Targeted CRISPR screening identifies PRMT5 as synthetic lethality combinatorial target with gemcitabine in pancreatic cancer cells

Abstract

Pancreatic ductal adenocarcinoma (PDAC) remains one of the most challenging cancers to treat. Due to the asymptomatic nature of the disease and lack of curative treatment modalities, the 5-y survival rate of PDAC patients is one of the lowest of any cancer type. The recurrent genetic alterations in PDAC are yet to be targeted. Therefore, identification of effective drug combinations is desperately needed. Here, we performed an in vivo CRISPR screen in an orthotopic patient-derived xenograft (PDX) model to identify gene targets whose inhibition creates synergistic tumor growth inhibition with gemcitabine (Gem), a first- or second-line chemotherapeutic agent for PDAC treatment. The approach revealed protein arginine methyltransferase gene 5 (PRMT5) as an effective druggable candidate whose inhibition creates synergistic vulnerability of PDAC cells to Gem. Genetic depletion and pharmacological inhibition indicate that loss of PRMT5 activity synergistically enhances Gem cytotoxicity due to the accumulation of excessive DNA damage. At the molecular level, we show that inhibition of PRMT5 results in RPA depletion and impaired homology-directed DNA repair (HDR) activity. The combination (Gem + PRMT5 inhibition) creates conditional lethality and synergistic reduction of PDAC tumors in vivo. The findings demonstrate that unbiased genetic screenings combined with a clinically relevant model system is a practical approach in identifying synthetic lethal drug combinations for cancer treatment.

Functional Genomics Approaches to Elucidate Vulnerabilities of Intrinsic and Acquired Chemotherapy Resistance

“…As previously mentioned, epigenetic factors can also contribute to chemotherapy resistance. To investigate the role of genes involved in epigenetic control of chromatin regulation, Wei et al conducted a CRISPR/Cas knockout screen and found the protein arginine methyltransferase gene 5 (PRMT5) to act as a synthetic lethal with gemcitabine in a patient-derived pancreatic cancer cell line [ 192 ]. PRMT5 is implicated in several functions, including genome organization, transcription, cell cycle, and spliceosome assembly.…”

Cancer nanotechnology: current status and perspectives

“…CRISPR-Cas9 gene editing has the potential to permanently disrupt tumor survival genes, which could supersede current limitations and pitfalls of traditional therapies [ 226 ]. Several companies are currently developing CRISPR–Cas9 therapeutics, but development of safe and efficient delivery modes remains a need for CRISPR-based therapies to be utilized in clinical applications.…”

Cancer Models to Defeat Therapy Resistance in Pancreatic Ductal Adenocarcinoma

“…94 95 Wei et al used in vivo CRISPR gene knockout screening in PDX mice to identify effective lethal drug combinations that synergize with GEM for treating PDAC. 96 Using a clinically relevant PDX model of PDAC with a patient tumor being propagated within the pancreas of athymic nude mice, they screened for chromatin regulators whose depletion may create conditional lethality with GEM. They found that inhibition of the protein PRMT5 led to synergistic vulnerability of PDAC cells to GEM.…”

“…This study suggests that GEM treatment combined with inhibition of PRMT5 will have stronger effects and selectivity towards PDAC. 96…”