Efficacy of a Novel Cytotoxic Polybisphosphonate for Treatment of Bone Metastasis in Castration-Resistant Prostate Cancer (CRPC).

236 Background: A cytostatic polybisphosphonate was developed for Tx of mCRPC. It has a) anti-resorptive effects, osteoclast inhib., b) tum. cell spec./tox, confirmed in in-vivo models. Tox. study shows high tolerability. Animal PK study has shown T½ < 3 hrs; principal accumulation in liver, spleen, kidneys. Methods: Clin phase I/IIa (clinicaltrials.gov NCT01595087): Prim obj: to define MTD of ODX given every 3rd week. Sec. obj: OS, bone metab. and resp. markers, PSA, QoL and PK. Explorative in vitrostudies (basis for rand. phase IIb trial in pts. with docetax-res. mCRPC). A docetax-resist. cell-line was developed from DU145 in escalating conc. of docetax, then continuous growth in docetax 500 µg/ml. Cells subj. to cytotox. exp. with ODX (iCELLigence system and fluorom microculture cytotox assay). Results: Clin Phase I/IIa first-in-man trial (clinicaltrials.gov NCT01595087): 17/28 patients rec. 4-7 doses every 3rd week. No DLTs; max dose adm.: 3.0 mg/kg: no drug-related SAEs. Tx was well tolerated. Efficacy and QoL data w. considerable variability as to be expected in this population of pts. w. mCRPC. Max blood conc. ODX: 110-160 fmol/mL; 85-90 % cleared within first 1 hr. Efficacy of ODX in docetax-res DU145TR: A dose-dependent cytotox effect seen when adding ODX in “sub-clin.” doses. All cells were apparently killed in the clin. relevant dose 6 uM. Conclusions: ODX is a novel drug cand. w. high cytotox. efficacy in vivo and in vitro, even in highly docetax-res. cells. Animal studies and Phase I trial show excellent tolerability. Studies now ongoing to elucidate whether short-term treatment is as efficacious as continuous treatment and whether some cells de facto may develop resistance also to this new treatment concept. A multicenter rand. double-blind pbo. controlled trial (EudraCT 2014-002054-39) starts Q4 2014 in mCRPC pts failing docetax and/or cabazitaxel AND abiraterone and/or enzalutamide. Clinical trial information: NCT01595087.