A Study to Assess Adverse Events, and How Intravenously (IV) Infused ABBV-969 Moves Through the Bodies of Adult Participants With Metastatic Castration-Resistant Prostate Cancer

Prostate cancer has the second highest incidence rate and is the fifth leading cause of cancer-related deaths among men worldwide. The purpose of this study is to assess safety, pharmacokinetics, and efficacy of ABBV-969 as a monotherapy.

ABBV-969 is an investigational drug being developed for the treatment of metastatic castration-resistant prostate cancer (mCRPC). There are parts to this study. Participants will receive ABBV-969 as a single agent at different doses. Approximately 140 adult participants will be enrolled in the study across sites worldwide.

In part 1 (dose escalation), ABBV-969 will be intravenously infused in escalating doses as a monotherapy. In part 2, multiple doses will be selected from Part 1 and mCRPC participants will be assigned to one of these doses in a randomized fashion to determine the recommended Phase 2 dose. The estimated duration of the study is up to 3 years.

There may be higher treatment burden for participants in this trial compared to their standard of care. Participants will attend regular visits during the study at a hospital or clinic and may require frequent medical assessments, blood tests, and scans.


Eligibility Criteria:
Inclusion Criteria:

* Histological, pathological, and/or cytological confirmation of adenocarcinoma of the prostate.
* Estimated life expectancy \> 6 months.
* Must have progressed on prior novel hormonal agents (NHAs) (e.g., abiraterone acetate and/or enzalutamide) for the treatment of metastatic prostate cancer and/or castration-resistant prostate cancer (CRPC). Determination of progression is done per local investigator according to Response Evaluation Criteria in Solid Tumors (RECIST), version 1.1 and/or Prostate Cancer Working Group 3 (PCWG3).
* Serum testosterone levels \<= 50 ng/dL (\<= 1.73 nmol/L) within the screening period and prior to the first dose of the study drug.
* Must have received at least one NHA (e.g., enzalutamide and/or abiraterone). Additionally, participants must have received at least one taxane for prostate cancer (or have refused, or are intolerant to, or unable to get access to taxanes).
* Must have \>= 1 metastatic lesion that is present on baseline computed tomography (CT), magnetic resonance imaging (MRI), or bone scan imaging obtained \<= 28 days prior to beginning study therapy.
* Serum prostate specific antigen (PSA) level \>= 1.0 ng/mL.
* Availability of representative baseline tumor tissue (most recent archived tumor tissue after any novel hormonal agent (NHA) and/or any Prostate-Specific Membrane Antigen (PSMA) targeted therapy or fresh biopsy collected during screening phase) suitable for immunohistochemistry (IHC) testing. This requirement may be waived at the discretion of the AbbVie Medical Monitor if collecting a biopsy at screening would place the subject at risk of harm or would require a technically complicated procedure based on tumor location as assessed by the investigator.
* Laboratory values meeting the criteria laid out in the protocol.
* QT interval corrected for heart rate (QTc) \<= 470 msec (using Fridericia's correction), no \>= Grade 3 arrythmia, and no other clinically significant cardiac abnormalities.

Exclusion Criteria:

* Unresolved Grade 2 or higher toxicities related to previous anticancer therapy except alopecia.
* History of other active malignancy, as laid out in the protocol.
* History of interstitial lung disease (ILD) or pneumonitis that required treatment with systemic steroids, nor any evidence of active ILD or pneumonitis on screening chest CT scan.
* History of or active idiopathic pulmonary fibrosis, organizing pneumonia (e.g., bronchiolitis obliterans), drug-induced pneumonitis, or idiopathic pneumonitis.
* History of or active clinically significant, intercurrent lung-specific illnesses including, but not limited to those listed in the protocol.