ERBB3 and neoplasm: The acid-sensitive hydrazone linkage exploitsthe natural variationin pH between healthy (pH7.4) and tumor tissue (pH 6.8) and the endosomecompartment (pH 4.5–6.8) to achieve controlled drug release.To confirm selective drug release under desired pH conditions, weevaluated DOX release from the HBP semiqualitatively by dialyzingHBP-DOX with or without HER3 bsAb (HER3-HBP-DOX) in PBS buffers withspecific pH levels.