A Phase 2 Open-Label, Multicenter, Dose Optimization Clinical Study of the Safety, Tolerability, and Pharmacokinetic (PK) and Pharmacodynamic (PD) Profiles of Cfi-400945 As a Single Agent or in Combination with Azacitidine or Decitabine in Patients with Acute Myeloid Leukemia, Myelodysplastic Syndrome or Chronic Myelomonocytic Leukemia (TWT-202)

Background: CFI-400945 is a potent, selective, orally administered, first-in-class inhibitor of the serine/threonine kinase, Polo-like kinase 4 (PLK4). PLK4 is a highly conserved master upstream regulator of centriole duplication and is critical for maintenance of genomic integrity. Aberrant expression of PLK4 results in a number of effects including the centrosome amplification often seen in aneuploid cancers, pointing to a potentially causative role for PLK4 in genome instability and cancer progression. A Phase 1 study has been completed evaluating CFI-400945 as a monotherapy in solid tumors, showing a tolerable safety profile and promising signs of activity. Given acute myeloid leukemia (AML) is characterized by genomic instability, CFI-400945 has been evaluated in pre-clinical and clinical studies in AML. In pre-clinical studies, CFI-400945 showed potent activity towards leukemia cell lines and primary human samples in vitro, as well as marked efficacy in two subcutaneous models of leukemia. A prior Phase 1 trial in AML was initiated at the Princess Margaret Cancer Center (PMCC), and of six patients evaluable for response, two (33%) achieved complete remission (CR) at 96 mg and 128 mg, and 3 patients (50%) had stable disease (with one patient having a 78% reduction in marrow blast count) at 64 mg (2 patients) and 96 mg [re: Murphy et al, ASH 2020]. Responses were seen in patients with adverse cytogenetics. The optimal dosing of CFI-400945 and its potential role as a combination agent are not yet clinically defined.

Study Design and Methods: The study (TWT-202) has 4 parts, Part 1A (1A): a single agent dose escalation portion, Part 1B (1B): a food effect portion once the MTD of 1A is determined, and combinations with azacitidine (2A), and decitabine (2B). TWT-202 uses an updated version of investigational product which is identical in formulation to the drug used in the PMCC study, but which may result in higher exposures at a given dose. This study will therefore refine the dose through escalation cohorts. For parts 1A and 1B, patients with relapsed and/or refractory AML, MDS, or CMML after >1 prior therapy will be included. Patients with MDS or CMML must have progressed or had a lack of response after at least 4 cycles of hypomethylating agents. For parts 2A and 2B, patients should have relapsed and/or refractory AML or untreated MDS or CMML. Untreated patients who decline or are ineligible for intensive therapy may be included. The study will use a standard 3 + 3 design. The maximum tolerated dose (MTD) will be defined as the dose level where the number of dose limiting toxicities (DLTs) is <1 out of 6 at highest dose level below the maximally administered dose. Pharmacokinetics (PK) and pharmacodynamic (PD) markers will be assessed.

Results: As of June 21, 2021, 2 patients had been enrolled into the study, one of the patients (50%) received >3 prior therapies (including venetoclax). Neither patient had had stem cell transplant at study entry. Both patients had secondary AML (one with antecedent MDS with excess blasts and the other with CMML). Both patients received 32 mg of CFI-400945 for 21 days followed by a 7-day rest. Both patients completed cycle 1 and neither experienced a DLT. Both patients experienced a single serious treatment emergent adverse event (SAE) of febrile neutropenia each, with neither event considered related to CFI-400945. There were 13 Grade 3 or greater TEAE's, including anemia, thrombocytopenia (3 events each), febrile neutropenia (2 events), agitation, angioinvasive fungal sinusitis, acute kidney injury, hypotension and neutropenia (1 event each). None of the grade 3 or greater TEAE's were considered related to CFI-400945. Neither patient responded to therapy at 32 mg and both came off treatment after one cycle due to progressive disease. PK and PD studies are pending.

Conclusion: CFI-400945 has been generally well tolerated and TWT-202 continues to enroll in the Part 1A and Part 1B monotherapy cohorts. Updated safety, efficacy, PK, and PD data for the study will be presented at the time of the meeting.