ISTITUTO NAZIONALE TUMORI REGINA ELENA Roma Paolo Carlini UOC Oncologia Medica 1 ISTITUTO NAZIONALE TUMORI REGINA ELENA Roma

Summary of evidences in mCRPC Trial N° di pts Fase della malattia Disegno dello studio HR OS (mesi) TAX327 N=1006 mCRPC Docetaxel/prednisone vs. mitoxantrone/prednisone 0.76 18.9 vs. 16.5 TROPIC N=755 Post docetaxel Cabazitaxel/prednisone vs. mitoxantrone/prednisone 0.70 15.1 vs. 12.7 COU-AA-301 N=1195 Abiraterone/prednisone vs. placebo/prednisone 0.65 14.8 vs. 10.9 ALSYMPCA N=921 Post docetaxel o non eleggibili a docetaxel Ra223/BSC vs. placebo/BSC 14.9 vs. 11.3 AFFIRM N=1199 Enzalutamide vs. placebo 0.63 18.4 vs. 13.6 N=1088 Asintomatici o moderatamente sintomatici 0.81 34.7 vs. 30.3 PREVAIL N=1717 0.71 32.4 vs. 30.2

Although Enzalutamide and Abiraterone arguably represent significant advances in the treatment of mCRPC, approximately 20%–40% of patients have primary resistance to these agents and exhibit no response with respect to prostate-specific antigen (PSA) levels or other measures of clinical benefit. Ryan CJ et al N Engl J Med. 2013;368(2):138–48. Scher HI et al Lancet. 2010;375(9724):1437–46. Scher HI et al N Engl J Med. 2012;367(13):1187–97. de Bono JS et al N Engl J Med. 2011;364(21):1995–2005.

Primary Resistance to hormonal therapy

10-40% Buttigliero C et al Cancer Treatment Reviews 41 (2015) 884–892

The mechanisms of resistance to these agents are not fully defined

1) AR and CYP17 Upregulation AR gene amplification and protein overexpression have been frequently observed in response to treatment with androgen deprivation therapy (ADT) Over 80% of CRPC shows high levels of AR expression due to gene amplification and/or mRNA/protein overexpression (Taplin et al 1995) Treatment of human CRPC xenografts with abiraterone increased the expression of both full-length AR (FL-AR) and truncated AR splice variants by threefold (Mostaghel et al 2011) Enzalutamide-resistant LNCaP cells express high levels of both FL-AR and AR splice variants compared with CRPC LNCaP cells (Yamamoto et al 2015) Other studies have shown that AR amplification and AR gene aberrations in circulating cell-free DNA are associated with resistance to enzalutamide and abiraterone in mCRPC (Azad, Romanel 2015) It has also been reported that AR activity in CRPC xenografts is driven by CYP17A1-dependent de novo intratumor androgen synthesis (Locke JA et al 2008)

Selected ongoing clinical trials attempting to overcome resistance to abiraterone and/or enzalutamide

COMBINATION STRATEGIES: HT+HT Recent results support the view that persistent androgen signaling in the castrate-resistant state is functionally significant and a validated therapeutic target in CRPC. COMBINATION STRATEGIES: HT+HT Testosterone Androgen Receptor Geller J. J Clin Endocrinol Metab 80:1074-1078, 1995. Scher HI et al Lancet 375: 1437-1446, 2010 de Bono JS et al. N Engl J Med 364:1995-2005, 2011 Mostaghel EA et al. Cancer Res 67:5033-5041, 2007 Stanbrough M et al. Cancer Res 66: 2815-2825, 2006

COMBINATION STRATEGIES: HT+HT Abiraterone Enzalutamide Testosterone Testosterone Androgen Receptor Androgen Receptor

Primary Refractory 

PLATO Trial ENZA plus ABI results negative, waiting for ENZA plus ABI Alliance Trial

2) AR Splice Variants At least 22 AR splice variants have been reported in the literature to date with AR-V7 and ARv567es (Lu C et al 2013; Robinson D et al 2015) The expression of splice variants such as ARV-567es and AR-V7 is upregulated or induced by inhibition of the AR pathway with hormonal agents, such as abiraterone and enzalutamide (Mostaghel et al 2011, Hu R et al 2012) The most commonly expressed variants that drive PC progression under ADT conditions are ARV-7 and ARV-567 (Nakazawa M et al 2014) It is known that ARV levels are correlated with PC progression and that ARV expression significantly increases during ADT (Hu R et al 2009; Guo Z et al 2009; Hornberg E et al 2011; Yu Z et al 2014;Zhang X et al 2011) In CRPC xenografts, both abiraterone and enzalutamide are associated with increased expression of truncated variants (Mostaghel EA et al 2011; Yamamoto Y et al 2015)

DNA-Binding Domain Ligand-Binding Domain NH2-Terminal Domain

AR-V7 as a predictor of treatment outcome to enzalutamide and abiraterone in mCRPC AR-V7 characteristics: Most abundant splice variant Costitutively active 20-fold increased expression in mCRPC Produces functional protein product unaffected by nonsense-mediated mRNA decay Rimane costitutivamente attivo come fattore di trascrizione Pelekanou V et al., Hormones 2013; 12:224- 35

RESULTS: PSA RESPONSE RATE Enzalutamide-treated patients Abiraterone-treated patients Among men receiving enzalutamide or abiraterone, AR-V7-positive patients had lower PSA response rates than AR-V7-negative patients (0% vs 53%, p=0.004 and 0% vs 68%, p=0.004, respectively). Antonarakis et al., NEJM 2014.

RESULTS: SECONDARY END POINTS Among men receiving enzalutamide- and abiraterone-treated, AR-V7-positive patients had lower PSA-PFS and clinical or radiographic PFS than AR-V7-negative patients. Antonarakis et al., NEJM 2014.

OS Results per ARV7 status Antonarakis et al. ESMO 2014; Abstract 7980 (oral presentation)

Moreover, ARV-7 was present in 9–15% of treatment-naive mCRPC patients but it increased during treatment with abiraterone (55%) or enzalutamide (50%), supporting the hypothesis that both intrinsic and acquired resistance to these agents may be associated with ARV-7

were evaluated for treatment response to abiraterone and enzalutamide Overall, 18 of 37 patients (48%) were found to express AR-V7 Incidence of AR-V7 expression in patients receiving multiple prior AR-directed therapies compared with patients progressing after ADT alone (80% vs 28.6%, respectively). Ten of 14 AR-V7-negative patients (71%) demonstrated a PSA response to therapy, whereas only 1 of 15 AR-V7-positive patients (7%) had a PSA response to therapy, in this case to abiraterone. it also suggests the possibility of occasional responses to abiraterone/enzalutamide, despite tumoral expression of AR-V7. First, the presence of AR-V7 may merely represent a marker of aggressive disease rather than being a driver of therapeutic resistance

AR-V7

Scher et al. JAMA Oncol. 2016 Jun 4.

Clin Cancer Res. 2017 May 4. pii: clincanres. 0017. 2017. doi: 10 Clin Cancer Res. 2017 May 4. pii: clincanres.0017.2017. doi: 10.1158/1078-0432.CCR-17-0017

Selected ongoing clinical trials attempting to overcome resistance to abiraterone and/or enzalutamide

potential to overcome many of these resistance mechanisms The development of AR-targeted therapies that function independently of the LBD represents an unmet medical need and has the potential to overcome many of these resistance mechanisms EPI-506 is related to the EPI compound family originally discovered by functional assay screening of marine sponge extracts ANTONARAKIS ES et al The Oncologist 2016;21:1427–1435

Three mechanisms of action of galeterone The figure also demonstrates potential mechanisms of resistance to AR therapies, including the development of AR splice variants (AR-V) and AR mutations. Finally, it highlights galeterone’s mechanisms of action in each of these AR signaling pathways implicated in resistance to novel androgen/AR-directed therapies: 1) CYP lyase inhibition; 2) AR antagonism to both full-length and mutant AR; and 3) degradation of the AR, including AR splice variants

Clin Cancer Res; 20(12); 3198–210. 2014 Niclosamide, an FDA approved anthelminthic drug, as a potent ARV-7 inhibitor in PC cells, suggesting that enhances enzalutamide activity and overcomes enzalutamide resistance in CRPC cells

3) AR Point Mutations The point mutations in the AR gene have been reported to occur at a comparatively high incidence (>10%) in patients with CRPC, especially in tumors progressing under systemic hormonal therapy and novel antiandrogens (Taplin et al 2003). Mutations in the AR ligand-binding domain can alter its structure and enable its activation by alternative ligands including progesterone, hydrocortisone, estradiol and certain AR antagonists. (Taplin et al 1995). Since serum levels of progesterone and other upstream steroids are increased during treatment with CYP17A1 inhibitors mutant AR, that are activated by these upstream steroids, may represent a relevant resistance mechanism.

The reason for this remains unclear Cancer Discov; 3(9); 1020–9; 2013 Cancer Discov; 3(9); 1030–43;2013 Studies in PC cell lines treated with Enzalutamide and ARN-509 have identified a new missense mutation (F876L) in the LBD of the AR, that confers an antagonist-to-agonist switch driving the resistance to Enzalutamide and ARN-509 while maintains sensitivity to first generation agents such as bicalutamide. The reason for this remains unclear

Schematic representation of the therapeutic strategies that can be applied to target AR F876L Cancer Discov; 3(9); 1030–43;2013

Cancer Res; 72(9); 2176–82;2012 Other AR point mutations that result in glucocorticoid activation of the AR have also been described. The L702H mutation has been reported in patients taking abiraterone together with dexamethasone or prednisone (Carreira et al 2014) The expression of the L702H mutation prior to treatment with abiraterone appeared to be associated with primary refractory disease to subsequent treatment with abiraterone The emergence of L702H and T878A AR point mutations in 13% of tumors at progression on abiraterone.(Romanel et al 2015)

Higher AR-FL levels correlate with AR-V7 posity Higher AR-FL correlate with inferior clinical outcomes

4) Glucocorticoid Receptor Upregulation Acquired resistance to enzalutamide and abiraterone can occur through an increased expression of glucocorticoid receptor (GR) Cell 155, 1309–1322, 2013 The prevalence and the clinical relevance of GR-driven CRPC are unknown. The progesterone receptor (PR) has been shown to be increased in CRPC and its two isoforms A and B are expressed in stromal fibroblast and smooth muscle cells of the prostate and are known to regulate cell proliferation. PR may be involved in resistance to enzalutamide and abiraterone due to continue progesterone production. J Clin Endocrinol Metab 98: 2887–2896, 2013

5) Other Oncogenic Signaling Pathways Parallel pathways have been also implicated in acquired resistance to abiraterone and enzalutamide, including EGFR-, Scr- and Pi3K pathway, that may crosstalk with the AR pathway. Activation of Pi3K-AKT-mTOR signaling pathway is strongly implicated in prostate cancer progression. The AR and Pi3K signaling pathways are cross-regulated by reciprocal feedback. (Carver et al 2011) AR pathway inhibition results in a stronger activation of the Pi3K pathway, and may promote resistance to AR pathway inhibitors.

Crumbaker M et al Cancers 2017, 9, 34

The Oncologist 2017; 22:503–e43 NEGATIVE The combination of standard-dose abiraterone/ prednisone with BEZ235 200 mg twice daily was poorly tolerated in patients with mCRPC. The on-target and off-target effects of dual PI3K and mTORC inhibition likely contributed to the unacceptable toxicity profile. European Journal of Cancer 76 (2017) 36-44 NEGATIVE Based on the assessment of available pharmacokinetics, safety, and efficacy data, no further study is planned for either buparlisib or dactolisib in combination with AA in CRPC.

NEGATIVE Phase II trial of the PI3 kinase inhibitor buparlisib (BKM-120) with or without enzalutamide in men with metastatic castration resistant prostate cancer. Eur J Cancer. 2017 May 11 Armstrong AJ1, Halabi S2, Healy P2, Alumkal JJ3, Winters C4, Kephart J4, Bitting RL5, Hobbs C4, Soleau CF6, Beer TM3, Slottke R3, Mundy K4, Yu EY6, George DJ4. Buparlisib did not demonstrate significant activity in men with mCRPC, suggesting that PI3K inhibition is not sufficient to reverse resistant mCRPC progression. Future studies of PI3K pathway inhibitors with concurrent enzalutamide should develop optimal dosing and focus on selected patients more likely to benefit.

POSITIVE

POSITIVE

6) Neuroendocrine/Small Cell Transdifferentiation Neuroendocrine carcinoma of the prostate represents a subset of PC phenotypes that may be linked to resistance to AR signaling inhibition, aggressive tumor characteristics and poor prognosis. Many cases of neuroendocrine prostate cancer, and even pure small cell prostate cancer, can arise after hormone therapy (Aparicio et al 2011)

hormone-naïve and -treated prostate cancers that progressed to neuroendocrine carcinoma Mosquera et al Neoplasia 2013

Clin Cancer Res; 20(4); 890–903; 2013 It showed loss of retinoblastoma protein (Rb) in 90% of small cell carcinomas compared with only 7% of primary high-grade acinar carcinomas. Loss of PTEN protein was observed in 63% of small cell carcinomas, and TP53 mutation was seen in 60% of cases.

Aggarwal et al J Clin Oncol. 2015;33(suppl):abstr5068.

NEGATIVE The Oncologist 2016; 21:1296–1297e A tolerable dose of alisertib in combination with AP in mCRPC was not established in this study. There was no clear signal indicating that alisertib might be beneficial for patients with mCRPC progressing on abiraterone

6) Programmed Death-Ligand 1/Programmed death-1 Upregulation The treatment of certain prostate cancer cell lines with antiandrogens (including enzalutamide) can induce tumoral programmed death-ligand 1 (PD-L1) expression and that enzalutamide-resistant prostate cancer cell lines demonstrate striking expression of PD-L1. . Oncotarget 2015;6:234-42.

Conclusion Abiraterone and Enzalutamide represent advances in the treatment of mCRPC and have demonstrated survival benefits, a significant proportion of patients have primary resistance to these agents and virtually all patients develop secondary resistance. Primary and acquired resistance to abiraterone and enzalutamide depend from both AR-dependent or AR-independent mechanisms. A deeper understanding of resistance mechanisms to these drugs is essential to maximize their efficacy and develop new strategies to overcome them. The combination of these new drugs and hormonal therapies may synergically act to improve the clinical activity of systemic therapy in CRPC.