Phase II clinical trial of six mercaptopurine (6MP) and methotrexate in patients with BRCA-defective tumors.

Abstract

TPS5615 Background: BRCA1 and BRCA2 genes are critical in homologous recombination DNA repair and have been implicated in familial breast and ovarian cancer tumorigenesis. Tumor cells with these mutations demonstrate increased sensitivity to cisplatin and poly(ADP-ribose) polymerase (PARP) inhibitors. 6MP was identified in a screen for novel drugs and found to selectively kill BRCA-defective cells in a xenograft model as effectively as the PARP inhibitor, AGO14699, even after these cells had acquired resistance to a PARP inhibitor or cisplatin (Issaeva 2010). Exploiting the genetic basis of these tumours enables us to develop a more tailored approach to therapy for patients with BRCA mutated cancers. This multi-center phase II single arm trial was set up to investigate the activity and safety of 6MP with methotrexate in patients with breast or ovarian cancer who are known to have a BRCA mutation. Methods: Two-stage Simon compromise design (Jung 2001, Jung 2004) with α=0.20, power=90% to detect an increase in activity from 10 to 20%. 1st stage: if ≤ 3/30 evaluable patients respond at 8 weeks the trial will be stopped for futility; 2nd stage: if ≥9/65 evaluable patients respond at 8 weeks the treatment will be regarded as potentially effective and a phase III trial will be considered if the treatment appears safe and well-tolerated. 65 patients with BRCA defective cancer progressing after at least one prior chemotherapy or relapsed platinum resistant ovarian cancer, ECOG performance status 0-2 will be recruited and treated with daily 6MP (75mg/m2 ) and weekly methotrexate (20mg/m2) until progression. The starting dose was later reduced by 25% due to excess of expected toxicity. Patients with low TPMT activity or a low/low genotype are excluded due to the risk of increased toxicity. Prior treatment with a PARP inhibitor is permissible. Primary outcome: objective response at 8 weeks: complete, partial response or stable disease defined by RECIST 1.1. Secondary outcomes include safety, PFS, OS and quality of life. Of the 46 patients screened for TMPT activity between 15 Jun2009 and 05Dec 2012 from 12 UK sites, 31 patients were recruited. The pre-specified activity goal for the 1st stage was met and accrual into the 2nd stage continues. Clinical trial information: 2009-016846-16.