Aerosolized pentamidine in HIV. Promising new treatment for Pneumocystis carinii pneumonia

Understanding the characteristics of nonspecific binding of drug-like compounds to canonical stem-loop RNAs and their implications for functional cellular assays

Identifying small molecules that selectively bind an RNA target while discriminating against all other cellular RNAs is an important challenge in RNA-targeted drug discovery. Much effort has been directed toward identifying drug-like small molecules that minimize electrostatic and stacking interactions that lead to nonspecific binding of aminoglycosides and intercalators to many stem-loop RNAs. Many such compounds have been reported to bind RNAs and inhibit their cellular activities. However, target engagement and cellular selectivity assays are not routinely performed, and it is often unclear whether functional activity directly results from specific binding to the target RNA. Here, we examined the propensities of three drug-like compounds, previously shown to bind and inhibit the cellular activities of distinct stem-loop RNAs, to bind and inhibit the cellular activities of two unrelated HIV-1 stem-loop RNAs: the transactivation response element (TAR) and the rev response element stem IIB (RREIIB). All compounds bound TAR and RREIIB in vitro, and two inhibited TAR-dependent transactivation and RRE-dependent viral export in cell-based assays while also exhibiting off-target interactions consistent with nonspecific activity. A survey of X-ray and NMR structures of RNA-small molecule complexes revealed that aminoglycosides and drug-like molecules form hydrogen bonds with functional groups commonly accessible in canonical stem-loop RNA motifs, in contrast to ligands that specifically bind riboswitches. Our results demonstrate that drug-like molecules can nonspecifically bind stem-loop RNAs most likely through hydrogen bonding and electrostatic interactions and reinforce the importance of assaying for off-target interactions and RNA selectivity in vitro and in cells when assessing novel RNA-binders.

Upper lobe pulmonary parenchymal calcification in a patient with AIDS and Pneumocystis carinii pneumonia receiving aerosolized pentamidine

In patients with AIDS-related Pneumocystis carinii infection occurring during aerosolized pentamidine prophylaxis, roentgenographic findings may be atypical. Pulmonary parenchymal calcification due to P carinii is rare. In this case, extensive upper lobe pulmonary parenchymal, splenic, and nodal calcifications occurred after two years of monthly treatments with aerosolized pentamidine.

The evolving challenge of Pneumocystis carinii. A deadly opportunist in AIDS

Considerable progress has been made in the identification and treatment of Pneumocystis carinii pneumonia related to acquired immunodeficiency syndrome (AIDS). Prophylaxis, either primary or secondary, represents a major advance and should be used appropriately by physicians caring for patients infected with human immunodeficiency virus. Yet with success come new challenges. Centers for treatment of AIDS that aggressively use prophylaxis have seen a shift toward severe illness due to other pathogens and generalized wasting. The strategies employed in combating P carinii pneumonia are likely to be tried against other AIDS-related infections.