|Ph.D Student||Atia-Glikin Dana|
|Subject||Structure-Activity-Toxicity Relationship Study of Novel|
Semi-Synthetic Aminoglycosides: Towards
Development of New Drug for the
|Department||Department of Biotechnology||Supervisor||Professor Timor Baasov|
|Full Thesis text|
Aminoglycosides are highly potent, broad-spectrum antibiotics that exert their antibacterial activity by selectively targeting the decoding A-site of the bacterial ribosome, leading to aberrant protein synthesis. Recent studies suggested that aminoglycosides activity is not limited to the bacterial ribosome; several natural aminoglycosides such as gentamicin and G418 can bind to the eukaryotic ribosome and interfere with the translation process. Those studies have highlighted aminoglycosides as promising therapeutic agents to treat human genetic disorders caused by nonsense mutations. Approximately 11% of the total single gene mutations have been identified as nonsense mutations, which account to more than 1,800 of inherited human diseases, including cystic fibrosis, Duchenne muscular dystrophy, Hurler syndrome, and more. Most of these disorders have no effective treatment to date. One potential approach considers the use of small molecule drugs to selectively suppress the normal proofreading function at the mutated stop codon but not at the normal termination codon. This approach, also called “translational readthrough”, was first validated with aminoglycoside antibiotics. However, the use of aminoglycosides for this purpose is highly restricted due to their severe side effects, especially nephrotoxicity and ototoxicity, along with their reduced readthrough efficiency at subtoxic doses.
Our main objective is to design and synthesize novel aminoglycoside-based structures with improved readthrough activity and reduced toxicity. Recently, two novel pseudo-trisaccharides derivatives were systematically developed in our lab, namely NB30 and NB54; they represent our 1st and 2nd generations of paromamine-based structures, which exhibit relatively high suppression potency and reduced toxicity in comparison to gentamicin and paromomycin. Based on these findings, we have continued the systematic fine-tuning of the developed leads in order to further improve their properties. In the present work, additional new generations of improved aminoglycoside-based readthrough inducers with reduced toxicity were discovered; the new structures are based on the discovery of four pharmacophores, as follows: (i) N1-AHB, (ii) (R)-6'-methyl, (iii) (S)-5''-methyl and (iv) (R)-5''-methyl. The additive effect of these pharmacophores was explored and generated our most powerful lead compound, NB127, which demonstrated similar to better activity to that of G418 while retaining significantly lower cytotoxicity. In the current study we provide proof of principle that antibacterial activity and toxicity of aminoglycosides can be dissected from their suppression activity. The data further indicate that the increased specificity towards cytoplasmic ribosome correlates with the increased activity, and that the decreased specificity towards mitochondrial ribosome confers to the lowered cytotoxicity.