial period with three patients continuing progression free at 663, 1559 and 1573 days after initiating treatment. Median progression-free survival was less among patients having increased urinary polyamines, especially diacetylspermine, although this result was not statistically significant (p=0.056).

Conclusions: DFMO doses of 500-1500 mg/m2/day are safe and well tolerated in children with relapsed NB. Children with the minor T allele at rs2302616 of the ODC gene with relapsed or refractory NB had higher levels of urinary polyamine markers and responded better to therapy containing DFMO, compared to those with the major G allele at this locus. These findings suggest that this patient subset may display dependence on polyamines and be uniquely susceptible to therapies targeting this pathway.

Trial registration: Clinicaltrials.gov NCT#01059071.

Trial registration: ClinicalTrials.gov NCT01059071.

Conflict of interest statement

Competing Interests: The authors of this manuscript have the following competing interests: E.W.G. is a paid employee of Cancer Prevention Pharmaceuticals (CPP). He has an ownership interest in, and serves on the board of, CPP. This does not alter the authors' adherence to PLOS ONE policies on sharing data and materials.

Figures

Fig 1. NMTRC002 CONSORT Flow Diagram- modified for non-randomized trial design.

Fig 2. Flowchart of NMTRC 002—Safety Study for Refractory or Relapsed Neuroblastoma With DFMO Alone and in Combination With Etoposide.

Fig 3. Serum DFMO concentration versus time measurements for three patients receiving 750 mg/m2 PO BID during cycle 1 of therapy.

Fig 4. Rationale for DFMO- and specific genetic and metabolic markers of DFMO effect, in neuroblastoma

. ODC transcription is influenced by specific genetic variability, including the SNPs rs2302615 [19, 22] and rs2302616 [24]. The DFMO target ODC decarboxylates ornithine to form the diamine putrescine, which is then metabolized into longer chain amines. Spermidine is a substrate for two acetyltransferases that monoacetylate this amine at either the N1 or N8 positions. Spermine is a substrate for one of these transferases (SAT1), which diacetylates this amine. Putrescine, the monoacetylspermidines and diacetylspermine are all substrates for the solute carrier transporter SLC3A2/Y+LAT, which exports these amines.

Fig 5. Progression free survival (PFS) and overall survival (OS) rates in patients enrolled in NMTRC 002 (N = 21).

The number of patients shown at risk for disease progression (PFS) or death (OS) is shown in the figure.