HYDROXYCHLOROQUINE INCREASES TUMOR SUPPRESSOR PAR-4 LEVELS IN PATIENTS WITH OLIGOMETASATIC PROSTATE CANCER: RESULTS FROM A PHASE-2 TRIAL

Introduction

In oligometastatic prostate cancer (OMPC), delaying time to initiation of androgen deprivation therapy (ADT) may have oncologic and quality of life benefits. Additionally, there is an emerging role for metastatic/primary tumor site-directed therapy for patients with OMPC. Prostate apoptosis response-4 (PAR-4) is a potent tumor suppressor, facilitating apoptosis in prostate cancer cells. Hydroxychloroquine (HCQ) has been identified to be a potent inducer of PAR-4 secretion and downstream tumor inhibition in preclinical models and Phase I trials. We present a single institution Phase II trial assessing induction of PAR-4 levels in the plasma of patients in response to HCQ administration in combination with radiation therapy (RT) for OMPC.

Methods

Men with OMPC (≤5 synchronous metastatic lesions) following primary tumor treatment were eligible. Patients received 400 mg HCQ daily for 2 weeks prior to metastatic site-directed RT and 400 mg HCQ daily for 90 days post-radiation. Plasma samples were collected on Day 0, 14, 30, 60, and 90. The primary endpoint was induction of ≥50% serum PAR-4 expression above baseline level within 90 days of treatment initiation. We hypothesized that over half of patients would exhibit ≥50% induction of serum PAR-4 expression.

Results

Nineteen participants met inclusion criteria and were treated with 90 days of HCQ and RT to oligometastatic lesions. Median age was 68 years (range 55-77), the majority of patients were Caucasian (94%), and the median baseline PSA was 6.30 ng/ml (range 0.99 to 27.80). Prior primary tumor treatment included radiation therapy in 26%, radical prostatectomy in 32%, and radical prostatectomy with radiation in 42%. Eleven patients (58%) showed ≥50% increase in plasma PAR-4 above baseline levels (p=0.0006). This was associated with a concomitant PSA decline at 6-months (mean -0.98 ng/ml, 95% CI -6.61 to 4.65) and 12-months (mean -7.21 ng/ml, 95% CI -12.45 to -1.97). At 12-month follow-up, seven patients (37%) were free from ADT and median progression-free survival was 9.3 months (95% CI 6.4 to N/A). Twelve patients (63%) reported at least one adverse event, with 2 patients (11%) experiencing grade 3 toxicity.

Conclusions

Oral administration of HCQ is well tolerated and effectively induces plasma expression of the potent tumor suppressor PAR-4 in patients with OMPC. Given the promising findings, further investigation into possible radiosensitizing and anti-tumor benefits of HQC in a larger cohort of OMPC is necessary.