A clinical study demonstrates the feasibility of RNA interference therapy targeting ribonucleotide reductase in melanoma patients
Melanoma continues to be the focus of an intensive investigation therapeutically. While most melanomas occur in the skin, it may also occur in other tissues like eye or intestine. Though melanoma accounts for a minority (less than 1%) of skin cancers, it is responsible for a large fraction of skin cancer-associated mortality. Presently, over 1,190,000 individuals are living in the U. S. alone with melanoma and the rate for new cases continues to rise. In addition to the conventional therapies, other innovative treatments such as targeted therapy and immunotherapy have been increasingly used.
Antimetabolite drugs represent a significant arsenal against cancer (Tiwari, 2019). Numerous commonly used chemotherapeutics fall under this category, which include gemcitabine, capecitabine, 5-fluorouracil, cytosine arabinoside (ara-C), and methotrexate. Antimetabolites have been used extensively to treat cancer as they interfere with the biosynthesis of deoxyribonucleotides, the building blocks of DNA necessary for replication. As cancer cells tend to divide more frequently than the normal cells, these drugs have been used extensively to treat leukemia and various solid human tumors.
One of the current targets of antimetabolite chemotherapy is ribonucleotide reductase (RR), which is highly conserved as it represents the sole enzyme catalyzing the reduction of ribonucleotides to their corresponding deoxyribonucleotides. Its catalysis requires the generation of tyrosine free radicals by its iron center. Among the RR inhibitors are gemcitabine and hydroxyurea, with the latter quenching tyrosyl free radicals in the active site to inactivate the enzyme (Shao et al, 2013).
RNA interference by small interfering RNA (siRNA) refers to a post-transcriptional mechanism through which gene expression could be silenced through degrading the target mRNA molecules. It involves cleaving long double stranded RNA (dsRNA) into short dsRNA fragments, which is then unwound into single strand RNA to hybridize to the complementary target mRNA for degradation by the RNA-induced silencing complex (RISC) (Wilson et al, 2013). Its discovery has generated an intense pharmaceutical interest as it provided a unique opportunity to suppress gene expression without permanently inactivating the gene.
In a phase I clinical trial conducted at the City of Hope National Medical Center, the plausibility of RNA interference therapy targeting ribonucleotide reductase was assessed in melanoma patients (Davis et al, 2010). The siRNA was delivered using a nanoparticle assembled at California Institute of Technology. After a systemic administration, the siRNA reduced the expression of the endogenous RR gene by degrading its mRNA in melanoma cells. The study demonstrated the feasibility of triggering RNA interference using systemically delivered siRNA in humans, establishing siRNA as a novel therapeutic.
Bio-Synthesis, Inc. is the major supplier of the RNA interference technology as it has extensive experience in the synthesis and modification of siRNA or shRNA. The constructs consist of highly purified double-stranded RNA molecules, made of up to 30 RNA nucleotides with two nucleotides 3' overhangs. They have been used extensively to suppress the expression of a specific gene of interest for identifying its function, elucidating pathways, and screening for potential new drug targets. Highly modified RNA oligomers of various lengths (100mers or longer) are available as well as bioconjugates to tether the RNAs (single or double stranded) to a number of other moieties.
Additionally, for siRNA synthesis, Bio-Synthesis, Inc. offers the BNA technology, which provides superior, unequalled advantages in base stacking, binding affinity, aqueous solubility and nuclease resistance. It also improves the formation of duplexes by reducing the repulsion between the negatively charged phosphates of the oligonucleotide backbone. We recently acquired a license from BNA Inc. of Osaka, Japan, for the manufacturing and distribution of BNANC, a third generation of BNA oligonucleotides. BNA oligonucleotide exhibits lesser toxicity than other modified nucleotides for clinical application.
https://www.biosyn.com/sirna-synthesis.aspx
References
Tiwari M. Antimetabolites: established cancer therapy. (2012). J Cancer Res Ther. 8:510-9. PMID: 23361267 doi: 10.4103/0973-1482.106526.
Davis ME, Zuckerman JE, Choi CH, Seligson D, Tolcher A, Alabi CA, Yen Y, Heidel JD, Ribas A. Evidence of RNAi in humans from systemically administered siRNA via targeted nanoparticles. (2010). Nature. 464:1067-70. PMID: 20305636 doi: 10.1038/nature08956.
Shao J, Liu X, Zhu L, Yen Y. Targeting ribonucleotide reductase for cancer therapy. (2013). Expert Opin Ther Targets. 17:1423-37. PMID: 24083455 doi: 10.1517/14728222.2013.840293.
Wilson RC, Doudna JA. Molecular mechanisms of RNA interference. (2013). Annu Rev Biophys. 42:217-39. PMID: 23654304 PMCID: PMC5895182 doi: 10.1146/annurev-biophys-083012-130404.