Liver-Specific Nanoparticle-Mediated Delivery and MMP-Triggered Release of Veratridine, a Potent Pro-Apoptotic Molecule, to Effectively Target Metastatic Colorectal Cancer

Despite considerable advances to improve colorectal cancer (CRC) survival over the last decade, therapeutic challenges remain due to the rapid metastatic dissemination of primary tumors. Nearly 50% of colorectal cancer (CRC) patients develop liver metastases. This shows the pressing need to develop more effective targeted therapies to decrease the high mortality rates associated with metastatic disease. This study revealed the apoptotic and anti-growth mechanism of veratridine (VTD), a previously used anti-hypertensive supplement. VTD can elevate UBXN2A, a known tumor suppressor protein in CRC, and simultaneously enhance intrinsic and extrinsic apoptosis in metastatic cancer cells. An AOM/DSS mouse model of CRC showed that UBXN2A haplosufficient (UBXN2A +/-) mice treated with VTD had less tumor burden than mice with the full UBXN2A gene treated with vehicle. Recently, we reported that the trypsin-triggered release of anti-cancer small molecules from casein-coated mesoporous silica nanoparticles (MSNs) offers an effective local delivery of drugs at tumor sites. Our findings demonstrate that the high rate of extracellular release of MMPs, particularly MMP-7 by metastatic colon cancer cells, triggers the release of VTD from casein-coated mesoporous MSNs. This shows the "Zip Code" mechanism for the local enrichment of VTD at the tumor sites. MMPs, particularly MMP-7, play a crucial role in CRC liver tumor invasion and formation of metastatic lesions due to their ability to degrade extracellular matrix proteins. Under physiological conditions in non-cancerous cells, the extracellular release of MMPs is limited to a low physiological range; therefore, VTD will not be released at normal non-cancer tissues. After in vitro drug release experiments, two independent mouse experiments, a xenograft and a spleno-hepatic metastatic mouse model of CRC, were used to evaluate the therapeutic efficacy of VTD-loaded and casein-coated carboxylated mesoporous silica nanoparticles, MSN-COOH/VTD/CAS (VTD, 0.2mg/kg). The number and size of developed tumor masses revealed that MSN-COOH/VTD/CAS (VTD, 0.2mg/kg) slows down the progress of tumors in both xenograft and CRC liver mouse models. Based on the in vivo results, we decided we could further improve nanoparticle targeting and drug release; hence, we refocused on calcium-based particles. Calcium carbonate microparticles (CCMPs) and calcium carbonate submicroparticles (CCSMPs) demonstrated higher drug-releasing performance compared to silica-based nanoparticles, MSNs. Without the MMPs trigger, MSNs show slow and continuous “drug leak” over longer period of time whereas CCSMPs stops leakage within an hour. Additionally, CCSMPs showed higher sensitivity to MMP-7 than MMP-9, enhancing the targetability of CCSMPs for CRC metastatic tumors with excessive extracellular MMP-7. The ability of MMP-7 and MMP-9 to release a drug from casein-coated calcium carbonate particles further expands the material platform for the development of targeted gated drug delivery and release using small anti-metastatic molecules. The target delivery strategy offers the dual benefit of enhancing anticancer effects while minimizing potential side effects on healthy cells, maximizing overall therapeutic efficacy.