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Objective: The aim of this study was to understand the influence of disease and patient characteristics on exposure to daratumumab, an immunoglobulin Gκ (IgGκ) monoclonal antibody, and clinical outcomes in relapsed or refractory multiple myeloma (MM).Patients and Methods: Baseline myeloma type, albumin levels, renal/hepatic function, age, sex, race, weight, Eastern Cooperative Oncology Group (ECOG) status, refractory status, and number of prior therapies were evaluated using data from two clinical studies-GEN501 (N = 104) and SIRIUS (N = 124).Results: Daratumumab clearance was approximately 110% higher in IgG myeloma patients than non-IgG myeloma patients, leading to significantly lower exposure in IgG myeloma patients based on maximum trough serum concentrations (p < 0.0001). However, the overall response rate was similar for IgG and non-IgG myeloma patients (odds ratio 1.08, 95% confidence interval 0.54-2.17, p = 0.82). For a given exposure, the drug effect was significantly higher (approximately two times) in IgG versus non-IgG patients (p = 0.03). The influence of other patient and disease characteristics on daratumumab exposure was minimal and no significant effect on efficacy was observed (p ≥ 0.1). The incidences of infections and overall grade 3 or higher adverse events in subpopulations were generally consistent with that of the overall population.Conclusion: Due to competition with the MM-produced IgG M-protein for neonatal Fc receptor protection from clearance, IgG-based monoclonal antibodies in general may have significantly higher clearance and lower concentrations in IgG MM patients compared with non-IgG MM patients. Careful evaluation of the impact of exposure and patient and disease characteristics on safety and efficacy is warranted for all IgG-based monoclonal antibodies used in MM. [ABSTRACT FROM AUTHOR]

Background: Histone deacetylase (HDAC) inhibitors are an important new class of therapeutics for treating multiple myeloma. Ricolinostat (ACY-1215) is the first oral selective HDAC6 inhibitor with reduced class I HDAC activity to be studied clinically. Motivated by findings from preclinical studies showing potent synergistic activity with ricolinostat and lenalidomide, our goal was to assess the safety and preliminary activity of the combination of ricolinostat with lenalidomide and dexamethasone in relapsed or refractory multiple myeloma.Methods: In this multicentre phase 1b trial, we recruited patients aged 18 years or older with previously treated relapsed or refractory multiple myeloma from five cancer centres in the USA. Inclusion criteria included a Karnofsky Performance Status score of at least 70, measureable disease, adequate bone marrow reserve, adequate hepatic function, and a creatinine clearance of at least 50 mL per min. Exclusion criteria included previous exposure to HDAC inhibitors; previous allogeneic stem-cell transplantation; previous autologous stem-cell transplantation within 12 weeks of baseline; active systemic infection; malignancy within the last 5 years; known or suspected HIV, hepatitis B, or hepatitis C infection; a QTc Fridericia of more than 480 ms; and substantial cardiovascular, gastrointestinal, psychiatric, or other medical disorders. We gave escalating doses (from 40-240 mg once daily to 160 mg twice daily) of oral ricolinostat according to a standard 3 + 3 design according to three different regimens on days 1-21 with a conventional 28 day schedule of oral lenalidomide (from 15 mg [in one cohort] to 25 mg [in all other cohorts] once daily) and oral dexamethasone (40 mg weekly). Primary outcomes were dose-limiting toxicities, the maximum tolerated dose of ricolinostat in this combination, and the dose and schedule of ricolinostat recommended for further phase 2 investigation. Secondary outcomes were the pharmacokinetics and pharmacodynamics of ricolinostat in this combination and the preliminary anti-tumour activity of this treatment. The trial is closed to accrual and is registered at ClinicalTrials.gov, number NCT01583283.Findings: Between July 12, 2012, and Aug 20, 2015, we enrolled 38 patients. We observed two dose-limiting toxicities with ricolinostat 160 mg twice daily: one (2%) grade 3 syncope and one (2%) grade 3 myalgia event in different cohorts. A maximum tolerated dose was not reached. We chose ricolinostat 160 mg once daily on days 1-21 of a 28 day cycle as the recommended dose for future phase 2 studies in combination with lenalidomide 25 mg and dexamethasone 40 mg. The most common adverse events were fatigue (grade 1-2 in 14 [37%] patients; grade 3 in seven [18%]) and diarrhoea (grade 1-2 in 15 [39%] patients; grade 3 in two [5%]). Our pharmacodynamic studies showed that at clinically relevant doses, ricolinostat selectively inhibits HDAC6 while retaining a low and tolerable level of class I HDAC inhibition. The pharmacokinetics of ricolinostat and lenalidomide were not affected by co-administration. In a preliminary assessment of antitumour activity, 21 (55% [95% CI 38-71]) of 38 patients had an overall response.Interpretation: The findings from this study provide preliminary evidence that ricolinostat is a safe and well tolerated selective HDAC6 inhibitor, which might partner well with lenalidomide and dexamethasone to enhance their efficacy in relapsed or refractory multiple myeloma.Funding: Acetylon Pharmaceuticals. [ABSTRACT FROM AUTHOR]