A Study Evaluating the Pain Palliation Benefit of Adding Custirsen to Docetaxel Retreatment or Cabazitaxel as Second Line Therapy in Men With Metastatic Castrate Resistant Prostate Cancer (mCRPC)

This is a randomized, double-blind, placebo-controlled, multicenter, international trial
enrolling patients with metastatic CRPC who had a response to first-line docetaxel therapy
and have prostate cancer-related pain with progression of disease. The intended intervention
is second-line treatment with docetaxel retreatment or cabazitaxel plus study agent, where
custirsen is to be administered in the investigational arm and placebo is to be administered
in the control arm.

Selection of the chemotherapy (docetaxel re-treatment or cabazitaxel) is to be determined by
the treating physician, based on the patient's first-line response.

The study will primarily assess pain and analgesic use for evaluation of durable pain
palliation in response to study treatment. Pain and analgesic use will be obtained via a 3rd
party contact center (direct contact with patient).

Study treatment starts with a Loading Dose Period during which three infusions of study
agent (custirsen vs. placebo) will be administered. Following the Loading Dose Period, study
treatment will consist of docetaxel or cabazitaxel on a 21-day cycle with weekly study agent
(custirsen vs. placebo) infusions on Day 1, 8 and 15 of each 21-day cycle and oral
prednisone BID.

Patients will continue study treatment until pain progression, unacceptable toxicity,
completion of 10 cycles or other specific criteria for withdrawal identified in the
protocol. If study treatment is completed or discontinued prior to pain progression, 6-day
assessments will continue every 3 weeks until pain progression is documented. Follow-up
after study treatment will occur for safety parameters for 3 weeks after the last study
agent infusion in all patients. Survival status updates are to be reported every 12 weeks
following documentation of pain progression. The amount of time that patients remain on the
study will vary; but the average survival of these patients who receive second line taxane
treatment is expected to be 14 to 15 months.

Inclusion Criteria

1. Age ≥ 18 years on the date of consent.

2. Histological or cytological diagnosis of adenocarcinoma of the prostate.

3. Metastatic disease at screening on a chest, abdomen or pelvic CT or bone scan.

4. Concurrent pain and analgesic use that is viewed by the Investigator to be related to
prostate cancer.

5. Received at least 4 cycles of prior docetaxel-based first-line chemotherapy for
metastatic disease based on a q3 week schedule of docetaxel. Patients treated on a
weekly or alternate schedule for first-line docetaxel must have received an
accumulated dose of docetaxel of at least 300 mg/M2.

6. Current progressive disease during or after completing first-line docetaxel
treatment.

7. Baseline laboratory values at screening visit within protocol defined limits.

8. Must be willing to continue primary androgen suppression with luteinizing hormone
releasing hormone (LHRH) analogues throughout the study, if not treated with
bilateral orchiectomy.

9. Adequate bone marrow function.

10. Karnofsky score ≥ 70% at screening visit.

11. At least 21 days have passed since completing radiotherapy at the time of
randomization.

12. At least 21 days have passed since completing any cytotoxic agent or investigational
agent given in combination with the docetaxel-based first-line therapy, including
ASOs (except custirsen which is an exclusion criterion), at the time of
randomization.

13. Has recovered from all therapy related toxicity to ≤ grade 2 (except alopecia, anemia
and any signs or symptoms of androgen deprivation therapy).

14. Patient can tolerate a starting dose of docetaxel of 75 mg/M2 or cabazitaxel at 25
mg/M2.

15. Patient must have remained on the same bisphosphonate or denosumab usage for a
minimum of 12 weeks prior to randomization.

16. Written informed consent must be obtained prior to any protocol-specific procedures
being performed.

Exclusion Criteria

1. More than two interruptions in first-line docetaxel therapy. An interruption will be
defined as more than 6 weeks between doses.

2. Life expectancy less than 12 weeks.

3. Previously participated in any clinical trial evaluating custirsen.

4. Received any other cytotoxic chemotherapy as a second-line treatment after first-line
docetaxel-based therapy.

5. Not on any opioid analgesic regimen for their prostate cancer-related pain.

6. Receiving more than one drug within each of the separate categories of long-acting
opioid, short-acting opioid, and non-opioid.

7. Receiving any analgesic specified in the protocol as unacceptable for this study.

8. Planned concomitant participation in another clinical trial of an experimental agent,
vaccine or device. Concomitant participation in observational studies is acceptable.

9. Inability to communicate and read in English, Spanish or French.