HPMA copolymer–anticancer drug–OV-TL16 antibody conjugates. II. Processing in epithelial ovarian carcinoma cells in vitro

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Abstract
The binding, internalization, subcellular trafficking and in vitro cytotoxicity of N‐(2‐hydroxypropyl)methacrylamide (HPMA) copolymer–anti‐cancer drug–OV‐TL16 antibody (Ab) conjugates in the ovarian carcinoma OVCAR‐3 cell line have been investigated. Adriamycin (ADR) and meso chlorin e6 mono(N‐2‐aminoethylamide) (Mce6) photosensitizer were used as anti‐cancer drugs. Targeted (Ab‐containing) conjugates were compared with non‐targeted HPMA copolymer–drug conjugates and with free drugs. Targeted conjugates were taken up rapidly by cells and detected within lysosomes by confocal fluorescence microscopy. The ADR attached to polymer chains via a degradable GFLG spacer was released from the conjugate, diffused via the lysosomal membrane into the cytoplasm and ultimately accumulated in the cell nuclei. In contrast, conjugates containing ADR bound via the GG spacer accumulated in the lysosomes, but no fluorescence could be detected in the cell nuclei. Binding the drugs to a non‐targeted HPMA copolymer decreased their cytotoxicity in vitro. The IC50 dose increased from 2 μM for free ADR to 150 μM for P(GFLG)–ADR (P is the HPMA copolymer backbone) and from 0.34 μM for free Mce6 (with light) to 290 μM for P–(GG)–Mce6. However, attachment of OV‐TL16 Abs rendered HPMA copolymer–drug conjugates biorecognizable by OVCAR‐3 cells and markedly increased their cytotoxicity. The IC50 doses were 4.4 and 0.38 μM for the targeted conjugates P(GFLG)–ADR–Ab and P(GG)–Mce6–Ab (with light), respectively. Biorecognition was shown to be specific by inhibition experiments with free Ab. The findings indicate the potential of these conjugates as effective agents in the treatment of ovarian cancer. Int. J. Cancer 75:600–608, 1998.

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