A Phase 1/2 multicenter trial of DKN-01 as monotherapy or in combination with docetaxel for the treatment of metastatic castration-resistant prostate cancer (mCRPC)

BACKGROUND

Dickkopf-related protein 1 (DKK1) is a Wingless-related integrate site (Wnt) signaling modulator that is upregulated in prostate cancers (PCa) with low androgen receptor expression. DKN-01, an IgG4 that neutralizes DKK1, delays PCa growth in pre-clinical DKK1-expressing models. These data provided the rationale for a clinical trial testing DKN-01 in patients with metastatic castration-resistant PCa (mCRPC).

METHODS

This was an investigator-initiated parallel-arm phase 1/2 clinical trial testing DKN-01 alone (monotherapy) or in combination with docetaxel 75 mg/m2 (combination) for men with mCRPC who progressed on ≥1 AR signaling inhibitors. DKK1 status was determined by RNA in-situ expression. The primary endpoint of the phase 1 dose escalation cohorts was the determination of the recommended phase 2 dose (RP2D). The primary endpoint of the phase 2 expansion cohorts was objective response rate by iRECIST criteria in patients treated with the combination.

RESULTS

18 pts were enrolled into the study-10 patients in the monotherapy cohorts and 8 patients in the combination cohorts. No DLTs were observed and DKN-01 600 mg was determined as the RP2D. A best overall response of stable disease occurred in two out of seven (29%) evaluable patients in the monotherapy cohort. In the combination cohort, five out of seven (71%) evaluable patients had a partial response (PR). A median rPFS of 5.7 months was observed in the combination cohort. In the combination cohort, the median tumoral DKK1 expression H-score was 0.75 and the rPFS observed was similar between patients with DKK1 H-score ≥1 versus H-score = 0.

CONCLUSION

DKN-01 600 mg was well tolerated. DKK1 blockade has modest anti-tumor activity as a monotherapy for mCRPC. Anti-tumor activity was observed in the combination cohorts, but the response duration was limited. DKK1 expression in the majority of mCRPC is low and did not clearly correlate with anti-tumor activity of DKN-01 plus docetaxel.

A phase 1/2 multicenter investigator-initiated trial of DKN-01 as monotherapy or in combination with docetaxel for the treatment of metastatic castration-resistant prostate cancer (mCRPC)

5048

Background: Dickkopf-1 (DKK1) is a secreted Wnt signaling modulator that is upregulated in prostate cancers with low androgen receptor (AR) expression and co-occurring mutations in Wnt signaling family genes. DKN-01, a potent humanized monoclonal antibody (IgG4) with neutralizing activity against DKK1, delays prostate cancer growth in pre-clinical DKK1-expressing models in an NK cell dependent manner. These data provided the rationale for a prospective clinical trial testing DKN-01 in patients with mCRPC and elevated DKK1. Here, we report the safety and efficacy results of the phase 1 dose escalation cohorts. Methods: This is an investigator-initiated parallel-arm non-randomized phase 1/2 clinical trial testing DKN-01 alone or in combination with docetaxel 75 mg/m2 for men with mCRPC who progressed on ≥1 AR signaling inhibitor. Eligible patients who had progressed on or were intolerant of docetaxel were assigned to the monotherapy cohort whereas taxane-naïve patients were assigned to the DKN-01 plus docetaxel combination cohort. DKK1 status was determined by RNA in-situ expression. The primary endpoint of the phase 1 dose escalation cohorts was safety, characterized by dose-limiting toxicity (DLT). A secondary endpoint of the study was to correlate anti-tumor activity, DKK1 expression (cutoff H-score ≥ 1), and clinical evidence of aggressive variant prostate cancer (AVPC). Results: 13 pts were enrolled in the completed phase 1 portion of this study – 7 patients in the monotherapy cohort and 6 patients in the combination cohort. No DLTs were observed at DKN-01 300mg or 600mg dose levels as monotherapy or in combination with docetaxel. No treatment-related serious adverse events occurred in either cohort. A best overall response of stable disease occurred in 2 out of 7 patients in the monotherapy cohort. In the combination cohort, all 5 evaluable patients had a partial response (PR) – 3 confirmed and 2 unconfirmed. All evaluable combination patients had ≥ 50% reduction in either PSA or CEA. Confirmed PRs in the combination cohort were observed in both DKK1 low (DKK1 H-score < 1) and high expressing tumors (H-score ≥1), including in 2 out of 3 patients with AVPC. Conclusions: DKN-01 600mg was well tolerated and selected as the recommended phase 2 dose as monotherapy and in combination with docetaxel. DKN-01 in combination with docetaxel showed promising clinical activity in prostate cancers regardless of DKK1 expression and was particularly promising in patients with AVPC. Further accrual into the phase 2 portion of this study is ongoing alongside preclinical and correlative studies aiming to investigate the mechanism of action of this combination therapeutic strategy. Clinical trial information: NCT03837353.

Pembrolizumab (pembro) in combination with gemcitabine (Gem) and concurrent hypofractionated radiation therapy (RT) as bladder sparing treatment for muscle-invasive urothelial cancer of the bladder (MIBC): A multicenter phase 2 trial

4504

Background: Trimodality bladder preservation therapy (TMT) is a standard treatment option for clinically localized MIBC with curative intent. Pembro has shown activity in MIBC in the neoadjuvant setting and may combine well with TMT to improve outcomes. This trial evaluated the safety and efficacy of pembro added to TMT in MIBC. Methods: This multicenter phase 2 trial included pts with cT2 – T4aN0M0 MIBC who declined or were ineligible for cystectomy (RC), ECOG PS 0/1, eGFR > 30 cc/min, and no contraindications to pelvic RT or pembro. No perioperative chemotx for MIBC was permitted. Pts received pembro 200 mg x 1 followed 2-3 weeks by maximal TURBT and then whole bladder RT (52 Gy/20 fx; IMRT preferred) with twice wkly gem 27 mg/m2 and pembro Q3 wks x 3 treatments. 12 wks post-RT, CT/MR AP, TUR of tumor bed and cytology were performed to document response. Up to 6 pts were enrolled to a safety cohort (SC) followed by 48 pts in efficacy cohort (EC). The primary endpt is 2-yr bladder-intact disease-free survival (BIDFS: first of MIBC or regional nodal recurrence, distant metastases, or death) assessed by serial cysto/cytology and CT/MRI. EC had 85% power to detect a 20% absolute improvement in 2-yr BIDFS rate over 60% historical rate (RTOG Pooled analysis; Mak JCO 2014). Key secondary endpts were safety, 12 wks CR rate, metastases-free survival and overall survival. Tumor tissue was collected at study entry, maximal TURBT and post-treatment TUR of tumor bed with serial PBMCs for correlative analyses. Results: From 5/2016 to 10/2020, 54 pts (6 SC, 48 EC; 72% M) enrolled at 5 centers; Median age 67 (65-89) for SC and 74 (51-97) for EC. C-stage (74% cT2, 22% cT3, and 4% cT4). 39 (72%) declined RC. All 6 pts in SC and 42/48 (88%) of EC pts completed all study therapy; 1/48 (2%), 2/48 (4%), and 4/48 (8%) discontinued RT/Gem, Gem or Pembro, respectively, most often due to toxicity. As of 1/2021 (median F/U 40.9 mos (38.6-50.8) SC and 11.7 mos (0.6 – 32.2) EC), no recurrences in SC, and 12/48 EC pts had any recurrence (6 NMIBC, 0 MIBC, 2 regional and 4 distant). The estimated 1 yr BIDFS rate is 77% (95% CI: 0.60-0.87). 12 wks CR rate was 100% in SC and 83% for EC (1 PR, 3 NR, 1 Progression, 11 NE; 2 still on active study). In the EC, 35% of pts had a Gr ≥3 TEAE (Gr 3 events included UTI 8%, diarrhea 4%, colitis 4%, bladder pain/obstruction 4%, neutropenia 2%, thrombocytopenia 2%). Notable Pembro Gr ≥3 TRAE included 3 pts (6%) Gr 3 GI toxicity and 1 pt Gr 4 colonic perforation. 1 patient died due to fungemia, unrelated to study therapy. Conclusions: Pembro added to hypofractionated RT and twice weekly gem was well-tolerated with promising efficacy in this early analysis. Pembro-related toxicity was consistent with prior monotherapy trials. Selected correlative analyses from serially collected blood and tissue specimens will be presented. Clinical trial information: NCT02621151.