In recent decades, there have been numerous impressive breakthroughs in oncology drug development, with new drugs and therapies emerging, and the industry expects global oncology drug sales to reach $250 billion by 2024. Currently, oncology drugs account for about ⅓ of the total product development in the pharmaceutical industry. In drug development, as a small size, ease of handing, and powerful genetic tool, C. elegans provide a sophisticated in vivo toxicity assay that combines the technical advantages of a microorganism with greater biological complexity and a gene complement more akin to that of humans. Here in today's blog post, we'll briefly share a paper related to the use of C. elegans as a platform to characterize the anticancer therapeutic CX-5461.
CX-5461 is an emerging anticancer therapeutic that's currently in clinical trials. It's been previously shown in murine xenograft models to have displayed anticancer properties as an RNA polymerase I inhibitor. Recently, scientists found that, beyond being an RNA pol I inhibitor, there exist many other pathways under which CX-5461 is capable of killing tumor cells. Most of these mechanisms rely on the popular photodynamic therapy (PDT) in recent years. Cancer cells specifically take up and retain photosensitizers, and PDT can stimulate photosensitizers to react with oxygen by using appropriate wavelengths and doses of light to produce reactive oxygen ions with toxic effects, thus destroying cancer cells.
As an anti-cancer drug candidate, the mechanism of action of CX-5461 and its possible toxic side effects have yet to be studied. Therefore, researchers used C. elegans to detect CX-5461-mediated photosensitivity, mutagenicity and mutational signatures and to identify genotypes sensitive to CX-5461. In the analysis of pharmacogenetic map (Table 1), the authors found that CX-4561 tolerance requires multiple repair pathways, including homology directed repair(HDR), microhomology-mediated end joining(MMEJ), nucleotide excision repair(NER), and translesion synthesis(TLS).
Table 1. Pharmacogenetic profiles of C. elegans DNA damage response mutants
CX5461 could act as a photosensitizer that brings oxidative stress to cell structures due to the ROS generated upon exposure to UVA. Wild-type nematodes were not sensitive to CX5461 or UVA exposure alone, however, when the two combined they found a dose-dependent cytotoxicity (Figure 1). It's worth noting that human colorectal cancer cell lines and wildtype and rad52 yeast all exhibit similar CX5461-mediated UVA-dose-dependent toxicity, so, we are looking at a common feature across a spectrum of physiology. Another DNA-damaging property imposed by the CX5461+UVA combo was the creation of transcription-blocking lesions. It was known that NER (nucleotide excision repair) is a pathway for repairing bulky single-stranded DNA lesions often caused by exposure to UV radiation. And most NER activities are transcription-coupled. NER mutant xpa-1 was arrested in L1 stage after CX-5461 and UVA treatment, and it could be determined that the NER functioning was sabotaged by the CX5461+UVA exposure and the resulting transcription-blocking lesions (Figure 1B).
Figure 1. UVA enhances the toxicity of CX-5461
CX-5461 is also mutagenic, and the treated nematode genome has a complex mutational profiles, including large copy number variations(CNVs) and a high frequency of single-nucleotide variations(SNVs), which is consistent with the pharmacogenetic characteristics of CX-5461 (Figure 2). Together, the data from C. elegans demonstrate that CX-5461 is a multimodal DNA-damaging acticancer agent.
Figure 2. Exposure to CX-5461 or CX-5461+100J/m2 UVA results in high frequencies of mutations.
C. elegans is a powerful platform. After all, it's a species whose entire genome has been sequenced, and so many mutant strains are being developed every day for every specific purpose desired by each individual researcher. It's not just worms that we are working with, but an extremely powerful tool we're developing — a platform that eventually is going to carry the hopes of millions. This is also the direction that SunyBiotech has been working towards.
Ye FB, Hamza A, Singh T, Flibotte S, Hieter P, O'Neil NJ. A Multimodal Genotoxic Anticancer Drug Characterized by Pharmacogenetic Analysis in Caenorhabditis elegans. Genetics. 2020 Jul;215(3):609-621. doi: 10.1534/genetics.120.303169. Epub 2020 May 15. PMID: 32414869; PMCID: PMC7337070.