Phase I study of intravenous CCI-779 in combination with bryostatin-1 in solid tumors
3067 Background: mTOR regulates translation of messenger RNA critical for angiogenesis and cell growth. CCI-779 inhibits mTOR signaling through p70S6 kinase (S6K), which phosphorylates the ribosomal S6 protein (S6). CCI-779 is active in renal carcinoma (RCC) and other solid tumors. Based on our finding that bryostatin-1 (bryo) inhibits S6K, and that CCI-779 + Bryo additively inhibit S6K and RCC growth in vitro, we initiated a phase I trial to determine the maximum tolerable (MTD) doses and dose-limiting toxicities of this novel combination in patients with solid tumors. Methods: Bryo (20 μg/m2) was administered over 60 minutes IV followed by CCI-779 (10 and 15 mg, planned escalation to 75 mg) IV over 30 minutes, both weekly for 3 of 4 weeks. Serum and peripheral blood mononuclear cell (PBMC) samples were collected for analysis of pharmacokinetics and markers of mTOR inhibition (phospho-S6 and p21waf1). Results: Nine patients (median age 57, 6 RCC, 2 sarcoma and 1 neuroendocrine) are evaluable for toxicity (total cycles=27 cycles, median 4, range 1–7) at the initial 2 dose levels (Bryo 20 μg/m2, CCI-779 10 mg and 15 mg). Cycle 1 toxicity includes grade 3 hypophosphatemia and myelosuppression in one patient each and grade 2 fatigue, stomatitis, and anemia. One patient developed reversible grade 3 pneumonitis after 7 cycles. Of 7 patients with therapy-resistant disease, 5 (4 RCC and 1 sarcoma) had stable disease lasting up to 7 months. A therapy-naive patient with RCC has 23% tumor reduction after 2 cycles at dose level 2 (CCI-779=15 mg). PBMC proteins from 5 patients show consistent decreases in phospho-S6 at 2–6 hours-post treatment compared with pre-treatment baseline measurement, with recovery by 24–72 hours after dosing. In parallel with inhibition of phosphorylation of S6, PBMC levels of p21waf1 were completely inhibited in all 5 patients. Conclusions: The combination of bryo and CCI-779 is feasible, with antitumor activity in RCC and mTOR pathway inhibition observed at submaximal doses. Dose escalation is continuing. No significant financial relationships to disclose.