Poster Presentation First Malaria World Congress 2018

Development of novel defence peptides from human platelet factor 4 that kill Plasmodium by selective membrane disruption (#345)

Brendan J McMorran 1 , Nicole Lawrence 2 , Adelaide Denis 3 , Adele Lehane 3 , Anna Ehmann 1 , Peta Harvey 2 , Aurélie Benfield 2 , Olivier Cheneval 2 , Sónia Troeira Henriques 2 , David Craik 2
  1. The John Curtin School of Medical Research, The Australian National University, Canberra, ACT, Australia
  2. Institute for Molecular Bioscience, University of Queensland, Brisbane, QLD, Australia
  3. Research School of Biology, The Australian National University, Canberra, ACT, Australia

We have reported that platelets can interact specifically with infected RBCs (iRBCs) and kill Plasmodium (1). Platelets release an anti-plasmodial agent called platelet factor 4 (PF4), a cytotoxic host-defence protein that enters iRBCs via interaction with erythrocyte Duffy antigen chemokine receptor (DARC) (2), where it then disrupts the parasite digestive vacuole (DV) membrane (3). Despite this desirable activity, PF4 is a poor antimalarial drug lead because it has a chemokine sequence that induces immunotoxic side-effects at high doses (4), and its activity is dependent on DARC, and so is ineffective in people with suppressed DARC expression. Early attempts to remove the undesired chemokine and DARC-dependent functions, while retaining anti-plasmodial activity of PF4, resulted in peptides with poor potency (3).

Using a new approach, we engineered a novel peptide containing the isolated anti-plasmodial domain of PF4, which through cyclization retained the critical structure of the parent protein. The peptide, called cPF4PD (cyclic PF4 peptide dimer) has an anti-plasmodial potency similar to PF4, but it lacks
 chemokine functions and does not require DARC. A comprehensive characterisation of the parasite killing mechanism revealed several unique biophysical and biological properties, including: i)
 stability in human serum; ii) selective targeting and accumulation within iRBCs; iii) ability to cross host and parasite cell membranes without lysis; iv) killing of
 intracellular parasites by disruption of the DV
 membrane. This selective and completely novel activity against Plasmodium was accounted by observations of the peptide’s specific binding to and penetration of membranes with exposed negatively-charged phospholipid headgroups.

As well as demonstrating a promising example of a novel anti-plasmodial molecule based on a human host defence protein, our findings indicate the potential of cPF4PD as a novel cell-penetrating scaffold for delivering bioactive cargoes to inhibit intracellular Plasmodium-specific proteins critical for parasite survival.

  1. McMorran BJ, Marshall VM, de Graaf C, Drysdale KE, Shabbar M, et al. Platelets kill intraerythrocytic malarial parasites and mediate survival to infection. Science 2009, 323, 797-800.
  2. McMorran BJ, Wieczorski L, Drysdale KE, Chan JA, Huang HM, et al. Platelet factor 4 and Duffy antigen required for platelet killing of Plasmodium falciparum. Science 2012, 338, 1348- 1351.
  3. Love MS, Millholland MG, Mishra S, Kulkarni S, Freeman KB, et al. Platelet factor 4 activity against P. falciparum and its translation to nonpeptidic mimics as antimalarials. Cell Host Microbe 2012, 12, 815-823.
  4. Srivastava K, Field DJ, Aggrey A, Yamakuchi M, Morrell CN. Platelet factor 4 regulation of monocyte KLF4 in experimental cerebral malaria. PLoS ONE 2010, 5, e10413.