Gene therapy encompasses the treatment of diseases by silencing the ambiguous genes, incorporation of new genes for achieving a desired gene expression and replacing the erroneous genes with healthier ones. However, the conventional gene delivery paradigm faces substantial challenges pertaining to an inefficient transfection efficacy, safety concerns such as immunogenicity, and strenuous operational procedures of gene handling and delivery [[1], [2], [3], [4], [5]]. Proneness of the naked genetic material in the form of nucleic acids towards degradation by endonucleases is a major hurdle in an effective gene therapy as it results in their deactivation and elimination [[6], [7], [8]]. Furthermore, the presence of negative charge on nucleic acids is another drawback in transfection as the presence of surface charge limits their cellular internalization [[9], [10], [11], [12]]. Over the past decades, substantial strides have been accomplished for the development of viral and non-viral gene delivery vectors with an adequate transfection efficiency aimed for the treatment of life-threatening diseases which have a limited established treatment intervention [[13], [14], [15]] (see Table 1, Fig. 4, Fig. 5, Fig. 6, Fig. 7).

Systematic developments have led to the identification of several viral and non-viral vectors depending on the nature of genetic material to be delivered and the route of its administration [26]. Especially, the viral vectors provide a remarkable transfection efficacy with a sustained gene expression, and they provide protection to the cargo genes from enzymatic degradation by nucleases [27]. However, the viral vector-based gene delivery systems are susceptible to immunogenicity, resulting in toxicity, high operational cost, and poor targeting efficacy [28]. Non-viral vector systems overcome the immunogenicity-associated toxicity limitations, possess high loading capacity of cargo genes, and are economical [29]. However, vulnerability towards extra- and intracellular barriers and a poor transfection efficacy leading to a much lower gene expression than anticipated are major drawbacks of the non-viral vector-based approaches [30].

The expedition for innovative drug delivery systems that overwhelm the intricacies associated with the contemporary technologies has led to the exploration of unconventional materials with unique properties. Cycloamylose, which is a cyclic form of the resistant starch (amylose) and categorized as a cyclodextrin presents intriguing characteristics pertinent to its candidature as a potential drug delivery system [31]. The amphiphilic nature of cycloamylose arising from its hydrophobic interior and hydrophilic periphery is of particular interest as it enables the delivery of a wide range of pharmaceuticals [32]. One of the challenges faced by several of the existing pharmaceutical formulations is poor solubility of certain drugs [[33], [34], [35]]. Cycloamylose presents the potential of encapsulating the hydrophobic drugs in its cavity where the solubilization effect improves the aqueous solubility of these drugs eventually improving their bioavailability and hence the therapeutic efficacy [36,37]. The encapsulation of therapeutics in cycloamylose further prevents their degradation or premature activation pertaining to its stability towards enzymatic hydrolysis thereby preserving the drug potency during storage and transportation [38]. Ingenious integration of Cycloamylose in formulations and tailoring of the interactions between drug molecules and cycloamylose has been performed to modulate the release kinetics mainly to achieve a controlled drug release for specific therapeutic needs [39,40]. In addition to prolonging the duration of drug action, these approaches also minimize the fluctuations in plasma drug concentration hence reducing the likelihood of side effects [[41], [42], [43]]. Functionalization of cycloamylose with specific ligands, targeting moieties, or functional head groups result in the generation of formulations that are used for a selective delivery of cargo drug molecules to specific cells or tissues [44,45]. Apparently, the targeted delivery approach with cycloamylose enhances the therapeutic outcomes while dismissing the impact on healthy tissues [[46], [47], [48]]. Hence, the side effects associated with the traditional systemic drug delivery are significantly reduced with the application of cycloamylose-based precision medicine. This review article starts with the discussion and comparison of different viral and non-viral gene delivery systems, followed by the introduction of cycloamylose in the gene delivery regime. Synthesis and transfection/nucleic acid delivery potential of cationic cycloamylose has been emphasized on in the later sections of the review as the cationic charge is a cornerstone to bestowing the membrane penetrating potential to the non-viral delivery vectors, such as cycloamylose which are already equipped with encapsulation efficacy for providing protection to cargo genes from enzymatic degradation.

The process of transfecting nucleic acids entails introducing foreign genetic material (DNA or RNA) into the nucleus of eukaryotic cells to express an encoded protein. Despite the structural and functional disparities between DNA and RNA, the crucial factor influencing the choice of an appropriate delivery method is the negative charge on both nucleic acids [49,50]. Notably, with the elucidation of RNA silencing mechanisms, small interfering RNA, small hairpin RNA, and micro-RNA have rapidly gained prominence in nucleic acid delivery systems [51]. However, the transfection journey for RNA is directed to the cytosol, whereas for DNA, it targets the cell nucleus [52,53]. This distinction makes RNA molecules more susceptible to degradation compared to DNA, necessitating higher doses of the former to achieve the desired level of gene silencing [54,55]. Viral and non-viral delivery systems find application in transfecting nucleic acids in various fields, including cell culture technology, vaccination, recombinant protein production, cell line development, regenerative medicine, and gene therapy [[56], [57], [58], [59], [60]]. In ex vivo approaches, the desired nucleic acid is applied to extracted cells, followed by the introduction of the resulting modified cells to subjects receiving therapy [61,62]. Alternatively, the in vivo methods involve a direct delivery of nucleic acid to specific tissues [63,64]. While viruses are extensively explored as highly efficient nucleic acid delivery systems, challenges such as immunogenicity, production cost, tissue tropism, and biosafety hinder their marketable translation for commercial gene-based therapy [[65], [66], [67]]. Notwithstanding, viral vectors, including type 2 and 5 adenovirus, herpes virus, adeno-associated virus, pox virus, lentivirus, retrovirus, and adeno-associated virus, are reported as the most effective gene delivery systems [[68], [69], [70]]. Editing viral vector genomes to impair replication is necessary for safety, but concerns about immunogenicity, inflammatory responses, insertional mutagenesis, and toxin production persist [71,72]. To overcome limitations associated with viral vectors, nonviral methods, involving physical forces on target cells or the formation of nucleic acid-based composite structures, have been deployed [73]. These nonviral systems, generated through chemical (e.g., cationic liposomes and polymers) or physical (e.g., gene gun, electroporation, particle bombardment, ultrasound, and magnetofection) methods, are less efficient than viral systems in gene transduction [[74], [75], [76], [77]]. However, their cost-effectiveness, availability, lower immunogenicity, and lack of limitations in transgenic DNA size make them more effective for gene delivery [[78], [79], [80]]. Clinical trials focusing on DNA immunization against infectious diseases often utilize injectable physical techniques followed by electroporation [[81], [82], [83]]. Functionalized cationic polymers and lipids are also explored for DNA transfection in managing viral infections and cancer [[84], [85], [86]]. For RNA, particle-based mediation approaches, often administered systemically, prove more efficacious in terms of pharmacokinetics compared to naked RNA approaches [[87], [88], [89]]. Therapeutic siRNA is frequently combined with liposomal particles and administered via injection for various therapeutic purposes [90,91].

Despite advancements, nucleic acid vectors face challenges in trafficking, depending on the biological environment and delivery route, before reaching target cells [[92], [93], [94]]. Achieving successful in vivo gene delivery is complex due to increased extracellular and physiological obstacles [[95], [96], [97]]. While physical force in cell transfection yields localized effects, particle-based systems are optimized for systemic delivery, offering potential for precisely targeting specific tissues or organs [[98], [99], [100]]. Overcoming challenges like endosomal escape and nuclear localization for RNA and DNA delivery, respectively, remains a focus for future advancements [101,102]. Despite ongoing progress, no nucleic acid delivery system, whether viral or non-viral, has fully met current scientific and clinical requirements.