The purpose of this study is to evaluate the effects of single and multiple doses of ABCL635 administered by subcutaneous (SC) injection to healthy men and to postmenopausal women with or without any vasomotor symptoms (VMS) or hot flashes, and to postmenopausal women with moderate-to-severe VMS associated with menopause. The safety, tolerability, pharmacokinetic (PK) and pharmacodynamic (PD) parameters of ABCL635 will be assessed in all study participants; the effects on frequency and severity of VMS will be assessed in postmenopausal women who experience moderate-to-severe symptoms.

The study consists of 3 parts: Part A and Part B (Phase 1) and Part C (Phase 2). In Part A, single ascending doses (SAD) of ABCL635 or placebo will be administered to healthy male and female participants. In Part B, up to 3 multiple ascending doses (MAD) of ABCL635 or placebo will be administered to healthy postmenopausal women with or without VMS. In Part C, a single dose of ABCL635 or placebo will be administered to postmenopausal women experiencing moderate-to-severe VMS associated with menopause. In Part C, all participants will be offered to participate in an open label extension (OLE) cohort and receive a single dose of ABCL635 upon completion of a 12-week assessment.

Inclusion Criteria:

• Good general health as determined through a review of their medical history and after conducting a general physical examination

• Body weight ≥ 45 to ≤ 120 kg

• Body mass index (BMI) between 18.5 kg/m2 and 35.0 kg/m2

• Non- or ex-smoker (an ex-smoker is defined as someone who completely stopped using nicotine products for at least 90 days prior to the first study drug administration)

• Healthy man or a postmenopausal woman who is ≥ 40 and ≤ 75 years of age OR a postmenopausal woman with or without VMS and who is ≥ 40 and ≤ 75 years of age OR a postmenopausal woman who is ≥ 40 and ≤ 75 years of age seeking treatment for relief for VMS

• If a woman:

  1. has been compliant with local and/or national guidelines for breast cancer screening with documentation of a mammogram with normal/negative or no clinically significant findings. A screening mammogram may be conducted during study screening period, if needed
  2. has spontaneous amenorrhea for at least 12 consecutive months; or spontaneous amenorrhea for at least 6 months with biochemical criteria of menopause (follicle-stimulating hormone [FSH] > 40 IU/L); or had a bilateral oophorectomy > 6 weeks prior to screening, or s/p hysterectomy at least 6 weeks prior to screening and meeting the biochemical criteria of menopause (FSH > 40 IU/L)

• If a man:

  1. possess a testosterone concentration of ≥ 15 nmol/L at the time of screening
  2. can procreate and agree to use one of the acceptable contraceptive regimens and not to donate sperm from the first study drug administration to at least 90 days after the last drug administration OR is unable to procreate; defined as surgically sterile

Exclusion Criteria:

• Pregnancy and/or lactation.
• Has endometrial hyperplasia or history of abnormal uterine bleeding without an identified cause in the past 6 months
• Previous or current history of a malignant tumor, except for non-melanoma skin cancer.
• Seated pulse rate less than 50 beats per minute (bpm) or more than 100 bpm or a seated blood pressure < 90/50 mmHg or > 140/90 mmHg
• eGFR < 60 mL/min/1.73 m2
• Severe hypersensitivity reactions (like angioedema) to any drugs.
• Significant uncontrolled cardiovascular, pulmonary, gastrointestinal, hepatic, renal, hematologic, neurological, psychiatric, endocrine, immunologic, or dermatologic disease.
• Clinically significant ECG abnormalities
• Presence or history of cardiogenic syncope in the past 6 months.
• Use of any over-the-counter products (including supplements) containing testosterone or any medication (hormonal, prescription, over the counter, herbal, or natural) for the treatment of hot flashes during the screening period and throughout the study; must be discontinued at least 28 days prior to study drug administration
• Employees of the sponsor or the investigator site and other individuals who are directly involved in the conduct of the study