1. Assembly of Biomaterials

We design and synthesize new polymetric materials that allow assembly with therapeutic molecules. These systems are invented and investigated at the cellular and animal levels at Caltech. Two systems developed in our labs have been translated into clinical materials and are currently used in human clinical trials.

Selected Recent Publications:

D. W. Bartlett and M. E. Davis, “Physicochemical and biological characterization of targeted, nucleic acid-containing nanoparticles,” Bioconjugate Chem., 18, 456 (2007).

M. E. Davis, “Design and development of IT-101, a cyclodextrin-containing polymer conjugate of camptothecin,” Adv. Drug Del. Rev. 61, 1189 (2009).

M. E. Davis, “The first targeted delivery of siRNA in humans via a self-assembling, cyclodextrin polymer-based nanoparticle:  From concept to clinic,” Mol. Pharm. 6, 659 (2009). (see schematics in this section)

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2. In Vivo Biodistribution

Recent studies aim at developing a mechanism to explain the apparent efficacy of targeted nanoparticles in vivo.

With the simultaneous use of positron emission tomography (PET) and bioluminescence imaging (BLI), Bartlett et al. (2007) tracked the biodistribution of siRNA-containing, transferrin (Tf)-targeted nanoparticles and the tumor growth, to establish correlation between distribution in the tumor and efficacy due to targeting with transferrin. From this study, targeting does not change the organ level distribution of particles, but does lead to knockdown of target gene.

Schulep et al. (2009) tracked in vivo distribution data (from PET) of i.v. injected IT-101 particles in mice, and used a three-compartment model to deduce the vascular permeability and tumor retention of IT-101 that matched well with experimental data. Confocal microscopy reveals the intracellular localization of IT-101 particles in cancer cells within the tumor, validating a key assumption of the above model that a sink must be present to collect particles over time.

Choi et al. (2010) probed the quantitative effect of ligand targeting by monitoring the in vivo distribution of PEGylated gold particles containing different contents of Tf. While inductively coupled plasmonic mass spectrometry (ICP-MS) data show no difference in bulk tumor particle content as a function of Tf, transmission electron microscopy (TEM) reveal clear intracellular accumulation of gold particles with a critical Tf content.

Selected Recent Publications:

D. W. Bartlett, H. Su, I. J. Hildebrandt, W. A. Weber and M. E. Davis, “Impact of tumor-specific targeting on the biodistribution and efficacy of siRNA nanoparticles measured by multimodality in vivo imaging,” Proc. Nat. Acad. Sci. USA, 104, 15549 (2007). (top panel)

T. Schluep, J. Hwang, I. J. Hildebrandt, J. Czernin, C. H. J. Choi, C. A. Alabi, B. C. Mack and M. E. Davis, “Pharmacokinetics and tumor dynamics of the nanoparticle IT-101 from PET imaging and tumor histological measurements,” Proc. Nat. Acad. Sci. USA 106, 11394 (2009). (middle panel)

C. H. J. Choi, C. A. Alabi, P. Webster and M. E. Davis, “Mechanism of active targeting in solid tumors with transferrin-containing gold nanoparticles,” Proc. Nat. Acad. Sci. USA, 107, 13, 1235-1240 (2010). (bottom panel)

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3. Pharmacodynamics

Current work also investigates the pharmacodynamics of particles of CDP encapsulated with small interfering RNA (siRNA). This entails studies that focus on the use of in vitro studies and in vivo animal tumor models, coupled with mathematical modeling, to discern the factors that influence the kinetics of gene silencing after siRNA administration to develop reasonable dosing regimens for current and future siRNA based therapeutics.

The duration of gene silencing depends on the dilution due to cell doubling, not intracellular siRNA stability (Bartlett et al, 2006). Nuclease stabilization of siRNAs does not significantly enhance the duration or magnitude of gene silencing once siRNAs achieve cytosolic localization (Bartlett et al, 2007). Further studies also show no advantage in dosing regimens shorter than once every three days (Bartlett et al, 2008).

Selected Recent Publications:

D. W. Bartlett and M. E. Davis, “Insights into the kinetics of siRNA-mediated gene silencing from live-cell and live-animal bioluminescent imaging,” Nucl. Acids Res., 34, 322 (2006). (top panel)

D. W. Bartlett and M. E. Davis, “Effect of siRNA nuclease stability on the in vitro and in vivo kinetics of siRNA-mediated gene silencing,” Bioeng. and Biotechnol., 97, 909 (2007). (middle panel)

D. W. Bartlett and M. E. Davis, “Impact of tumor-specific targeting and dosing schedule on tumor growth inhibition after intravenous administration of siRNA-containing nanoparticles,” Biotechnol. Bioeng., 99, 975 (2008) (bottom panel)

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4. Clinical Studies

Following the synthesis of targeted nanoparticles, recent studies entail their translation from laboratory to clinic.

siRNA-CDP Nanoparticles:

Hu-Lieskovan et al.(2005) showed the safety and efficacy of CDP-siRNA nanoparticles with Tf targeting as a non-viral drug delivery system of siRNA, given the abrogation of EWS-FLI1 expression and inhibit Ewing’s sarcoma tumor growth in vivo. For clinical applications, Heidel et al. (2007) first identified an anti-RRM2 siRNA duplex (siR2B+5) that demonstrates significant anti-proliferative activity in cancer cells of various human types and species. Heidel et al. (2007) proved the safe administration of multiple, systemic doses of Tf-targeted CDP nanoparticles containing siRNA in non-human primates. Very recently, Davis et al. (2010) provided first evidence of a specific gene inhibition (reduction both in mRNA and protein) by an RNAi mechanism of action via the administration of Tf-targeted, siRNA-containing CDP nanoparticles in humans. It also showed the presence of intracellularly localized such particles in tumor biopsies in amounts that correlate with administered dose levels (first for systemically delivered particles of any kind).

Selected Recent Publications:

S. Hu-Lieskovan, J. D. Heidel, D. W. Bartlett, M. E. Davis and T. J. Triche, “Sequence-specific knockdown of EWS-FLI1 by targeted, non-viral delivery of siRNA inhibits tumor growth in a murine model of metastatic Ewing’s sarcoma,” Cancer Res., 65, 8984 (2005). (top panel)

T. Schluep, S. J. Hwang, J. Cheng, J. D. Heidel, D. W. Bartlett and M. E. Davis, “Preclinical efficacy of the camptothecin-polymer conjugate IT-101 in multiple cancer models,” Clin. Cancer Res., 12, 1606 (2006).

J. D. Heidel, J. Y. C. Liu, Y. Yen, B. Zhou, B. S. E. Heale, J. J. Rossi, D. W. Bartlett and M. E. Davis, “Potent siRNA inhibitors of ribonucleotide reductase subunit RRM2 reduce cell proliferation in vitro and in vivo,” Clin. Cancer Res., 13, 2207 (2007).(second panel)

J. D. Heidel, Z. Yu, J. Y.-C. Liu, S. M. Rele, Y. Liang, R. K. Zeidan, D. J. Kornbrust and M. E. Davis, “Administration in non-human primates of escalating intravenous doses of targeted nanoparticles containing ribonucleotide reductase sub-unit M2 siRNA,” Proc. Nat. Acad. Sci. USA, 104, 5715 (2007). (third panel)

T. Numbenjapon, J. Wang, D. Colcher, T. Schluep, M. E. Davis, J. Duringer, L. Kretzner, Y. Yen, S. J. Forman and A. Raubitschek, “Preclinical efficacy of camptothecin-polymer conjugate IT-101 in multiple human lymphoma xenograft models,” Clin. Cancer Res. 15, 4365 (2009).

Davis, M.E., Zuckerman, J.E., Choi, C.H.J., Seligson, D., Tolcher, A., Alabi, C.A., Yen, Y., Heidel, J.D., Ribas, A., “Evidence of RNAi in humans from systemically adminstered siRNA via targeted nanoparticles,” Nature, 464, 1067. (2010). (bottom panel)

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5. Targeted Delivery System for Camptothecin

IT-101 has shown great success in both animal studies and clinical trials. However it is unable to achieve targeted delivery. We have therefore designed and synthesized a new delivery system for Camptothecin (CPT) that addresses this issue (Figure A).

MAP-CPT nanoparticles are ~30 nm (Figure B) with a slightly negative surface charge. It shows prolonged in vitro release and pharmacokinetic profile as well as targeting ability. We are currently examining our CPT delivery system in BT-474 (a HER-2 over-expressing human breast cancer cell line) tumor bearing mice with Herceptin antibody as the targeting agent.

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6. Therapeutic Delivery to the Brain

Current work in this lab also includes the delivery of nanoparticles to the brain by designing particles that circumvent the blood-brain barrier through a receptor-mediated transcytosis pathway. Optimal nanoparticle design parameters (size, charge, ligand density) are being discovered using a gold nanoparticle system. Future work will incorporate the optimized nanoparticle parameters into a therapeutic-containing nanoparticle for the treatment of neurologic diseases in mouse models.