Albumin as a drug delivery carrier to overcome biological barriers in cancer
Creators: name: Liu, Xinquan
Publisher: name: The University of Texas at Austin
Year: 2022
Subjects: Albumin
Albumin nanoparticles
KRAS mutation
Macropinocytosis
Conjugation
Monomethyl auristatin E
Cysteine 34
Albumin drug conjugate
Pancreatic cancer

description: In disease, especially cancer, biological barriers impede the delivery of therapeutic agents to effectively reach their intended targets after administration. Developing delivery strategies that understand and take into account the biological environment is critical to improve the efficiency of drug delivery. Nature provides a biological toolkit from which effective drug delivery systems can be developed. In particular, albumin is an attractive delivery carrier with favorable intrinsic properties to overcome intracellular and extracellular delivery barriers in cancer. In a subset of cancers, the RAS family of oncogenes (KRAS, HRAS, NRAS) are the most frequent mutations in cancers and regulate key signaling pathways that drive tumor progression, including hyperactive cell proliferation and metabolism. As a result, drug delivery targeting RAS-driven tumors has been a long-standing challenge in cancer therapy. Looking for solutions inspired by nature, recent observations indicate that extracellular nutrients, including glucose, lipids, and albumin, were found to be actively scavenged by mutant RAS activated cancer cells via macropinocytosis to fulfill the energetic requirements of cancer cells to survive and proliferate. Here, we exploit this mechanism to deliver albumin nanoparticles in cancer cells harboring activating KRAS mutations. We synthesized stable albumin nanoparticles that demonstrate significantly greater uptake in cancer cells with activating mutations of KRAS than monomeric albumin (i.e. dissociated form of clinically used nab-paclitaxel). From pharmacological inhibition and semi-quantitative fluorescent microscopy studies, these nanoparticles exhibit significantly increased uptake in mutant KRAS cancer cells than wild-type KRAS cells by macropinocytosis. Importantly, we demonstrate that their uptake is driven by KRAS. This nanoparticle-based strategy targeting KRAS-driven macropinocytosis is a facile approach towards improved delivery into KRAS-driven cancers. Through our studies with albumin nanoparticles, it was realized that albumin itself potentially possesses excellent pharmacokinetics that could be leveraged to improve drug delivery. To further harness the intrinsic transport properties of albumin yet improve the therapeutic index of current in situ albumin-binding prodrugs, we developed albumin-drug conjugates with a controlled loading that achieved better antitumor efficacy. Model drug monomethyl auristatin E (MMAE) was conjugated ex vivo to Cys34 of albumin via a cathepsin B-sensitive dipeptide linker to ensure that all drugs would be bound specifically to albumin. The resulting albumin-drug conjugate with a drug to albumin ratio (DAR) of 1 (ALDC1) retained the native structure of albumin compared to conjugate with a higher DAR of 3 (ALDC3). ALDC1 exhibited improved drug release and cytotoxicity compared to ALDC3 in vitro. Slower plasma clearance and increased drug exposure over time of ALDC1 were observed compared to ALDC3 and MMAE prodrug. In single dose studies with MIA PaCa2 xenografts, cohorts treated with ALDC1 had the highest amount of MMAE drug in tumor tissues compared to other treatment arms. After multiple dosing, ALDC1 significantly delayed the tumor growth compared to control treatment arms MMAE, MMAE-linker conjugate, and ALDC3. When dosed with the maximum tolerated dose of ALDC1, there was complete eradication of 83.33% of the tumors in the treatment group. Ex vivo conjugated ALDC1 also significantly inhibited tumor growth in an immunocompetent syngeneic mouse model that recapitulates the phenotype and clinical features of human pancreatic cancers. In summary, site-specific loading of drug to albumin at 1:1 ratio allowed the conjugate to maintain the native structure of albumin and its intrinsic properties. By conjugating the drug to albumin prior to administration minimized premature cleavage and instability of the drug in plasma and enabled higher drug accumulation in tumors compared to in situ albumin-binding prodrugs. This strategy to control drug loading ex vivo ensures complete drug binding to the albumin carrier and achieves excellent antitumor efficacy, and it has the potential to greatly improve the outcomes of anticancer therapy. Collectively, these findings suggest that albumin can serve as an effective drug delivery carrier for drug delivery in solid tumors when the intrinsic properties of albumin were carefully utilized.