Potential of RH5 Antisense on Plasmodium falciparum Proliferation Abatement

Background: Infections by Plasmodium falciparum, are becoming increasingly difficult to treat. Therefore, there is an urgent need for novel antimalarial agents’ discovery against infection. In present study, we described a 2’-O-Methyl gapmer phosphorothioate oligonucleotide antisense targeting translation initiation region of 3D7 strain RH5 gene. 
Methods: The study was conducted in Pasteur Institute of Iran in 2020. ODNs effects were measured by microscopic examination and real time RT-PCR. For microscopy, microplates were charged with 2’-OMe ODNs at different dilutions. Unsynchronized parasites were added to a total of 0.4 ml (0.4% parasitemia, 5% red blood cells), and slides were prepared. Proportion of infected cells was measured by counting at least 500 red blood cells. 
Results: RH5 genes start codon regions selected as conserved region besed on alignment results. Gap-RH5-As which was complementary to sequence surrounding AUG RH5 start codon signiﬁcantly reduced parasite growth (>90% at 50 nM) compared to sense sequence control (Gap-RH5-Se) (17%), (P<0.001). RH5 transcripts were dramatically reduced after exposed to ODNs at a concentration of 5-500 nM for 48 h. 
Conclusion: Gemnosis delivery of a chimeric gapmer PS-ODN with 2’-OMe modifications at both sides had high antisense activity at low concentrations (10-100 nM) and shown a good efficiency to reach to target mRNA in human RBCs. Anti-parasite effect was correlated to reduction of target gene mRNA level. In addition, 2’-OMe ODNs free delivery is an effective way and does not need any carrier molecules or particles.