Mechanism of Action

●    As an inhibitor of SGLT2, tofogliflozin selectively inhibited human SGLT2 (Ki = 2.9 nM, IC₅₀ = 2.9 nM, selectivity for SGLT1: 2069 fold) in kidneys, which resulted in decrease of renal glucose reabsorption, thereby increasing urinary glucose excretion (UGE) and lowering plasma glucose in type 2 diabetes patients.

●    The metabolites had a pharmacological profile similar to tofogliflozin on inhibiting SGLT2 with less potent (M6, IC₅₀ = 4.6 nM; M4, IC₅₀ = 4.9 nM; M5, IC₅₀ = 16 nM).

●    Tofogliflozin showed no binding inhibition activity at 10 μM in a penal of receptors or ion channels, except SGLT2 and the secondary hydroide epimer 2 (64%).^[8]

In Vivo Efficacy

●    Increased urinary glucose excretion (UGE):

v    db/db diabetic mice: MED = 0.005%.

v    ZDF diabetic rats: MED = 3 mg/kg.

v    DIO non-diabetic rats: Increased UGE at 0.05%.

v    SD non-diabetic rats: MED = 1 mg/kg for AUC_0-6.

●    Decreased blood glucose concentration and blood glucose AUC:

v    db/db diabetic mice:

Ø    Dose-dependently reduced the level and AUC_0-12h of blood glucose at ≥0.1 mg/kg.

Ø    In OGTT: Dose-dependently reduced glucose concentration and blood glucose AUC_0-4h at ≥3 mg/kg.

v    ZDF diabetic rats: Dose-dependently reduced the level and AUC_0-12 of blood glucose at ≥0.1 mg/kg.

v    Wistar non-diabetic rats：No significant difference at 24 h.

v    GK non-fatty diabetic rats: Significant reduced glucose concentration and blood glucose AUC_0-4 at ≥1 mg/kg.

v    KKAy diabetic with obesity mice: Decreased plasma glucose level at 0.015% in diets.

●    Increased insulin levels at 3 mg/kg in db/db diabetic mice.

●    Attenuated body weight gain: At 0.05% in diets in DIO non-diabetic rats and at 0.015% in KKAy mice.

Absorption of Tofogliflozin

●    Had high oral bioavailabilities in rats (75%), monkeys (58.6%) and humans (97.5%).

●    Was absorbed rapidly (T_max = 0.75-1.92 h) in rats, monkeys and humans.

●    Showed half-life of 5.02 h in monkeys, longer than that in humans (4.65 h) and rats (1.15 h), after intravenous administration.

●    Had moderate clearances in rats (19.4 mL/kg/min) and humans (9.96 L/h), but low in monkeys (3.65 mL/kg/min), compared to liver blood flow, after intravenous administration.

●    Exhibited extensive tissue distribution in rats, monkeys and humans, with apparent volumes of distribution at 1.15, 0.919 L/kg and 50.6 L, after intravenous administration.

Distribution of Tofogliflozin

●    Exhibited moderate plasma protein bindings in mice (77.3%-78.2%), rats (83.0%-83.8%), monkeys (76.2%-76.9%) and humans (82.3%-82.6%).

●    Had a blood cell association of 24.8%-29.1% in humans.

●    SD and Long-Evans male rats following a single oral administration:

v    The drug was rapidly and well distributed into most tissues including the central nervous system since the blood-brain barrier.

v    Relatively higher concentration levels were observed in liver, kidneys, stomach, small intestine and adrenal gland.  The lowest concentration levels were observed in cerebrum.

v    The radioactivity elimination was completed at 168 h post-dose.

Metabolite of Tofogliflozin

●    The major metabolites were M2, M3 (CH5098293, hydroxide) and M5 (CH5098291, ketone) in rat plasma.  The parent drug and the two major metabolites accounted for 80%-100% of the total radioactivity in rat plasma, kidneys, liver, urine and feces.

●    The major metabolite in human plasma was M1 (CH5234447, carboxylic metabolite).

●    CYP 2C18, 4A11 and 4F3B were found to be primarily responsible for the first hydroxylated metabolite (M4).  CYP 2C18, 3A4 and 3A5 were responsible for secondary hydroxylated metabolite (M2, M3) and ADH for the carboxylic metabolite (M1).

Excretion of Tofogliflozin

●    Was predominantly eliminated in urine in humans, with M1 as the significant component in human urine.

●    Urinary and feces excretion were 44.6% and 52.7% respectively, and the total excretion was 97.4% after administration 168 h in rats.

●    Biliary excretion generally accounted for 28.2% of the balance of drug equivalents in monkeys.

Drug-Drug Interaction

●    Tofogliflozin didn’t inhibit major human CYP450 enzymes at the expected human dose.  The carboxylic metabolite showed the limited potential to inhibit CYP2C19 (IC₅₀ = 27.1 μM).  Tofogliflozin didn’t induce CYP450 enzymes (CYP1A2, CYP3A4 and CYP2B6).

●    Tofogliflozin was a substrate of P-gp but not the inhibitor of it.  M1 was not the substrate or inhibitor of P-gp.

●    Tofogliflozin was not a substrate of transporters OCT2, OAT1, OAT3, OATP1B1 or OATP1B3.

●    Tofogliflozin and M1 were not the inhibitors of OCT2, OAT1 or OAT1B1.

Single-Dose Toxicity

●    Acute toxicity by the oral route in rodents:

v    Rat ALD: 1000 mg/kg.

Repeated-Dose Toxicity

●    Sub- and chronic toxicity for up to 3 months in mice, 6 months in rats and 12 months in monkeys:

v    By the longest studies employed, the average exposure at NOAELs was approximate 5-7 fold in mice, 2-4 fold in rats, and 36-fold in monkeys, respectively, when compared to that of RHD (20 mg/day).

v    Most lethality derived from the pharmacology of tofogliflozin, i.e., promotion of glaucous excretion and reduction of energy supply in turn.  Meanwhile, increases of AST, ALT, BUN and T-KB reflected enhancement of gluconeogenesis, protein catabolism and lipid metabolism, which was consistent with the pathological finding of elevated glycogen in liver cells.^[8]

v    As kidneys were the major pharmaceutical target organ, renal lesions were verified, e.g., mineral deposition in the renal cortex and medulla, and proliferation of renal tubular epithelium.  Other toxicities, such as increase in trabecular (femur and sternum) and reduction of RBCs, were considered species-specific.

Safety Pharmacology

●    Safety pharmacology was illustrated by core battery of studies on tofogliflozin, as well as M2, M3 (CH5098293, hydroxide) and M1 (CH5234447, carboxylic), which raised no concern on CNS, CVS and RS.

Genotoxicity

●    Tofogliflozin, and its primary human metabolite M1, got least potential for genotoxicity, based on the negative results in the standard battery of in vitro/in vivo mutagenicity and clastogenicity studies.

Reproductive and Developmental Toxicity

●    Fertility and early embryonic development in rats:

v    NOAELs were 320 mg/kg/day for fertility and early embryonic development.

●    Embryo-fetal development in rats and rabbits:

v    Maternal (malnutrition, premature delivery and abortion) and fetal (slight developmental retardation and anomalies) effects occurred at HD in both species, which is considered to be hypoglycaemia-mediated.  NOAELs for embryo-fetal development and dams were 80 and 60 mg/kg/day in rats and rabbits, respectively, approximately 50-fold clinical exposure.

●    Pre- and postnatal development in rats:

v    Similar effects to EFD studies occurred in F0 dams and F1 fetus, but no effects emerged on F1 physiological behavior and sexual maturity.  NOAEL was 200 and 80 mg/kg/day for maternal and offspring, respectively.

●    Tofogliflozin distributed to fetal tissues in pregnant rat, including membrane, fetus, brain, liver, kidney, gastrointestinal tract, the ratio of concentration relative to plasma was below 5.48.^[8]

●    Milk excretion of tofogliflozin was also found in lactating rats and excretion ration was: milk/plasma = 0.28~1.84.^[8]

Carcinogenicity

●    For mice, NOAELs were 11× and 38 × MRHD for male and female respectively.

●    For rats, NOAELs were 37× and 76 × MRHD for male and female respectively.

●    No increase in incidence of neoplasm.