A Phase 1 dose escalation and expansion trial of the next-generation oral SERD camizestrant in women with ER-positive, HER2-negative advanced breast cancer: SERENA-1 monotherapy results

BACKGROUND

SERENA-1 (NCT03616587) is a Phase 1, multi-part, open-label study of camizestrant in pre- and post-menopausal women with ER+, HER2- advanced breast cancer. Parts A and B aim to determine the safety and tolerability of camizestrant monotherapy and define doses for clinical evaluation. Patients and Methods Women aged 18 years or older with metastatic or recurrent ER+, HER2- breast cancer, refractory (or intolerant) to therapy were assigned 25 mg up to 450 mg once daily (QD; escalation) or 75, 150, or 300 mg QD (expansion). Safety and tolerability, anti-tumor efficacy, pharmacokinetics, and impact on ESR1m circulating tumor (ct)DNA levels were assessed.

RESULTS

By 9 March 2021, 108 patients received camizestrant monotherapy at 25-450 mg doses. Of these, 93 (86.1%) experienced treatment-related adverse events (TRAEs), 82.4% of which were grade 1 or 2. The most common TRAEs were visual effects (56%), (sinus) bradycardia (44%), fatigue (26%), and nausea (15%). There were no TRAEs grade 3 or higher, or treatment-related serious adverse events (TRSAEs) at doses ≤150 mg. Median tmax was achieved ∼2-4 hours post-dose at all doses investigated, with an estimated half-life of 20-23 hours. Efficacy was observed at all doses investigated, including in patients with prior CDK4/6 inhibitor and/or fulvestrant treatment, with and without baseline ESR1 mutations, and with visceral disease, including liver metastases.

CONCLUSIONS

Camizestrant is a next-generation oral SERD and pure ER antagonist with a tolerable safety profile. The pharmacokinetics profile supports once-daily dosing, with evidence of pharmacodynamic and clinical efficacy in heavily pre-treated patients, regardless of ESR1m. This study established 75, 150 and 300 mg QD doses for Phase 2 testing (SERENA-2, NCT04214288 and SERENA-3, NCT04588298).

BEECH: a dose-finding run-in followed by a randomised phase II study assessing the efficacy of AKT inhibitor capivasertib (AZD5363) combined with paclitaxel in patients with estrogen receptor-positive advanced or metastatic breast cancer, and in a PIK3CA mutant sub-population

BACKGROUND

BEECH investigated the efficacy of capivasertib (AZD5363), an oral inhibitor of AKT isoforms 1-3, in combination with the first-line weekly paclitaxel for advanced or metastatic estrogen receptor-positive (ER+)/human epidermal growth factor receptor 2-negative (HER2-) breast cancer, and in a phosphoinositide 3-kinase, catalytic, alpha polypeptide mutation sub-population (PIK3CA+).

PATIENTS AND METHODS

BEECH consisted of an open-label, phase Ib safety run-in (part A) in 38 patients with advanced breast cancer, and a randomised, placebo-controlled, double-blind, phase II expansion (part B) in 110 women with ER+/HER2- metastatic breast cancer. In part A, patients received paclitaxel 90 mg/m2 (days 1, 8 and 15 of a 28-day cycle) with capivasertib taken twice daily (b.i.d.) at two intermittent ascending dosing schedules. In part B, patients were randomly assigned, stratified by PIK3CA mutation status, to receive paclitaxel with either capivasertib or placebo. The primary end point for part A was safety to recommend a dose and schedule for part B; primary end points for part B were progression-free survival (PFS) in the overall and PIK3CA+ sub-population.

RESULTS

Capivasertib was well tolerated, with a 400 mg b.i.d. 4 days on/3 days off treatment schedule selected in part A. In part B, median PFS in the overall population was 10.9 months with capivasertib versus 8.4 months with placebo [hazard ratio (HR) 0.80; P = 0.308]. In the PIK3CA+ sub-population, median PFS was 10.9 months with capivasertib versus 10.8 months with placebo (HR 1.11; P = 0.760). Based on the Common Terminology Criteria for Adverse Event v4.0, the most common grade ≥3 adverse events in the capivasertib group were diarrhoea, hyperglycaemia, neutropoenia and maculopapular rash. Dose intensity of paclitaxel was similar in both groups.

CONCLUSIONS

Capivasertib had no apparent impact on the tolerability and dose intensity of paclitaxel. Adding capivasertib to weekly paclitaxel did not prolong PFS in the overall population or PIK3CA+ sub-population of ER+/HER2- advanced/metastatic breast cancer patients.ClinicalTrials.gov: NCT01625286.

Abstract P4-04-06: AZD5363, an AKT inhibitor, significantly inhibits key biomarkers of the AKT pathway and Ki67, in a randomized, placebo, controlled study (STAKT) in human breast cancers

Background: AKT is an important intracellular control point through which Type 1 growth factors and IGFR signal. Mutations in PIK3CA, AKT and PTEN are prevalent in estrogen receptor positive (ER+) breast cancer (BC) and have been implicated in resistance to endocrine therapies. AZD5363 is an inhibitor of AKT 1, 2 and 3 currently in Phase 2 trials for BC and other solid cancers.

Design: The study examined whether AZD5363 impacts on key biomarkers within the AKT pathway and their subsequent effects on Ki67, a marker of tumor proliferation. STAKT is a multi-center, two-stage, double blind, randomized, placebo controlled, biomarker 'window-of-opportunity' trial in women with newly diagnosed, previously untreated ER+ BC who were deemed would require chemotherapy as part of their primary treatment regimen. Stage 1 assessed AZD5363 at a dose of 480mg bd p.o. versus matching placebo. Up to 30 patients per arm were permitted, to allow 12 subjects per arm with evaluable paired biopsies - obtained at baseline, and after 4.5 days of AZD5363 / placebo. Primary endpoint markers were pPRAS40, pGSK3β and Ki67 assessed by immunohistochemistry. pPRAS40 and pGSK3β were assessed by H-scores and measured separately for cytoplasmic (cyto), nuclear (nuc) and total (cyto+nuc) staining. Ki67 was assessed as % positive staining of 500 tumor nuclei. Laboratory staff were blinded to treatment arm and whether the biopsies were taken before or after AZD5363/placebo. Changes in marker expression (both absolute and %) between biopsies were calculated, and compared between the two groups. An ANOVA test was applied for normally distributed data and Wilcoxon Mann-Whitney used if not normally distributed.

Results: 28/36 patients were evaluable with patient & tumor characteristics as follows: 17 received AZD5363 and 11 placebo; the median ages were 48 & 49 years respectively. 27 patients were Caucasian and 1 African-American. Tumors were all ER+. For HER2 status 8 were positive & 9 negative in the AZD5363 treated group compared to 2 & 9 respectively in the placebo group.

For pPRAS40 and pGSK3β cyto was the predominant staining while for Ki67 staining was nuclear. Changes in each marker with associated p-values are shown in the table.

MarkerType of change vs baselineDegree of change in AZD5363 arm (n=17)p-value versus placebo arm (n=11)pPRAS40 (H-score)TotalAbsolute-83.8<0.0001Total%-50.2<0.0001CytoAbsolute-90.0<0.0001Cyto%-55.8<0.0001NucAbsolute+6.90.42Nuc%+8.90.94pGSK3β (H-score)TotalAbsolute-55.30.006Total%-39.00.006CytoAbsolute-53.60.006Cyto%-39.20.006NucAbsolute-2.80.065Nuc%-36.50.058Ki67 (% cells+)Absolute-9.60.031%-29.40.052

Conclusions• AZD5363 for 4.5 days caused highly significant falls in pGSK3β and pPRAS40, key markers of AKT pathway activation

• AZD53643 also caused a significant decline in Ki67 even after only 4.5 days of drug. This is one of the shortest 'window'-studies to report such an early effect on proliferation.

• Placebo controlled 'window' studies of this short duration can provide important evidence of the therapeutic potential early in a drug's development.

Citation Format: Robertson JFR, Coleman RE, Cheung KL, Evans A, Holcombe C, Skene A, Rea D, Ahmed S, Jahan A, Kelly S, Horgan K, Rauchhaus P, Littleford R, Foxley A, Lindemann JPO, Pass M, Rugman P, Deb R, Finlay P, Gee JMW. AZD5363, an AKT inhibitor, significantly inhibits key biomarkers of the AKT pathway and Ki67, in a randomized, placebo, controlled study (STAKT) in human breast cancers [abstract]. In: Proceedings of the 2017 San Antonio Breast Cancer Symposium; 2017 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2018;78(4 Suppl):Abstract nr P4-04-06.

Abstract P5-21-32: AZD5363 in combination with fulvestrant in AKT1-mutant ER-positive metastatic breast cancer

Background: E17K is the most common activating AKT1 mutation and was shown to be a therapeutic target in this multipart Phase 1 study of AZD5363 (NCT01226316), an oral and selective pan-AKT kinase inhibitor, in patients (pts) with AKT1-mutant (AKT1m) advanced solid tumors. In heavily pretreated AKT1m (E17K) ER+ metastatic breast cancer (MBC) pts, monotherapy achieved an objective response rate (ORR) of 20% and a median progression-free survival of 5.5 months (95% CI, 2.9−6.9). Suppression of PI3K-AKT signaling results in induction of ER-dependent transcription, potentially limiting the response to single-agent PI3K/AKT inhibitors. We explored the hypothesis that simultaneous inhibition of AKT and ER signaling would enhance antitumor efficacy in AKT1m ER+ MBC.

Methods: In an expansion of this study, we administered oral AZD5363 400 mg twice daily, 4 days on 3 days off, and fulvestrant 500 mg, to AKT1m (detected in tumor tissue by local screening and/or plasma BEAMing) ER+ HER2– MBC pts, enrolled into a fulvestrant-naïve (FN) or fulvestrant-resistant (FR) cohort (max 24 pts/cohort). Key objectives included safety and efficacy by RECIST v1.1. We report results of a planned interim analysis conducted when 12 pts/cohort reached maturity for assessment of 24-week clinical benefit rate (CBR), defined as the percentage of responders plus those with stable disease (SD) ≥24 weeks.Data cut-off occurred in June 2017.

Results: At the time of analysis, 24 AKT1m pts (23 E17K, 1 E40K) had received treatment. FN had more visceral disease (83.3% vs 66.7%) and ER+/PR– status (25% vs 8.3%) than FR. Median number of prior anticancer regimens was 4.5 (range 1–9) and 6 (2–11) in FN and FR, respectively, with more chemotherapy (CT) and less hormone therapy (HT) exposure in FN vs FR [3 (0–5) vs 2 (0–6) and 2 (0–4) vs 4 (2–6) prior CT and HT, respectively]. Prior palbociclib was received by 1 (8.3%) and 4 (33.3%) pts in FN and FR, respectively. Clinical efficacy is detailed below; CBR was 33% and 42% in FN and FR, respectively (Table 1). There was 1 unconfirmed partial response in patients treated with prior palbociclib and 3 SD. At data cut-off, 18 pts had discontinued treatment: progressive disease, n=12; adverse events (AEs), n=2; other reasons, n=4. AEs were observed in all 24 pts, most commonly diarrhea (71%), nausea (63%), vomiting and decreased appetite (29%). Grade ≥3 AEs occurred in 13 (54%) pts, most frequently maculopapular rash (n=3), nausea, hyperglycemia and back pain (all n=2). Dose reduction due to AEs occurred in 3 pts.

Table 1. Clinical efficacy FNFREligible for interim data cut-off, n1212ORR, n (%)2 (17)4 (33)CBR, n (%)4 (33)5 (42)Confirmed response (complete/partial response), n (%)2 (17)4 (33)SD ≥24 weeks, n (%)2 (17)1 (8)

Conclusions: AZD5363 plus fulvestrant is clinically active in AKT1m ER+ MBC pts, including in pts with demonstrated prior resistance to fulvestrant. Comparatively lower efficacy was observed in the FN cohort; factors that may have potentially contributed (eg disease characteristics) will be explored. cfDNA and genomic data will also be presented.

Citation Format: Smyth LM, Oliveira M, Ciruelos E, Tamura K, El-Khoueiry A, Mita A, You B, Renouf DJ, Sablin M-P, Lluch A, Mayer IA, Bando H, Yamashita H, Ambrose H, de Bruin E, Carr TH, Corcoran C, Foxley A, Lindemann JPO, Maudsley R, Pass M, Rutkowski A, Schiavon G, Banerji U, Scaltriti M, Taylor BS, Chandarlapaty S, Baselga J, Hyman DM. AZD5363 in combination with fulvestrant in AKT1-mutant ER-positive metastatic breast cancer [abstract]. In: Proceedings of the 2017 San Antonio Breast Cancer Symposium; 2017 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2018;78(4 Suppl):Abstract nr P5-21-32.

Abstract P5-21-05: Withdrawn

This abstract was withdrawn by the authors.