Evaluation of Indolocarbazoles from Streptomyces sanyensis as a Novel Source of Therapeutic Agents against the Brain-Eating Amoeba Naegleria fowleri

Abstract

Naegleria fowleri is an opportunistic pathogenic free-living amoeba which is able to rapidly colonize the central nervous system (CNS) and causes a lethal infection known as primary amoebic meningoencephalitis (PAM). Furthermore, more than 98% of the known cases of PAM are fatal and affect mainly children under 12 and young adults. Until now, no fully effective therapeutic agents against N. fowleri are available and hence the urgent need to find novel agents to treat PAM. At present, PAM therapy is based on the combination of amphotericin B, miltefosine, among others, with unwanted toxic effects. Recently, our team isolated various indolocarbazoles (ICZs) from the culture of a mangrove strain of Streptomyces sanyensis which showed activity against kinetoplastids and the Acanthamoeba genus. Hence, in this study, the activity of the previously isolated ICZs, staurosporine (STS), 7-oxostaurosporine (7OSTS), 4′-demethylamino-4′-oxostaurosporine, and streptocarbazole B, was evaluated against two type strains of N. fowleri. Furthermore, the performed activity assays revealed that STS was the most active ICZ presenting an inhibitory concentration 50 (IC50) of 0.08 ± 0.02 µM (SI 109.3). Moreover, STS induced programmed cell death (PCD) in the treated amoebae by triggering DNA condensation, mitochondrial disfunction, cell membrane disruption, and reactive oxygen species (ROS) generation. Therefore, STS could be a promising therapeutic agent against PAM.

The therapeutic potential of novel isobenzofuranones against Naegleria fowleri

“…In previous works of our group, PCD process in Naegleria fowleri was evaluated after detection of specific metabolic events such as DNA condensation, plasmatic membrane and mitochondrial membrane damage, collapse of ATP levels and intracellular ROS generation(A. Rizo-Liendo et al, 2020 ; Zeouk et al, 2020 ). The isobenzofuranones selected in this study were able to induce all the metabolic events mentioned above hence showing signs of PCD induction (early apoptosis) leading to a safer therapy if used in the near future.…”

“…The isobenzofuranones selected in this study were able to induce all the metabolic events mentioned above hence showing signs of PCD induction (early apoptosis) leading to a safer therapy if used in the near future. In addition, cell death induction by necrosis could cause undesired inflammation processes in the patient whereas PCD (apoptosis) events do not induce inflammation ( Rizo-Liendo et al, 2020 ).…”

“…In addition, with the absence of specific PAM therapy protocols the treatment of patients becomes an arduous challenge. Currently the experimental therapy options involve Amphotericin B (Amp B) and Miltefosine, alone or in combination with other drugs (rifampin, azithromycin or azoles) or with hypothermia, reporting successful results in PAM cases ( Grace et al, 2015 ; Heggie and Küpper, 2017 ; Aitor Rizo-Liendo et al, 2020b ), but also showing, undesired toxic side effects, such as in patients treated with Amp B that showed nephrotoxicity, anaemia or even brain damage ( Laniado-Laborín and Cabrales-Vargas, 2009 ; Rizo-Liendo et al, 2019 ). Consequently, there is a correlation between the high mortality rate data with the late diagnosis and the non-specific treatment ( Cope and Ali, 2016 ).…”

Primary Amoebic Meningoencephalitis by Naegleria fowleri: Pathogenesis and Treatments

“…It has been suggested that its amoebicidal activity occurs by inhibiting the amoeba’s protein kinase (PK) and inducing an apoptosis-like mechanism via the mitochondrial pathway, but, more studies are required to confirm the mechanism of action. The natural compound demonstrated a half-maximum inhibitory concentration (IC 50 ) value of 0.08 µM for two different N. fowleri strains and showed lower levels of cell cytotoxicity against murine macrophage J774A.1 than MLT [ 71 ].…”

Whole-genome sequence of bioactive streptomycete derived from mangrove forest in Malaysia, Streptomyces sp. MUSC 14

“…Gifted with the ability to form spores, streptomycetes are ubiquitous in nature and produce a diverse array of secondary metabolites that can be exploited for the benefit of humanity [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16] . One of the significant breakthroughs in streptomycetes research is the discovery of streptomycin (from the soil bacterium, Streptomyces griseus) by Professor Waksman and his teamwhich subsequently led him to the Nobel Award in Medicine later in 1960 [13,[17][18][19][20][21] .…”