A Randomized Phase II Study of AGS‐16C3F Versus Axitinib in Previously Treated Patients with Metastatic Renal Cell Carcinoma

Abstract

Lessons Learned

• The primary endpoint of this phase II study that evaluated the efficacy and safety of the investigational compound, AGS‐16C3F, versus axitinib in previously treated patients with metastatic renal cell carcinoma (mRCC) was not met.

• Median progression‐free survival, the primary endpoint, was 2.9 months with AGS‐16C3F and 5.7 months with axitinib (HR, 1.676; 95% CI, 1.107–2.537; p = .015), per investigator assessment

• The safety profile for each study drug was as expected, with the most commonly reported adverse events being fatigue (53%) and nausea (47%) in the AGS‐16C3F arm and fatigue (57%) and diarrhea (48%) in the axitinib arm.

• These results provide a benchmark for axitinib use in heavily pretreated patients with mRCC.

Background

AGS‐16C3F is a novel antibody‐drug conjugate that targets cell‐surface ectonucleotide pyrophosphatase/phosphodiesterase 3 (ENPP3) and is conjugated to a microtubule disruptive agent. Here we present findings from a phase II study of AGS‐16C3F versus axitinib in metastatic renal cell carcinoma (mRCC).

Methods

Patients with mRCC of any histology and disease progression during or after their last treatment regimen were randomized 1:1 to intravenous AGS‐16C3F 1.8 mg/kg every 3 weeks or oral axitinib 5 mg twice daily (starting dose). The primary objective was investigator‐assessed progression‐free survival (PFS) of AGS‐16C3F versus axitinib (RECIST version 1.1).

Results

In the total population (N = 133), 63% (n = 84) of patients had completed the study at data cutoff (August 21, 2019). Median PFS was 2.9 months with AGS‐16C3F and 5.7 months with axitinib (hazard ratio [HR], 1.676; 95% confidence interval [CI], 1.107–2.537; p = .015). There were no significant differences between arms in secondary efficacy endpoints, including overall survival (13.1 months, AGS‐16C3F and 15.4 months, axitinib; HR, 1.079; 95% CI, 0.681–1.707; p = .747). In the safety population (n = 131), the most commonly reported adverse events were fatigue (53%) and nausea (47%) in the AGS‐16C3F arm and fatigue (57%) and diarrhea (48%) in the axitinib arm. The incidence of diarrhea was lower in the AGS‐16C3F arm than in the axitinib arm (17% vs. 48%), and ocular toxicities were more frequent in the AGS‐16C3F arm than in the axitinib arm (44% vs. 26%).

Conclusion

The investigational compound, AGS‐16C3F, did not meet the primary endpoint of this trial. These study results provide a benchmark for axitinib use in heavily pretreated patients with mRCC.

Discussion

The primary endpoint of this study, PFS of patients with mRCC of any histology treated with AGS‐16C3F, compared with axitinib, was not met. Our results showed that AGS‐16C3F did not improve PFS compared with axitinib. Per the protocol, a median PFS of 4 months was anticipated for axitinib, and it was hypothesized that AGS‐16C3F would improve median PFS by 2 months relative to axitinib. Results of the primary endpoint showed a median PFS of 2.9 months with AGS‐16C3F and 5.6 months with axitinib (p = .015) per investigator assessment (Fig. 1). There were no significant differences between AGS‐16C3F and axitinib in secondary endpoints. Median overall survival (OS) was 13.1 months with AGS‐16C3F and 15.4 months with axitinib (p = .747). In this study, axitinib performed as expected when the median PFS from the current study is viewed in context with the median PFS from the AXIS study. Results of the AXIS study showed that axitinib significantly prolonged PFS compared with sorafenib (6.7 and 4.7 months, respectively; p < .0001) [1]. To put the PFS results into context, there were differences between patient populations in the current study and the AXIS study. For example, patients were not as heavily pretreated in the AXIS study as they were in the current study; patients in AXIS received axitinib as a purely second‐line agent after sunitinib, bevacizumab plus interferon‐alfa, temsirolimus, or cytokine therapy [1].

Figure 1.

Kaplan‐Meier estimate of progression‐free survival in the full analysis set per investigator assessment (RECIST version 1.1).

The safety profiles of AGS‐16C3F and axitinib were consistent with the known safety profiles of each agent. In the current study, the incidence of ocular adverse events (AEs) was higher in the AGS‐16C3F arm than in the axitinib arm (44% vs. 26%), and the incidence of diarrhea was higher in the axitinib arm than in the AGS‐16C3F arm (48% vs. 17%). It should be noted that eye disorders were reported in patients treated with other antigen‐targeted antibody‐drug conjugates (ADCs) conjugated to monomethyl auristatin F (MMAF); thus, ocular toxicities may be a class effect of these compounds [2, 3]. Regular eye examinations should be administered to patients receiving investigational agents within this class of drugs.

In conclusion, our investigational compound, AGS‐16C3F, did not meet the primary endpoint of this trial. Most clinical trials that enroll patients with advanced renal cell carcinoma (RCC) exclude patients with non‐clear cell RCC histology. This trial included patients with RCC of any histology, and the resulting heterogenous patient population is a potential limitation of this study. Moreover, RCC may not be responsive to chemotherapy despite targeted delivery. Based on the current results, further development of AGS‐16C3F in mRCC will not be pursued. These study results provide a benchmark for axitinib use in heavily pretreated patients with mRCC.

Trial Information

Disease	Renal cell carcinoma – clear cell
Disease	Renal cell carcinoma – non‐clear cell
Stage of Disease/Treatment	Metastatic
Prior Therapy	More than two prior systemic regimens
Type of Study	Phase II, randomized
Primary Endpoint	Progression‐free survival, investigator's assessment
Secondary Endpoints	Progression‐free survival, central assessment; overall survival; objective response rate; disease control rate; duration of response; safety; pharmacokinetics
Additional Details of Endpoints or Study Design
Study design and patients. This was a phase II, open‐label, multicenter, randomized study of previously treated patients with mRCC.
This study included adult patients (≥18 years) with mRCC whose disease progressed during or after the last treatment regimen. Patients with clear cell RCC must have previously received at least two systemic regimens, one of which was an anti‐VEGF agent. Because the non‐clear cell group of tumors is heterogenous and has varying sensitivities to anti‐VEGF agents, patients with non‐clear cell RCC histology were required to have progressed during or after at least one anti‐VEGF regimen. Previous treatment with axitinib, AGS‐16C3F, or AGS‐16M8F was not permitted. Enrolled patients were required to have histologically confirmed RCC that was measurable per RECIST version 1.1 [4]. The number of patients with non‐clear cell RCC histology was limited to 26, and those patients were required to have ENPP3‐positive immunohistochemical (IHC) staining at prescreening, which was defined as an IHC H‐score of ≥15. Patients with clear cell RCC were not required to be screened for ENPP3, but they were required to submit tissue during the study for retrospective target expression assessment by IHC. Patients were required to have an Eastern Cooperative Oncology Group (ECOG) performance status of 0 or 1, to have adequate organ function, and to have provided tissue from the primary tumor or metastatic site (excluding bone). Patients with untreated brain metastasis, uncontrolled hypertension, gastrointestinal abnormalities, and specific ocular conditions were excluded from the study.
This study was conducted in accordance with the protocol, International Council for Harmonisation guidelines, applicable regulations and guidelines governing clinical study conduct, and the ethical principles that have their origin in the Declaration of Helsinki. All patients provided written informed consent.
Treatment. Patients were randomly assigned 1:1 to receive either intravenous AGS‐16C3F 1.8 mg/kg every 3 weeks or oral axitinib at a starting dosage of 5 mg twice daily. Axitinib dose adjustments were made as needed during the study, as defined in the product label and local institutional guidelines, and in dosages ranging from 2 mg to 10 mg twice daily. Randomization was stratified according to ECOG performance status (0 or 1), the number of prior systemic RCC regimens (2 or > 2), and RCC histology (clear cell or non‐clear cell). Treatment continued until disease progression per RECIST version 1.1, unacceptable toxicity, investigator's decision, or study withdrawal.
Outcome measures. The primary objective of the study was to evaluate the PFS of AGS‐16C3F, compared with axitinib, based on investigator assessment. The definition of PFS was the time from the date of randomization to the earliest date of documented disease progression as defined by RECIST version 1.1 or death from any cause. Secondary objectives were PFS based on central assessment, OS, objective response rate (ORR), disease control rate (DCR), duration of response (DoR), safety, and pharmacokinetics (PK). Efficacy assessments of response and progression were based on RECIST version 1.1. Disease assessments were performed every 8 weeks from cycle 1 day 1. For patients with bone disease at screening, bone imaging was performed every 12 weeks from cycle 1 day 1. Imaging was performed using computed tomography scan with contrast or magnetic resonance imaging.
Pharmacokinetic parameters included maximum observed concentration (Cmax), time to maximum observed concentration, area under the concentration‐time curve (AUC0–21), and terminal half‐life (t1/2) of AGS‐16C3F at cycle 1 and cycle 4.
Safety was monitored throughout the study, and safety follow‐up assessments were performed at least 28 days after the last dose. Patients who received AGS‐16C3F underwent a complete eye exam between day 1 of cycle 2 and day 1 of cycle 3, and between day 1 of cycle 5 and day 1 of cycle 6, then as clinically indicated thereafter. Although not specifically designated as AEs of special interest in the protocol, the following AEs were of potential interest in the study: infusion‐related reactions, neuropathy, leukoencephalopathy, myelosuppression, ocular changes, and drug‐induced liver injury. Clinical ocular AEs were recorded as objective findings (e.g., keratitis, macular edema, retinal degeneration) from the ophthalmology evaluation, and grading of ocular AEs was based on visual acuity changes from baseline. Follow‐up for survival was evaluated every 8 weeks after the safety follow‐up assessment.
Statistical methods. The full analysis set (FAS) comprised all randomly assigned patients in accordance with the intention‐to‐treat principle and was used for efficacy analyses. The per protocol set (PPS) was a subset of the FAS who did not meet criteria for PPS exclusion for nonadherence to the protocol and was used for sensitivity analyses of the primary and key secondary endpoints. The safety analysis set included all patients who received at least one dose of study drug. The PK analysis set included patients for whom sufficient serum concentration data were available to facilitate derivation of at least one PK parameter and for whom the time of dosing on the day of sampling was known. A median PFS of 4 months was anticipated for axitinib; it was hypothesized that AGS‐16C3F would improve median PFS by 2 months. Under the assumption of exponential distribution of PFS, a 2‐month improvement corresponded to a hypothesized HR of 0.667, with 110 PFS events providing 80% power to achieve a one‐sided value of p ≤ .1.
Progression‐free survival was defined as the time from the date of randomization to the earliest documented disease progression as defined by RECIST version 1.1 per investigator radiology review, or death from any cause. Overall survival was defined as the time from the date of randomization until the date of death from any cause. Outcomes for PFS, OS, ORR, DCR, and DoR were summarized using descriptive statistics. The survival curve and medians for time‐to‐event variables were estimated using the Kaplan‐Meier method and are reported with the corresponding 95% CIs, which were calculated using Greenwood's formula. The PK data for ADC and MMAF were analyzed using the noncompartmental method. Adverse events were graded according to the National Cancer Institute Common Toxicity Criteria for Adverse Events, version 4.03 [5]. The data cutoff date was August 21, 2019.
Investigator's Analysis	Level of activity did not meet planned endpoint

Drug Information: Axitinib

Generic/Working Name	Axitinib
Company Name	Pfizer
Drug Type	Targeted agent
Drug Class	Tyrosine kinase inhibitor
Dose	5 milligrams (mg) (starting dose)
Route	Oral (p.o.)
Schedule of Administration	Twice daily until disease progression per RECIST version 1.1, unacceptable toxicity, investigator's decision, or study withdrawal

Drug Information: AGS‐16C3F

Generic/Working Name	AGS‐16C3F
Company Name	Astellas Pharma, Inc.
Drug Type	Investigational
Drug Class	Monoclonal antibody
Dose	1.8 milligrams (mg) per kilogram (kg)
Route	Intravenous
Schedule of Administration	Every 3 weeks until disease progression per RECIST version 1.1, unacceptable toxicity, investigator's decision, or study withdrawal

Patient Characteristics: Axitinib

Number of Patients, Male	49
Number of Patients, Female	17
Age	Median (range): 60 (37–88) years
Performance Status: ECOG	0 — 19 1 — 47
Detailed Patient Characteristics (n = 66)
Sex, n (%)
Male	49 (74.2)
Female	17 (25.8)
Race, n (%)
White	56 (84.8)
Asian	7 (10.6)
American Indian or Alaska Native	1 (1.5)
Other	2 (3.0)
Age, years
Median (range)	60 (37–88)
<65, n (%)	47 (71.2)
ECOG performance status, n (%)
0	19 (28.8)
1	47 (71.2)
Histological type, n (%)
Clear cell	55 (83.3)
Non‐clear cell	11 (16.7)
No. prior systemic RCC regimens, n (%)
2 (clear cell) or 1 (non‐clear cell)	33 (50.0)
˃2 (clear cell) or ˃1 (non‐clear cell)	33 (50.0)
IMDC/Heng prognostic risk group, n (%)
Favorable	10 (15.2)
Intermediate	43 (65.2)
Poor	13 (19.7)

Abbreviations: ECOG, Eastern Cooperative Oncology Group; IMDC, International Metastatic RCC Database Consortium; RCC, renal cell carcinoma.

Patient Characteristics: AGS‐16C3F

Number of Patients, Male	49
Number of Patients, Female	18
Age	Median (range): 63 (33–77) years
Performance Status: ECOG	0 — 19 1 — 48
Detailed Patient Characteristics (n = 67)
Sex, n (%)
Male	49 (73.1)
Female	18 (26.9)
Race, n (%)
White	59 (88.1)
Asian	6 (9.0)
American Indian or Alaska Native	1 (1.5)
Other	1 (1.5)
Age, years
Median (range)	63 (33–77)
<65, n (%)	40 (59.7)
ECOG performance status, n (%)
0	19 (28.4)
1	48 (71.6)
Histological type, n (%)
Clear cell	55 (82.1)
Non‐clear cell	12 (17.9)
No. prior systemic RCC regimens, n (%)
2 (clear cell) or 1 (non‐clear cell)	35 (52.2)
˃2 (clear cell) or ˃1 (non‐clear cell)	32 (47.8)
IMDC/Heng prognostic risk group, n (%)
Favorable	5 (7.5)
Intermediate	48 (71.6)
Poor	14 (20.9)

Abbreviations: ECOG, Eastern Cooperative Oncology Group; IMDC, International Metastatic RCC Database Consortium; RCC, renal cell carcinoma.

Baseline characteristics were generally balanced between treatment arms. In the overall population, most patients were White (86.5%) and male (73.7%), most patients had RCC of clear cell histology (82.7%), and most patients were of intermediate prognostic risk (68.4%).

In the total population (N = 133), 92.5% of patients had discontinued treatment at the time of data cutoff (Fig. 2). Three of 67 (4.5%) patients in the AGS‐16C3F treatment group, and five of 66 (7.6%) patients in the axitinib treatment group remained on study drug at the time of data cutoff (Fig. 2). The primary reason for discontinuation of study drug was disease progression (61.7%, n = 82 of 133).

Figure 2.

CONSORT diagram. ^aPatients were considered to be continuing in the study if they were on treatment or continuing in progression follow‐up and/or survival follow‐up.

Primary Assessment Method: Axitinib

Title	Progression‐Free Survival (PFS, Investigator's Assessment)
Number of Patients Evaluated for Efficacy	66
Evaluation Method	Kaplan‐Meier method
(Median) Duration Assessments PFS	5.7 months (95% CI, 5.3–9.1)

Secondary Assessment Method: Axitinib

Title  Number of Patients Evaluated for Efficacy  Evaluation Method	Disease Control Rate (DCR) 66 RECIST v1.1
(Percent) Response Assessment DCR	22.7 (95% CI, 13.3‐34.7)
Title  Number of Patients Evaluated for Efficacy  Evaluation Method  (Median) Duration Assessment DoR	Duration of Response (DoR) 66 Kaplan‐Meier method 6.7 months (95% CI, 1.8–9.2)
Title  Number of Patients Evaluated for Efficacy  Evaluation Method  (Percent) Response Assessment ORR	Objective Response Rate (ORR) 66 RECIST v1.1 18.2 (95% CI, 9.8–29.6)
Title  Number of Patients Evaluated for Efficacy  Evaluation Method  (Median) Duration Assessment OS	Overall Survival (OS) 66 Kaplan‐Meier method 15.4 months (95% CI, 12.5–21.6)
Title  Number of Patients Evaluated for Efficacy  Evaluation Method  (Median) Duration Assessment PFS	PFS (Central Review) 66 Kaplan‐Meier method 4.5 months (95% CI, 3.5–7.6)
Outcome Notes	There were no significant differences between treatment groups in secondary efficacy endpoints.

Primary Assessment Method: AGS‐16C3F

Title  Number of Patients Evaluated for Efficacy  Evaluation Method  (Median) Duration Assessment PFS	Progression‐Free Survival (PFS, Investigator's Assessment) 67 Kaplan‐Meier method 2.9 months (95% CI, 2.0–4.0)
Outcome Notes	Median PFS was 2.9 months (95% CI, 2.0–4.0) with AGS‐16C3F and 5.7 months (95% CI, 5.3–9.1) with axitinib (HR, 1.676; 95% CI, 1.107–2.537; p = 0.015).

Secondary Assessment Method: AGS‐16C3F

Title  Number of Patients Evaluated for Efficacy  Evaluation Method  (Percent) Response Assessment DCR	Disease Control Rate (DCR) 67 RECIST v1.1 13.4 (95% CI, 6.3–24.0)
Outcome Notes	DCR was 13.4% (95% CI, 6.3–24.0) with AGS‐16C3F and 22.7% (95% CI, 13.3–34.7) with axitinib (odds ratio, 0.5; 95% CI, 0.2–1.3; p = 0.152).
Title  Number of Patients Evaluated for Efficacy  Evaluation Method  (Median) Response Assessment DoR	Duration of Response (DoR) 67 Kaplan‐Meier method 6.8 months (95% CI, 3.8–18.4)
Outcome Notes	Median DoR was 6.8 months (95% CI, 3.8–18.4) with AGS‐16C3F and 6.7 months (95% CI, 1.8–9.2) with axitinib (HR, 0.376; 95% CI, 0.031–4.482; p = 0.439).
Title  Number of Patients Evaluated for Efficacy  Evaluation Method  Response Assessment ORR	Objective Response Rate (ORR) 67 RECIST v1.1 7.5% (95% CI, 2.5–16.6)
Outcome Notes	ORR was 7.5% (95% CI, 2.5–16.6) with AGS‐16C3F and 18.2% (95% CI, 9.8–29.6) with axitinib (odds ratio, 0.4; 95% CI, 0.1–1.1; p = .062).
Title  Number of Patients Evaluated for Efficacy  Evaluation Method  (Median) Duration Assessment OS	Overall Survival (OS) 67 Kaplan‐Meier method 13.1 months (95% CI, 10.1–23.0)
Outcome Notes	Median OS was 13.1 months with AGS‐16C3F and 15.4 months with axitinib (HR, 1.079; 95% CI, 0.681–1.707; p = .747) (Fig. 3).
Title  Number of Patients Evaluated for Efficacy  Evaluation Method (Median) Duration Assessment PFS	PFS (Central Review) 67 Kaplan‐Meier method 3.5 months (95% CI, 2.1–3.8)
Outcome Notes	PFS per central review was 3.5 months with AGS‐16C3F and 4.5 months with axitinib (HR, 1.423; 95% CI, 0.924–2.192; p = .110).

Figure 3.

Kaplan‐Meier estimate of overall survival in the full analysis set per investigator assessment (RECIST version 1.1)

Adverse Events: Axitinib

All CyclesName	NC/NA, %	Grade 1, %	Grade 2, %	Grade 3, %	Grade 4, %	Grade 5, %	All grades, %
Fatigue	43	19	28	11	0	0	57
Nausea	60	22	17	2	0	0	40
Diarrhea	52	23	15	9	0	0	48
Vomiting	66	25	8	2	0	0	34
Decreased appetite	63	8	25	5	0	0	37
Constipation	69	19	12	0	0	0	31
Back pain	63	14	20	3	0	0	37
Blurred vision	89	9	0	2	0	0	11
Cough	77	15	8	0	0	0	23
Dyspnea	72	11	11	6	0	0	28
Headache	75	12	11	2	0	0	25
Hypertension	58	3	14	25	0	0	42
Dizziness	81	14	3	2	0	0	19
Dysphonia	61	37	2	0	0	0	39
Decreased weight	72	17	5	6	0	0	28
Abdominal pain	85	12	2	2	0	0	15
Musculoskeletal pain	83	9	6	2	0	0	17
Dehydration	77	2	15	6	0	0	23
Pain in extremity	78	6	14	2	0	0	22
Anemia	94	2	2	3	0	0	6
Arthralgia	86	9	3	2	0	0	14
Dry eye	92	8	0	0	0	0	8
Epistaxis	92	5	3	0	0	0	8
Peripheral edema	89	11	0	0	0	0	11
Chills	97	3	0	0	0	0	3
Stomatitis	77	11	8	5	0	0	23
Muscular weakness	85	5	11	0	0	0	15
Palmar‐plantar erythrodysesthesia syndrome	78	9	12	0	0	0	22
Asthenia	91	3	3	3	0	0	9
Insomnia	89	5	6	0	0	0	11
Pleural effusion	88	5	6	0	0	0	12
Pruritis	97	3	0	0	0	0	3

Treatment‐emergent adverse events with axitinib (n = 65, ≥10% of total population).

Abbreviation: NC/NA, no change from baseline/no adverse event.

Serious Adverse Events: Axitinib

Name	Grade	Attribution
Cardiopulmonary arrest	5	Unrelated
Cardiac arrest	5	Unrelated
Pleural effusion	5	Unrelated

Adverse Events: AGS‐16C3F

All CyclesName	NC/NA, %	Grade 1, %	Grade 2, %	Grade 3, %	Grade 4, %	Grade 5, %	All grades, %
Fatigue	47	18	27	8	0	0	53
Nausea	53	27	18	2	0	0	47
Diarrhea	83	12	3	2	0	0	17
Vomiting	73	24	2	2	0	0	27
Decreased appetite	79	11	9	2	0	0	21
Constipation	76	20	5	0	0	0	24
Back pain	83	11	5	2	0	0	17
Blurred vision	61	23	15	2	0	0	39
Cough	74	20	6	0	0	0	26
Dyspnea	79	9	9	3	0	0	21
Headache	76	23	2	0	0	0	24
Hypertension	94	0	2	5	0	0	6
Dizziness	79	17	3	2	0	0	21
Dysphonia	98	2	0	0	0	0	2
Decreased weight	89	5	6	0	0	0	11
Abdominal pain	82	5	8	6	0	0	18
Musculoskeletal pain	83	9	8	0	0	0	17
Dehydration	91	0	8	2	0	0	9
Pain in extremity	91	6	2	2	0	0	9
Anemia	77	2	11	11	0	0	23
Arthralgia	85	8	5	3	0	0	15
Dry eye	79	12	6	3	0	0	21
Epistaxis	79	17	3	2	0	0	21
Peripheral edema	83	12	5	0	0	0	17
Chills	77	20	3	0	0	0	23
Stomatitis	97	3	0	0	0	0	3
Muscular weakness	92	3	3	2	0	0	8
Palmar‐plantar erythrodysesthesia syndrome	100	0	0	0	0	0	0
Asthenia	89	8	0	3	0	0	11
Insomnia	91	5	5	0	0	0	9
Pleural effusion	92	5	6	0	0	2	8
Pruritis	83	15	2	0	0	0	17

Treatment‐emergent adverse events with AGS‐16C3F (n = 66, ≥10% of total population).

Abbreviation: NC/NA, no change from baseline/no adverse event.

Serious Adverse Events: AGS‐16C3F

Name	Grade	Attribution
Cardiac arrest	5	Unrelated

In the overall safety population (n = 131), 99% of patients in each treatment arm (AGS‐16C3F, n = 65; axitinib, n = 64) experienced at least one AE. Commonly reported AEs were fatigue (53%), nausea (47%), blurred vision (39%), vomiting (27%), and cough (26%) in the AGS‐16C3F arm and fatigue (57%), diarrhea (48%), hypertension (42%), nausea (40%), dysphonia (39%), back pain (37%), decreased appetite (37%), vomiting (34%), constipation (31%), dyspnea (28%), and decreased weight (28%) in the axitinib arm. The incidence of diarrhea was lower in the AGS‐16C3F arm than in the axitinib arm (17% vs. 48%).

Treatment‐related AEs of any grade and of grade 3 or 4 were reported in 79% and 26% of patients, respectively, in the AGS‐16C3F arm and in 92% and 45% of patients, respectively, in the axitinib arm. In the AGS‐16C3F arm, commonly reported treatment‐related AEs were nausea (35%), fatigue (33%), and blurred vision (27%). Commonly reported treatment‐related AEs in the axitinib arm were diarrhea (40%), fatigue (40%), hypertension (40%), dysphonia (32%), and decreased appetite (26%). In the AGS‐16C3F arm, fatigue (5%, n = 3), dry eye (3%, n = 2), and thrombocytopenia (3%, n = 2) were the only grade 3 or grade 4 treatment‐related AEs reported in more than one patient. In the axitinib arm, the grade 3 or grade 4 treatment‐related AEs reported in more than one patient were hypertension (22%, n = 14), diarrhea (8%, n = 5), fatigue (8%, n = 5), decreased weight (5%, n = 3), decreased appetite (3%, n = 2), proteinuria (3%, n = 2), and stomatitis (3%, n = 2). Seven patients in the AGS‐16C3F arm and four patients in the axitinib arm discontinued study drug treatment because of an AE. One patient in the AGS‐16C3F arm (cardiac arrest) and three patients in the axitinib arm (cardiopulmonary arrest, cardiac arrest, and pleural effusion) died as a result of AEs. None of the fatal AEs were considered by the investigator to be related to the study drug.

Eight patients (12%) in the AGS‐16C3F arm experienced infusion‐related reactions (Table 1). All infusion‐related reactions were grade 1 or grade 2 except for one serious grade 3 event, from which the patient recovered, continued in the study, and did not experience another event. A higher percentage of patients in the AGS‐16C3F arm experienced peripheral sensory neuropathy, compared with patients in the axitinib arm (8% vs. 3%, respectively). One patient in each treatment group experienced peripheral neuropathy. All cases of neuropathy were grade 1 or grade 2. There were no AEs of leukoencephalopathy. A higher percentage of patients in the AGS‐16C3F arm had myelosuppression AEs than patients in the axitinib arm, with anemia being the most common AE in both treatment arms (23% vs. 6%) (Table 1). Postbaseline ocular diagnoses (from eye examinations and a patient questionnaire) occurred at a higher percentage in the AGS‐16C3F arm than in the axitinib arm (44% vs. 26%); most ocular AEs were of grade 1–2. Keratopathy in 12 patients (20%), dry eye in six patients (10%), and other ocular events in three patients (5%) were considered related to AGS‐16C3F. The occurrence of alanine aminotransferase or aspartate aminotransferase ˃3× the ULN was similar in the treatment arms: 7.6% in the AGS‐16C3F arm (n = 5) and 7.7% in the axitinib arm (n = 5). Total bilirubin ˃2× ULN was numerically higher in the AGS‐16C3F arm than in the axitinib arm (7.6% [n = 5] and 3.1% [n = 2], respectively).

Pharmacokinetics/Pharmacodynamics

Exposure was similar for ADC and total antibody (total Ab) in AGS‐16C3F treatment cycles 1 and 4 (Table 2). The t1/2 was approximately 7–8 days for ADC and approximately 9–12 days for total Ab. After a single dose of AGS‐16C3F (cycle 1), the mean Cmax and AUC0–21 were 52.2 μg/mL and 200 μg/mL × day, respectively, for ADC and 37.5 μg/mL and 246 μg/mL × day, respectively, for total Ab. The mean Cmax and AUC0–21 of cysteine adducts of maleimidocaproyl monomethyl auristatin F were 6.09 ng/mL and 9.61 ng/mL × day, respectively, at cycle 1; mean Cmax in cycle 4 was 3.78 ng/mL.

Table 2.

Summary of pharmacokinetic parameters of AGS‐16C3F

Treatment cycle	Cmax, geometric mean (CV%), ng or μg/mL a	Tmax, median (range), days	AUC0–21, geometric mean (CV%), ng or μg/mL×day a	t1/2, geometric mean (range), days
Cycle 1
Patients with available data, n	64	64	21	1
Cys‐mcMMAF	6.09 (67.0)	0.207 (0.139–0.954)	9.61 (107)	2.72 (2.72–2.72)
Patients with available data, n	59	59	52	49
ADC	52.2 (112)	0.04 (0.0–1.0)	200 (34.4)	7.28 (3.9–19.6)
Patients with available data, n	59	60	48	45
Total Ab	37.5 (33.4)	0.05 (0.0–2.2)	246 (36.1)	8.85 (4.3–16.6)
Cycle 4
Patients with available data, n	25	25	0	0
Cys‐mcMMAF	3.78 (45.1)	0.208 (0.197–1.11)	0	0
Patients with available data, n	23	23	18	18
ADC	48.7 (79.8)	0.05 (0.0–3.9)	294 (34.1)	7.81 (3.6–14.5)
Patients with available data, n	23	23	13	13
Total Ab	42.8 (28.8)	0.05 (0.0–3.9)	346 (45.7)	11.9 (1.8–38.1)

^aPresented as ng for cys‐mcMMAF and as μg for ADC and total Ab.

Abbreviations: Ab, antibody; ADC, antibody‐drug conjugate; AUC_0–21, area under the plasma concentration‐time curve from time of drug administration to time (21 hours); C_max, maximum observed plasma concentration; cys‐mcMMAF, cysteine adducts of maleimidocaproyl monomethyl auristatin F; CV, coefficient of variation; t_1/2, elimination half‐life; T_max, time to reach C_max.

Assessment, Analysis, and Discussion

Completion	Study completed
Investigator's Assessment	Level of activity did not meet planned endpoint. No further development of AGS‐16C3F in mRCC.

First‐line and second‐line treatment options for patients with mRCC include a variety of antiangiogenic agents and immune checkpoint inhibitors [6, 7]. Nivolumab, a programmed death‐1 receptor inhibitor, and the tyrosine kinase inhibitors (TKIs) cabozantinib and axitinib are recommended second‐line agents for patients with clear cell renal cell carcinoma (RCC) who received a first‐line vascular endothelial growth factor–TKI [8]. Second‐line therapy is associated with a median overall survival of 35.3 months, 16.6 months, and 5.4 months for patients with favorable, intermediate, and poor International Metastatic Database Consortium risk, respectively [8]. Axitinib was approved for the treatment of patients with advanced RCC after failure of one prior systemic therapy, based on results of the pivotal phase III AXIS study [1, 9]. Results of the AXIS study showed a median progression‐free survival of 6.7 months for axitinib and 4.7 months for sorafenib (hazard ratio [HR], 0.665; 95% confidence interval [CI], 0.544–0.812; p < .0001) [1]. Overall survival was not significantly different between treatment groups, with a median of 20.1 months with axitinib and 19.2 months with sorafenib (HR, 0.969; 95% CI, 0.800–1.174; p = .3744) [10]. Because clinical data for patients with non‐clear cell RCC are limited, patients are encouraged to participate in clinical trials when they are available and appropriate. The approved antiangiogenic agents and immune checkpoint inhibitors have increased treatment options and improved survival of patients with clear cell and non‐clear cell mRCC.

AGS‐16C3F is a novel antibody‐drug conjugate (ADC) comprising an antibody against ectonucleotide pyrophosphatase/phosphodiesterase 3 (ENPP3) conjugated to microtubule disruptive agent monomethyl auristatin F (MMAF), via a noncleavable maleimidocaproyl (mc) linker. The cell surface ENPP3 catalyzes extracellular nucleotides and plays a role in the pathophysiology of cancer by increasing tumor invasion [11, 12]. Results of preclinical studies showed that AGS‐16C3F binds with high affinity to ENPP3 that is expressed on the surface of renal, hepatocellular, and chronic myelogenous leukemia cells [13]. After binding, AGS‐16C3F is internalized and trafficked to lysosomes where it catabolizes and releases cysteine adducts (cys) of maleimidocaproyl monomethyl auristatin F (mcMMAF) that subsequently bind to and inhibit microtubules. Release of mcMMAF was assessed by measuring tumor concentrations of mcMMAF (free conjugate) and AGS‐16CF (conjugated ADC) after a single 10 mg/kg intravenous dose of AGS‐16C3F in mice bearing UG‐K3 renal cancer xenografts (data on file). The peak unconjugated mcMMAF in tumors was achieved on day 1 and subsequently decreased on days 3 and 5 suggesting ADC cleavage and resulting in free mcMMAF (data on file). In a phase I trial of AGS‐16C3F in subjects with mRCC, 34 patients received AGS‐16C3F in four dose cohorts, and 1.8 mg/kg was determined to be the recommended phase II dose.

The population of the current study included patients with the less common non‐clear cell RCC histology. This is an important point considering the differences in histological characteristics and treatment outcomes between patients with clear cell RCC and non‐clear cell RCC [6]. For example, patients with non‐clear cell RCC generally do not respond as well to systemic therapy as patients with clear cell RCC. However, trial data regarding these patients are limited because they are frequently excluded from controlled phase III studies [6]. Thus, European Society for Medical Oncology guidelines recommend that patients with non‐clear cell RCC enroll into clinical trials when possible [8]. It should be noted that despite the heterogenous patient population in the current study, axitinib yielded results consistent with those previously reported [1].

The pharmacokinetic profile of AGS‐16C3F was consistent with findings from a previous phase I study [14] and did not contribute to the study's failure to meet its primary endpoint. Results of the phase I study showed that concentrations of total antibody (Ab) were generally higher than concentrations of ADC and that area under the concentration‐time curve and maximum observed concentration increased in an approximately dose‐proportional manner (AGS‐16C3F doses: 1.8, 2.7, 3.6, and 4.8 mg/kg). In the current study, concentrations of ADC and total Ab were similar, with ADC concentrations being slightly higher than total Ab concentrations. Across all dose cohorts in the phase I study, the median half‐life (T_1/2) of total Ab after the first dose of AGS‐16C3F was 8.29 days (range: 4.01–14.2). Median T_1/2 of total Ab after the first dose of AGS‐16C3F was 8.85 days (range: 4.3–16.6) in the current study. In both the phase I study and the current study, cys‐mcMMAF reached maximum concentration at a median time of approximately 5 hours after the first dose of AGS‐16C3F. Median T_1/2 of cys‐mcMMAF after the first dose of AGS‐16C3F was approximately 4 days in the phase I study and approximately 3 days in the current study. Results of the phase I study showed no apparent accumulation of cys‐mcMMAF after repeated administration of AGS‐16C3F every 3 weeks.

In a related analysis (data not reported), the median H‐score (on a scale of 0–300) of ENPP3 expression was 255. High tumor ENPP3 expression suggests that there should be internalization of ADC and high concentrations of MMAF within the tumor cell. Likewise, a lack of ENPP3 expression, or antigen downregulation, is associated with ADC resistance [15]. There may be a target‐expression threshold that must be met in order for an ADC to be effective [16]. The relatively high expression of ENPP3 in the majority of patients does not explain the lack of effect seen with AGS‐16C3F.

The safety and tolerability profile of axitinib in patients with mRCC has been established [1, 17]. In the AXIS trial, adverse events (AEs) commonly reported (>30%) in the axitinib arm were diarrhea (55%), hypertension (40%), fatigue (39%), decreased appetite (34%), nausea (32%), and dysphonia (31%) [1]. This is similar to the current study, where the most commonly reported AEs in the axitinib arm were fatigue (57%) and diarrhea (48%). The incidence of diarrhea was higher in the axitinib arm than in the AGS‐16C3F arm (48% vs. 17%). This is not surprising because diarrhea is associated with axitinib use and has been reported as one of the most common AEs of any grade and of grade ≥ 3 AEs in the phase II and phase III trials [17].

In conclusion, our investigational compound, AGS‐16C3F, did not meet the primary endpoint of this trial. Most clinical trials that enroll patients with advanced RCC exclude patients with non‐clear cell RCC histology. This trial included patients with RCC of any histology, and the resulting heterogenous patient population is a potential limitation of this study. Moreover, RCC may not be responsive to chemotherapy despite targeted delivery. Based on the current results, further development of AGS‐16C3F in mRCC will not be pursued. These study results provide a benchmark for axitinib use in heavily pretreated patients with mRCC.

Disclosures

Christian Kollmannsberger: Pfizer, Bristol‐Myers Squibb, Ipsen, Eisai, Roche, Merck/EMD Serono, Astellas, Janssen (C/A), Pfizer, Bristol‐Myers Squibb, Ipsen, Eisai (SAB); Toni K. Choueiri: AstraZeneca, Alexion, Bayer, Bristol Myers‐Squibb/ER Squibb and Sons LLC, Cerulean, Eisai, Foundation Medicine Inc., Exelixis, Ipsen, Tracon, Genentech, Roche, Roche Products Limited, F. Hoffmann‐La Roche, GlaxoSmithKline, Eli Lilly & Co., Merck, Novartis, Peloton, Pfizer, Prometheus Labs, Corvus, Calithera, Analysis Group, Sanofi/Aventis, Takeda (RF), AstraZeneca, Alexion, Sanofi/Aventis, Bayer, Bristol Myers‐Squibb/ER Squibb and Sons LLC, Cerulean, Eisai, Foundation Medicine Inc., Exelixis, Genentech, Roche, Roche Products Limited, F. Hoffmann‐La Roche, GlaxoSmithKline, Merck, Novartis, Peloton, Pfizer, EMD Serono, Prometheus Labs, Corvus, Ipsen, Up‐to‐Date, NCCN, Analysis Group, Michael J. Hennessy Associates, Inc., Research to Practice, L‐path, Clinical Care Options, Platform Q, Navinata Healthcare, Heron Therapeutics, Eli Lilly & Co. (H), AstraZeneca, Alexion, Sanofi/Aventis, Bayer, Bristol Myers‐Squibb/ER Squibb and Sons LLC, Cerulean, Eisai, Foundation Medicine Inc., Exelixis, Genentech, Heron Therapeutics, Eli Lilly & Co., Roche, GlaxoSmithKline, Merck, Novartis, Peloton, Pfizer, EMD Serono, Prometheus Labs, Corvus, Ipsen, Up‐to‐Date, NCCN, Analysis Group, Pionyr, Tempest (C/A), Pionyr, Tempest (OI), Patents PCT/US2018/12209 and PCT/US2018/058430 (IP); Daniel Y.C. Heng: Alberta Health Services from Agensys (RF), Pfizer, Astellas Pharma, Inc. (C/A); Saby George: Bayer, Bristol‐Myers Squibb, Novartis, Corvus, Pfizer, Acceleron, Merck, Agensys, Eisai (RF), Bayer, Bristol‐Myers Squibb, Exelixis, Janssen, Corvus, Genentech, Sanofi/Genzyme, Pfizer, EMD Serono (C/A); Fei Jie: Astellas Pharma, Inc. (E); Ruslan Croitoru: Astellas Pharma, Inc. (E); Srinivasu Poondru: Astellas Pharma, Inc. (E). John A. Thompson indicated no financial relationships.

(C/A) Consulting/advisory relationship; (RF) Research funding; (E) Employment; (ET) Expert testimony; (H) Honoraria received; (OI) Ownership interests; (IP) Intellectual property rights/inventor/patent holder; (SAB) Scientific advisory board

Figures and Tables

Table 1.

Adverse events of potential interest in the study

Adverse event	AGS‐16C3F (n = 66), n (%)		Axitinib (n = 65), n (%)
	All AEs	Treatment‐related AEs	All AEs	Treatment‐related AEs
Infusion‐related reactions and neuropathy
Infusion‐related reaction	8 (12)	8 (12)	0	0
Peripheral sensory neuropathy	5 (8)	2 (3)	2 (3)	0
Peripheral neuropathy	1 (2)	1 (2)	1 (2)	1 (2)
Myelosuppression AEs
Anemia	15 (23)	6 (9)	4 (6)	0
Decreased platelet count	5 (8)	4 (6)	2 (3)	1 (2)
Thrombocytopenia	5 (8)	5 (8)	0	0
Ocular diagnoses a
Any	26 (44)	15 (25)	10 (26)	0
Keratopathy	13 (22)	12 (20)	1 (3)	0
Dry eye	7 (12)	6 (10)	0	0
Cataract	1 (2)	0	4 (10)	0
Retinopathy	1 (2)	0	1 (3)	0
Other	14 (24)	3 (5)	4 (10)	0

^aThe number of patients who had ophthalmology assessment data during the assessment period was used as the denominator for the percentages: n = 59 for the AGS‐16C3F treatment group and n = 39 for the axitinib treatment group.

Abbreviation: AE, adverse event.