Abstract CT027: Safety, pharmacokinetics (PK) & pharmacodynamics (PD) of idasanutlin (idasa), combined with abiraterone (abi)/prednisolone (pred) or enzalutamide (enza) in castrate resistant prostate cancer (CRPC)
Authors: Roxburgh Patricia , Currie Dawn , Morrison Paula , Kelly Caroline , Thomson Fiona , McCormick Carol , Bilsland Alan , Jones Robert H. , Quinton Amy , McCartney Elaine , Barwell Lorraine , Jones Rob J. 
Published: August 2018

Introduction MDM2 inhibitor idasa aims to treat cancers retaining functional TP53, inactivated by binding of negative regulator, MDM2. Many CRPCs retain functional TP53. Pre-clinical data suggest addition of MDM2 inhibition to androgen deprivation enhances tumour regression & survival in xenografts. This phase 1b study explored safety, PK & PD of idasa with abi or enza to define optimum biological dose & combination.

Methods Patients (pts) received oral (PO) idasa in a 3+3 dose escalation design with PO abi 1000mg once daily (OD) & PO pred 5mg twice daily (BD) (Part A) or PO enza 160mg OD (Part B) in 28 day cycles (C). In the first two cohorts (Part A), pts received a single dose of idasa on day (D) -7. Two different formulations for idasa were explored (microprecipitated bulk powder (MBP) and spray-dried powder (SDP)). Toxicity was assessed by CTCAE v4.03. Plasma idasa/M4 metabolite & plasma abi was measured (Part A). In Part B idasa/M4 metabolite & enza PK were examined. Macrophage inhibitory cytokine 1 (MIC-1) was measured to assess target modulation. Biochemical response was assessed monthly & radiological response 8 weekly.

Results 24 pts were enrolled. In part A, 3 pts were treated in cohort 1 with idasa MBP 200mg, D -7 and D1-5, OD, q28; 2 pts experienced a suspected unexpected serious adverse reaction (SUSAR) (pulmonary embolism and myocardial infarction). The dose of idasa was de-escalated for cohort-1 (idasa MBP 200mg, D-7, D1-3, OD); no DLTs were reported (n=3). 3 pts treated in cohort 1* (idasa MBP 200mg, D1-5, OD) & 3 pts in cohort 2 (idasa MBP 400mg, D1-5, OD) had no DLTs. The formulation of idasa was switched to SDP (cohort 3) & a further 3 pts were treated at a dose equivalent to mono-agent MTD (MBP 500mg = SDP 250mg, D1-5, OD) & 1 DLT (grade 4 thrombocytopenia) was reported. A further 3 pts treated at this dose reported no DLTs. 4 additional SUSARs in 3 pts have been reported to date (grade 3 (G3) depression, G3 thromboembolic events, G3 vomiting and prolonged G4 thrombocytopenia/neutropenia). 4 serious adverse reactions (SAR)s have also been reported (G2 decreased platelet count, G3 atrial fibrillation, G3 lung infection & G4 decreased platelet count). In Part B pts received idasa SDP 250mg, D1-5, OD and no DLTs were reported. Dose escalation beyond this mono-agent MTD of idasa was not permitted. Idasa had a dose-proportional PK profile. There was no clinically significant PK interaction with abi, although idasa exposure was reduced when combined with enza (known strong CYP3A inducer). MIC-1 was induced by idasa & abi, but less so by idasa & enza. 7 pts remain on combination & 4 remain on hormonal monotherapy. Efficacy data are immature.

Conclusions Idasa can be safely given with abi to achieve exposure comparable with previous data & sufficient to activate p53. Idasa can also be given with enza albeit with reduction in exposure to idasa and less robust p53 activation.

Citation Format: Patricia Roxburgh, Dawn Currie, Paula Morrison, Caroline Kelly, Fiona Thomson, Carol McCormick, Alan Bilsland, Robert H. Jones, Amy Quinton, Elaine McCartney, Lorraine Barwell, Rob J. Jones. Safety, pharmacokinetics (PK) & pharmacodynamics (PD) of idasanutlin (idasa), combined with abiraterone (abi)/prednisolone (pred) or enzalutamide (enza) in castrate resistant prostate cancer (CRPC) [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr CT027.