Improved intratumoral delivery of PEG-coated siRNA-lipoplexes by combination with metronomic S-1 dosing in a murine solid tumor model

Metronomic chemotherapy and nanocarrier platforms

The therapeutic concept of administering chemotherapeutic agents continuously at lower doses, relative to the maximum tolerated dose (MTD) without drug-free breaks over extended periods -known as "metronomic chemotherapy"- is a promising approach for anti-angiogenic cancer therapy. In comparison with MTD chemotherapy regimens, metronomic chemotherapy has demonstrated reduced toxicity. However, as a monotherapy, metronomic chemotherapy has failed to provide convincing results in clinical trials. Therapeutic approaches including combining the anti-angiogenic "metronomic" therapy with conventional radio-/chemo-therapy and/or targeted delivery of chemotherapeutic agents to tumor tissues via their encapsulation with nanocarrier-based platforms have proven to potentiate the overall therapeutic outcomes. In this review, therefore, we focused on the mutual contribution made by nanoscale drug delivery platforms to the therapeutic efficacy of metronomic-based chemotherapy. In addition, the influence that the dosing schedule has on the overall therapeutic efficacy of metronomic chemotherapy is discussed.

Bridging small interfering RNA with giant therapeutic outcomes using nanometric liposomes

The scope of RNAi based therapeutics is unquestionable. However, if we dissect the current trend of clinical trials for afore mentioned drug class, some stark trends appear: 1) naked siRNA only exerts influence in topical mode whilst systemic delivery requires a carrier and 2) even after two decades of extensive efforts, not even a single siRNA containing product is commercially available. It was therefore felt that a perspective simplifying the unique intricacies of working with a merger of siRNA and liposomes from a pharmaceutical viewpoint could draw the attention of a wider array of interested researchers. We begin from the beginning and attempt to conduit the gap between theoretical logic and experimental/actual constraints. This, in turn could stimulate the next generation of investigators, gearing them to tackle the conundrum, which is siRNA delivery.

[Development of siRNA delivery strategy by active control of tumor microenvironment]

Efficient systemic siRNA delivery to cells in the target tissue is a current critical challenge in the drug delivery field. Several studies have demonstrated that nanoparticles such as polyethylene glycol (PEG)-coated siRNA-lipoplexes may enhance the systemic delivery of siRNA to tumor. However, the disordered tumor microenvironment still poses a potential impediment with respect to the efficient delivery of PEG-coated siRNA-lipoplexes. We recently showed that metronomic S-1 dosing (daily oral administration) enhanced the accumulation of PEG-coated liposome containing anticancer drug in solid tumor tissue and thereby increased therapeutic efficacy in tumor-bearing mouse model. To extend this work, we tried to investigate the effect of metronomic S-1 dosing on the intratumoral accumulation of PEG-coated siRNA-lipoplex and, thereby, their therapeutic efficacy in solid tumor-bearing mouse model. Results showed that metronomic S-1 dosing improved systemic delivery of intravenously injected PEG-coated siRNA-lipoplexes into solid tumor tissue. In addition, the combined therapy of S-1 and PEG-coated siRNA-lipoplexes showed potent tumor growth suppressive effect. Our proposed strategy may pose a promising therapeutic one to conquer cancer progression with siRNA.