Vaccine development for the blood stages of malaria has focused on the induction of antibodies to parasite surface antigens, most of which are highly polymorphic. An alternate strategy has evolved from observations that low-density infections can induce antibody-independent immunity to different strains. To test this strategy, we treated parasitized red blood cells from the rodent parasite Plasmodium chabaudi with secocyclopropyl pyrrolo indole analogs. These drugs irreversibly alkylate parasite DNA, blocking their ability to replicate. After administration in mice, DNA from the vaccine could be detected in the blood for over 110 days and a single vaccination induced profound immunity to different malaria parasite species. Immunity was mediated by CD4 + T cells and was dependent on the red blood cell membrane remaining intact. The human parasite, Plasmodium falciparum, could also be attenuated by treatment with seco-cyclopropyl pyrrolo indole analogs. These data demonstrate that vaccination with chemically attenuated parasites induces protective immunity and provide a compelling rationale for testing a blood-stage parasite-based vaccine targeting human Plasmodium species.

The rise of bacterial antibiotic resistance coupled with a reduction in new antibiotic development has placed significant burdens on global health care. Resistant bacterial pathogens such as methicillin-resistant Staphylococcus aureus and vancomycin-resistant Enterococcus are leading causes of community- and hospital-acquired infection and present a significant clinical challenge. These pathogens have acquired resistance to broad classes of antimicrobials. Furthermore, Streptococcus pyogenes, a significant disease agent among Indigenous Australians, has now acquired resistance to several antibiotic classes. With a rise in antibiotic resistance and reduction in new antibiotic discovery, it is imperative to investigate alternative therapeutic regimens that complement the use of current antibiotic treatment strategies. As stated by the WHO Director-General, “On current trends, common diseases may become untreatable. Doctors facing patients will have to say, Sorry, there is nothing I can do for you.”

Human parainfluenza viruses (hPIVs) cause upper and lower respiratory tract disease in children that results in a significant number of hospitalizations and impacts health systems worldwide. To date, neither antiviral drugs nor vaccines are approved for clinical use against parainfluenza virus, which reinforces the urgent need for new therapeutic discovery strategies. Here we use a multidisciplinary approach to develop potent inhibitors that target a structural feature within the hPIV type 3 haemagglutinin-neuraminidase (hPIV-3 HN). These dual-acting designer inhibitors represent the most potent designer compounds and efficiently block both hPIV cell entry and virion progeny release. We also define the binding mode of these inhibitors in the presence of whole-inactivated hPIV and recombinantly expressed hPIV-3 HN by Saturation Transfer Difference NMR spectroscopy. Collectively, our study provides an antiviral preclinical candidate and a new direction towards the discovery of potential anti-parainfluenza drugs.

Human parainfluenza virus type 1 is the major cause of croup in infants and young children. There is currently neither vaccine nor clinically effective treatment for parainfluenza virus infection. Hemagglutinin-neuraminidase glycoprotein is a key protein in viral infection, and its inhibition has been a target for 2-deoxy-2,3-didehydro-d-N-acetylneuraminic acid (Neu5Ac2en)-based inhibitor development. In this study, we explore the effect of C-5 modifications on the potency of Neu5Ac2en derivatives that target the human parainfluenza type-1 hemagglutinin-neuraminidase protein. Our study demonstrates that the replacement of the Neu5Ac2en C-5 acetamido moiety with more hydrophobic alkane-based moieties improves the inhibitory potency for both hemagglutinin-neuraminidase functions. These findings shed light on the importance of C-5 substitution on Neu5Ac2en in the design of novel sialic acid-based inhibitors that target human parainfluenza type-1 hemagglutinin-neuraminidase.

Human parainfluenza virus type 3 (hPIV-3) is one of the leading causes for lower respiratory tract disease in children, with neither an approved antiviral drug nor vaccine available to date. Understanding the catalytic mechanism of human parainfluenza virus haemagglutinin-neuraminidase (HN) protein is key to the design of specific inhibitors against this virus. Herein, we used (1) H NMR spectroscopy, X-ray crystallography, and virological assays to study the catalytic mechanism of the HN enzyme activity and have identified the conserved Tyr530 as a key amino acid involved in catalysis. A novel 2,3-difluorosialic acid derivative showed prolonged enzyme inhibition and was found to react and form a covalent bond with Tyr530. Furthermore, the novel derivative exhibited enhanced potency in virus blockade assays relative to its Neu2en analogue. These outcomes open the door for a new generation of potent inhibitors against hPIV-3 HN.