title: HIV-1 Tat peptide immunoconjugates differentially sensitize breast cancer cells to selected antiproliferative agents that induce the cyclin-dependent kinase inhibitor p21WAF-1/CIP-1.
abstract: In this study, we evaluated the ability of anti-p21 antibodies conjugated to 17-mer peptides [GRKKRRQRRRPPQGYGC] harboring the membrane-translocating and nuclear import sequences [underlined] of HIV-1 tat protein to inhibit the cyclin-dependent kinase inhibitor, p21(WAF-1/Cip-1) (p21) and differentially sensitize MDA-MB-468 and MCF-7 human breast cancer (BC) cells to the antiproliferative effects of treatments that induce or do not induce p21. BC cells were treated with increasing concentrations of epidermal growth factor (EGF; 0.5-10 nM), the topoisomerase I inhibitor, camptothecin (CPT; 0.1-4 muM), or increasing doses of gamma-radiation (2-20 Gy). Western blot was used to evaluate p21 expression. The effect of treatment on cell cycle distribution was studied. Growth inhibition was measured by the WST-1 assay. Expression of p21 was increased in MDA-MB-468 cells treated with EGF or CPT but not by gamma-irradiation. MCF-7 cells exhibited p21 upregulation following exposure to CPT and gamma-radiation but not EGF. EGF caused cell cycle arrest in G(1) phase for MDA-MB-468 cells. CPT caused G(1)-phase arrest in MDA-MB-468 cells and prolonged S phase in MCF-7 cells. gamma-Radiation caused an increase in cells in G(2)/M phase for MDA-MB-468 and MCF-7. MDA-MB-468 cells were growth-inhibited by EGF, CPT, and gamma-radiation. MCF-7 cells were growth-stimulated by EGF and inhibited by CPT and gamma-radiation. Combining EGF with tat-anti-p21 immunoconjugates (ICs) amplified the growth-inhibitory effect on MDA-MB-468 cells 1.2-fold to 2.3-fold, but had no effect on the growth stimulation of MCF-7 cells by EGF. Tat-anti-p21 ICs sensitized MCF-7 cells 1.4-fold to gamma-radiation but had no effect on the growth of gamma-irradiated MDA-MB-468 cells. Tat-anti-p21 ICs sensitized both MDA-MB-468 and MCF-7 cells 1.7-fold to CPT. We conclude that tat-anti-p21 ICs are promising sensitizers for cytotoxic cancer therapies and that their sensitization is dependent on treatment-related p21 expression. This general approach could potentially be extended to other growth-regulatory molecules that are associated with tumor growth and progression.
authors.affiliation: Division of Nuclear Medicine, University Health Network, Toronto, Canada.
authors.forename: Meiduo
authors.initials: M
authors.lastname: Hu
authors.forename: Judy
authors.initials: J
authors.lastname: Wang
authors.forename: Paul
authors.initials: P
authors.lastname: Chen
authors.forename: Raymond M
authors.initials: RM
authors.lastname: Reilly
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D000906:Antibodies / Q000235:genetics / Q000378:metabolism*; D000970:Antineoplastic Agents / Q000378:metabolism* / Q000627:therapeutic use; D001943:Breast Neoplasms / Q000188:drug therapy / Q000378:metabolism*; D002453:Cell Cycle / Q000502:physiology; D045744:Cell Line, Tumor; D049109:Cell Proliferation; D050759:Cyclin-Dependent Kinase Inhibitor p21 / Q000235:genetics / Q000378:metabolism*; D004305:Dose-Response Relationship, Drug; D005260:Female; D005786:Gene Expression Regulation; D015696:Gene Products, tat / Q000235:genetics / Q000378:metabolism*; D015497:HIV-1; D006801:Humans; D018796:Immunoconjugates / Q000235:genetics / Q000378:metabolism* / Q000627:therapeutic use; D008969:Molecular Sequence Data; D010446:Peptide Fragments / Q000235:genetics / Q000378:metabolism*; D054322:tat Gene Products, Human Immunodeficiency Virus
chemical_list: D000906:Antibodies; D000970:Antineoplastic Agents; D050759:Cyclin-Dependent Kinase Inhibitor p21; D015696:Gene Products, tat; D018796:Immunoconjugates; D010446:Peptide Fragments; D054322:tat Gene Products, Human Immunodeficiency Virus