Vol.:(0123456789) 1 3 International Journal of Peptide Research and Therapeutics https://doi.org/10.1007/s10989-018-9715-8 Analogues of Human Granulysin as Antimycobacterial Agents Alvaro Siano 1,2  · Georgina Tonarelli 1  · Daniel Larpin 1  · María Susana Imaz 3  · Claudia Alvarez 3  · Elsa Zerbini 1,3 Accepted: 4 May 2018 © Springer Science+Business Media, LLC, part of Springer Nature 2018 Abstract Antimicrobial peptides are essential components of innate defense mechanisms and make promising candidates for novel anti-infective agents. The advantages of these peptides in clinical applications include their potential for broad-spectrum and rapid bactericidal activities, and low propensity for resistance development, whereas possible disadvantages include their high cost, limited stability, and unknown toxicology and pharmacokinetics. Granulysin (Gr) is a cytolytic and proin- fammatory molecule expressed by activated human cytotoxic T lymphocytes and natural killer (NK) cells. This paper aims to study bacteriostatic and bactericidal activity against Mycobacterium tuberculosis by synthetic analogues of human Gr between 12 and 26 amino acids (AA) and their acyl derivatives. Considering results of previous studies, fve new peptides were designed: a cyclic of 20 AA (Gr-SL1); one of 21 AA (linear) (Gr-SL2), another of 12 AA (cyclic) (Gr-SL3) and two lipopeptides (Gr-SL3-lauric and Gr-SL3-palmitic). Peptides were manually synthesized as C-terminal carboxamides by the solid-phase method following Fmoc chemistry. Gr synthetic analogues were purifed by reverse phase HPLC and analyzed by analytical C18RP-HPLC and Maldi Tof. The antimycobacterial activity of synthesized Gr analogues was assessed using a microdilution susceptibility test as described previously. Although peptides studied here had neither higher antimycobacte- rial activity nor lower toxicity than analogs of human Gr previously evaluated, fresh knowledge concerning the infuence of acylation and structural aspects analyzed will optimize the design of novel peptides combining the most favorable aspects for the maintenance of antimycobacterial activity with minimum toxicity. Keywords Antimicrobial peptides · Granulysin · Mycobacterium tuberculosis · Acyl derivatives Introduction The evolving public health threat of antimicrobial resist- ance is driven by both appropiate and inappropiate use of anti-infective medicines for human and animal health and food production, and inadequate measures to control the spread of infections. One of the WHO global strategies for the containment of antimicrobial resistance is to encourage development of appropiate new drugs and vaccines (WHO 2012). Antimicrobial peptides (AMPs) are essential com- ponents of innate defense mechanisms and make promis- ing candidates for novel anti-infective agents. Experiments have revealed that small changes in the primary structure of a peptide may lead to drastic changes in its specifcity and activity (Zhao et al. 2013). Other authors observed that features of the sequence of longer peptides contribute to the predictability of peptide bioactivity, whereas in shorter pep- tides the predictive power is more dominated by amino acid (AA) composition (Mooney et al. 2012). The toxicity of AMPs against eukaryotic cells is the key obstacle for their clinical application. Numerous studies have been performed to optimize their potentials for these appli- cations, i.e., to improve antimicrobial activity and reduce the toxicity against normal human cells (Pag et al. 2004; Wang et al. 2009; Huang et al. 2010). The advantages of these peptides in clinical applications include their potential for broad-spectrum and rapid bacte- ricidal activities, and low propensity for resistance devel- opment, whereas possible disadvantages include their high * Elsa Zerbini elsazerbini@arnet.com.ar; ezerbini@anlis.gov.ar 1 Departamento de Química Orgánica, Facultad de Bioquímica y Ciencias Biológicas, Universidad Nacional del Litoral, Santa Fe, Argentina 2 Consejo Nacional de Investigaciones Científcas y Técnicas (CONICET), Buenos Aires, Argentina 3 Instituto Nacional de Enfermedades Respiratorias “Dr. Emilio Coni”, Administración Nacional de Laboratorios e Institutos de Salud “Dr. Carlos Malbrán”, Santa Fe, Argentina