High-throughput Screening and Sensitized Bacteria Identify an M. tuberculosis Dihydrofolate Reductase Inhibitor with Whole Cell Activity

Mycobacterium tuberculosis (Mtb), the causative agent of tuberculosis, is a bacterial pathogen that claims roughly 1.4 million lives every year. Current drug regimens are inefficient at clearing infection, requiring at least 6 months of chemotherapy, and resistance to existing agents is rising. There is an urgent need for new drugs that are more effective and faster acting. The folate pathway has been successfully targeted in other pathogens and diseases, but has not yielded a lead drug against tuberculosis. We developed a high-throughput screening assay against Mtb dihydrofolate reductase (DHFR), a critical enzyme in the folate pathway, and screened a library consisting of 32,000 synthetic and natural product-derived compounds. One potent inhibitor containing a quinazoline ring was identified. This compound was active against the wild-type laboratory strain H37Rv (MIC99 = 207 µM). In addition, an Mtb strain with artificially lowered DHFR levels showed increased sensitivity to this compound (MIC99 = 70.7 µM), supporting that the inhibition was target-specific. Our results demonstrate the potential to identify Mtb DHFR inhibitors with activity against whole cells, and indicate the power of using a recombinant strain of Mtb expressing lower levels of DHFR to facilitate the discovery of antimycobacterial agents. With these new tools, we highlight the folate pathway as a potential target for new drugs to combat the tuberculosis epidemic

Trigeminal Neuralgia

Trigeminal Neuralgia (TN) is the most common cranio-facial pain syndrome, with an incidence of up to 5 in 100,000. Long-term medical treatment is commonly required, with up to 10% of cases suffering adverse drug-related events. In 1951, Lars Leksell pioneered the application of stereotactic irradiation for the treatment of TN, which may now achieve up to 90% pain control at 1 year and 60% at 3-5 years. Radiosurgical treatment targets either the nerve\u2019s emergence (the root entry zone) or the retrogasserian portion of the nerve (pars triangularis). Targeting the latter may reduce the risk of complications, but requires a higher maximum dose to obtain optimal results. Generally speaking, radiosurgical treatment achieves optimal results in patients receiving high doses of radiations ranging from 70 to 90 Gy. Hypoesthesia and facial numbness are frequently observed after high-dose trigeminal irradiation. Mild hypoesthesia is acceptable and is considered by many an efficacy endpoint of the procedure. Bothersome facial numbness is relatively rare. Sensitive trigeminal disturbances and paresthesia after treatment have been reported to range respectively 6%\u201354% and 0%\u201317%. The prescribed dose and brainstem-delivered dose are correlated with the subsequent rate of sensitive trigeminal disturbances. CyberKnife frameless non-isocentric radiosurgery is an emerging and non-invasive treatment for TN. Because of the non-isocentric geometry of radiation beams delivery, CyberKnife technique offers the possibility of homogeneous irradiation of an extended segment of the trigeminal nerve, so introducing some new concepts for the radiosurgical treatment of TN. Clinical results of CyberKnife radiosurgery seems to be satisfactory. We here review the basics of radiosurgery for TN and present a detailed analysis of the technique using the CyberKnife frameless system