MT-125 is a potent, selective, and central nervous system (CNS) permeable dual small
molecule inhibitor of the non-muscle myosin II (NMII) paralogs, IIA and IIB. MT-125 is
being developed by Myosin Therapeutics Inc. as a potential treatment for glioblastoma
(GBM). NMIIs are molecular motor ATPases that act directly on actin to regulate the
cytoskeleton's control of cellular processes such as movement, division, signaling and
mitochondrial biology. As a result, simultaneous inhibition of NMIIA and IIB with MT-125
interferes with tumor cell proliferation, invasion and metastasis, while also generating
reactive oxygen species (ROS) in tumor cells. The latter is due to the role of NMII in
mitochondrial quality control and underlies the synergistic survival benefit observed in
preclinical studies when MT-125 and radiation therapy (RT) are combined. Additionally,
NMIIA is upregulated in several types of cancer, including GBM, speaking to its
importance in cancer physiology and making these tumor cells highly sensitive to its
inhibition. The focus of this first-in-human (FIH) clinical study is GBM.
Patients with GBM have a poor prognosis, and there have been no new Food and Drug
Administration (FDA) approved drugs for these patients since 2008, when bevacizumab was
approved. The current well-known standard of care for newly diagnosed GBM is maximal safe
surgical resection followed by concurrent RT with temozolomide (TMZ). O6-methylguanine-
DNA methyltransferase (MGMT) promoter methylation status is the most predictive biomarker
for TMZ responsiveness, where patients with unmethylated MGMT do not respond to TMZ.
There is, therefore, an urgent unmet need for effective systemic therapy in patients with
unmethylated MGMT.
MT-125 significantly prolongs survival as a monotherapy in animal models and is
synergistic with both RT and with FDA-approved oncogenic kinase inhibitors to further
enhance survival. In order to develop highly effective combinations of MT-125 with other
pharmacologic therapies, we will start with an evaluation of MT-125 as a monotherapy in a
first-in-human (FIH) Phase 1 trial with RT in newly diagnosed isocitrate dehydrogenase
(IDH) wild type / MGMT unmethylated GBM. In the pivotal 28-day nonclinical safety
studies, no dose-limiting toxicities (DLT) or adverse effects (AE) were noted in any of
the parameters evaluated (clinical observations, functional endpoints, clinical
pathology, macroscopic and histologic tissue assessments) at doses up to the NOAELs, 20
mg/kg/day and 30 mg/kg/day in dogs and rats, respectively, which yielded systemic MT-125
exposures 10- to 16-fold greater than efficacious exposures in pharmacodynamic in vivo
models. As the NOAELs in both studies were below the STD10 (rats) and HNSTD (dogs), the
calculated safety margins are conservative. Here we will perform a FIH monotherapy trial
in newly diagnosed IDH wild type/ MGMT unmethylated GBM with RT.
The goal of this FIH, Phase 1, single arm MT-125 dose escalation study is to evaluate the
safety and tolerability of MT-125 administered 5 consecutive days per week with 2 days
off for the 6 weeks of outpatient RT. Participants with newly diagnosed GBM with
histologically or molecularly confirmed IDH wild type and MGMT unmethylated will be
eligible to enroll. We have chosen this subpopulation of patients, as they do not
historically benefit from TMZ therapy, which justifies not including treatment with this
alkylator in the clinical trial. The DLT observation window will be 6 weeks following
first treatment administration, and a Bayesian Optimal Interval (BOIN) trial design will
be used to efficiently evaluate up to four dose levels. Secondary endpoints for this
Phase 1 study will include determining the maximum tolerated dose (MTD), which will
contribute to the selection of the recommended phase 2 dose (RP2D) and evaluating the
systemic pharmacokinetics (PK) of MT-125.
Once the MTD is determined, additional participants will be enrolled into a randomized,
parallel dose expansion cohort, consisting of up to 2 potential doses of MT-125. The dose
levels for the expansion cohort will be selected as the MTD and the dose below the MTD.
Overall response rate (ORR) in those participants with measurable disease,
progression-free survival (PFS6) in all participants, and Overall Survival (OS) in all
participants are included as exploratory endpoints.
If no MTD is identified within the initially defined dose range and all tested doses are
deemed well-tolerated based on the observed DLTs, the study may be paused temporarily to
allow consideration of dose levels beyond those originally planned.