Abstract

<jats:p> 3592 </jats:p><jats:p> Background: Vorinostat is a novel histone deacetylase (HDAC) inhibitor that potentiates 5-FU and platinum antitumor activity. This potentiation is associated with ∼ 40 fold decrease in thymidilate synthase (TS) expression, the main target of 5-FU, in preclinical models. We conducted a phase I study of vorinostat plus FOLFOX in patients with CRC to determine the recommended dose of this combination. Methods: Vorinostat was escalated in a standard 3+3 design. FOLFOX was administered at a fixed dose every 2 weeks: leucovorin 400mg/m<jats:sup>2</jats:sup> and oxaliplatin 85mg/m<jats:sup>2</jats:sup> over 2 hours followed by 5-FU bolus 400mg/m<jats:sup>2</jats:sup> and 5-FU infusion 2400mg/m<jats:sup>2</jats:sup> over 46 hours. Vorinostat started 3 days prior to FOLFOX and was given twice daily for 1 week followed by 1 week break. Investigated dose levels of vorinostat (twice daily) include 100, 200, and 300 mg. Tumor biopsies were obtained from patients with accessible liver metastases before and on the 4<jats:sup>th</jats:sup> day of vorinostat (prior to FOLFOX) to assess TS expression. Results: 9 patients (pts) enrolled (M/F: 8/1; median age: 57, ECOG 0/1: 5/4). All pts had failed prior FOLFOX, irinotecan, and cetuximab therapy. One pt at dose level (DL) 1 was not evaluable due to rapid clinical progression. No dose-limiting toxicities were noted among the 8 evaluable pts. No grade (G) 3 toxicities were noted on the first cycle of treatment (within 2 weeks after 1<jats:sup>st</jats:sup> FOLFOX) and accrual continues on DL3. Cycle 1 toxicities were attributed to FOLFOX and consisted of 1 G2 neutropenia, 1 G2 mucositis, and 2 G2 nausea/vomiting. Responses were evaluable in 6 pts: 1 pt with peritoneal carcinomatosis on DL 1 has stable disease 5 months + along with a stable CEA; 3 patients at DL2 have stable disease at 2 months along with declining CEA in 2/3 pts. Two pts (DL1) with liver metastases biopsies had a major decrease in TS expression by IHC after 4 days of vorinostat. Conclusions: Vorinostat at 100–200mg PO BID × 1 week every 2 weeks in combination with FOLFOX is well tolerated. The lowest DL of 100 mg PO BID is associated with down-regulation of TS. Disease stabilization in highly refractory patients is promising. The investigation of this regimen in the first or second-line treatment of metastatic CRC is warranted. </jats:p><jats:p> No significant financial relationships to disclose. </jats:p>