On June 29, 2018 Aptose Biosciences Inc. (NASDAQ:APTO) (TSX:APS) reported that the U.S. Food and Drug Administration (FDA) has notified the company that it has lifted the clinical hold on APTO-253, Aptose’s investigational drug for hematologic cancers (Press release, Aptose Biosciences, JUN 29, 2018, View Source;p=RssLanding&cat=news&id=2356603 [SID1234527515]). APTO-253 is the only known clinical-stage molecule that has the potential to directly inhibit expression of the MYC oncogene, shown to be a causative factor in many malignancies, including acute myeloid leukemia (AML).

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Up to fifteen clinical centers are expected to participate in the Phase 1b trial, and the screening and dosing will resume as soon as practicable for patients with relapsed or refractory AML or with high risk myelodysplastic syndromes (MDS). Recent data also highlight the role of MYC gene dysregulation in B-cell malignancies1, and Aptose hopes to pursue this patient population in the coming months.

The Phase 1b trial of APTO-253 had been placed on clinical hold as a consequence of an event that occurred at a clinical site with the infusion procedure. Ultimately, a root cause investigation determined that the event resulted from chemistry and manufacturing based issues, all of which were incorporated into a Chemistry, Manufacturing and Control (CMC) amendment to the Investigational New Drug (IND) application.

"We are eager to return APTO-253 back into the clinic," said William G. Rice, Ph.D., Chairman, President and Chief Executive Officer. "Our understanding of this molecule has evolved dramatically, and we are excited to deliver a MYC gene expression inhibitor to patients with debilitating hematologic malignancies."

About the Study

The Phase 1b, multicenter, open-label, dose-escalation clinical trial of APTO-253 is designed to assess the safety, tolerability, pharmacokinetics and pharmacodynamic responses and efficacy of APTO-253 as a single agent and determine the recommended Phase 2 dose. APTO-253 will be administered once weekly, over a 28-day cycle. The dose escalation cohort of the study could potentially enroll up to 20 patients with relapsed or refractory acute myeloid leukemia (AML) or high-risk myelodysplastic syndromes (MDS). The study is designed to then transition, as appropriate, to single-agent expansion cohorts in AML and MDS.

MYC dysregulation is a common driver in many malignancies, making it an attractive therapeutic target. Repression of MYC expression by bromodomain (BET) inhibitors has proven effective at triggering apoptosis in leukemia cells; however, inhibition of bromodomain proteins can cause severe toxicities and myelosuppression due to the presence of bromodomain proteins on all active genes. Unlike BET inhibitors and other cancer chemotherapies, APTO-253 acts through a distinct targeted mechanism. As a first in class, small molecule MYC inhibitor, APTO-253 may be particularly appropriate for the management of patients having AML and other hematologic malignancies with compromised bone marrow function. Earlier this month, Aptose announced the publication of preclinical data further elucidating the mechanism of action of APTO-253 (here).

About APTO-253

APTO-253 is a clinical-stage small molecule targeted therapeutic agent that inhibits expression of the MYC oncogene, leading to cell cycle arrest and programmed cell death (apoptosis) in human-derived solid tumor and hematologic cancer cells. The MYC oncogene is overexpressed in hematologic cancers, including acute myeloid leukemia (AML). Aptose researchers have reported the ability of APTO-253 to induce cell death, or apoptosis, in multiple blood cancer cell lines including AML, as well as in vitro synergy with various classes of conventional approved and investigational therapies for AML or myelodysplastic syndromes (MDS). New findings reveal that APTO-253 might also serve certain solid tumor patients with BRCA1/2 mutations, but without causing toxicity to the normal bone marrow functions.