(621a) Engineering Carfilzomib Loaded Nanoparticles for Improved Efficacy and Reduced Systemic Toxicity in the Treatment of Multiple Myeloma

Multiple myeloma (MM), a B-cell malignancy, is characterized by the uncontrolled proliferation of plasma cells in the bone marrow, forming lesions in the bone.  While in the bone marrow microenvironment, the MM cells acquire drug resistance by adhering to the bone marrow stroma cells. Current therapies utilized chemotherapeutics to treat MM, however with limited success due to the development of drug resistance.  This is a major contributor to the incurability of the disease (median survival 3-5 years), fueling the continued search for better therapies and targets for improved efficacy of treatments. 

The proteasome, a class of intracellular proteins responsible for the degradation of proteins, has been recently identified as a viable target for cancer therapy. These proteins also play a vital role in several different signaling pathways within a cell.  Malignant cells have been shown to have increased proteasome activity, and thus a greater sensitivity to disruptions in proteasome activity compared to healthy tissue. Carfilzomib, an epoxomicin derivative, is a second generation proteasome inhibitor approved by the FDA for the treatment of multiple myeloma.  It irreversibly binds to the chymotrypsin catalytic site of the 20S proteasome, disrupting these pathways and increases the accumulation of pro-apoptotic proteins in tumor cells which results in cell cycle arrest and apoptosis.

Although carfilzomib is an effective treatment, much could be done to improve the therapeutic efficacy.  Carfilzomib, like many other chemotherapeutics, suffers from poor water solubility and has to be administered with the aid of sulfobutyl ether beta cyclodextrin (Captisol®) to improve its solubility for clinical use. In addition, studies have shown that carfilzomib causes thrombocytopenia and anemia, among others, in patients. These side-effects are the result of the non-specific interactions of the drug within the body.  Limiting these non-specific interactions will reduce these adverse events, improving the therapeutic index and patient quality of life.  One means to address both of these issues is through the administration of the drug using a nanoparticle based drug delivery system.

Nanotechnology possesses immense potential for improving the diagnosis and treatment of different cancers. Nanoparticle based drug delivery takes advantage of the enhanced permeability and retention effect created by the “leaky” tumor vasculature.  This phenomenon allows for the increased tumor accumulation of nanoparticles having a diameter of 10 - 100nm. The polymer poly(ethylene glycol) is typically used to coat the surface of the particles to provide the particles with the ability to evade clearance by the reticuloendothelial system, allowing for increased circulation time and tumor accumulation in vivo. In addition, targeting ligands, such as antibodies, peptides, or small molecules, can be conjugated to the distal ends of the polymer to further enhance the particle’s ability to target the tumor cells by binding to receptors on the surface of the malignant cells.

Liposomal nanoparticles are a particularly attractive vehicle for drug delivery. Their facile synthesis and multifunctional capabilities allows them to be used in a wide range of applications. Being generally composed of naturally occurring materials allows them to be biodegradable, a desirable quality in pharmaceutical applications. Therapeutic and diagnostic agents can be loaded in the interior aqueous phase, conjugated to the surface, or embedded in the bilayer of the liposome, allowing for the incorporation of a diverse array of molecules with inherently different properties. This provides a significant benefit especially when this is applied to therapeutics with poor drug-like properties. Nanoparticle incorporation can improve one or more of the drug’s properties that hinder its therapeutic effectiveness, such as solubility, bioavailability, or stability, in addition to the advantages of enhanced tumor targeting and circulation properties conferred by the nanoparticle. In addition, incorporating therapeutics within these nanoparticles can reduce the non-specific toxicities associated with the free drug by sequestering the drug within the nanoparticle until its designed release.

In this study, we engineered carfilzomib loaded pegylated liposomal nanoparticles to decrease systemic toxicity while simultaneously enhancing drug efficacy by increasing its accumulation in the tumor. To further increase tumor accumulation and to promote nanoparticle uptake by MM cells, VLA-4 antagonist peptides were conjugated to the engineered nanoparticles to actively target malignant cells via a multifaceted synthetic procedure. The nanoparticles, exhibiting a size of ~70 nm, were internalized by the MM cells and efficiently induced cell death through cytotoxicity.  Notably, non-targeting and targeting multifunctional nanoparticles were 2 and 4 fold more efficacious than free carfilzomib in vitro, respectively.  Most importantly, in vivo MM xenograph models established that the nanoparticles demonstrated reduced systemic toxicity with improved tumor growth inhibition compared to the free drug.  Combined, this study demonstrates the successful incorporation and administration of carfilzomib loaded nanoparticles with improved therapeutic index for the long term goal of improving MM patient outcomes.