Javidi-Sharifi, Nathalie

Abstract The antiapoptotic protein, myeloid cell leukemia-1 (Mcl-1), contributes to the pathophysiology of acute myeloid leukemia (AML) and certain B-cell malignancies. Tumor dependence on Mcl-1 is associated with resistance to venetoclax. Voruciclib, an oral cyclin-dependent kinase (CDK) inhibitor targeting CDK9, indirectly decreases Mcl-1 protein expression and synergizes with venetoclax in preclinical models. This dose escalation study evaluated voruciclib in patients with previously treated hematologic malignancies. Initially, voruciclib was administered daily, continuously, on a 28-day cycle (group 1). After 2 patients with prior allogeneic stem cell transplantation had a dose-limiting toxicity (DLT) of interstitial pneumonitis at 100 mg, voruciclib administration was changed to days 1 to 14 of a 28-day cycle (group 2). Forty patients, 21 with AML and 19 with B-cell malignancies, were enrolled. Patients had a median of 3 prior lines of therapy (range, 1-8). Dose escalation in group 2 was stopped at 200 mg, a dose that achieved plasma concentrations sufficient for target inhibition, without DLTs observed. The most common adverse events were diarrhea (30%), nausea (25%), anemia (22%), fatigue (22%), constipation (17%), dizziness (15%), and dyspnea (15%). In AML, 1 patient achieved a morphologic leukemia-free state, and 2 had stable disease. Voruciclib treatment led to a decrease in MCL1 messenger RNA expression, downregulation of myelocytomatosis (MYC) and NF-κB transcriptional gene sets, and reduced phosphorylation of RNA polymerase 2. Voruciclib on intermittent dosing was well tolerated, with no DLTs, paving the way for evaluation of the combination of voruciclib with venetoclax for patients with previously treated AML. This trial was registered at www.clinicaltrials.gov as #NCT03547115.

Background: Venetoclax in combination with hypomethylating agents (HMA) or low dose cytarabine is the standard of care for patients (pts) with newly diagnosed AML ineligible for intensive chemotherapy. However, responses are transient, and loss of response is associated with poor outcome. The antiapoptotic protein Mcl-1 promotes cell survival in AML and its overexpression is associated with resistance to venetoclax. Voruciclib, a potent oral CDK9 inhibitor (CDK9i), indirectly decreases Mcl-1 protein expression, and has synergistic activity with venetoclax in AML preclinical models. In the initial part of this study in 40 pts with R/R AML and B-cell malignancies, voruciclib at doses up to 200 mg administered on days 1-14 in a 28-day cycle was well tolerated, had no dose limiting toxicities (DLTs), and showed biologic and clinical activity in heavily pretreated pts (Blood 2023:142; Supp 1:4286). We hypothesized that voruciclib in combination with venetoclax may achieve greater antileukemic effect. Methods: Pts with R/R AML were eligible if aged ≥18 years, ECOG performance status ≤1, adequate organ function, and no prior CDK9i therapy. Dose escalation followed a 3+3 design, and DLTs were assessed in Cycle 1. Voruciclib was administered at 7 dose levels between 50 mg and 300 mg on days 1-14 of 28-day cycles. Venetoclax was administered at 200 mg on days 1-21 and 400 mg on days 22-28. Disease response was assessed by the 2017 ELN criteria. Mcl-1 protein expression and phosphorylation of RNA Pol IISer2 were evaluated in PBMC in cycle 1. The study is registered at clinicaltrials.gov (NCT03547115). Results: Enrollment in this portion of the study is complete with 41 pts. Median age was 67 years (range 34-89). Median number of prior lines of therapy was 2 (range 1-7), with 93% of pts having received venetoclax and HMAs, 51% having received an anthracycline, and 20% having had prior allogeneic hematopoietic stem cell transplant (HSCT). 2017 ELN risk was adverse in 73% of pts and intermediate in 17%. The median duration on therapy was 1.5 months (range 0.2 to 9+). No DLTs were observed, and based on PK/PD analysis, dose escalation was stopped at 300 mg without reaching the maximum tolerated dose. The most common adverse events (all grades/grade ≥3) were nausea (32%/0%), febrile neutropenia (27%/24%), dyspnea (22%/2%) diarrhea (22%/2%), hypokalemia (22%/5%) and thrombocytopenia (22%/20%). Seven pts died during treatment, 5 due to an infection and 2 due to hemorrhagic events. Anti-leukemic activity was observed in 10 (31%) of 32 pts treated with voruciclib at doses from 100-300 mg; 2 pts had CRi (one referred to HSCT and one with 6 months of remission prior to progression), 1 pt had MLFS (ongoing at 9 months), and 7 pts had stable disease lasting ≥3 months. Among 25 pts with circulating peripheral blood blasts, 18 (75%) showed a significant reduction of circulating blasts by day 14 of the first cycle; however, circulating blasts increased again in 8 of 18 pts during single agent venetoclax administration on days 15 to 28. Voruciclib pharmacokinetics (PK) was dose proportional. At 300 mg steady state, mean AUC0-24 was 21,526 ng x hr/mL and mean Ctrough was 644 ng/mL, exceeding concentrations needed for target inhibition in preclinical models. Voruciclib did not affect venetoclax PK. Pharmacodynamic studies including Mcl-1 protein expression and RNA Pol IISer2 phosphorylation in PBMC by flow cytometry showed on target effects and is reported separately. Conclusion: The combination of voruciclib with venetoclax is well-tolerated and has activity in pts with AML and disease progression after venetoclax. Because of the rebound in peripheral blasts after 14 days off voruciclib, voruciclib administered on days 1-21 per cycle merits further evaluation.

Background: The anti-apoptotic protein Mcl-1 contributes to the pathophysiology of certain B-cell malignancies and AML, and dependence on Mcl-1 is associated with resistance to venetoclax. Efforts to target Mcl-1 through direct inhibition have faced challenges due to cardiovascular toxicities. Voruciclib, a potent oral CDK9 inhibitor (CDK9i), was shown to indirectly downregulate Mcl-1 protein levels and synergize with venetoclax in preclinical models in lymphoid and myeloid malignancies. In solid tumors, voruciclib maximum tolerated dose (MTD) was defined as 350 mg with continuous daily dosing, and 600 mg when used on days 1-14 on a 21-day cycle. This phase 1 study is the first to evaluate the safety, dose-limiting toxicities (DLT), preliminary efficacy, pharmacokinetics, and pharmacodynamics of voruciclib in R/R hematologic malignancies (NCT03547115). Methods: Patients (pts) with relapsed B-cell NHL, CLL, or AML aged ≥18 years who had ECOG performance status ≤1, disease progression after standard therapies, adequate hepatic and renal function, and no prior CDK9i were eligible. The study followed a 3+3 design and DLTs were assessed in Cycle 1. Voruciclib was administered daily continuously at a starting dose of 50 mg on a 28-day cycle (Cohort I). After 2 DLTs were observed at 100 mg in AML pts, dosing was changed to daily on days 1-14 on a 28-day cycle (Cohort II). Also, pts with prior allogeneic transplant were excluded and dose escalation (100, 150, 200 mg) proceeded separately in AML and B-cell malignancies. Disease response was assessed by investigators using the Lugano, 2008 iwCLL, and 2017 ELN criteria. Results: 40 pts were enrolled: 21 AML, 19 NHL (9 DLBCL, 3 CLL, 3 MCL, 3 FL and 1 MZL). Cohort I enrolled 16 pts, 8 each at 50 mg and 100 mg. Cohort II enrolled 24 pts (17 AML and 7 B-cell malignancies), including 6 at 100 mg, 7 at 150 mg, and 11 at 200 mg. Dose escalation in Cohort II did not reach the MTD and was stopped at 200 mg, a dose that achieved plasma concentrations sufficient for target inhibition. Median age was 70 years (range 40-90), 72.5% of pts were ≥65 years, and 77.5% had ECOG performance status = 1. Pts had a median of 3 prior therapies (range, 1-8). Median duration on drug was 5 weeks (range 1-22). Drug-related serious adverse events (AEs) were reported in Cohort I only. Two pts with AML had a DLT of Grade (Gr) 3 interstitial pneumonitis at 100 mg; both had had allogeneic transplant and active graft versus host disease, one of whom also had a concurrent Gr 3 differentiation syndrome. One pt with DLBCL at 50 mg had Gr 3 hypoxemic respiratory failure in Cycle 4. In Cohort II, no DLTs were observed and there were no non-hematologic Gr 3-5 drug-related AEs. In the overall population, the most common AEs were diarrhea (30%), nausea (25%), anemia (22.5%), fatigue (22.5%), constipation (17.5%), dizziness (15%) and dyspnea (15%) [Table 1). One pt with AML had Gr 3 hyperbilirubinemia. There was no evidence of drug-related neutropenia in pts with NHL. No significant cardiovascular AEs were observed. One pt with AML in Cohort I achieved a morphologic leukemia-free state. At 200 mg, 5 of 10 AML pts (50%) had stable disease. Voruciclib pharmacokinetics was dose proportional, mean accumulation ratio was 2.4, mean T max was 4 hours, and at 200 mg, steady state C max was 925 ng/mL and mean C trough was 442 ng/mL (~1 microM). Analysis of Mcl-1 protein expression in normal lymphocytes by flow cytometry showed a trend of decrease in on-treatment samples compared to pre-treatment. Consistent with this, RNA-Seq analysis of 3 paired CLL samples confirmed rapid (after 6 hours) downregulation of Mcl-1 mRNA transcript in the malignant B-cells. Furthermore, scRNA-Seq analysis of 2 longitudinal AML samples demonstrated downregulation of MYC transcriptional program and oxidative phosphorylation in circulating AML blasts, both evident 24 hours after start of voruciclib and ongoing at C1D15. Conclusions: Voruciclib at doses up to 200 mg administered on 14 consecutive days on a 28-day cycle was well tolerated, with no DLTs observed, and no cardiovascular toxicities. There was no significant myelosuppression in pts with B-cell malignancies. As the safety profile suggested non-overlapping toxicities with venetoclax, the study is now evaluating voruciclib in combination with venetoclax in pts with R/R AML to exploit dual inhibition of Bcl-2 and Mcl-1.