Feasibility and safety of targeting mitochondria for cancer therapy – preclinical characterization of gamitrinib, a first-in-class, mitochondriaL-targeted small molecule Hsp90 inhibitor

Abstract

Mitochondria are key tumor drivers, but their suitability as a therapeutic target is unknown. Here, we report on the preclinical characterization of Gamitrinib ( GA mit ochondrial ma tri x in h ib itor), a first-in-class anticancer agent that couples the Heat Shock Protein-90 (Hsp90) inhibitor 17-allylamino-geldanamycin (17-AAG) to the mitochondrial-targeting moiety, triphenylphosphonium. Formulated as a stable (≥24 weeks at −20°C) injectable suspension produced by microfluidization (<200 nm particle size), Gamitrinib (>99.5% purity) is heavily bound to plasma proteins (>99%), has intrinsic clearance from liver microsomes of 3.30 mL/min/g and minimally penetrates a Caco-2 intestinal monolayer. Compared to 17-AAG, Gamitrinib has slower clearance (85.6 ± 5.8 mL/min/kg), longer t 1/2 (12.2 ± 1.55 h), mean AUC 0-t of 783.1 ± 71.3 h∙ng/mL, and unique metabolism without generation of 17-AG. Concentrations of Gamitrinib that trigger tumor cell killing (IC 50 ~1-4 µM) do not affect cytochrome P450 isoforms CYP1A2, CYP2A6, CYP2B6, CYP2C8 or ion channel conductance (Nav1.5, Kv4.3/KChIP2, Cav1.2, Kv1.5, KCNQ1/mink, HCN4, Kir2). Twice weekly IV administration of Gamitrinib to Sprague-Dawley rats or beagle dogs for up to 36 d is feasible. At dose levels of up to 5 (rats)- and 12 (dogs)-fold higher than therapeutically effective doses in mice (10 mg/kg), Gamitrinib treatment is unremarkable in dogs with no alterations in clinical-chemistry parameters, heart function, or tissue histology, and causes occasional inflammation at the infusion site and mild elevation of serum urea nitrogen in rats (≥10 mg/kg/dose). Therefore, targeting mitochondria for cancer therapy is feasible and well tolerated. A publicly funded, first-in-human phase I clinical trial of Gamitrinib in patients with advanced cancer is ongoing (ClinicalTrials.gov NCT04827810)

Targeting HSP90 as a Novel Therapy for Cancer: Mechanistic Insights and Translational Relevance

“…Therefore, inhibitors can be rationally designed, specifically for targeting mtHSP90 or eHSP90 [ 44 , 48 , 267 ]. Gamitrinibs are mtHSP90 inhibitors that showed substantial anti-tumor activity with minimal to no side effects, and they have been under clinical evaluation [ 139 , 191 ]. While the selective inhibitors of eHSP90 are still in development, the concept of developing organelle-specific drugs is being tested not only for HSP90 inhibitors, but also for other therapeutics targeting organelle-specific oncoproteins, with the ultimate goal of improving drug activity and minimizing side effects [ 96 ].…”

“…Gamitrinib was accumulated in the mitochondria, which caused a rapid tumor regression due to its “mitochondriotoxic” mechanism of action [ 138 ]. Subsequent studies also showed the substantial anti-tumor activity of gamitrinib both in vitro and in vivo while sparing the normal counterpart [ 139 , 188 , 189 , 190 , 191 ].…”

Structure, Function, and Inhibitors of the Mitochondrial Chaperone TRAP1

“…In contrast to shepherdin ( 18 ) and Ant-GA ( 19 ), gamitrinib ( 20 ) does not significantly inhibit cytoplasmic Hsp90, indicating efficient and immediate mitochondrial accumulation . The preclinical evaluation of gamitrinib ( 20 ) is complete, and a phase I clinical trial is underway to treat advanced cancer. , One of the pitfalls of gamitrinib ( 20 ) is weak TRAP1 binding affinity of the inhibitory moiety geldanamycin ( 1 ). Thus, the geldanamycin moiety in gamitrinib ( 20 ) is replaced to PU-H71 ( 8 ), a smaller and stronger TRAP1 binder, and conjugated with TPP using a C 6 carbon linker to afford SMTIN-P01 ( 21 ). , Although the compound displayed TRAP1-specific activity such as TRAP1 client degradation in a cancer cell without affecting the expression of Hsp90 clients and Hsp70, , the overall drug activity of SMTIN-P01 ( 21 ) is not dramatically elevated compared with gamitrinib in vitro and in vivo because of reduced mitochondrial accumulation …”

“…10 The preclinical evaluation of gamitrinib ( 20) is complete, and a phase I clinical trial is underway to treat advanced cancer. 116,117 One of the pitfalls of gamitrinib ( 20) is weak TRAP1 binding affinity of the inhibitory moiety geldanamycin (1). Thus, the geldanamycin moiety in gamitrinib ( 20) is replaced to PU-H71 ( 8), a smaller and stronger TRAP1 binder, and conjugated with TPP using a C 6 carbon linker to afford SMTIN-P01 (21).…”

Heterocyclic Compounds as Hsp90 Inhibitors: A Perspective on Anticancer Applications

“…Due to the unique effectiveness of Hsp90 inhibitors in cancer therapy, researchers have focused on them in recent decades [ 35 , 36 , 37 , 38 , 39 , 40 , 41 , 42 , 43 , 44 , 45 , 46 , 47 ]. Hsp90 is responsible for the conformational maturation of 500 client protein substrates embracing transcription factors, receptors, kinases, or oncoproteins, which might be overexpressed and/or mutated in most cancers [ 48 ].…”