The excellent potencies selectivities and improved PK
The excellent potencies, selectivities and improved PK associated with the piperazine class triggered more extensive off-target screenings of the highlighted compounds. A screen of more than 100 enzymes, receptors, and ion channels resulted in activity at the norepinephrine transporter (NET). This modest NET binding activity justified a follow-up to better understand its impact on the series. Therefore, a functional NET reuptake inhibition screening assay was performed.
The results of this assay, documented in , indicate functional activity among the lead compounds in the series. Overall, a notable improvement in NET selectivity was observed with the piperazine tetrazoles relative to other compounds in the series. To better define the relevance of this activity, was evaluated in an rat microdialysis study, depicted in , in which norepinephrine (NE) levels in the sc9 were monitored after oral dosing at 10 and 100mpk. Compound exhibited weak activity of β-AR at 100mpk in rat (EC=4500nM) indicating that any observed increase in NE is not β-AR mediated. The results in illustrate a dose dependent trend with no significant effect at 10mpk and a sustained, ∼2-fold increased efflux of norepinephrine in the medial prefrontal cortex after 1h post-dose at 100mpk. Norepinephrine reuptake inhibitors designed for the treatment of CNS indications such as depression and anxiety generally show a 3–5-fold increase in this model. Unfortunately, the liabilities associated with regard to NE activity in this piperazine class therefore warranted further investigation to identify a new series that is more selective over the NET.
In summary, the piperazine class of benzamides afforded a promising new lead class for further optimization for the treatment of OAB by providing compounds with excellent β-AR potencies, selectivities and PK profiles suitable for QD dosing in humans. However, due to the risk of CNS-mediated effects associated with NET reuptake inhibition, further progression of as well as other compounds in this series was halted. Compound designs leading to enhanced NET selectivity will be described in due course.
The authors thank Drs. Christopher Sinz and Dong-Ming Shen for their helpful comments in the preparation of this manuscript. In addition, we’d like to acknowledge Judy Morris, Regina Black, and Lisa Frey for purification assistance and Alka Bansal, Donna Hreniuk, and Scott Feigner for in vitro assay support.
Introduction The primary source of energy for life is glucose. Glucose is the major energy for all mammalian cells. The human brain consumes approximately 25% of glucose supply however, it represents only about 2% of total body mass of an adult. Neurons need a continuous supply of glucose. Astrocytes produce lactate from anaerobic metabolism of glucose  and from glycogenolysis . Lactate is another source of energy utilized by neuronal cells , . Ketones can also be the source of energy for brain , . In adult brain, the fatty acid transport, the source of ketones, across the blood-brain barrier (BBB) is extremely slow . Therefore, fatty acids do not provide carbon to the Krebs cycle or the precursor for the lactate production  and continuous supply of glucose is required for mammalian brain function. In the case of heart, this organ consumes more energy than any other organ. The heart can utilize various metabolic substrates as a source of energy. The primary substrates are free fatty acids (FFAs), especially long-chain fatty acids (LCFA), and glucose. Glucose generates about 25%–30% of total energy ; therefore oxidation of FFAs is a major metabolic process for myocardial ATP production. In this way, a minimum of 60% of ATP is derived. During anoxic conditions, glucose is the predominant fuel for the heart to maintain ATP production by anaerobic glycolysis . Considerably, lactate can be used in place of glucose if there is lack of exogenous supply, and during long-term starvation ketone bodies can be used . As mentioned above, the source of energy for cardiac muscle depends on substrate availability.