Inclusion Criteria:

          1. Age ≥ 18 years

          2. Histologically or cytologically proven prostate cancer with evidence of progressive
             mCRPC, defined as:

               1. Castrate levels of testosterone, defined as ≤ 50 ng/dL (or ≤ 0.50 ng/mL or 1.73
                  nmol/L)

               2. Evidence of progressive metastatic disease as defined by radiographic disease
                  progression or PSA progression

               3. With an indication for systemic treatment with docetaxel according to the
                  standard of care

          3. Measurable tumour lesions, defined as pelvic and/or extra-pelvic nodal lesions ≥1.5 cm
             in the short axis or visceral lesions ≥1.0 cm in the longest dimensions and measurable
             according to RECIST v1.1, bone metastasis as evaluated with 99mTc-methylene
             diphosphonate (MDP) radionuclide bone scintigraphy

          4. Resolution of toxicity of prior therapy to < grade 2 (except for alopecia), as defined
             by CTCAE v5.0

          5. Adequate haematological, renal and hepatic functions:

               1. Hemoglobin ≥ 6.0 mmol/l (>9.6 g/dL)

               2. ANC ≥ 1.5 x 109 /L

               3. Platelet count ≥ 100 x 109 /L

               4. Hepatic function defined by serum bilirubin ≤ ULN, ALAT and ASAT ≤ 1.5 x ULN
                  concomitant with alkaline phosphatase ≤ 2.5 × ULN.

               5. Renal function defined by serum creatinine ≤ 1.5 x ULN or creatinine clearance ≥
                  50 ml/min (by Cockcroft-Gault formula, or MDRD).

          6. WHO performance status of 0-2

          7. Estimated life expectancy of at least 12 weeks

          8. Able and willing to swallow oral medication

          9. Able and willing to undergo radiologic scans (CT scan)

         10. Able and willing to give written informed consent according to local guidelines

        Exclusion Criteria:

          1. Any treatment with investigational drugs, chemotherapy or immunotherapy within 4 weeks
             prior to receiving the first dose of investigational treatment. Palliative
             radiotherapy (1x8 Gy dose) is allowed before and during the study, but not in the week
             prior to start of study treatment.

          2. Subjects who have had prior treatment with taxanes.

          3. Subjects with symptomatic brain metastases. Subjects asymptomatic in the absence of
             corticosteroids and anticonvulsant therapy for ≥6 weeks are eligible. Radiotherapy for
             brain metastasis must have been completed ≥6 weeks prior to start of trial. Brain
             metastasis must be stable with verification by imaging (e.g. brain MRI or CT completed
             at screening, demonstrating no current evidence of progressive brain metastases).
             Subjects are not permitted to receive anti-epileptic drugs or corticosteroid treatment
             indicated for brain metastasis. Subjects with a history of leptomeningeal metastases
             are not eligible.

          4. Current malignancies other than mCRPC with exception of adequately treated basal or
             squamous cell carcinoma of the skin, or adequately treated non-muscular invasive
             bladder cancer.

          5. Absence of highly effective method of contraception as of cycle one day one (C1D1).
             Men enrolled in this trial must agree to use a highly effective contraceptive method
             throughout the study.

          6. Uncontrolled hypertension (systolic > 150 mm Hg and/or diastolic > 100 mm Hg)

          7. Unresolved (>grade 0 as defined by CTCAE version 5.0) gastrointestinal toxicities
             (pre-existing mucositis, diarrhea or nausea/vomiting)

          8. Grade ≥ 2 motor ≥ 2 motor or sensory neuropathy symptoms (as defined by CTCAE version
             5.0)

          9. Known hypersensitivity to any of the study drugs or excipients or taxanes

         10. Concomitant use of P-glycoprotein (P-gp , MDR), CYP3A, OATP1B1, OATP1B3 and MRP2
             modulating drugs such as Ca+- entry blockers (verapamil, dihydropyridines),
             cyclosporine, quinidine and grapefruit juice, concomitant use of HIV medications,
             other protease inhibitors, (non) nucleoside analogues, or St. John's wort

         11. Bowel obstruction or motility disorder that may influence the resorption of drugs as
             judged by the treating physician

         12. Major surgical procedures within 21 days prior to providing informed consent

         13. Active acute or chronic infection, which is not controlled by appropriate medication
             (at the discretion of the treating physician)

         14. Known positivity for Human Immunodeficiency Virus HIV-1 or HIV-2 type

         15. Patients with known active infection of hepatitis B, C, or E (patients who are
             anti-HBC positive but HBsAg negative are eligible to participate in this study)

         16. Clinically significant (i.e. active) cardiovascular disease defined as stroke,
             transient ischemic attack (TIA), myocardial infarction, unstable angina, or congestive
             heart failure within ≤ 6 months prior to first trial treatment

         17. Evidence of any other medical conditions (such as treatment-resistant peptic ulcer
             disease, erosive oesophagitis or gastritis, infectious or inflammatory bowel disease,
             diverticulitis, or pulmonary embolism within 4 weeks of randomization, or psychiatric
             illness, drug or alcohol abuse, physical examination or laboratory findings) that may
             interfere with the planned treatment, affect subject compliance or place the subject
             at high risk of treatment-related complications

         18. Legal incapacity