A phase II study of the antisense oligonucleotide GTI-2040 plus docetaxel and prednisone as first line treatment in hormone refractory prostate cancer (HRPC)
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13015 Background: Despite initial responses to chemotherapy, median survival in HRPC remains a dismal 18 mos. Novel therapeutic approaches are clearly needed. The enzyme ribonucleotide reductase (RNR) composed of 2 subunits, R1 and R2 is essential for DNA synthesis and repair. The R2 subunit is often overexpressed in tumors increasing their malignant potential and promoting drug resistance. GTI-2040 (Lorus Therapeutics, Canada) is an antisense oligonucleotide to the R2 subunit downregulating its expression. In preclinical studies, GTI-2040 has shown antitumor activity in prostate cancer xenografts, synergy and non-overlapping toxicity with the taxanes. It is therefore a rational choice for combination with docetaxel in HRPC. Objectives: To determine efficacy of this regimen using PSA response rate. Secondary objectives include: duration of response, TTP, objective tumor response rate, safety and tolerability. Pharmacokinetic (PK) studies will be performed. PBMC will be used to determine RNR activity and R2 subunit quantitation. Methods: HRPC patients with PS 0–2, adequate organ function and no prior chemotherapy were treated with GTI-2040 5mg/kg/d continuous infusion for 14d, docetaxel 75 mg/m2 IV every 21d, and prednisone 5mg twice daily. Results: Twenty-two pts in 5 centers have been enrolled. Pts have received a total of 107 cycles to date. Median age 63 (52–77); median baseline PSA 140 (26–1256); ECOG 0:1:2: 14:7:1; prior radiotherapy in 14 pts. Pts received a median of 5 cycles (2–10). Grade 3/4 hematologic toxicities were lymphophenia (10pts), leukopenia (7pts), and neutropenia (7pts). Anemia (any grade) was seen in 19 pts across 92 cycles. Most frequent non-hematologic toxicities were fatigue and pain. PSA responses seen in 9/22 pts. Objective tumor response:1 PR, 9 SD, 3 PD, 3 off due to toxicity prior to objective response measurement, 3 no measureable lesions, 3 to be assessed. 19 pts off treatment: 9 PD, 4 toxicity (1 toxic death), 2 completed 10 cycles, 2 at investigator’s discretion and 2 withdrew consent. Three pts remain on study. Median TTP estimated at 17 wks. Accrual has been sufficient to meet stage 1 requirements. Final response, toxicity, pK, RNR and R2 subunit analysis will be available and presented. No significant financial relationships to disclose.
