Phase I/II dose-escalation study of PI3K inhibitors pilaralisib or voxtalisib in combination with letrozole in patients
with hormone-receptor-positive and HER2-negative metastatic breast cancer refractory to a non-steroidal aromatase inhibitor
Kimberly Blackwell1 • Howard Burris2 • Patricia Gomez3 • N. Lynn Henry4 • Steven Isakoff5 • Frank Campana6 • Lei Gao6 • Jason Jiang7 • Sandrine ´Mace8 • Sara M. Tolaney9
Received: 19 October 2015 / Accepted: 19 October 2015 ti Springer Science+Business Media New York 2015
Abstract This phase I/II dose-escalation study evaluated the efficacy, safety, and pharmacokinetics of pilaralisib (SAR245408), a pan-class I phosphoinositide 3-kinase (PI3K) inhibitor, or voxtalisib (SAR245409), a PI3K and mammalian target of rapamycin inhibitor, in combination with letrozole in hormone-receptor-positive (HR?), human epidermal growth factor receptor 2 (HER2)-negative, non- steroidal aromatase inhibitor-refractory, recurrent or metastatic breast cancer. Maximum tolerated doses (MTDs) were determined using a 3 ? 3 design in phase I. Efficacy was evaluated at the MTDs in phase II. Twenty- one patients were enrolled in phase I; MTDs were deter- mined to be pilaralisib tablets 400 mg once daily (QD) or voxtalisib capsules 50 mg twice daily in combination with letrozole tablets 2.5 mg QD. Fifty-one patients were enrolled in phase II; one patient had a partial response in
the pilaralisib arm. Rates of progression-free survival at 6 months were 17 and 8 % in the pilaralisib and voxtalisib arms, respectively. The most frequently reported treatment- related grade C 3 adverse events were aspartate amino- transferase increased (5 %) and rash (5 %) in the pilaralisib arm, and alanine aminotransferase increased (11 %) and rash (9 %) in the voxtalisib arm. Pilaralisib and voxtalisib did not interact pharmacokinetically with letrozole. Pilar- alisib had a greater pharmacodynamic impact than vox- talisib, as demonstrated by its impact on glucose homeostasis. There was no association between molecular alterations in the PI3K pathway and efficacy. In summary, pilaralisib or voxtalisib, in combination with letrozole, was associated with an acceptable safety profile and limited efficacy in endocrine therapy-resistant HR? , HER2-neg- ative metastatic breast cancer.
Electronic supplementary material The online version of this article (doi:10.1007/s10549-015-3615-9) contains supplementary material, which is available to authorized users.
& Kimberly Blackwell [email protected]
1 Duke University Medical Center, 2301 Erwin Road, Durham, NC 27710, USA
Keywords HER2-negative ti Hormone-receptor-positive metastatic breast cancer ti PI3K ti Pilaralisib ti Voxtalisib
Approximately 75 % of breast tumors are hormone-re- ceptor positive (HR?), expressing estrogen receptor (ER)
Sarah Cannon Research Institute, Nashville, TN, USA Vall d’Hebron, Barcelona, Spain
University of Michigan Medical School, Ann Arbor, MI, USA
Massachusetts General Hospital, Boston, MA, USA Sanofi, Cambridge, MA, USA
Sanofi, Bridgewater, NJ, USA Sanofi, Vitry sur Seine, France
Dana-Farber Cancer Institute, Boston, MA, USA
and/or progesterone receptor (PgR) . Endocrine therapy (anti-estrogens or aromatase inhibitors) is a central treat- ment strategy for patients with HR? advanced breast cancer [2, 3]. Aromatase inhibitors inhibit stimulation of estrogen-mediated breast cancer by suppressing estrogen biosynthesis . Letrozole, which specifically blocks estrogen synthesis by competitive, reversible binding to the heme of the cytochrome P450 subunit of the aro- matase enzyme, is approved for use in both early and advanced HR? breast cancers in postmenopausal women.
However, resistance to aromatase inhibitors occurs in the majority of patients and is a major challenge to disease management .
The phosphoinositide 3-kinase (PI3K)/mammalian tar- get of rapamycin (mTOR) pathway is involved in numer- ous normal cellular processes, including growth and survival, and its dysregulation is implicated in tumorigen- esis of multiple tumor types, including breast cancer [5–8]. PI3K pathway molecular alterations occur frequently in breast cancer, and include PI3K catalytic subunit alpha (PIK3CA) mutation, phosphatase and tensin homolog (PTEN) mutation or deficiency and AKT mutation [6–8]. PIK3CA is one of the most frequently mutated genes in breast cancer, with mutations occurring in 36 % of all breast tumors and in approximately 40 % of ER? tumors [7, 9]. Resistance to endocrine therapy has been associated with compensatory signaling via alternate pathways, including the PI3K pathway [10, 11]. In addition, preclin- ical data suggest that inhibitors of the PI3K pathway can restore sensitivity to aromatase inhibitors [12, 13]. There- fore, investigating combinations of inhibitors of aromatase and the PI3K pathway is a rational strategy in HR? ad- vanced breast cancer that is refractory to aromatase inhi- bitor treatment.
Recently, several PI3K pathway inhibitors have been investigated in combination with endocrine therapy in HR? , human epidermal growth factor receptor (HER2)- negative advanced breast cancer, including mTOR inhibi- tors [14, 15] and PI3K inhibitors [16, 17]. In the phase III BOLERO-2 trial, adding the mTOR inhibitor everolimus to exemestane significantly improved progression-free sur- vival (PFS) in patients with HR? , HER2-negative advanced breast cancer previously treated with non-ster- oidal aromatase inhibitor therapy, both in first-line and later-line settings (median PFS 10.6 months with ever- olimus plus exemestane vs 4.1 months with exemestane; hazard ratio 0.36; P \ 0.001) ; overall survival benefits were not seen (median OS 31.0 months versus 26.6 months; hazard ratio 0.89; P = 0.14) .
Pilaralisib (SAR245408, XL147), an oral selective pan- class I PI3K inhibitor , has been investigated in phase I/II trials in several solid tumors [19–21] and lymphomas . Pilaralisib showed clinical activity as monotherapy in a phase I study in solid tumors, in which the maximum tolerated dose (MTD) of pilaralisib in capsule formulation was established at 600 mg once daily (QD) . The MTD for pilaralisib in tablet formulation has not been estab- lished; the phase II recommended dose was determined at 400 mg QD in a phase I trial (Sanofi, data on file). Pilar- alisib was also investigated in a phase I/II study in com- bination with trastuzumab with and without paclitaxel in patients with HER2-positive metastatic breast cancer;
clinical activity was observed in the pilaralisib, trastuzu- mab, and paclitaxel arm .
Voxtalisib (SAR245409, XL765), an oral inhibitor of PI3K and mTOR , has also been investigated in trials in several solid tumors [24–26] and lymphomas [27, 28]. Voxtalisib showed clinical activity as monotherapy in a phase I trial in solid tumors; the MTD of voxtalisib cap- sules was established at 50 mg twice daily (BID) . This phase I/II dose-escalation study evaluated the MTD, safety, efficacy, pharmacokinetics (PK), and pharmacodynamics of pilaralisib or voxtalisib in combination with the non- steroidal aromatase inhibitor letrozole in patients with HR? , HER2-negative, recurrent or metastatic breast cancer whose disease was refractory to non-steroidal aro- matase inhibitor treatment (NCT01082068).
Patients and methods
Eligible patients were postmenopausal women who had histologically confirmed breast cancer that was ER? and/
or PgR? (as defined by any staining), and negative for HER2 overexpression by immunohistochemistry or for HER2 gene amplification by fluorescent in situ hybridiza- tion or an equivalent method. Patients also had recurrent or metastatic disease that was refractory to any non-steroidal aromatase inhibitor, and were required to have measurable disease, an Eastern Cooperative Oncology Group perfor- mance status of B 1, and adequate organ and marrow function. In phase I of the study, patients were permitted to have received no more than five prior cytotoxic chemotherapeutic regimens for metastatic breast cancer; in phase II, patients were permitted to have received no more than two prior cytotoxic chemotherapeutic regimens for metastatic breast cancer. Patients were ineligible if they had received prior treatment with an inhibitor of PI3K, AKT and/or mTOR.
The study adhered to the principles outlined in the ‘‘Guideline for Good Clinical Practice,’’ and was con- ducted in compliance with all international laws and reg- ulations. All patients provided written, informed consent.
This was a multicenter, phase I/II, open-label study. Patients received either pilaralisib tablets QD (starting dose 200 mg) or voxtalisib capsules (HCl salt, with a correction factor of 0.88 for API) BID (starting dose 30 mg), each in combina- tion with letrozole tablets 2.5 mg QD administered 30 min after the pilaralisib dose or first (morning) voxtalisib dose.
Primary objectives were to determine the MTD of pilaralisib or voxtalisib in combination with standard doses of letrozole (phase I), to evaluate the co-primary efficacy endpoints of objective response rate (ORR) and PFS rate at 6 months (24 weeks; phase II), and to evaluate the safety of pilaralisib or voxtalisib in combination with standard doses of letrozole. Secondary objectives included estima- tion of PFS, duration of response and clinical benefit rate (phase II), and to assess the pharmacodynamics and plasma PK of pilaralisib, voxtalisib, and letrozole.
Dose-limiting toxicities and maximum tolerated dose
In phase I, MTD was determined using a 3 ? 3 dose- escalation design. The MTD was defined as the highest dose level at which \33 % of a cohort of at least six patients had a dose-limiting toxicity (DLT) in the first 28 days of study treatment (Cycle 1). Dose escalation in the voxtalisib arm was not to exceed a voxtalisib dose of 50 mg BID (MTD identified in the phase I study in solid tumors) . DLTs were assessed in phase I only. Defi- nition of DLTs is described in the Supplementary Methods. In phase II, patients were treated with the MTD of pilar- alisib or voxtalisib established in phase I in combination with letrozole 2.5 mg QD.
In phase II, the co-primary efficacy endpoints were ORR and PFS rate at 6 months (24 weeks) in each arm. A two- stage design was used; in Stage 1, it was planned that 24 evaluable patients would be enrolled in each arm; if two or more patients achieved an objective response, or four or more patients were alive and progression free for at least 6 months, then that arm was to continue to Stage 2 until 48 evaluable patients had been enrolled in total.
Tumor response was assessed using RECIST Version
1.1; magnetic resonance imaging or computed tomography scans were performed at screening, 8 weeks after the first dose of study treatment, and every 8 weeks thereafter until documented radiographic progression, the initiation of other anticancer therapy or death. Responses were confirmed by repeat assessments performed at least 4 weeks after response criteria were met.
Safety was assessed by evaluation of adverse events (AEs), vital signs, electrocardiogram, and laboratory tests. AE seriousness, severity grade, and relationship to study treat- ment were assessed by the investigator. AEs were graded in accordance with the National Cancer Institute Common Terminology Criteria for Adverse Events v3.0 .
Blood samples for PK assessment of pilaralisib, voxtalisib, and letrozole plasma concentrations were obtained at pre- defined timepoints. Plasma concentrations were determined using a validated liquid chromatography and tandem mass spectrometry (LC–MS/MS) method (Sanofi, data on file). Non-compartmental PK analysis with WinNonlin Profes- sional 5.2 (Pharsight Corp., Mountain View, CA, USA) was used to assess maximum concentration (Cmax), time to maximum concentration (tmax), and area under the concen- tration–time curve up to 12 or 24 h (AUC0–12 or AUC0–24).
Blood samples were obtained from consenting patients for analysis of established and exploratory pharmacodynamic markers at pre-defined timepoints throughout the study. The pharmacodynamic impact of pilaralisib or voxtalisib on the PI3K pathway was evaluated by analyzing fasting glucose levels and C-peptide levels in serial plasma sam- ples. Full methods are provided in supplementary methods.
Molecular profiling of tumor material
Alterations in components/modulators of the PI3K pathway detected in archival formalin-fixed, paraffin-embedded (FFPE) tumor tissue and in plasma circulating tumor DNA (ctDNA) were characterized to identify molecular markers associated with response or resistance to pilaralisib and vox- talisib. Full methods are provided in supplementary materials.
Patient baseline characteristics are summarized in Table 1. Thirty-seven patients were enrolled in the pilaralisib arm (12 in phase I, 25 in phase II) and 35 patients were enrolled in the voxtalisib arm (9 in phase I and 26 in phase II). In the pilaralisib and voxtalisib arms, the median number of prior endocrine regimens received in the advanced/metastatic setting was 2.0 (range 0–4) and 2.0 (range 1–4) in phase I, and 2.0 (range 0–8) and 2.5 (range 1–8) in phase II, respectively. The duration of most recent endocrine therapy regimens in the metastatic setting was short, indicating a fairly endocrine-resistant population of patients; in the pilaralisib and voxtalisib arms, median durations of most recent endocrine regimens were 28.0 weeks (range 12.1–109.3) and 19.0 weeks (range 7.6–206.0) in phase I, and 33.3 weeks (5.6–444.1) and 27.7 weeks (range 1.9–234.4) in phase II, respectively.
Table 1 Patient baseline characteristics in phase I and phase II
Phase I Phase II
Pilaralisib ? letrozole (n = 12)
Voxtalisib ? letrozole (n = 9)
Pilaralisib ? letrozole (n = 25)
Voxtalisib ? letrozole (n = 26)
Median age, years (range) 59.5 (47–68) 57.0 (37–66) 66.0 (49–84) 63.0 (33–87) ECOG PS, n (%)
0 8 (66.7) 7 (77.8) 18 (72.0) 16 (61.5)
1 4 (33.3) 2 (22.2) 7 (28.0) 10 (38.5) Histologic grade, n (%)
Unknown 6 (50.0) 3 (33.3) 5 (20.0) 4 (15.4)
I 2 (16.7) 1 (11.1) 4 (16.0) 3 (11.5)
II 3 (25.0) 2 (22.2) 11 (44.0) 13 (50.0)
III 1 (8.3) 3 (33.3) 5 (20.0) 6 (23.1)
ER-positive tumor, n (%) 12 (100) 9 (100) 25 (100) 26 (100)
PgR-positive tumor, n (%) 9 (75.0) 8 (88.9) 17 (68.0) 20 (76.9) Disease stage at enrollment, n (%)
II 0 0 0 1 (3.8)
IIIA 1 (8.3) 0 2 (8.0) 0
IIIC 1 (8.3) 0 0 0
IV 10 (83.3) 9 (100.0) 23 (92.0) 25 (96.2)
Median time from initial diagnosis, years (range)
5.8 (0–33) 12.2 (8–18) 8.7 (1–25) 8.8 (2–29)
Median time from metastatic diagnosis, years (range)
Median prior endocrine regimens in advanced/metastatic setting, number (range)
Median prior chemotherapy regimens in advanced/metastatic setting, number (range)
Median time on last letrozole/
anastrozole regimen in advanced/
metastatic setting, weeks (range)
Median time on last endocrine regimen in advanced/metastatic setting, weeks (range)
ECOG PS Eastern Cooperative Oncology Group performance status, ER estrogen receptor, PgR progesterone receptor
Treatment, dose-limiting toxicities, and maximum tolerated dose
In phase I, 12 patients received pilaralisib (six at 200 mg QD, six at 400 mg QD) and nine patients received vox- talisib (three at 30 mg BID, six at 50 mg BID). All patients in phase I completed the first cycle of study treatment and were evaluable for DLT. Two DLTs occurred: grade 3 drug reaction with eosinophilia and systemic symptoms in one patient receiving pilaralisib 400 mg QD, and grade 3 rash in one patient receiving voxtalisib 50 mg BID. MTDs in combination with letrozole 2.5 mg were determined to be pilaralisib 400 mg QD and voxtalisib 50 mg BID. In phase
II, 25 and 26 patients received the MTD of pilaralisib and voxtalisib, respectively, combined with 2.5 mg letrozole.
Disease progression was the most common reason for discontinuing study treatment, occurring in 29 patients (78 %) in the pilaralisib arm and in 24 patients (69 %) in the voxtalisib arm. Treatment was discontinued because of an AE in seven (19 %) and nine (26 %) patients in the pilaralisib and voxtalisib arms, respectively.
The primary efficacy analysis was based on patients in phase II only. One patient treated with pilaralisib had a
partial response (PR), resulting in an ORR of 4 % (90 % CI 0.2–18.3 %) in the pilaralisib arm (Table 2). No patient treated with voxtalisib achieved an objective response. PFS rates at 6 months were 4/24 (17 %; 90 % CI 6–34 %) in the pilaralisib arm and 2/26 (8 %; 90 % CI 1–22 %) in the voxtalisib arm. Median PFS was 8.0 weeks (90 % CI 7.7–16.1) in the pilaralisib arm and 7.9 weeks (90 % CI 7.1–15.7) in the voxtalisib arm. Among patients treated in phase I, 4/12 (33 %) patients in the pilaralisib arm and 2/9 (22 %) patients in the voxtalisib arm were progression free at 24 weeks. No objective responses were observed in phase I. Maximum reduction from baseline in tumor bur- den per patient is shown in Fig. 1.
Median duration of treatment was 14.7 weeks (range 0.3–70.0) for patients treated with pilaralisib and 8.0 weeks (range 0.3–71.9) for patients treated with voxtalisib. The most frequently reported AEs in the pilaralisib arm, irre- spective of causality, were rash (43 %), diarrhea (38 %), nausea (32 %), and vomiting (24 %). The most frequently reported AEs in the voxtalisib arm were nausea (60 %), diarrhea (43 %), vomiting (34 %), and fatigue (31 %). The most frequently reported grade C 3 AEs (in the pilaralisib and voxtalisib arms, respectively) were alanine amino- transferase (ALT) increased (5 and 11 %), aspartate aminotransferase (AST) increased (5 and 9 %), gamma- glutamyl transpeptidase increased (8 and 6 %), and rash (5 and 9 %).
The most frequently reported treatment-related AEs were rash (41 %) and diarrhea (22 %) in the pilaralisib arm and nausea (46 %) and diarrhea (31 %) in the voxtalisib arm (Table 3). The most frequently reported treatment-re- lated grade C 3 AEs were AST increased (5 %) and rash
(5%) in the pilaralisib arm, and ALT increased (11 %) and rash (9 %) in the voxtalisib arm.
Table 2 Efficacy of pilaralisib or voxtalisib plus letrozole in phase II
AEs in the hyperglycemia grouping (including blood glucose increased, hyperglycemia and diabetes mellitus) were reported in seven patients in the pilaralisib arm (19 %) and three patients in the voxtalisib arm (9 %), and were considered treatment related in three (9 %) and two
(6%) patients, respectively. Of these, one patient receiving 400 mg pilaralisib had serious AEs (SAEs) of grade 4 hyperglycemia and diabetes mellitus. AEs in the liver toxicities grouping were reported in 10 patients in the pilaralisib arm (27 %) and 11 patients in the voxtalisib arm (34 %), and were considered treatment related in five (14 %) and eight (23 %) patients, respectively. The most commonly reported liver toxicities were AST increased (11 % in the pilaralisib arm and 23 % in the voxtalisib arm) and ALT increased (11 and 17 %, respectively). AEs in the rash grouping (including rash, pruritus, maculo- papular rash, dry skin, etc.) were reported in 19 patients in the pilaralisib arm (51 %) and 13 patients in the voxtalisib arm (37 %), and were considered treatment related in 16 (43 %) and 11 (31 %) patients, respectively. The only grade C 3 hematologic laboratory abnormality occurring in more than one patient in a treatment arm was lym- phopenia (5 % in the pilaralisib arm and 11 % in the voxtalisib arm).
Ten patients in each treatment arm experienced an SAE, of which five patients in the pilaralisib arm and six patients in the voxtalisib arm had a treatment-related SAE. The only treatment-related SAE occurring in more than one patient was maculo-papular rash [two patients (6 %), in the voxtalisib arm]. An SAE of treatment-related pneumonitis occurred in one patient approximately 1 month after the last dose of study drug, resulting in the patient’s death approximately 4 months after discontinuing study treatment.
AEs led to dose reduction or interruptions in eight and 24 patients, respectively. Sixteen patients had an AE that led to discontinuation of study drug, of which only rash
Pilaralisib ? letrozole 400 mg QD (n = 24) Voxtalisib ? letrozole 50 mg BID (n = 26)
Best overall response, n (%)
Complete response 0 0
Partial response 1 (4.2) 0
Stable disease 10 (41.7) 8 (30.8)
Progressive disease 11 (45.8) 12 (46.2)
Not evaluable 2 (8.3) 6 (23.1)
Objective response rate, n (%) [90 % CI] 1 (4.2) [0.2–18.3] 0 [0–10.9]
PFS at 6 months, n (%) [90 % CI] 4 (16.7) [5.9–34.2] 2 (7.7) [1.4–22.3]
Median PFS, weeks (90 % CI) 8.0 (7.7–16.1) 7.9 (7.1–15.7) BID twice daily, CI confidence interval, PFS progression-free survival, QD once daily
Fig. 1 Waterfall plot of maximum reduction from
baseline in tumor burden per patient with a pilaralisib and
b voxtalisib, with corresponding status of phosphatase and tensin homolog (PTEN) and phosphoinositide 3-kinase catalytic subunit alpha (PIK3CA) alterations in all evaluable patients enrolled in phase I and phase II
200 mg QD 400 mg QD
PTEN protein PTEN mutation PIK3CA mutation
10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28
Normal Altered Unknown
30 mg BID 50 mg BID
PTEN protein PTEN mutation PIK3CA mutation
12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27
Normal Altered Unknown
Table 3 Most frequently occurring treatment-related adverse events in all treated patients
n, (%) Pilaralisib dose (? letrozole) Voxtalisib dose (? letrozole)
200 mg QD (n = 6)
400 mg QD (n = 31)
(n = 37)
30 mg BID (n = 3)
50 mg BID (n = 32)
(n = 35)
Any grade ([10 %)
Rash 3 (50.0) 12 (38.7) 15 (40.5) 0 8 (25.0) 8 (22.9)
Nausea 0 5 (16.1) 5 (13.5) 1 (33.3) 15 (46.9) 16 (45.7)
Diarrhea 3 (50.0) 5 (16.1) 8 (21.6) 0 11 (34.4) 11 (31.4)
Asthenia 0 5 (16.1) 5 (13.5) 1 (33.3) 4 (12.5) 5 (14.3)
Fatigue 1 (16.7) 2 (6.5) 3 (8.1) 2 (66.7) 8 (25.0) 10 (28.6)
AST increased 1 (16.7) 2 (6.5) 3 (8.1) 0 6 (18.8) 6 (17.1)
Dyspepsia 0 1 (3.2) 1 (2.7) 0 8 (25.0) 8 (22.9)
Decreased appetite 1 (16.7) 0 1 (2.7) 1 (33.3) 6 (18.8) 7 (20.0)
Vomiting 0 3 (9.7) 3 (8.1) 1 (33.3) 4 (12.5) 5 (14.3) Grade C 3 ([2 %)
ALT increased 0 1 (3.2) 1 (2.7) 0 4 (12.5) 4 (11.4)
Rash 1 (16.7) 1 (3.2) 2 (5.4) 0 3 (9.4) 3 (8.6)
AST increased 0 2 (6.5) 2 (5.4) 0 2 (6.3) 2 (5.7)
GGT increased 0 1 (3.2) 1 (2.7) 0 1 (3.1) 1 (2.9)
Rash maculo-papular 0 0 0 0 2 (6.3) 2 (5.7) ALT alanine aminotransferase, AST aspartate aminotransferase, BID twice daily, GGT gamma-glutamyl transpeptidase, QD once daily
[two patients (5 %) in the pilaralisib arm], ALT increased [two patients (6 %) in the voxtalisib arm], and AST increased [two patients (6 %) in the voxtalisib arm] led to discontinuation in more than one patient in a treatment arm. No death occurred within 30 days of study treatment in either treatment arm.
PK parameters for pilaralisib, voxtalisib, and letrozole at steady state (Week 5, day 1) are summarized in Table 4. Cmax and AUC were similar to published data for pilaral- isib, voxtalisib, and letrozole [19, 24, 31], suggesting that letrozole does not have a major impact on pilaralisib and voxtalisib PK, and pilaralisib and voxtalisib do not have a major impact on letrozole PK.
Molecular profiling of tumor material
Maximum reduction from baseline in tumor burden per patient and corresponding PTEN and PIK3CA alteration status is shown in Fig. 1. No association between molec- ular alterations and efficacy was observed, including PIK3CA mutation and PTEN mutation, or loss of protein expression.
PIK3CA alteration status was obtained for 55 evaluable patients either from tumor tissue and plasma (31 patients) or from plasma only (24 patients). Eighteen patient samples
had mutations [N345 K (1), C420R (1) E542 K (2), E545 K (1), Q546 K (1) H1047R (10), H1047L (2)]. PIK3CA mutations detected in plasma ctDNA had an acceptable level of concordance with PIK3CA mutations detected in FFPE archival tumor tissue. Discrepancies between mutation analysis of ctDNA and tumor tissue were rare (6 %, two of 31 samples tested in both tumor material, one found in tumor tissue only and the other in ctDNA only). Additional mutations (N345 K and C420R) were found in two patients in tumor tissue only, as they were not included in the plasma ctDNA mutation panel (nine mutations tested). PTEN alteration status was obtained for 39 evaluable patients, of whom 6 had PTEN alteration. Despite a partial sample mutation analysis (due to lack of tissue availability), alteration in PI3K pathway was present in 22 patients (40 %). Detailed mutational profiling of 38 tumor samples is shown in Supplementary Fig. S1 (67 cancer-related genes were mutated out of 296 sequenced).
Overall, the mutation profile, alteration frequency, and rate of co-occurrence detected in this study were in good agreement with recently reported data in HR? breast cancers [9, 32].
Increases in glucose levels were more evident for pilaral- isib compared with voxtalisib (Fig. 2). At day 29, 21 % of patients who received pilaralisib 400 mg QD had
grade C 1 hyperglycemia, compared with 4 % of patients who received voxtalisib 50 mg QD. Grade 4 hyper- glycemia was an SAE in one patient treated with pilaralisib 400 mg QD. Increases in C-peptide were seen at all doses tested for pilaralisib and voxtalisib. However, 50 % of patients who received pilaralisib had C-peptide plasma concentrations greater than the upper normal values at day 29, compared with 34 % of patients who received voxtal- isib (supplementary Fig. S2). Post-treatment increases in C-peptide occurred for both compounds; for pilaralisib, there was a time-dependent effect with a maximum increase at day 57 (Supplementary Fig. S3). No time-de- pendent effect was observed for voxtalisib.
This phase I/II study investigated the MTD, efficacy, and safety of the pan-class I PI3K inhibitor pilaralisib and the PI3K and mTOR inhibitor voxtalisib, in combination with letrozole in patients with HR? , HER2-negative breast cancer whose disease was refractory to non-steroidal aro- matase inhibitor treatment. Patients were heavily pre- treated and had short durations of response on their most recent endocrine therapy (median 19–28 weeks).
MTDs were determined to be pilaralisib tablets 400 mg QD or voxtalisib capsules 50 mg BID, in combination with letrozole tablets 2.5 mg QD. Safety profiles observed were consistent with previous trials of pilaralisib or voxtalisib monotherapy in other tumor types [19, 21, 24, 27, 28, 33], with rash and gastrointestinal toxicities (nausea and diar- rhea) among the most frequently reported treatment-related AEs. Observed safety profiles are also consistent with other PI3K inhibitors in development in breast cancer [17, 34].
PK results in this trial were consistent with previous trials of pilaralisib, voxtalisib, and letrozole [19, 24, 31], suggesting that pilaralisib and voxtalisib do not interact with letrozole. In pharmacodynamic analyses, pilaralisib had a greater impact on glucose metabolism than voxtal- isib, which could potentially be related to the superior (although limited) efficacy seen in the pilaralisib arm.
Single-agent PI3K inhibitors and PI3K inhibitor com- binations with other anti-cancer agents have generally been associated with modest efficacy in the majority of tumor types tested [19, 21, 24, 26, 27, 33, 35–37], including breast cancer [16, 17, 23, 34]. Because all patients were refractory to a non-steroidal aromatase inhibitor, the phase II portion of this study is unique in that it evaluated the ability of a PI3K inhibitor to overcome resistance to non- steroidal aromatase inhibitor therapy. In the pilaralisib arm of this trial, one patient had a PR (ORR 4 %) and the PFS rate at 6 months was 17 % (4 of 24 patients), meeting the efficacy threshold to proceed with Stage 2 of phase II. In
Fig. 2 Fasting glucose concentrations over time with
apilaralisib 200 mg,
bpilaralisib 400 mg,
cvoxtalisib 30 mg or
dvoxtalisib 50 mg in samples from patients enrolled in phase I and phase II. Each line represents a single patient. Samples taken before drug dosing on days 1, 8, 15, 22, 29 (week 5), 36, 43, 50, 57, 64, 71, 85, and 99 were analyzed. Common terminology criteria for adverse events (CTCAE) grades for hyperglycemia grade
1(126–160 mg/dL), grade 2 (161–250 mg/dL), and grade 3 (251–500 mg/dL) are indicated
Grade 2 Grade 1
1 8 15 22 29 36 43 50 57 64 71 78 85 92 99
Grade 3 Grade 2
1 8 15 22 29 36 43 50 57 64 71 78 85 92 99
Grade 2 Grade 1
1 8 15 22 29 36 43 50 57 64 71 78 85 92 99
Grade 2 Grade 1
1 8 15 22 29 36 43 50 57 64 71 78 85 92 99
the voxtalisib arm, however, the efficacy threshold was not reached; no patient had a response and the PFS rate at 6 months was 8 % (2 of 26 patients). Because of limited efficacy, particularly in the voxtalisib arm, enrollment of the phase II component was not completed, and pilaralisib and voxtalisib are no longer being investigated in combi- nation with letrozole in HR? , HER2-negative advanced breast cancer.
Since PI3K mutations are present in approximately 40 % of HR? breast cancer and PI3K/mTOR signaling is thought to be a potential resistance mechanism to anti- estrogen therapy, there is much interest in exploring these drugs further in the setting of metastatic breast cancer. A recent randomized phase II trial (FERGI; N = 168) found that adding the pan-PI3K inhibitor pictilisib to fulvestrant did not increase efficacy in patients with aromatase inhi- bitor-resistant advanced HR ? breast cancer . How- ever, sub-analyses suggested that patients whose cancers were both ER? and PgR? benefitted from the combina- tion. Mutations in PIK3CA did not predict benefit with pictilisib. The molecular alterations examined did not identify an enriched patient population associated with increased benefit of PI3K inhibitor therapy in this study. Of note, PI3K pathway molecular alteration status did not seem to predict response to pan-PI3K inhibitors in this trial and other recent trials in metastatic breast cancer, sug- gesting that the PI3K pathway may also be activated by alternative mechanisms [17, 23]. It will be important to evaluate whether PI3K pathway alteration can predict response to alpha-specific PI3K inhibitors (e.g., BYL719) in ongoing trials in metastatic breast cancer.
In summary, pilaralisib or voxtalisib, in combination with letrozole, were associated with acceptable safety profiles and limited efficacy in HR ?, HER2-negative metastatic breast cancer. In this study, addition of PI3K inhibitors did not restore sensitivity to endocrine therapy.
Acknowledgments This study was funded by Sanofi. The authors received editorial support from Simone Blagg of MediTech Media, funded by Sanofi.
Conflict of interest Frank Campana, Lei Gao, Jason Jiang, and Sandrine Mace´ are employees of Sanofi. Jason Jiang has stock ownership in Sanofi. Sara Tolaney has received research funding from Genentech. The other authors have no conflicts to declare.
Ethical declaration These experiments comply with the current laws of the countries in which they were performed.
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