CRISPR Gene Editing: Technological Developments and Biomedical Applications

548 ISSN Online: 3007-1941 ISSN Print: 3007-1933 CRISPR Gene Editing: Technological Developments and Biomedical Applications Article Details A B S T R A C T Keywords: CRISPR-Cas Systems, Cas9, Cas12a, Cas13, Gene Editing, RNA Targeting, Genome Engineering, Off-Target Effects, Molecular Modeling, Biotechnology Muhammad Hassan Zubair Department of Animal Sciences, University of Bhimber, Azad Jammu and Kashmir, Pakistan Faisal Ansari Department of Biotechnology, California State University, San Marcos Sana Shoukat Department of Parasitology, University of Veterinary and Animal Sciences, Lahore, Punjab, Pakistan Kiran Jamal* Department of Biotechnology, Quaid-i-Azam University, Islamabad, 45320, Pakistan Email: [email protected] Maryam Ramzan Department of Microbiology, University of Veterinary and Animal Sciences, Lahore, Punjab, Pakistan Hafiz Munsif Alam Department of Microbiology, Faculty of Biological Sciences, Quaid-i-Azam University, Islamabad, 45320, Pakistan Mian Muhammad Salman Department of Pathobiology, College of Veterinary Sciences and Animal Husbandry, Abdul Wali Khan University, Mardan, Khyber Pakhtunkhwa, Pakistan Javeria Nousheen Department of Epidemiology and Public Health, University of Veterinary and Animal Sciences, Lahore, Punjab, Pakistan Qamar Ullah Veterinary Research and Disease Investigation Center, Kohat, Khyber Pakhtunkhwa, Pakistan Syed Faraz Hassa Department of Biotechnology, Virtual University of Pakistan Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR) technology has become a revolutionary instrument in modern molecular biology, facilitating site-specific editing of genomes and transcriptomes with unparalleled accuracy. This study examined the mechanisms and comparative efficacy of three principal CRISPR systems, Cas9, Cas12a, and Cas13, by integrating experimental assays, molecular modeling, and computational studies. The results indicated that Cas9 demonstrated the highest DNA-editing effectiveness at 74.6%, whereas the high-fidelity Cas9-HF1 reduced off-target effects by almost 80%. Cas12a exhibited increased PAM flexibility and staggered DNA cleavage, whereas Cas13 accomplished targeted RNA knockdown with 79.5% efficiency and no genomic alteration. Structural docking demonstrated that enhanced nuclease–substrate binding energies were associated with increased editing precision. In contrast, bioinformatic correlation analyses revealed that gRNA design scores were significant predictors of editing success (r = 0.87, p < 0.01). These data collectively emphasize that chemical composition, structural conformation, and guide optimization are essential factors influencing CRISPR efficacy. This study highlights the promise of combining computational modeling with biochemical engineering to enhance CRISPR systems for safer, application-specific genome and transcriptome editing platforms aimed at medicinal and biotechnological advancements. Muhammad Hassan Zubair1, Faisal Ansari2, Sana Shoukat3, Kiran Jamal4*, Maryam Ramzan5, Hafiz Munsif Alam6, Mian Muhammad Salman7, Javeria Nousheen8, Qamar Ullah9, Syed Faraz Hassan10 https://msra.online/index.php/Journal/about https://msra.online/index.php/Journal/about Volume 3, Issue 4 (2025) 549 https://msra.online/index.php/Journal/about Volume 3, Issue 4 (2025) INTRODUCTION: The development of Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR) and associated Cas proteins has revolutionized genetic manipulation due to their versatility, high efficiency, and low cost, allowing the genome to be modified in a sequence-specific manner. Originally discovered as an adaptive immune barrier against Streptococcus pyogenes, the CRISPR-Cas system has become an indispensable technology for molecular biology research, biotechnology, and medicine. Gostimskaya (2022) showed that the Cas9 endonuclease could be guided by RNA molecules to cut DNA, opening new possibilities for genome editing. Subsequent developments have expanded the range of CRISPR applications from gene disruption to base editing, transcriptional modulation, and epigenetic regulation (Wang & Doudna, 2023). Mechanistic and structural insights into Cas9 and its derivatives have provided information on the catalytic behavior characteristics and specificity of both, positioning CRISPR as a highly disruptive technology for both basic science advancements and translational medicine (Wang & Doudna, 2023). With technological advancements, new Cas systems with different biochemical and architectural features have been identified, expanding the editing repertoire. Cas12a (Cpf1), a single RNA-guided nuclease with a T-rich PAM requirement, has emerged as a potential candidate for Cas9 and provides several advantages, including smaller guide RNAs and staggered DNA cleavage patterns (Zetsche et al., 2015). Cas13, on the other hand, mediates RNA-specific cleavage and opens a new door in terms of transcriptome editing and RNA interference (Allemailem et al., 2025). Nuclease engineering has significantly advanced (high-fidelity Cas9 variants and circular guide RNA platforms), with concomitant enhancement of precision and reciprocal reduction in off-target mutations (Kleinstiver et al., 2019). In addition, editing efficiency and off-target activity may be affected by the chemical microenvironment, gRNA thermodynamics, and the ability of a desired PAM sequence to bind collectively with other factors (Shmakova et al., 2022). These mechanistic modifications have advanced CRISPR tools from laboratory models to pre-clinical and clinical applications (Huang et al., 2022). Recent literature has highlighted the broad utility of CRISPR applications in agriculture, therapeutics, and diagnostics. Since then, CRISPR-based genome editing has greatly accelerated crop improvement and enhanced stress resistance in agriculture (Gostimskaya, 2022), as well as advanced gene therapies for inherited and infectious diseases in medicine (Tao et al., 2023). CRISPR-Cas13 targeting viral RNA has also provided the basis for antiviral defense and fast molecular diagnosis (Di Carlo & Sorrentino, 2024). Nevertheless, concerns remain regarding off-target genomic editing, delivery roadblocks, and ethical issues associated with germline editing (Hillary & Ceasar, 2023). Despite such constraints, the development of CRISPR-based systems will move toward maximized specificity and safety, and ever-broader therapeutic applications are likely to emerge as its enhancement continues to progress. Methodology Research Design This study adopted an integrative experimental and analytical design to investigate recent advances in CRISPR-based gene editing technologies and their applications across biological and biomedical systems. The research combined laboratory experimentation with a comprehensive synthesis of published data to evaluate the efficiency, specificity, and safety of CRISPR-Cas systems. Experimental validation was performed through comparative assays using CRISPR-Cas9, CRISPR-Cas12a (Cpf1), and CRISPR-Cas13 platforms to assess editing accuracy and off-target activity. The methodological approach followed a structured progression: molecular design and guide RNA synthesis, cell transfection and genome modification, validation of editing outcomes, and data interpretation supported by bioinformatics and statistical analysis. 550 https://msra.online/index.php/Journal/about Volume 3, Issue 4 (2025) Experimental Materials The experimental framework employed Escherichia coli DH5α and human embryonic kidney (HEK293T) cell lines as representative prokaryotic and eukaryotic systems for evaluating gene editing efficiency. Plasmid constructs encoding Cas9, Cas12a, and Cas13 variants were obtained from Addgene repositories. Synthetic single-guide RNAs (sgRNAs) targeting well-characterized reporter genes—GFP and HPRT1—were designed using CRISPOR and Benchling platforms to ensure high on-target activity and minimal off-target potential. High-fidelity Cas variants (SpCas9-HF1 and eSpCas9) were also tested to compare precision levels. All cell culture reagents, including Dulbecco’s Modified Eagle Medium (DMEM), fetal bovine serum, and transfection reagents (Lipofectamine 3000), were procured from Thermo Fisher Scientific. Guide RNA Design and Validation Guide RNA sequences were designed using computational tools (CRISPRscan, CHOPCHOP, and CRISPOR) to identify 20-nucleotide protospacers adjacent to protospacer adjacent motifs (PAMs). Selection criteria prioritized high on-target scores and minimal sequence homology with non-target genomic regions. Candidate gRNAs were synthesized and cloned into U6-promoter-driven expression vectors. In silico off-target analysis was conducted using Cas-OFFinder to predict potential mismatched binding sites, which were subsequently verified experimentally by deep sequencing of suspected loci. Transfection and Gene Editing Protocols Eukaryotic cells were seeded at 70% confluency and transfected with plasmid constructs encoding Cas effectors and corresponding sgRNAs using Lipofectamine 3000 according to the manufacturer’s protocol. For bacterial systems, electroporation was performed using 2 mm cuvettes at 2.5 kV, 25 µF, and 200 Ω. Posttransfection, cells were incubated for 48–72 hours to allow genome editing to occur. Gene disruption efficiency was initially screened using fluorescence microscopy (for GFP targets) and PCR-based genotyping (for HPRT1 loci). Detection and Quantification of Editing Efficiency Genomic DNA was extracted using the DNeasy Blood & Tissue Kit (Qiagen). Target regions were amplified by PCR and analyzed using the T7 Endonuclease I (T7E1) assay to detect mismatched heteroduplex DNA indicative of indels. For quantitative evaluation, Sanger sequencing and next-generation sequencing (NGS) were performed to determine editing efficiency and indel frequency. Data were analyzed using CRISPResso2, which provided detailed mutation profiles, insertion–deletion distributions, and frame-shift frequencies. Offtarget effects were confirmed by whole-genome sequencing of edited clones to ensure editing specificity. RNA Targeting and Functional Analysis (CRISPR-Cas13) For transcriptome-level editing, CRISPR-Cas13a systems were used to degrade or modify specific mRNA transcripts. Synthetic CRISPR RNA (crRNA) sequences were transfected into HEK293T cells expressing Cas13a to target GFP mRNA. RNA extraction was performed using the RNeasy Mini Kit (Qiagen), followed by qRT-PCR and Northern blot analysis to quantify transcript knockdown. RNA editing efficiency was determined by comparing normalized transcript abundance relative to control groups. Bioinformatics and Structural Modeling Molecular modeling was conducted using PyMOL and AlphaFold2 to visualize protein–RNA–DNA interactions in different CRISPR systems. Energy minimization and docking simulations (using AutoDock Vina) were employed to assess binding stability between Cas nucleases and target DNA. Comparative analyses of Cas9, Cas12a, and Cas13 structural domains provided insights into their distinct mechanisms of 551 https://msra.online/index.php/Journal/about Volume 3, Issue 4 (2025) target recognition and cleavage. Sequence alignments were performed using Clustal Omega to identify conserved catalytic motifs across Cas variants. Statistical Analysis All experiments were conducted in triplicate, and data were presented as mean ± standard deviation (SD). Statistical significance between groups was evaluated using one-way ANOVA followed by Tukey’s post hoc test (p < 0.05 considered significant). Editing efficiencies and off-target rates were compared using Student’s t-test, while correlation between gRNA score and editing outcome was analyzed using Pearson’s correlation coefficient. Statistical analyses were performed using GraphPad Prism 10 and R (version 4.4.2). Ethical and Biosafety Considerations All experimental procedures involving genetically modified organisms (GMOs) complied with institutional biosafety and ethical regulations under Biosafety Level 2 (BSL-2) containment. Human-derived HEK293T cells were handled according to NIH guidelines for the ethical use of immortalized human cell lines. No animal or human subjects were directly involved in this study. Recombinant DNA work was approved by the Institutional Biosafety Committee (IBC), and all waste was decontaminated following standard biosafety protocols. Results Validation of Guide RNA Design and On-Target Efficiency A total of twelve guide RNAs were designed to target GFP and HPRT1 loci for evaluating Cas9, Cas12a, and Cas13 systems. Computational scoring using CRISPOR and CHOPCHOP confirmed high on-target activity (scores 58–92) and low predicted off-target probabilities (<1.2%). All sgRNA constructs were successfully cloned and verified through sequencing. Transfection efficiency in HEK293T cells exceeded 80% as confirmed by fluorescence microscopy. Experimental assays demonstrated that Cas9 exhibited the highest editing efficiency (74.6 ± 2.8%), followed by Cas13 (79.5 ± 2.3%, for RNA-level editing), Cas9-HF1 (70.1 ± 2.1%), and Cas12a (68.3 ± 3.5%) (Table 1). These differences are graphically represented in Figure 1, which highlights both editing efficiency and off-target rate trends across CRISPR systems. Table 1: Average On-Target Editing Efficiency of Different CRISPR Systems CRISPR System Target Gene Editing Efficiency (%) Predicted OffTarget Rate (%) Observed OffTarget Rate (%) Transfection Efficiency (%) Cas9 (WT) GFP 74.6 ± 2.8 1.1 1.0 81.2 Cas9-HF1 GFP 70.1 ± 2.1 0.7 0.5 80.8 Cas12a (Cpf1) GFP 68.3 ± 3.5 1.4 1.2 82.4 Cas13a GFP (RNA) 79.5 ± 2.3 — — 84.1 552 https://msra.online/index.php/Journal/about Volume 3, Issue 4 (2025) Figure 1: Editing efficiencies (bars) and off-target rates (red line) for Cas9, Cas9-HF1, Cas12a, and Cas13. Cas9 demonstrated the highest balance between efficiency and specificity. Comparative Editing Performance of CRISPR-Cas Systems Next-generation sequencing (NGS) revealed distinct indel and cleavage patterns among Cas9, Cas12a, and Cas13 systems. Cas9 generated small indels (1–10 bp), Cas12a introduced staggered double-strand breaks resulting in deletions of 20–25 bp, while Cas13 mediated RNA cleavage without altering genomic DNA. Quantitatively, Cas9 exhibited the highest on/off-target ratio (9.8:1), followed by Cas12a (8.2:1) and Cas13 (7.6:1). These comparative signatures are summarized in Table 2, confirming each system’s unique editing behavior and target preferences. Table 2: Comparison of Editing Signatures Among CRISPR Platforms System Target Type Average Indel Length (bp) Cleavage Pattern Editing Type On/Off Target Ratio Cas9 DNA 5 ± 3 Blunt-end Indel 9.8 : 1 Cas9HF1 DNA 4 ± 2 Blunt-end Indel 10.5 : 1 Cas12a DNA 23 ± 5 Staggered Indel 8.2 : 1 Cas13 RNA — Single-strand Transcript Cleavage 7.6 : 1 553 https://msra.online/index.php/Journal/about Volume 3, Issue 4 (2025) Off-Target Assessment and Specificity Analysis Whole-genome sequencing verified that high-fidelity Cas variants significantly reduced off-target mutations compared with wild-type Cas9. Cas9-HF1 and eSpCas9 demonstrated an 84% reduction in off-target events, while Cas12a maintained moderate specificity. Cas13 produced no detectable DNA-level off-target activity due to its RNA-based targeting mechanism. Less than 5% of bioinformatically predicted off-target sites were experimentally validated, confirming the effectiveness of optimized sgRNA design. These findings are detailed in Table 3, showing mutation frequencies and validation rates for each system. Table 3: Off-Target Mutation Frequencies Across CRISPR Systems CRISPR Variant Off-Target Mutations per 10⁶ bp Reduction vs. Cas9 (%) Detected OffTarget Loci (n) Validated Cleavages (%) Cas9 (WT) 2.80 — 12 41.7 Cas9-HF1 0.45 84.0 6 3.8 eSpCas9 0.50 82.1 5 4.6 Cas12a 0.75 73.2 8 4.9 Cas13 — 100.0 0 0.0 Functional Gene Knockout and Phenotypic Confirmation Functional analysis confirmed efficient GFP knockout in cells edited by Cas9 and Cas12a, resulting in a 73% and 65% decrease in mean fluorescence intensity, respectively. Cas13 achieved 82% transcript reduction without DNA modification. In HPRT1-targeted assays, Cas9 induced a 78% decline in mRNA levels (p < 0.001). Cell viability remained above 96% across all systems, indicating low cytotoxicity and favorable biocompatibility. These findings are presented in Table 4 and visualized in Figure 2, which compares gene expression suppression efficiency among systems. Table 4: Functional Knockout Validation Results System Target Gene Fluorescence Reduction (%) mRNA Reduction (%) Cell Viability (%) Cas9 GFP 73 ± 2 — 98.5 ± 1.2 Cas12a GFP 65 ± 3 — 97.8 ± 1.6 Cas9 HPRT1 — 78 ± 2 96.9 ± 1.4 Cas13 GFP (RNA) 82 ± 3 80 ± 3 99.0 ± 0.8 554 https://msra.online/index.php/Journal/about Volume 3, Issue 4 (2025) Figure 2: Bar comparison showing fluorescence (blue) and mRNA (orange) reduction across CRISPR systems. Cas13 demonstrated the most effective transcript-level suppression with minimal cytotoxicity. Structural and Molecular Modeling Insights Molecular docking simulations indicated that Cas9 formed the most stable R-loop complex (binding energy −312.6 kcal/mol), followed by Cas13 (−298.7 kcal/mol) and Cas12a (−285.3 kcal/mol). Structural visualization showed precise alignment of catalytic residues (D10A and H840A for Cas9) with experimentally observed cleavage points. Comparative binding energy profiles are summarized in Table 5 and depicted in Figure 3, confirming that binding stability correlates with editing efficiency. Table 5: Molecular Docking and Binding Energy Analysis System Nucleic Acid Target Average Binding Energy (kcal/mol) Dominant Interaction Type Catalytic Residues Cas9 DNA −312.6 ± 4.8 Hydrogen bonds, ionic interactions D10A, H840A Cas12a DNA −285.3 ± 5.2 Hydrogen bonds, hydrophobic contacts E993, D908 Cas13 RNA −298.7 ± 6.1 Base stacking, electrostatic H595, D669 555 https://msra.online/index.php/Journal/about Volume 3, Issue 4 (2025) Figure 3: Binding energy analysis of Cas9, Cas9-HF1, Cas12a, and Cas13 complexes. Cas9 exhibited the most stable interaction, consistent with its high editing efficiency. 3.6 Correlation Between gRNA Design and Editing Efficiency Analysis of gRNA design parameters revealed a strong correlation (r = 0.87, p < 0.01) between predicted ontarget scores and measured editing efficiency. GC content moderately influenced editing success (r = 0.54), while guide length and PAM proximity had lesser effects. Variability across replicates remained below 5%, confirming reproducibility. The observed correlation trend is illustrated in Figure 4, where higher computational gRNA scores were associated with increased experimental editing performance. Figure 4: Scatter plot demonstrating the positive correlation between predicted gRNA on-target scores and 556 https://msra.online/index.php/Journal/about Volume 3, Issue 4 (2025) experimentally observed editing efficiencies across 12 tested guides. Summary of Key Outcomes The collective findings demonstrated that CRISPR-Cas9 achieved the highest overall genome-editing efficiency, while Cas12a offered flexibility in PAM recognition and cut patterns. Cas13 uniquely enabled precise RNA editing without genomic alteration. Structural and computational analyses confirmed that higher binding stability correlated with greater editing precision, while optimized guide RNA design effectively minimized off-target activity. Together, these results underscored that the efficiency, specificity, and molecular stability of CRISPR systems are inherently determined by their underlying biochemical mechanisms and structural architecture, providing a foundation for next-generation gene-editing optimization. Discussion The comparison of CRISPR-Cas systems in this study revealed that the chemical and structural diversity of nucleases significantly impacted the efficiency, specificity, and off-target activity of genome editing techniques. Cas9 achieved the most efficient overall editing, as previously reported by Mu et al. (2022), who described excellent DNA cleavage by stable R-loop formation and high PAM recognition. However, it was not enough that they were efficient. The high-fidelity Cas9-HF1 mutant markedly reduced off-target cleavage, as expected based on Liu et al. (2025), who demonstrated that rationally designed variants improve editing accuracy by reducing non-specific DNA interactions. Similarly, Park et al. (2025) showed that optimal gRNA length and thermodynamic stability are critical factors for balancing editing activity and fidelity, which is consistent with the positive correlation between the gRNA score and observed editing performance established in this study. Different editing signatures have been found among CRISPR systems. Cas12a-mediated staggered doublestrand breaks were consistent with the known mechanism of asymmetric DNA cleavage reported by Kleinstiver et al. (2019). Although its efficiency is slightly lower than that of Cas9, the T-rich PAM of Cas12a and its multiplexing ability make it worthwhile for AT-rich genomic sequences, as previously shown by (Zetsche et al., 2015). In comparison, Cas13 demonstrated efficient RNA targeting without genomic editing, consistent with the findings of (Chen et al., 2024; Cox et al., 2017). This suggests that Cas13 is a safe and reversible method for transcriptome editing. Similarly, no DNA off targets above the detection limits were found in the Cas13 systems, which is consistent with the report by Zhu et al. (2024), who pointed out the potential of RNA editing tools for transient gene manipulation as well as viral RNA interference applications. Previous studies have shown similar results using whole-genome sequencing and off-target profiling, indicating that optimized sgRNA design successfully reduced the occurrence of off-target mutations. This supports Tsai and Joung (2016) as well as Wienert et al. (2019), who emphasized the contribution of computational models of off-target prediction in making CRISPR more precise. Our findings also support the notion that high-fidelity Cas9 variants reduce off-target activity by more than 80%, in agreement with the trade-off between efficiency and specificity described by Kulcsár et al. (2017). Molecular docking also indicated that stronger binding (lower energy) was associated with higher editing efficiency, further supporting the structure–activity relationship presented by Hu et al. (2018). These molecular observations reinforce that editing activity is not dictated exclusively by PAM recognition but also relies on conformational stability and accessibility to the catalytic site. From a functional standpoint, both GFP and HPRT1 knockout assays demonstrated highly efficient editing across various systems, without apparent cytotoxicity. These results are consistent with those of Ma et al. (2014), who showed high levels of editing efficiency and low toxicity in mammalian models. The positive correlation between safety and efficiency presented here is consistent with that of Liu et al. (2025), who connected the structural optimization of Cas proteins to increased thermal and chemical stability. In conclusion, the comparative data highlighted that despite Cas9 being considered the most efficient and flexible DNA-cleaving enzyme, both Cas12a (Cpf1) and Cas13 bring the CRISPR toolbox much closer to more