A Phase 1 Study of EXT608 in Healthy Adults

EXT608 in Human Healthy Adults; A First-in-Human, Randomized, Double-Blind, Placebo-controlled, Single Dose Escalation Study

Status

Completed

Phases

Phase 1

Study type

Interventional

Source

ClinicalTrials.gov

Registry ID

NCT05408663

Enrollment

Registered

2022-06-07

Start date

2022-07-21

Completion date

2023-06-13

Last updated

2025-02-04

For informational purposes only — not medical advice. Sourced from public registries and may not reflect the latest updates. Terms

Conditions

Safety Issues

Brief summary

This is a Phase 1, randomized, double-blind, placebo-controlled, single ascending dose safety and tolerability study of EXT608 in healthy subjects. There will be up to 6 sequential dose escalation cohorts of 4 participants. In each cohort 3 participants will receive EXT608 and 1 participant will receive placebo.

Detailed description

This is a randomized, double-blind, first-in-human, placebo-controlled single ascending dose study to study the safety, tolerability, pharmacokinetics (PK), and pharmacodynamics (PD) of EXT608 in healthy adult participants. Participants will be enrolled into 1 of up to 6 planned single dose cohorts in ascending fashion. Each cohort will consist of 4 participants randomized to receive either EXT608 or placebo, whereby 3 will receive a single injection of EXT608 and 1 will receive matching placebo. Up to 6 dosing cohorts are planned with no single dose escalation to exceed a 3-fold dose increment. A Data Monitoring Board will review the seven-day safety data in each cohort before authorizing the initiation of the next cohort. A screening visit will take place within 28 days of dosing. Eligible participants for each cohort will be admitted to the Clinical Research Unit (CRU) 1 day prior to dosing and remain in the CRU through at least 72 hours after dosing for safety and PK assessments before discharge. The total confinement period will be 4 nights, unless extended for management of Adverse Events (AEs) at the discretion of the Investigator

Interventions

DRUGEXT608

EXT608 is an investigational drug administered via subcutaneous injection

OTHERPlacebo

matching placebo administered via subcutaneous injection

Study design

Allocation

RANDOMIZED

Intervention model

SEQUENTIAL

Primary purpose

TREATMENT

Masking

DOUBLE (Subject, Investigator)

Masking description

Double (Participant, investigator)

Intervention model description

Single ascending dose with up to 6 sequential dose escalation cohorts. Participants will be randomized to either study intervention (EXT608) or placebo

Eligibility

Sex/Gender

ALL

Age

18 Years to 55 Years

Healthy volunteers

Yes

Inclusion criteria

1. Male or female between 18 and 55 years of age. 2. Body mass index between 18.5 and 32 kilogram per square meter (kg/m2), inclusive, with a body weight greater than or equal to (\>=) 45 kg. 3. In general good medical health with no clinically significant or relevant abnormalities, 4. A clinical safety laboratory parameter of hemoglobin greater than (\>) 11.7 gram per deciliter (g/dl) (females) or 13.1 g/dl (males) and less than (\<) 16 g/dl (females) or 17.4 g/dl (males) or, if out of this range, deemed not clinically significant by the Investigator. 5. Total serum calcium (Se-Ca) within laboratory normal limits. 6. Serum parathyroid hormone (PTH) concentration within normal laboratory limits.

Exclusion criteria

1. Evidence of clinically significant (CS) neurologic, cardiovascular, pulmonary, hepatic, hematopoietic disease, renal, metabolic, gastrointestinal, urologic, immunologic, endocrine disease, serious allergy, allergic skin rash, or psychiatric disorder 2. History of drug abuse 3. Currently using any medication including over-the-counter (OTC), herbal or homeopathic preparations 4. Pregnant, nursing, or planning a pregnancy during the course of or within 3 months of completing this study 5. History of cancer or other malignancy, with the exception of basal cell carcinoma that has been in remission for at least 5 years 6. Positive test result for hepatitis B surface antigen (HBsAg), hepatitis C virus (HCV) antibody or a human immunodeficiency virus (HIV) 7. Alanine transaminase (ALT) and/or aspartate transaminase (AST) \>1.5 the upper limit of normal (ULN) 8. Increased baseline risk for osteosarcoma

Design outcomes

Primary

Measure	Time frame	Description
Characterize the Safety and Tolerability of EXT608	Day 0 to Day 28	Incidence, nature and severity of adverse events (AEs) and withdrawals due to Treatment-Emergent Adverse Events (TEAEs)

Secondary

Measure	Time frame	Description
Single Dose Pharmacokinetics (PK) - Area Under the Curve (AUC)	Day 0 to Day 7	Area under the curve
Single Dose PK - Cmax	0-24 hr	Maximum observed concentration
Single Dose PK - Tmax	Day 0 to Day 7	Time to reach maximum observed plasma concentration

Countries

United States

Participant flow

Participants by arm

Arm	Count
Placebo Comparator Six participants (one per cohort) received matching placebo administered as a subcutaneous injection	6
Experimental- EXT608 4ug Three participants received a single dose of EXT608 administered as a subcutaneous injection	3
Experimental- EXT608 12 ug Three participants received a single dose of EXT608 administered as a subcutaneous injection	3
Experimental- EXT608 36ug Three participants received a single dose of EXT608 administered as a subcutaneous injection	3
Experimental- EXT608 108ug Three participants received a single dose of EXT608 administered as a subcutaneous injection	3
Experimental- EXT608 324ug Three participants received a single dose of EXT608 administered as a subcutaneous injection	3
Experimental- EXT608 216ug Three participants received a single dose of EXT608 administered as a subcutaneous injection	3
Total	24

Baseline characteristics

Characteristic	Total	Experimental- EXT608 4ug	Experimental- EXT608 12 ug	Experimental- EXT608 36ug	Experimental- EXT608 108ug	Placebo Comparator	Experimental- EXT608 324ug	Experimental- EXT608 216ug
Age, Categorical <=18 years	0 Participants	0 Participants	0 Participants	0 Participants	0 Participants	0 Participants	0 Participants	0 Participants
Age, Categorical >=65 years	0 Participants	0 Participants	0 Participants	0 Participants	0 Participants	0 Participants	0 Participants	0 Participants
Age, Categorical Between 18 and 65 years	24 Participants	3 Participants	3 Participants	3 Participants	3 Participants	6 Participants	3 Participants	3 Participants
Ethnicity (NIH/OMB) Hispanic or Latino	3 Participants	0 Participants	1 Participants	0 Participants	1 Participants	0 Participants	1 Participants	0 Participants
Ethnicity (NIH/OMB) Not Hispanic or Latino	21 Participants	3 Participants	2 Participants	3 Participants	2 Participants	6 Participants	2 Participants	3 Participants
Ethnicity (NIH/OMB) Unknown or Not Reported	0 Participants	0 Participants	0 Participants	0 Participants	0 Participants	0 Participants	0 Participants	0 Participants
Race (NIH/OMB) American Indian or Alaska Native	2 Participants	0 Participants	1 Participants	0 Participants	0 Participants	1 Participants	0 Participants	0 Participants
Race (NIH/OMB) Asian	1 Participants	0 Participants	0 Participants	0 Participants	0 Participants	0 Participants	0 Participants	1 Participants
Race (NIH/OMB) Black or African American	6 Participants	1 Participants	1 Participants	3 Participants	0 Participants	1 Participants	0 Participants	0 Participants
Race (NIH/OMB) More than one race	1 Participants	1 Participants	0 Participants	0 Participants	0 Participants	0 Participants	0 Participants	0 Participants
Race (NIH/OMB) Native Hawaiian or Other Pacific Islander	0 Participants	0 Participants	0 Participants	0 Participants	0 Participants	0 Participants	0 Participants	0 Participants
Race (NIH/OMB) Unknown or Not Reported	0 Participants	0 Participants	0 Participants	0 Participants	0 Participants	0 Participants	0 Participants	0 Participants
Race (NIH/OMB) White	14 Participants	1 Participants	1 Participants	0 Participants	3 Participants	4 Participants	3 Participants	2 Participants
Region of Enrollment United States	24 participants	3 participants	3 participants	3 participants	3 participants	6 participants	3 participants	3 participants
Sex: Female, Male Female	13 Participants	2 Participants	2 Participants	1 Participants	3 Participants	1 Participants	2 Participants	2 Participants
Sex: Female, Male Male	11 Participants	1 Participants	1 Participants	2 Participants	0 Participants	5 Participants	1 Participants	1 Participants

Adverse events

Event type	EG000 affected / at risk	EG001 affected / at risk	EG002 affected / at risk	EG003 affected / at risk	EG004 affected / at risk	EG005 affected / at risk	EG006 affected / at risk
deaths Total, all-cause mortality	0 / 6	0 / 3	0 / 3	0 / 3	0 / 3	0 / 3	0 / 3
other Total, other adverse events	2 / 6	2 / 3	1 / 3	0 / 3	2 / 3	2 / 3	0 / 3
serious Total, serious adverse events	0 / 6	0 / 3	0 / 3	0 / 3	0 / 3	0 / 3	0 / 3

Outcome results

Primary

Characterize the Safety and Tolerability of EXT608

Incidence, nature and severity of adverse events (AEs) and withdrawals due to Treatment-Emergent Adverse Events (TEAEs)

Time frame: Day 0 to Day 28

Arm	Measure	Category	Value (COUNT_OF_PARTICIPANTS)
Placebo - Comparator	Characterize the Safety and Tolerability of EXT608	Any AE That Might Be Related to Study Drug	0 Participants
Placebo - Comparator	Characterize the Safety and Tolerability of EXT608	Withdrawal from Study	0 Participants
Placebo - Comparator	Characterize the Safety and Tolerability of EXT608	No Adverse Event	4 Participants
Placebo - Comparator	Characterize the Safety and Tolerability of EXT608	Serious Adverse Event	0 Participants
Placebo - Comparator	Characterize the Safety and Tolerability of EXT608	Adverse Event	2 Participants
Experimental - EXT608 4 ug	Characterize the Safety and Tolerability of EXT608	Withdrawal from Study	0 Participants
Experimental - EXT608 4 ug	Characterize the Safety and Tolerability of EXT608	Any AE That Might Be Related to Study Drug	0 Participants
Experimental - EXT608 4 ug	Characterize the Safety and Tolerability of EXT608	Serious Adverse Event	0 Participants
Experimental - EXT608 4 ug	Characterize the Safety and Tolerability of EXT608	No Adverse Event	1 Participants
Experimental - EXT608 4 ug	Characterize the Safety and Tolerability of EXT608	Adverse Event	2 Participants
Experimental - EXT608 12 ug	Characterize the Safety and Tolerability of EXT608	Serious Adverse Event	0 Participants
Experimental - EXT608 12 ug	Characterize the Safety and Tolerability of EXT608	Withdrawal from Study	0 Participants
Experimental - EXT608 12 ug	Characterize the Safety and Tolerability of EXT608	Adverse Event	0 Participants
Experimental - EXT608 12 ug	Characterize the Safety and Tolerability of EXT608	No Adverse Event	2 Participants
Experimental - EXT608 12 ug	Characterize the Safety and Tolerability of EXT608	Any AE That Might Be Related to Study Drug	1 Participants
Experimental - EXT608 36 ug	Characterize the Safety and Tolerability of EXT608	No Adverse Event	3 Participants
Experimental - EXT608 36 ug	Characterize the Safety and Tolerability of EXT608	Adverse Event	0 Participants
Experimental - EXT608 36 ug	Characterize the Safety and Tolerability of EXT608	Serious Adverse Event	0 Participants
Experimental - EXT608 36 ug	Characterize the Safety and Tolerability of EXT608	Any AE That Might Be Related to Study Drug	0 Participants
Experimental - EXT608 36 ug	Characterize the Safety and Tolerability of EXT608	Withdrawal from Study	0 Participants
Experimental - EXT608 108 ug	Characterize the Safety and Tolerability of EXT608	Adverse Event	0 Participants
Experimental - EXT608 108 ug	Characterize the Safety and Tolerability of EXT608	Withdrawal from Study	0 Participants
Experimental - EXT608 108 ug	Characterize the Safety and Tolerability of EXT608	Any AE That Might Be Related to Study Drug	1 Participants
Experimental - EXT608 108 ug	Characterize the Safety and Tolerability of EXT608	No Adverse Event	2 Participants
Experimental - EXT608 108 ug	Characterize the Safety and Tolerability of EXT608	Serious Adverse Event	0 Participants
Experimental - EXT608 324 ug	Characterize the Safety and Tolerability of EXT608	No Adverse Event	1 Participants
Experimental - EXT608 324 ug	Characterize the Safety and Tolerability of EXT608	Any AE That Might Be Related to Study Drug	2 Participants
Experimental - EXT608 324 ug	Characterize the Safety and Tolerability of EXT608	Withdrawal from Study	0 Participants
Experimental - EXT608 324 ug	Characterize the Safety and Tolerability of EXT608	Serious Adverse Event	0 Participants
Experimental - EXT608 324 ug	Characterize the Safety and Tolerability of EXT608	Adverse Event	0 Participants
Experimental - EXT608 216 ug	Characterize the Safety and Tolerability of EXT608	Withdrawal from Study	0 Participants
Experimental - EXT608 216 ug	Characterize the Safety and Tolerability of EXT608	Serious Adverse Event	0 Participants
Experimental - EXT608 216 ug	Characterize the Safety and Tolerability of EXT608	Any AE That Might Be Related to Study Drug	0 Participants
Experimental - EXT608 216 ug	Characterize the Safety and Tolerability of EXT608	No Adverse Event	3 Participants
Experimental - EXT608 216 ug	Characterize the Safety and Tolerability of EXT608	Adverse Event	0 Participants

Primary

Characterize the Safety and Tolerability of EXT608

Frequency and severity of post-dose change from baseline of hematology, serum chemistry, urinalysis, electrocardiogram (ECG), vital signs and physical examination findings

Time frame: Day 0 - Day 28

Arm	Measure	Value (COUNT_OF_PARTICIPANTS)
Placebo - Comparator	Characterize the Safety and Tolerability of EXT608	0 Participants
Experimental - EXT608 4 ug	Characterize the Safety and Tolerability of EXT608	0 Participants
Experimental - EXT608 12 ug	Characterize the Safety and Tolerability of EXT608	0 Participants
Experimental - EXT608 36 ug	Characterize the Safety and Tolerability of EXT608	0 Participants
Experimental - EXT608 108 ug	Characterize the Safety and Tolerability of EXT608	0 Participants
Experimental - EXT608 324 ug	Characterize the Safety and Tolerability of EXT608	0 Participants
Experimental - EXT608 216 ug	Characterize the Safety and Tolerability of EXT608	0 Participants

Primary

Characterize the Safety and Tolerability of EXT608

Percentage of participants with injection or infusion site reactions - edema

Time frame: Day 0 - Day 28

Arm	Measure	Value (COUNT_OF_PARTICIPANTS)
Placebo - Comparator	Characterize the Safety and Tolerability of EXT608	1 Participants
Experimental - EXT608 4 ug	Characterize the Safety and Tolerability of EXT608	0 Participants
Experimental - EXT608 12 ug	Characterize the Safety and Tolerability of EXT608	0 Participants
Experimental - EXT608 36 ug	Characterize the Safety and Tolerability of EXT608	0 Participants
Experimental - EXT608 108 ug	Characterize the Safety and Tolerability of EXT608	0 Participants
Experimental - EXT608 324 ug	Characterize the Safety and Tolerability of EXT608	0 Participants
Experimental - EXT608 216 ug	Characterize the Safety and Tolerability of EXT608	1 Participants

Secondary

Single Dose Pharmacokinetics (PK) - Area Under the Curve (AUC)

Area under the curve

Time frame: Day 0 to Day 7

Arm	Measure	Value (MEAN)	Dispersion
Placebo - Comparator	Single Dose Pharmacokinetics (PK) - Area Under the Curve (AUC)	NA pg*Day/mL	—
Experimental - EXT608 4 ug	Single Dose Pharmacokinetics (PK) - Area Under the Curve (AUC)	NA pg*Day/mL	—
Experimental - EXT608 12 ug	Single Dose Pharmacokinetics (PK) - Area Under the Curve (AUC)	NA pg*Day/mL	—
Experimental - EXT608 36 ug	Single Dose Pharmacokinetics (PK) - Area Under the Curve (AUC)	358.3 pg*Day/mL	Standard Deviation 119.2
Experimental - EXT608 108 ug	Single Dose Pharmacokinetics (PK) - Area Under the Curve (AUC)	1613 pg*Day/mL	Standard Deviation 379.3
Experimental - EXT608 324 ug	Single Dose Pharmacokinetics (PK) - Area Under the Curve (AUC)	4903 pg*Day/mL	Standard Deviation 475.7
Experimental - EXT608 216 ug	Single Dose Pharmacokinetics (PK) - Area Under the Curve (AUC)	2091 pg*Day/mL	Standard Deviation 794.3

Secondary

Single Dose PK - Cmax

Maximum observed concentration

Time frame: 0-24 hr

Arm	Measure	Value (MEAN)	Dispersion
Placebo - Comparator	Single Dose PK - Cmax	NA pg/mL	—
Experimental - EXT608 4 ug	Single Dose PK - Cmax	NA pg/mL	—
Experimental - EXT608 12 ug	Single Dose PK - Cmax	NA pg/mL	—
Experimental - EXT608 36 ug	Single Dose PK - Cmax	489.3 pg/mL	Standard Deviation 271.1
Experimental - EXT608 108 ug	Single Dose PK - Cmax	1156 pg/mL	Standard Deviation 339
Experimental - EXT608 324 ug	Single Dose PK - Cmax	4967 pg/mL	Standard Deviation 1950
Experimental - EXT608 216 ug	Single Dose PK - Cmax	1266 pg/mL	Standard Deviation 489.4

Secondary

Single Dose PK - Tmax

Time to reach maximum observed plasma concentration

Time frame: Day 0 to Day 7

Arm	Measure	Value (MEAN)	Dispersion
Placebo - Comparator	Single Dose PK - Tmax	NA hr	—
Experimental - EXT608 4 ug	Single Dose PK - Tmax	NA hr	—
Experimental - EXT608 12 ug	Single Dose PK - Tmax	NA hr	—
Experimental - EXT608 36 ug	Single Dose PK - Tmax	3.3 hr	Standard Deviation 1.15
Experimental - EXT608 108 ug	Single Dose PK - Tmax	5.3 hr	Standard Deviation 2.3
Experimental - EXT608 324 ug	Single Dose PK - Tmax	2.7 hr	Standard Deviation 1.16
Experimental - EXT608 216 ug	Single Dose PK - Tmax	4.0 hr	Standard Deviation 0.03

Source: ClinicalTrials.gov · Data processed: Feb 4, 2026

A Phase 1 Study of EXT608 in Healthy Adults

Conditions

Brief summary

Detailed description

Related papers

Interventions

Sponsors

Study design

Masking description

Intervention model description

Eligibility

Inclusion criteria

Exclusion criteria

Design outcomes

Primary

Secondary

Countries

Participant flow

Participants by arm

Baseline characteristics

Adverse events

Outcome results

Characterize the Safety and Tolerability of EXT608

Characterize the Safety and Tolerability of EXT608

Characterize the Safety and Tolerability of EXT608

Single Dose Pharmacokinetics (PK) - Area Under the Curve (AUC)

Single Dose PK - Cmax

Single Dose PK - Tmax