Results of an Open, Non-Comparative, Phase I/II Investigator Initiated Trial (IIT) in Relapsed or Refractory Multiple Myeloma Patients Using Vorinostat, Bortezomib, Doxorubicin and Dexamethasone (VBDD)

Introduction: Multiple myeloma (MM) relapse is common and may eventually lead to highly refractory/relapsed MM (RRMM). Therefore, novel treatment combinations are crucially needed for this highly challenging subgroup of patients (pts). The aim of the here presented phase I/II IIT was to test the tolerability and activity of a novel, so-called VBDD schedule within an outpatient regimen for extensively pretreated RRMM pts. In addition to Bortezomib, Doxorubicin and Dexamethason, which are all active and approved drugs in RRMM, Vorinostat has shown promising anti-tumor effects as a histone deacetylase inhibitor (HDACi). It inhibits the enzyme activity of HDAC 1, 2, 3 and 6, thereby allowing the activation of tumor suppressor genes. MM cells have been shown to escape from bortezomib treatment by formation of aggrosomes which desensitize cells to proteasome inhibitors and by microtubule mediated protein shuttling to lysosomes, where proteins are degradaded in order to prevent cytotoxic stress and ultimately escape from apoptosis (Fig.A). Albeit vorinostat has shown moderate activity when given alone, it has promising additive effects when combined with other antimyeloma agents, and was therefore used as an add-on agent within this RRMM regimen as it blocks microtubule coppling and aggrosome building and thereby may antagonize escape mechanisms in bortezomib-refractory pts.

Methods: Vorinostat was escalated from 100mg (dose level 0), to 200mg (+1) and 300mg (+2). Primary objectives (MTD; 3+3 dose escalation), secondary objectives (safety, IMWG responses, PFS, OS) and supplementary endpoints (organ function, prognostic factors, QoL, comorbidity and HDAC-activity in PBMCs/BM) were assessed throughout the trial. Dose limiting toxicities (DLTs) were defined as any possibly drug-related adverse event (AEs) ≥grade 3 (CTCAE) during the 1st cycle. After completing 6 cycles, patients could receive either a bortezomib maintenance therapy or next-line treatment (e.g. 2nd ASCT).

Results: 34 pts with RRMM with a median age of 63 years (47-78) and KPS of 90% (70-100%) have been enrolled, of which 33 received therapy according to the study protocol (1 pt deceased prior to study start due to aggressive MM progression and was therefore not included in the evaluation). The number of prior therapy lines was substantial with a median of 3 (1-8; with prior bortezomib, SCT and IMiDs in 88%, 94% and 42%, respectively). 3 pts each were treated in dose levels 0 and +1, and the remaining 27 pts in dose level +2. No DLTs were observed. In our current analysis, SAEs amounted to 15 and occurred in 9/33 pts (27%): Amongst them, 2 nonfatal SAEs were judged to be related to the investigational therapy (1 bacteraemia, 1 herpes zoster), for the others, no causal relationship to VBDD was found. The response according to IMWG criteria was rewarding with best ORR (>PR) and clinical benefit rate (CBR; >SD) of 42% and 94% (Fig.B), and end of treatment (EoT) ORR_EoT and CBR_EoT of 36% and 88%, respectively (Fig.C). Our data also revealed that the response was independent of the presence or absence of unfavorable cytogenetics. Comorbidity assessments assured no decline in pts' mental or physical condition and pts reported preserved or improved QoL with this well-tolerated 4-agent treatment regimen. Pharmacodynamic analyses in peripheral blood (PB) MCs showed substantial and early HDAC downregulation between VBDD cycles 1 and 2 in 11/16 pts (69%): median HDAC activity decreased to 52% of pre-treatment levels. Thereby, we were able to distinguish 3 groups of pts with substantial, more subtle or no PB HDAC decreases in 8, 3 and 5 pts, respectively. Of note, these HDAC changes correlated well with pts' serological and clinical responses, except in 2 pts. These intriguing results are currently further assessed and will be presented at the meeting.

Conclusions: VBDD demonstrated to be an effective and well-tolerated outpatient regimen with promising response rates in heavily pretreated RRMM pts. The employed VBDD regimen, with a continuous, rather than pulsed vorinostat-schedule, constitutes a promising treatment option, expands current standard therapies and, similarly to other HDACi (i.e. panobinostat), suggests HDACi as a valuable add-on within this combination schedule in order to stabilize the disease and/or bridge RRMM patients to next-line treatments (i.e. autologous/allogenic stem cell transplantation) or novel clinical trial drugs.

*AK and JW contributed equally