Yirinec, B.

4083 Background: Thymidylate synthase (TS) over-expression is associated with 5-FU resistance. Pre-clinical studies demonstrate that vorinostat down-regulates intra-tumor TS in a dose-dependent fashion and augments 5-FU antitumor activity in xenograft models. We conducted a phase I clinical trial of an intermittent schedule of QD x 3 vorinostat in combination with a fixed dose of fluorouracil (5-FU) and leucovorin (LV) in patients (pts) with refractory solid tumors. Methods: Vorinostat was escalated in a standard 3 x 3 design in combination with a fixed dose of 5-FU and LV (simplified de Gramont regimen, sFULV2). Vorinostat was given QD x 3 on an every-2-week cycle. sFULV2 started on day 2 of vorinostat and consisted of leucovorin 400 mg/m2 i.v. over 2 hrs followed by 5-FU 400 mg/m2 bolus and 5-FU 2400 mg/m2 over 46 hrs. Results: 24 pts were enrolled: Male/Female: 11/13; ECOG 0/1: 6/18; Age: median 60 (range 42–77) yrs. 21 pts had colorectal cancer (CRC), 1 had gastric, 1 had esophageal, and 1 had anal cancer. Vorinostat dose-levels (DL) were 600 mg, 800 mg, 1000 mg, 1200 mg, 1400 mg, 1700 mg, and 2000 mg. Dose-limiting toxicities (DLT), consisting of fatigue and hand-and-foot syndrome (H&F), were seen in 2 of 3 pts at the 2000 mg DL. None of the 6 pts at the 1700 mg DL had a DLT. Cycle 1 grade 3/4 toxicities consisted of thrombocytopenia, GI bleeding, fatigue, and H&F in 2 pts at the 2000 mg DL and a non-DLT G3 diarrhea (lasted <24 hrs) in 1 pt at the 1700 mg DL. Grade 2 nausea, fatigue, and anorexia were common; especially at DL ≥ 1700 mg. Antitumor activity was noted in pts with CRC despite prior refractoriness to 5-FU and failure to oxaliplatin, irinotecan, and cetuximab in all pts. 12/21 CRC pts had a confirmed SD (11) or PR (1). CRC pts had a median PFS of 4 months, a ≥ 6 months PFS rate of 43%, and a ≥ 8 months PFS rate of 33%. Conclusions: The maximum tolerated dose (MTD) of vorinostat in combination with sFULV2 is 1700 mg PO QD x 3 every 2 weeks. This combination is associated with considerable activity in pts with 5-FU-refractory CRC and warrants further investigation. An expanded MTD cohort is accruing to investigate 5-FU-vorinostat PK interaction and intra-tumor TS down-regulation. (This work was supported by a grant from CTEP and the ACS.) No significant financial relationships to disclose.