Neoadjuvant degarelix with or without apalutamide followed by radical prostatectomy for intermediate and high-risk prostate cancer: ARNEO, a randomized, double blind, placebo-controlled trial

The incidence of prostate cancer (PCa) in the European Union has increased during recent decades since the opportunistic implementation of PSA screening in the clinical practice [1]. Localized PCa is classified in risk groups: low (cT1-T2a, PSA < 10 ng/ml, biopsy Gleason score 6), intermediate (cT2b, PSA10–20 ng/ml, biopsy Gleason score 7), high-risk localized (cT2c, PSA > 20 ng/ml, biopsy Gleason score 8–10) or high-risk locally advanced (cT3–4, cN1) PCa [2]. Fifteen-year cancer-related mortality rate is 20% in intermediate and 36% in high-risk non-metastatic PCa patients treated without curative intent [3]. Conversely, 10-year cancer specific survival for low-risk patients who underwent active monitoring or active treatment is 99% without differences between treatment subgroups [4]. These findings support the notion that lethal disease is rare in the low-risk subgroup. During the last years, the rates of curative treatment for high-risk disease have increased progressively. Conversely, active surveillance has been more and more dedicated to low-risk PCa [5]. However, in the high-risk group, a large part of patients requires other treatments next to radical prostatectomy (adjuvant or salvage radiotherapy, adjuvant systemic treatment) [6]. Considering the increasing application of surgery for high-risk patients, there is an urgent need for studies that assess new treatment combinations in order to maximize cure rates. Treatment of patients with intermediate and high-risk PCa presents two challenges: the need for local control and treatment of possible micro-metastases. Unfortunately, there is still no validated test to detect micro-metastatic disease [7]. Radical prostatectomy with extended pelvic lymph node dissection (ePLND) represents an important therapeutic option within a multimodal approach (adjuvant or salvage radiotherapy, adjuvant systemic treatment) [2, 8].

Neoadjuvant therapy is routinely utilized for the treatment of muscle invasive bladder, esophageal and rectal cancer with the scope of down-staging the primary tumour and control of possible micro-metastatic clones. In this context, neoadjuvant therapy before radical prostatectomy is an interesting possibility in particular for intermediate and high-risk disease. PCa has the peculiarity to be largely dependent on androgen regulation, a mechanism that is routinely targeted in advanced cases. Neoadjuvant hormonal therapy using luteinizing hormone releasing hormone (LHRH) agonists and/or anti-androgens has already demonstrated to downstage primary PCa [9], however, there is a lack of survival data especially for patients with high-risk disease, considering that the previous controlled trials generally assessed low-intermediate risk patients with various ADT regimens and relatively short follow ups [9, 10]. Recently it was suggested that neoadjuvant ADT could decrease cancer related death in high-risk patients, especially when adjuvant EBRT is associated [11]. Considering the increasing availability of new generation androgen receptor pathway inhibitors, there is a new wave of studies that are assessing the anti-tumour effect of these compounds on the primary tumour using pathologic characteristics (pathologic complete response, minimal residual disease) as proxy of an anti-tumour effect [12]. Degarelix is a well-known LHRH antagonist that is commonly used in advanced prostate cancer, with the advantage that it avoids tumour flare-up with a faster depression of testosterone levels compared to LHRH agonists [13]. It was shown that degarelix is not inferior to goserelin + bicalutamide in decreasing the prostate volume in PCa patients [14], thus it was suggested to be a valuable alternative in the neoadjuvant setting. Degarelix was recently studied before prostatectomy but the results were controversial, showing higher intra-tumour levels of dihydrotestosteron compared to LHRH agonist + bicalutamide or degarelix + bicalutamide, generating the hypothesis of unknown mechanisms of action that should be better analyzed in other trials [15]. Interestingly, pathological complete response was obtained for degarelix when it was associated with bicalutamide, generating the hypothesis that a stronger androgen blockade can result in a stronger anti-tumour effect. Degarelix was compared to leuprolide in the pivot trial CS21 in hormone sensitive patients showing a sustained testosterone suppression with improved PSA progression-free survival for degarelix compared to LHRH analogue [16]. In the extension phase, those patients who crossed-over from leuprolide to degarelix, experienced an improved PSA response and progression-free survival supporting the better effect of the LHRH antagonist [17]. Neoadjuvant studies, in the surgical setting, are also a unique opportunity to complete our knowledge on mechanisms of action and molecular response to such new generation of compounds [18]. Apalutamide (alias ARN-509) is a second-generation antiandrogen with a pure antagonist mechanism with 7–10 fold higher affinity with the androgen receptor compared to bicalutamide [19]. It is currently studied in phase III trials for treatment of castration naïve (NCT02489318, NCT02531516) or castration resistant PCa (NCT02257736, NCT02106507, NCT01946204). The possibility to study the anti-tumour effect of the complete androgen blockade based on apalutamide + degarelix is of interest, considering the safety profile of these compounds [16, 20] and potential benefit for the patients.

The therapeutic effect of EBRT is mediated by DNA damage and hence the DNA repair mechanisms are the leading mechanisms in radio-resistance. In preclinical studies, even in the absence of radiation, antiandrogens induce an increased DNA damage and decreased DNA repair in PCa cell lines [21]. Thus, DNA repair is androgen dependent in cell lines, but a better insight in these mechanisms in localized tumour tissue and the assessment of possible novel therapies to decrease the activity of DNA repair mechanisms could help understanding and optimizing treatment modalities. We hypothesize that ARN-509 in combination with degarelix can inhibit DNA repair mechanism more intensively then classic hormonal treatment.

As described above for DNA repair, most studies on androgen-regulated phenomena in prostate cancer are based on preclinical models [22]. We will analyze transcriptomes of pre-treatment biopsies and compare them with the tumor at the moment of radical prostatectomy (after degarelix or degarelix + apalutamide). Transcriptomes will be further complemented with genomic analyses because of known and unknown links between mutations and treatment responses [23].

Second generation androgen receptor pathway inhibitors can induce resistance through different mechanisms [24, 25]. One of these mechanisms is the expression of androgen receptor splice variants. More specifically, the ARV7 variant was found to be a marker for second-generation antiandrogen resistance in mCRPC [26‐28]. There is a lack of data about ARV7 expression in primary PCa. Recently it was demonstrated that ARV7 can be expressed in patients treated with degarelix + bicalutamide + abiraterone + prednisolone before prostatectomy but this was not related to the therapy response [29].

PSA is commonly used as a tumour biomarker after RP in order to identify possible recurrences [30]. Early (< 3 year) biochemical failure was identified as a significant predictor of metastatic progression and cancer related death [31], thus representing a useful marker in the clinical practice. We expect an improvement of early biochemical failure in the study arm compared to the control arm. The prognostic value of PSA nadir to predict PCa survival after 3 months of hormonal treatment and before EBRT was tested [32]. PSA levels < 0.5 ng/ml can predict patient survival [32] and this observation was also confirmed recently for PSA levels ≤0.3 ng/ml [33]. PSA nadir before EBRT is, thus, an important biomarker of hormonal response and also a predictor of survival in this setting.

Novel imaging techniques are expected to overcome the problem of invasive sample collection in the near future by allowing accurate diagnosis, tumour staging and assessment of treatment response. Positron emission tomography (PET) is a recognized tool to detect tumour lesions by targeting their metabolic activity or their specific antigen expression. PSMA (prostate specific membrane antigen) is a type II trans-membrane protein that is specifically expressed on the surface of PCa cells and could be used as a tracer to investigate anti-androgen response [34]. PSMA can be targeted by a PSMA-ligand associated to ⁶⁸Gallium. This tracer has been implemented in PET-computed tomography (PET-CT) for the detection of PCa in the metastatic setting [35]. There is also evidence of PSMA regulation by androgens [36]. Immunohistochemical examination of FFPE (formalin fixed paraffin embedded) PCa tissues of patients treated by different anti-androgen therapies showed an over-expression of PSMA after therapy in 55% of primary tumour samples and 100% of metastatic lesions compared to the baseline [37]. Thus, a better insight on PSMA expression in castration naïve patients following new generation ADT is of interest. Recently, PET/MR hybrid imaging has been introduced next to PET/CT in order to allow the combination of specific properties of different imaging techniques.⁶⁸Ga-PSMA PET demonstrated high potential to detect minimal PCa lesions. In preliminary studies, hybrid ⁶⁸Ga-PSMA PET/MR technology has demonstrated to be promising in the diagnosis and follow up of PCa [38]. The same imaging technology might also represent an important improvement for treatment follow-up. The neoadjuvant setting offers an ideal platform to study this hypothesis.

ARNEO aims to assess the anti-tumour effect of a complete androgen blockade based on apalutamide + degarelix versus degarelix alone. The rapid decrease of testosterone demonstrated by degarelix obviates the need to add an antiandrogen in the placebo arm which could have masked the effect of the apalutamide, at least at the start of the treatment. The risk for selection bias due to the difference in preoperative tumour volume is compensated by the randomization process and the blinding of participants and personnel to ⁶⁸Ga -PSMA-11 PET/MR. In this study there is the unique possibility to evaluate the molecular response to two ADT regimens at once. From a translational point of view, the possibility to analyze the surgical PCa specimen after neoadjuvant therapy and compare this material to the prostate biopsy, represents a unique opportunity. Preoperative treatment provides a platform to evaluate pharmacodynamics endpoints of novel agents and enable the identification of signals of biologic activity. In addition, it may allow for the identification of molecular and biologic prognostic and predictive factors. In this respect, some promising but mainly preclinical data have been reported on the relationship between androgen receptor signalling and DNA damage response pathways [21, 50‐56]. We wish to explore this field through IHC, transcriptome analyses and genome analysis. We chose DNA-PKcs and PARP1 as target proteins for IHC because androgens can activate their transcription [21]. DNA-PKcs is implicated in double strand break (DSB) repair [55]. PARP1 is a nuclear enzyme implicated in DNA repair, tumour proliferation and mediation of androgen receptor-DNA interaction. It can activate the DNA repair process [56, 57]. The therapeutic potential of PARP1 inhibitors has been tested in an explant system of primary human tumours, showing that inhibiting PARP1 enzyme leads to a decrease in tumour proliferation [54]. TOPARP-A (The Trial of PARP Inhibition in Prostate Cancer) phase 2 trial studied the PARP inhibitor olaparib in mCRPC patients showing good response rates particularly for BRCA1/2 or ATM gene-mutated tumours that justified the breakthrough therapy designation by FDA (Food and Drug Administration) [23]. Changes in gene expression after hormonal treatment for PCa have been studied, and have consistently shown a relationship between androgen receptor signalling and DNA repair [50‐52]. This link might explain the beneficial effects of androgen deprivation therapy in combination with EBRT, as it is well known that targeting DNA repair mechanisms results in enhanced radio-sensitivity [53]. Although LHRH analogues are commonly used together with EBRT, it is well known that other androgen sources remain active during treatment. Therefore, a certain level of androgen receptor activity remains in PCa cells even under hormonal treatment. This mechanism could sustain the DNA repair mechanisms, potentially causing tumour resistance to ionizing irradiation. The effect of three, 6 and 9 months of neoadjuvant ADT on gene expression in radical prostatectomy samples has been assessed in earlier studies [58]. Medical castration reduced tissue androgens by 75% but also the expression of several androgen-regulated genes including NDRG1, FKBP5, and TMPRSS2; however, androgen receptor and PSA gene expression were not completely suppressed. These data suggest that suboptimal suppression of the androgen receptor axis may be the cause of resistance not only at the primary tumour site but probably also at the level of micro-metastases with important implications in the neoadjuvant treatment of PCa. The use of new generation compounds with more effective androgen receptor pathway inhibition could counteract this remnant androgen activity. The recent LATITUDE phase 3 trial demonstrated that the relative risk of death decreased of 38% in the abiraterone + prednisone + ADT arm vs placebo’s + ADT in metastatic castration sensitive PCa patients [59]. These data suggest that a more effective inhibition of the AR pathway had a therapeutic effect compared to first generation ADT. From this perspective, ATLAS phase 3 trial is randomizing patients to LHRH analogue or LHRH analogue + apalutamide together with EBRT to assess metastasis free survival (NCT02531516).