Olutasidenib for the Treatment of mIDH1 Acute Myeloid Leukemia in Patients Relapsed or Refractory to Hematopoietic Stem Cell Transplant, Prior mIDH1 Inhibitor, or Venetoclax

Introduction. Olutasidenib is a small molecule, oral, mutated-IDH1 (mIDH1) inhibitor approved for the treatment of relapsed/refractory (R/R) acute myeloid leukemia (AML). In the pivotal cohort of the registrational phase 1/2 trial, 51/147 (35%) patients achieved a complete remission (CR) or CR with partial hematologic recovery (CRh) to olutasidenib, with a duration of response of 25.9 months and an overall response rate (ORR) of 48%. The phase 1/2 study included 10 cohorts for a total of 335 patients, and there were patient subsets that were R/R to previous hematopoietic stem cell transplant (HSCT), ivosidenib (IVO) or venetoclax (VEN). We conducted post hoc analyses to better understand the response to olutasidenib in these poor-prognosis subgroups of mIDH1 AML.

Methods. This Phase 1/2, open-label, multi-center study enrolled patients with confirmed AML or intermediate, high-, or very high-risk myelodysplastic syndromes/neoplasms (MDS). Patients received olutasidenib 100mg QD, 150mg QD or 150mg BID monotherapy or the combination of olutasidenib 150mg BID plus azacitidine. Patients were grouped by prior therapy. Baseline demographics and disease characteristics are shown in Table 1. The study was not powered to statistically evaluate subpopulations; descriptive statistics are provided. Data cutoff date is June 2021.

Results. The post-HSCT group (n=31) had a relatively high median baseline bone marrow blast count (58%) and a median of 4 prior treatment regimens (Table 1). Six (19%) of these patients had a CR (including the 1 patient with MDS), and 3 (10%) patients had a CR with incomplete count recovery (CRi) resulting in a 29% composite complete remission (CRc) rate. One patient had a morphologic leukemia-free status, resulting in a 32% ORR. Half the responders received monotherapy, and half received a combination of olutasidenib and azacitidine. Two patients were enrolled in the monotherapy maintenance cohort while in CR to prior HSCT; one of these patients maintained a CR for 13 months before progressing, and the other patient progressed and discontinued due to a new central nervous system disease (Table 2). For the 10 patients with responses (ORR), the median duration of response was 7.1 months (range 1-23.4+). At data cutoff, 2 patients were ongoing responders, 3 patients proceeded to a second HSCT, and 3 to donor lymphocyte infusion (DLI).

The post-IVO group (n=9) had a high median baseline bone marrow blast count (83%) and a median of 4 prior treatment regimens (Table 1). Two patients (22%) achieved a CR; both CRc and ORR were 22% (Table 2). Both responders had received olutasidenib in combination with azacitidine. One responder proceeded to HSCT after 3.1 months, and one responded for 5.6 months and then had disease progression.

Response rates in the post-VEN group (n=20) included CR in 6 patients (30%), CRh in 1 (5%), and CRi in 2 (10%) resulting in a CRc of 9 (45%) and an ORR of 45% (Tables 1 and 2). One responder received combination olutasidenib and azacitidine. Two patients were enrolled in the monotherapy maintenance cohort while in CRi to prior treatment; both improved their response to a CR. Median duration of response was not reached and ongoing at 28.5 months. At data cutoff, 5 patients continued treatment, and 15 had discontinued.

Conclusions. This descriptive analysis suggests that olutasidenib alone or in combination with azacitidine may induce complete remissions in patients with mIDH1 AML or MDS that is R/R to VEN, IVO or even HSCT. Further investigation of these difficult-to-treat subpopulations is needed. Although only a small number of patients receiving maintenance therapy were included in this analysis, the data show that maintenance of a CR and even improvement of response from CRi to CR is possible with olutasidenib.