Published OnlineFirst September 17, 2018; DOI: 10.1158/1078-0432.CCR-18-1589 Research Article Clinical Cancer Research Epigenetic Therapy with Panobinostat Combined with Bicalutamide Rechallenge in Castration- Resistant Prostate Cancer Anna C. Ferrari1, Joshi J. Alumkal2, Mark N. Stein3, Mary-Ellen Taplin4, James Babb5, Ethan S. Barnett6, Alejandro Gomez-Pinillos5, Xiaomei Liu5, Dirk Moore6, Robert DiPaola7, and Tomasz M. Beer2 Abstract Purpose: This study assesses the action of panobinostat, AR activity. The dose-limiting toxicity was not reached. a histone deacetylase inhibitor (HDACI), in restoring sensi- The probability of remaining rPF exceeded protocol- tivity to bicalutamide in a castration-resistant prostate cancer specified 35% in the A arm and 47.5% and 38.5% in (CRPC) model and the efficacy and safety of the panobinostat/ the B arm. The probabilities of remaining rPF were bicalutamide combination in CRPC patients resistant to 47.5% in the A arm and 38.5% in the B arm, exceeding second-line antiandrogen therapy (2ndLAARx). the protocol-specified threshold of 35%. A arm/B arm: Patients and Methods: The CWR22PC xenograft and iso- adverse events (AE), 62%/19%; treatment stopped for genic cell line were tested for drug interactions on tumor cell AEs, 27.5%/11.5%; dose reduction required, 41%/4%; growth and on the androgen receptor (AR), AR-splice variant7, principal A-arm grade 3 AEs, thrombocytopenia (31%) and AR targets. A phase I trial had a 3 Â 3 panobinostat dose- and fatigue (14%). escalation design. The phase II study randomized 55 patients Conclusions: The 40 mg panobinostat/bicalutamide regi- to panobinostat 40 mg (A arm) or 20 mg (B arm) triweekly Â2 men increased rPF survival in CRPC patients resistant to weeks with bicalutamide 50 mg/day in 3-week cycles. The 2ndLAARx. Panobinostat toxicity was tolerable with dose primary endpoint was to determine the percentage of radio- reductions. Epigenetic HDACI therapy reduces AR-mediated graphic progression-free (rPF) patients at 36 weeks versus resistance to bicalutamide in CRPC models with clinical historic high-dose bicalutamide. benefit in patients. The combination merits validation using Results: In the model, panobinostat/bicalutamide a second-generation antiandrogen. Clin Cancer Res; 1–12. Ó2018 demonstrated synergistic antitumor effect while reducing AACR. Introduction (bicalutamide, flutamide, and nilutamide) or the adrenal androgen synthesis blocker ketoconazole, and the median The lineage dependence of prostate cancer on the androgen time to secondary progression was 6 to 8 months (4, 5). receptor (AR) pathway (1, 2) accounts for the therapeutic "Re-challenge" treatment with the same or an alternative anti- efficacy of castration (3) and for the response to antiandrogen androgen after progression on the first second-line antiandro- therapy after the development of castration resistance. How- gen treatment (2ndLAARx) yielded fewer responses and pro- ever, only a fraction of castration-resistant prostate cancer gressively shorter times to succeeding progression (5, 6). (CRPC) patients responded to first-generation antiandrogens Although, second-generation antiandrogens (enzalutamide and apalutamide) or the adrenal androgen synthesis blocker abiraterone acetate (7–10) significantly delays progression and 1Icahn School of Medicine Mount Sinai, New York, New York. 2OHSU Knight increases overall survival, resistance inevitably follows, and the Cancer Institute, Portland, Oregon. 3Columbia University Medical Center, response to taxanes is short (11). Therefore, preventing or 4 New York, New York. Dana-Farber Cancer Institute, Boston, Massachusetts. reversing resistance to AR-directed agents may potentially block 5 Perlmutter Cancer Center, NYU Langone Medical Center, New York, New lethal pathways of progression and prolong survival. York. 6Rutgers Cancer Institute of New Jersey, New Brunswick, New Jersey. 7University of Kentucky College of Medicine, Lexington, Kentucky. The development of resistance to AR-targeted agents involves a host of genomic alterations that directly affect AR Note: Supplementary data for this article are available at Clinical Cancer gene structure and function (12–16) as well as cross-talk with Research Online (http://clincancerres.aacrjournals.org/). growth factor signaling pathways (17–19). The most prevalent Prior Presentation: Presented at the 51st Annual Meeting American Society of AR alteration is overexpression (12–14), which is necessary Clinical Oncology (ASCO), Chicago, IL, May 29–June 2, 2015. and sufficient to lead to CRPC progression and resistance to Corresponding Author: Anna C. Ferrari, Icahn School of Medicine at Mount Sinai, antiandrogens (20). AR mutation frequency is low, but treat- One Gustave L. Levy Place, Box 1079, New York, NY 10029. Phone: 212-659- ment with antiandrogens can select for distinct mutations in 5600; Fax: 212-659-5599; E-mail: [email protected] the ligand-binding domain (LBD) that confer resistance and doi: 10.1158/1078-0432.CCR-18-1589 drive AR activity but not cross-resistance to other antiandro- Ó2018 American Association for Cancer Research. gens (21–25). Ligand-independent AR splice variants (ARSv) www.aacrjournals.org OF1 Downloaded from clincancerres.aacrjournals.org on September 30, 2021. © 2018 American Association for Cancer Research. Published OnlineFirst September 17, 2018; DOI: 10.1158/1078-0432.CCR-18-1589 Ferrari et al. pathways involved in disease progression and drug resistance, Translational Relevance including those not controlled by AR (30, 35, 40, 41). The development of resistance to androgen pathway– In prostate cancer cells, both HDAC1 and HDAC3 are required targeted agents is central to prostate cancer lethality. Pre- for optimal transcriptional modulation of nearly all AR target clinical studies indicate that this drug-resistant state can be genes (42), although HDAC1 alone can directly interact with AR attenuated or reversed by epigenetic modulation. We pro- protein, to produce transcriptional repression (39). By disrupting pose that to achieve this requires the real-time copresence of transcriptional activation, the HDACIs LBH589 (panobinostat) the epigenetic effector and resistance agent. The relevance of and suberoylanilide hydroxamic acid (SAHA, Vorinostat) this hypothesis in castrate-resistant prostate cancer (CRPC) decreased AR mRNA synthesis and repressed transcriptional acti- was tested in a phase I/II trial of the histone deacetylase vation of the AR target genes PSA and TMPRSS2 (42). In CRPC cell inhibitor panobinostat in combination with continuous bica- lines with AR overexpression, PSA expression was inhibited in a lutamide in patients who had secondarily progressed on dose-dependent manner: 30%, 50%, and 85%, respectively, by bicalutamide and/or other first-generation antiandrogen(s). 10, 20, and 40 nmol/L panobinostat (42). These findings sug- The results provide evidence that compared with historic gested that patients with AR-driven CRPC may require higher controls treated with bicalutamide alone, the combination of doses of panobinostat monotherapy for an antitumor response bicalutamide with high-dose panobinostat administered than the dose approved for use in myeloma (43). In a clinical intermittently delayed radiographic progression of the disease; setting, this could be achieved using an intermittent oral schedule toxicity was not limiting, although dose reductions were to decrease toxicity (42). In addition, given the effect of panobi- required to extend treatment. Our results provide initial nostat on AR transcriptional activity and, also, PSA expression in proof-of-concept support for the potential effectiveness of model systems, it was proposed to use PSA changes as a correlative epigenetic therapy to reverse/delay antiandrogen-resistant biomarker to monitor the effect of HDACI treatment on the AR CRPC and warrant confirmation with currently available, pathway and to guide dose selection in clinical trials (42). more potent antiandrogens to further increase their survival Using cell line prostate cancer models, we previously explored benefits. the hypothesis that resistance to bicalutamide can be overcome by concomitant administration of panobinostat (20). We demon- strated that the HDACIs trichostatin-A and panobinostat effec- tively reduced overexpressed AR mRNA and protein levels in an androgen-independent, bicalutamide-resistant LNCaP deriv- are also enhanced by antiandrogen treatment including bi- ative (44, 45). Further, although bicalutamide alone was in- calutamide, and they frequently sprout in response to second- effective, when combined with panobinostat, the combination generation antiandrogens (26–28). More importantly, the induced both synergistic growth arrest and apoptosis greater overexpression of ARv7 has been shown to accelerate CRPC than panobinostat alone (46). These results suggested that pano- progression via a distinct mitosis-dependent transcriptome binostat reverses resistance to bicalutamide and that both are program that imparts cross-resistance to antiandrogens necessary to achieve an antiproliferative effect. We now show (29–32). These observations of the importance of AR over- that this drug combination is also effective in an additional expression in antiandrogen resistance suggest that aberrant prostate cancer model, namely a paired isogenic in vitro/in vivo regulatory mechanisms could play an important role. Thus, system: the 22Rv1 prostate cancer cell line and the CWR22PC it is of interest that prostate cancer cells