Single Protein Encapsulated Doxorubicin as an Efficacious Anticancer Therapeutic

Single protein encapsulated SN38 for tumor-targeting treatment

BACKGROUND

The alkaloid camptothecin analog SN38 is a potent antineoplastic agent, but cannot be used directly for clinical application due to its poor water solubility. Currently, the prodrug approach on SN38 has resulted in 3 FDA-approved cancer therapeutics, irinotecan, ONIVYDE, and Trodelvy. However, only 2-8% of irinotecan can be transformed enzymatically in vivo into the active metabolite SN38, which severely limits the drug's efficacy. While numerous drug delivery systems have been attempted to achieve effective SN38 delivery, none have produced drug products with antitumor efficacy better than irinotecan in clinical trials. Therefore, novel approaches are urgently needed for effectively delivering SN38 to cancer cells with better efficacy and lower toxicity.

METHODS

Based on the unique properties of human serum albumin (HSA), we have developed a novel single protein encapsulation (SPE) technology to formulate cancer therapeutics for improving their pharmacokinetics (PK) and antitumor efficacy and reducing their side effects. Previous application of SPE technology to doxorubicin (DOX) formulation has led to a promising drug candidate SPEDOX-6 (FDA IND #, 152154), which will undergo a human phase I clinical trial. Using the same SPE platform on SN38, we have now produced two SPESN38 complexes, SPESN38-5 and SPESN38-8. We conducted their pharmacological evaluations with respect to maximum tolerated dose, PK, and in vivo efficacy against colorectal cancer (CRC) and soft tissue sarcoma (STS) in mouse models.

RESULTS

The lyophilized SPESN38 complexes can dissolve in aqueous media to form clear and stable solutions. Maximum tolerated dose (MTD) of SPESN38-5 is 250 mg/kg by oral route (PO) and 55 mg/kg by intravenous route (IV) in CD-1 mice. SPESN38-8 has the MTD of 45 mg/kg by IV in the same mouse model. PK of SPESN38-5 by PO at 250 mg/kg gave mouse plasma AUC0-∞ of 0.05 and 4.5 nmol × h/mL for SN38 and SN38 glucuronidate (SN38G), respectively, with a surprisingly high molar ratio of SN38G:SN38 = 90:1. However, PK of SPESN38-5 by IV at 55 mg/kg yielded much higher mouse plasma AUC0-∞ of 19 and 28 nmol × h/mL for SN38 and SN38G, producing a much lower molar ratio of SN38G:SN38 = 1.5:1. Antitumor efficacy of SPESN38-5 and irinotecan (control) was evaluated against HCT-116 CRC xenograft tumors. The data indicates that SPESN38-5 by IV at 55 mg/kg is more effective in suppressing HCT-116 tumor growth with lower systemic toxicity compared to irinotecan at 50 mg/kg. Additionally, SPESN38-8 and DOX (control) by IV were evaluated in the SK-LMS-1 STS mouse model. The results show that SPESN38-8 at 33 mg/kg is highly effective for inhibiting SK-LMS-1 tumor growth with low toxicity, in contrast to DOX's insensitivity to SK-LMS-1 with high toxicity.

CONCLUSION

SPESN38 complexes provide a water soluble SN38 formulation. SPESN38-5 and SPESN38-8 demonstrate better PK values, lower toxicity, and superior antitumor efficacy in mouse models, compared with irinotecan and DOX.

Human Serum Albumin-Oligothiophene Bioconjugate: A Phototheranostic Platform for Localized Killing of Cancer Cells by Precise Light Activation

The electronic, optical, and redox properties of thiophene-based materials have made them pivotal in nanoscience and nanotechnology. However, the exploitation of oligothiophenes in photodynamic therapy is hindered by their intrinsic hydrophobicity that lowers their biocompatibility and availability in water environments. Here, we developed human serum albumin (HSA)-oligothiophene bioconjugates that afford the use of insoluble oligothiophenes in physiological environments. UV-vis and electrophoresis proved the conjugation of the oligothiophene sensitizers to the protein. The bioconjugate is water-soluble and biocompatible, does not have any "dark toxicity", and preserves HSA in the physiological monomeric form, as confirmed by dynamic light scattering and circular dichroism measurements. In contrast, upon irradiation with ultralow light doses, the bioconjugate efficiently produces reactive oxygen species (ROS) and leads to the complete eradication of cancer cells. Real-time monitoring of the photokilling activity of the HSA-oligothiophene bioconjugate shows that living cells "explode" upon irradiation. Photodependent and dose-dependent apoptosis is one of the primary mechanisms of cell death activated by bioconjugate irradiation. The bioconjugate is a novel theranostic platform able to generate ROS intracellularly and provide imaging through the fluorescence of the oligothiophene. It is also a real-time self-reporting system able to monitor the apoptotic process. The induced phototoxicity is strongly confined to the irradiated region, showing localized killing of cancer cells by precise light activation of the bioconjugate.