Vorinostat in Combination with Pegylated Liposomal Doxorubicin (PLD) and Bortezomib (B) in Patients with Relapsed/Refractory Multiple Myeloma (R/R MM): Final Results of a Phase I Study,

Although the combination of PLD and B improved time to progression (TTP) compared with B alone in patients (pts) with R/R MM, the overall response rate (ORR) of the regimen was only 44%, while TTP was 9.3 months. As such, strategies that build upon the efficacy of this regimen are needed. Vorinostat (V) is a histone deacetylase inhibitor that has demonstrated additive to synergistic activity with proteasome inhibitors and anthracyclines in preclinical models of MM. We therefore conducted a phase I study evaluating the safety and preliminary efficacy of V when combined with the PLD/B backbone.

Patients and Methods: Pts were treated with standard doses of B and PLD (B 1.3mg/m² on D1, 4, 8, 11, and PLD 30mg/m² on D4) and escalating doses of V from either D4-11 or D1-14 of a 3-week cycle. Dose escalation followed a standard 3 + 3 design. Eligibility criteria included a diagnosis of relapsed or relapsed/refractory MM, absolute neutrophil count ≥1.0×10⁹/L, platelets ≥100×10⁹/L, creatinine clearance ≥30mL/min, and adequate hepatic and cardiac function. The primary objective was to determine the dose limiting toxicities (DLTs) and maximum tolerated dose (MTD) of the regimen and the secondary objective was to assess preliminary efficacy.

32 pts were enrolled at the following dose levels:

The median age was 61 (39–75) and median β2-microglobulin 3.57 mcg/mL (1.26–10.6). 69% of the pts were male, 31% female. The median time from diagnosis was 46 months (13–155) and median number of prior lines of therapy 2 (1–9). 78% of pts had received prior B, 56% PLD or doxorubicin, 91% thalidomide and/or lenalidomide, and 66% autologous and/or allogeneic stem cell transplantation. 44% (11 of 25 pts) had disease refractory to prior B-based therapy. The median number of complete cycles administered was 6 (0–15). No patients on dose level 1 or 2 suffered DLTs. One of 6 pts on dose level 3 had a DLT consisting of grade 4 systolic dysfunction in the setting of atrial flutter, which subsequently resolved. Two of 6 pts at dose level 4 experienced grade 4 thrombocytopenia in cycle 1, establishing dose level 3 as the MTD. Nine pts experienced serious adverse events at least possibly attributable to protocol therapy, including the 1 case of systolic dysfunction/atrial flutter noted above, 2 cases of nausea and vomiting with dehydration, and diarrhea, diastolic dysfunction, upper respiratory infection, syncopal episode and hypertension in 1 pt each. Grade 3 neutropenia was seen in 34% of pts (3% grade 4). 4 pts had grade 3 infections (1 attributed to protocol therapy), but no grade 4 infections were seen regardless of attribution. Grade 3 and 4 thrombocytopenia was documented in 16% and 34%, but no serious hemorrhagic events were seen. Non-hematologic toxicity at least possibly attributable to therapy included fatigue in 63% (16% grade 3, 0% grade 4). GI toxicity was common with anorexia, constipation, diarrhea, nausea and vomiting occurring in 47% (3% grade 3), 50%, 81% (16% grade 3, 3% grade 4), 78% (9% grade 3) and 50% (9% grade 3) of pts, respectively. Peripheral neuropathy at least possibly attributable to therapy was seen in 38% of pts (6% grade 3), while hand-foot syndrome was seen in 25% (9% grade 3). There were no deaths on study. Among 31 evaluable pts, the ORR using International Uniform criteria was 65% (95% confidence interval (CI): 45–81%), and the ≥very good partial remission (VGPR) rate was 29% (95% CI: 14–48%). The ORR + minimal response (MR) rate was 74% (95% CI: 55–88%). Of 14 pts with B-sensitive disease, there was 1 MR, 5 PRs and 5 VGPRs. Two PRs, 2 VGPRs and 1 complete remission (CR) were documented in 6 pts with B-naïve disease. Notably, there were 2 MRs, 4 PRs and 1 CR out of the 11 pts with B-refractory disease.

The MTD of vorinostat when added to the PLD/bortezomib backbone is 400 mg administered daily on days 4–11. The ORR is highly promising, with responses seen in pts with bortezomib-naïve, -sensitive and -refractory disease. Although serious toxicities were infrequent, constitutional and GI side effects were highly prevalent. All together, our data support further development of this combination in pts with MM, with special attention to developing strategies and guidelines to better ameliorate toxicity.

Voorhees:Merck: Research Funding; Celgene: Research Funding; Centocor Ortho Biotech: Research Funding; MedImmune: Consultancy; Pfizer: Research Funding. Off Label Use: Vorinostat for the treatment of relapsed and relapsed and refractory multiple myeloma. Gasparetto:Millennium Pharmaceuticals: Speakers Bureau; Celgene: Membership on an entity's Board of Directors or advisory committees. Richards:Merck: Consultancy. Garcia:Millennium Pharmaceuticals: Speakers Bureau; Sigma-Tau: Speakers Bureau. MacLean:Novartis: Speakers Bureau. Orlowski:Millennium Pharmaceuticals: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Janssen-Cilag: Honoraria; Johnson and Johnson: Research Funding.