Intracellular delivery of a proapoptotic peptide via conjugation to a RAFT synthesized endosomolytic polymer

Mol Pharm. 2010 Apr 5;7(2):468-76. doi: 10.1021/mp9002267.


Peptides derived from the third B-cell lymphoma 2 (Bcl-2) homology domain (BH3) can heterodimerize with antiapoptotic Bcl-2 family members to block their activity and trigger apoptosis. Use of these peptides presents a viable anticancer approach, but delivery barriers limit the broad application of intracellular-acting peptides as clinical therapeutics. Here, a novel diblock copolymer carrier is described that confers desirable pharmaceutical properties to intracellular-acting therapeutic peptides through site-specific molecular conjugation. This polymer was prepared using reversible addition-fragmentation chain transfer (RAFT) to form a pyridyl disulfide end-functionalized, modular diblock copolymer with precisely controlled molecular weight (M(n)) and low polydispersity (PDI). The diblock polymer (M(n) 19,000 g/mol, PDI 1.27) was composed of an N-(2-hydroxypropyl) methacrylamide (HPMA) first block (M(n) 13,800 g/mol, PDI 1.13) intended to enhance water solubility and circulation time. The second polymer block was a pH-responsive composition designed to enhance endosomal escape and consisted of equimolar quantities of dimethylaminoethyl methacrylate (DMAEMA), propylacrylic acid (PAA), and butyl methacrylate (BMA). A hemolysis assay indicated that the diblock polymer undergoes a physiologically relevant pH-dependent switch from a membrane inert (1% hemolysis, pH 7.4) to a membrane disruptive (61% hemolysis, pH 5.8) conformation. Thiol-disulfide exchange reactions were found to efficiently produce reversible polymer conjugates (75 mol % peptide reactivity with polymer) with a cell-internalized proapoptotic peptide. Microscopy studies showed that peptide delivered via polymer conjugates effectively escaped endosomes and achieved diffusion into the cytosol. Peptide-polymer conjugates also produced significantly increased apoptotic activity over peptide alone in HeLa cervical carcinoma cells as found using flow cytometric measurements of mitochondrial membrane depolarization (2.5-fold increase) and cell viability tests that showed 50% cytotoxicity after 6 h of treatment with 10 muM peptide conjugate. These results indicate that this multifunctional carrier shows significant promise for proapoptotic peptide cancer therapeutics and also as a general platform for delivery of peptide drugs with intracellular targets.

MeSH terms

  • Antineoplastic Agents / chemical synthesis
  • Antineoplastic Agents / chemistry
  • Antineoplastic Agents / metabolism
  • Antineoplastic Agents / pharmacology
  • Cell Proliferation / drug effects
  • Flow Cytometry
  • HeLa Cells
  • Hemolysis / drug effects
  • Humans
  • Hydrogen-Ion Concentration
  • Membrane Potential, Mitochondrial / drug effects
  • Models, Theoretical
  • Peptides / chemistry*
  • Polymers / chemical synthesis*
  • Polymers / chemistry*
  • Polymers / metabolism
  • Polymers / pharmacology


  • Antineoplastic Agents
  • Peptides
  • Polymers