This study is a single-arm, multicenter, phase II exploratory trial. The purpose is to explore the efficacy and safety of Darxicilib in combination with Abiraterone Acetate for the treatment of subjects with metastatic castration-resistant prostate cancer.The main questions it aims to answer are:

·PSA50 response rate at the end of week 12

Participants will:

• Darxicilib: 125mg per tablet, oral administration, once daily for 21 consecutive days followed by a 7-day break.
• Abiraterone Acetate tablets (II): 300mg per dose, oral administration, once daily for a 28-day cycle.
• Prednisone: 5mg per tablet, oral administration, twice daily.

1. This research constitutes a phase II, single-arm, multicenter exploratory study aimed at assessing the therapeutic efficacy and safety profile of the combination therapy involving Darxicilib and Abiraterone Acetate (II) in patients diagnosed with metastatic castration-resistant prostate cancer (mCRPC). The enrollment target is set at 43 participants who meet the eligibility criteria for the efficacy assessment phase of the trial.
2. (1)Main Research Objective To evaluate the efficacy of the treatment modality of Darxicilib in combination with Abiraterone Acetate (II) in patients with mCRPC (metastatic castration-resistant prostate cancer).

(2)Secondary Research Objectives

1. To assess the efficacy of the combination therapy in target mCRPC subjects through the time to PSA progression, PSA response rate at 12 weeks (PSA50, PSA90, and PSA ≤ 0.2 ng/ml), disease-free survival (PFS) rates at 6 and 12 months, overall survival (OS), and duration of response (DOR);
2. To evaluate the safety of the combination therapy for target mCRPC by assessing the incidence of adverse events, time to pain progression, and time to symptom progression.

(3)Exploratory Research Objective Quality of life.

Inclusion Criteria:

• Age ≥18 years old, male;
• ECOG performance status score of 0 to 1;
• Life expectancy of at least 3 months;
• Histologically or cytologically confirmed adenocarcinoma of the prostate, without a diagnosis of neuroendocrine or small cell carcinoma;
• Testosterone at castrate levels at screening (≤50 ng/dL or 1.73 nmol/L);
• Failure of previous treatment with new androgen receptor antagonists at the mHSPC stage (such as enzalutamide, apalutamide, ODM-201, SHR3680, HC-1119, and pucrol);
• Capable of complying with the study protocol as judged by the investigator;

Exclusion Criteria:

• Previously received abiraterone acetate treatment for prostate cancer;
• Previously received any cytotoxic chemotherapy for mCRPC stage;
• Previously received treatment with any other cyclin-dependent kinase 4 and 6 (CDK4 & 6) inhibitors;
• Previously received treatment with new androgen receptor antagonists at the mCRPC stage (such as enzalutamide, apalutamide, ODM-201, SHR3680, HC-1119, and pucrol);
• The washout period from the end of any previous anti-tumor treatment (including radiotherapy, surgery, molecular targeted therapy, immunotherapy, and first-generation androgen receptor antagonists) to the first administration of this study is less than 4 weeks (except for bicalutamide with a washout period less than 6 weeks);