Venetoclax Monotherapy for Relapsed/Refractory Multiple Myeloma: Safety and Efficacy Results from a Phase I Study

Background: Venetoclax (VEN) is a potent, selective, orally available small-molecule BCL-2 inhibitor that induces cell death in multiple myeloma (MM) cell lines and primary samples, particularly those with t(11;14), which mostly have a favorable high BCL-2, low BCL-XL, and low MCL-1 profile.

Methods: In this Phase 1, open-label study, patients (pts) with relapsed/refractory (R/R) MM received VEN monotherapy. Objectives of the study were to assess safety, pharmacokinetics, maximum tolerated dose, recommended phase 2 dose, and efficacy (objective response rate [ORR], time to progression [TTP], and duration of response [DoR]) of VEN. After a 2-week lead in period with weekly dose escalation, VEN was given daily at final doses of 300, 600, 900, or 1200mg in dose escalation cohorts and 1200mg in the safety expansion. Pts who progressed during VEN monotherapy could receive VEN plus dexamethasone and continue in the study.

Results: As of 01July2016, 66 pts were enrolled in the study (30 in dose escalation cohorts and 36 in safety expansion). Median age was 63 years and 39 (62%) pts were ISS stage II/III. The median number of prior therapies was 5 (range: 1-15), and 62 (94%) pts had received bortezomib (46 [70%] refractory), 62 (94%) received lenalidomide (51 [77%] refractory), and 50 (76%) had prior autologous stem cell transplant. Thirty (46%) pts had t(11;14) MM.

Median time on VEN monotherapy for all pts was 2.5 months (.2-23); 17 (26%) elected to receive VEN and dexamethasone combination after disease progression for a median of 1.4 months (.1-11). Fifty-one (77%) pts discontinued the study for the following primary reasons: 39 related to disease progression, 5 due to AEs/toxicity, 2 withdrew consent, 1 was lost to follow up, and 4 for other reasons not specified. Common adverse events (AEs) in ≥20% of pts were nausea (48%), diarrhea (36%), neutropenia (32%), thrombocytopenia (32%), fatigue (27%), anemia (23%), back pain (21%), and vomiting (21%). Grade 3/4 AEs in ≥10% of pts were thrombocytopenia (26%), neutropenia (20%), lymphopenia (15%), anemia (14%), and decreased white blood cells (12%). Serious AEs in ≥2 pts were pneumonia (n=5), sepsis (3), pain, pyrexia, cough, and hypotension (2 each). Two pts experienced dose-limiting toxicities at 600mg of abdominal pain and nausea. Eight deaths were reported: 6 due to disease progression, 1 due to lung disorder, and 1 due to brain hemorrhage following injury; neither were considered by the investigator as related to VEN. Steady state VEN exposures were approximately dose proportional at all doses but 900mg.

As of 20July2016, ORR for all pts on VEN monotherapy was 21% (14/66) and 10 (15%) achieved very good partial response (VGPR) or better (2 stringent complete response [sCR], 2 CR, 6 VGPR) (Figure); median DoR and TTP was 9.7 and 2.6 months, respectively. Most objective responses (12/14 [86%]) were reported in the subset of pts with t(11;14) MM. In this group, ORR was 40% (12/30) and 27% (8/30) achieved a response of ≥VGPR; median DoR for pts with t(11;14) was 9.7 months (95% CI: 6.3, -). Pts who achieved at least minimal response in the t(11;14) group (14/30) had a median of 4 prior therapies and were mostly refractory to bortezomib, lenalidomide, or double refractory (71% [10/14] each). For two pts with response in the non-t(11;14)/undetermined group, 1 had a translocation of chromosome 14 with an unidentified partner, and the other had no cytogenetics data available. DoR was 9.5 and 7.2 months in these pts and both are still ongoing. Median TTP for pts with or without/undetermined t(11;14) was 6.6 and 1.9 months, respectively.

The median best percent change in primary M protein for pts with t(11;14) (n=23) was -53% vs +11% in the non-t(11;14)/undetermined group (n=23). Additional biomarker subgroup analyses (n=32) showed that efficacy was primarily observed in pts with myeloma cells expressing a favorable BCL-2 family expression profile (high BCL-2, low BCL-XL, low MCL-1) by immunohistochemistry, which was significantly enriched in the t(11;14) population. Indeed, although high BCL-2 expression was observed in a majority of bone marrow core biopsy samples (88%), the t(11;14) subgroup was enriched (81% vs 25%) for tumors expressing high BCL-2, low BCL-XL, and low MCL-1.

Conclusions: VEN monotherapy has an acceptable safety profile and clear anti-myeloma activity in pts with R/R MM, primarily with t(11;14) having a high BCL-2, low BCL-XL and low MCL-1 expression levels.

Figure

View largeDownload slide

Figure

View largeDownload slide

Close modal