Panobinostat As a Maintenance Therapy after Autologous Hematopoietic Cell Transplantation for Patients with Multiple Myeloma

Background:

Autologous hematopoietic cell transplantation (HCT) followed by maintenance therapy with an immunomodulatory agent or a proteasome inhibitor remains an important strategy for upfront treatment in multiple myeloma (MM) with progression-free survival (PFS) and overall survival (OS) advantage. We designed a two-arm, open-label prospective study to examine the safety and tolerability of two different dosing schedules of an oral pan-histone deacetylase inhibitor, panobinostat (pano) as an alternative maintenance therapy option in patients with MM (NCT02722941).

Methods:

A total of 30 MM patients who underwent autologous HCT within the preceding 90 to 180 days were enrolled at Moffitt Cancer Center using a sequential alternating allocation to starting dose of either Cohort A: 20 mg PO 3/week, q 2 weeks on a 28-day cycle, or Cohort B: 10 mg PO daily for 7 days, q 2 weeks on a 28-day cycle, for 12 cycles. Dose level -1 was cohort A: 15 mg 3/week; and cohort B: 10 mg 4/week. Patients with clinically significant cardiac diseases, bradycardia, QTc > 470 msec, bifascicular block were ineligible. EKG was performed on pre- and post-dose on day 1 & 5 of cycle 1, and pre-dose on day 1 of cycles 2-4. Relative dose intensity (RDI), a ratio of amount of drug actually delivered in mg over the amount of planned dose in mg, was calculated to evaluate the treatment feasibility as a surrogate measure.

Results:

The median age of the entire cohort was 60 (range, 40-73) years with a male/female = 18/12. Disease characteristics are summarized in the Table. Patients initiated pano maintenance at a median of 131 (range 91 - 178) days after autologous HCT. As of 8/1/2019, 16 patients (8 in each cohort) completed full 12 cycles of pano. The RDI for the entire cohort, cohort A, and cohort B was 94.1% (33,750mg/35,860, 98% (16,350mg/16,680mg), and 90.7% (17,400mg/19,180mg), respectively. One patient in cohort A had dose reduction, and 6 patients in cohort B had dose reductions with cytopenias (43%) and GI toxicities (43%) being the most common reasons. No patients required dose modifications due to QT prolongation thus far. There were 3 possibly treatment-associated serious adverse events (pneumonia=2; colitis=1) but all patients successfully resumed pano. Three patients progressed while on pano maintenance. No mortality has been observed thus far. Ten patients are still on pano treatment. The median follow-up is 11 (range, 1-29) months.

Conclusions:

RDI is 90% overall and panobinostat as a single oral maintenance agent either at 20 mg three times per week or 10 mg po daily for 7 days on alternating weeks appears to be overall well tolerated. There were more dose reductions required in the 10 mg starting dose (cohort B). Panobinostat is a safe alternative for maintenance therapy after autologous HCT. Longer follow-up is needed to confirm the utility of this approach and updated results will be presented at the meeting.

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