Chemosensitization of tumors via simultaneous delivery of STAT3 inhibitor and doxorubicin through HPMA copolymer-based nanotherapeutics with pH-sensitive activation.

We synthesized three novel STAT3 inhibitors (S3iD1-S3iD3) possessing oxoheptanoic residue enabling linkage to HPMA copolymer carrier via a pH-sensitive hydrazone bond. HPMA copolymer conjugates bearing doxorubicin (Dox) and our STAT3 inhibitors were synthesized to evaluate the anticancer effect of Dox and STAT3 inhibitor co-delivery into tumors. S3iD1-3 and their copolymer-bound counterparts (P-S3iD1-P-S3iD3) showed considerable in vitro cytostatic activities in five mouse and human cancer cell lines with IC50 ~0.6-7.9 µM and 0.7-10.9 µM, respectively. S3iD2 and S3iD3 were confirmed to inhibit the STAT3 signaling pathway. The combination of HPMA copolymer-bound Dox (P-Dox) and P-S3iD3 at the dosage showing negligible toxicity demonstrated significant antitumor activity in B16F10 melanoma-bearing mice and completely cured 2 out of 15 mice. P-Dox alone had a significantly lower therapeutic activity with no completely cured mice. Thus, polymer conjugates bearing STAT3 inhibitors may be used for the chemosensitization of chemorefractory tumors.

Polymer nitric oxide donors potentiate the treatment of experimental solid tumours by increasing drug accumulation in the tumour tissue.

The delivery of nitric oxide (NO) specifically to solid tumours was explored in this study as a strategy to augment the passive accumulation of nanomedicines in tumours induced by the Enhanced Permeability and Retention (EPR) effect. An increase in accumulation was achieved by the binding of the chemical precursor of NO, based on an organic nitrate, to a water-soluble synthetic polymer drug carrier. Four structurally different N-(2-hydroxypropyl)methacrylamide (HPMA)-based polymer NO donors were synthesized. Depending on their chemical structure, two of these donors were hydrolytically stable, while two rapidly released the parent nitrate under acidic conditions, mimicking the intracellular environment. The polymer NO donors were shown to overcome the drawbacks related to low-molecular-weight NO releasing compounds, namely systemic toxicity, lack of site specificity, and fast blood clearance. The NO donors showed intracellular NO release upon incubation with tumour cells. In vivo, they potentiated the EPR effect, resulting in an increased accumulation of polymer-bound cytotoxic drug doxorubicin (Dox) in EL4 T-cell lymphoma inoculated in mice. This led to a better therapeutic outcome in the treatment of lymphoma with the high-molecular-weight polymer conjugates carrying Dox but not in the treatment with the free Dox. The localized augmentation of the EPR effect via the tumour-specific NO delivery system can be viewed as a promising strategy to potentiate polymer-based tumour therapy without increasing systemic toxicity.

Nanotherapeutics with anthracyclines: methods of determination and quantification of anthracyclines in biological samples.

Anthracyclines, e.g. doxorubicin, pirarubicin, are widely used as cytostatic agents in the polymer nanotherapeutics designed for the highly effective antitumor therapy with reduced side effects. However, their precise dosage scheme needs to be optimized, which requires an accurate method for their quantification on the cellular level in vitro during nanocarrier development and in body fluids and tissues during testing in vivo. Various methods detecting the anthracycline content in biological samples have already been designed. Most of them are highly demanding and they differ in exactness and reproducibility. The cellular uptake and localization is predominantly observed and determined by microscopy techniques, the anthracycline content is usually quantified by chromatographic analysis using fluorescence detection. We reviewed and compared published methods concerning the detection of anthracycline nanocarriers.

Polymer conjugates of the highly potent cytostatic drug 2-pyrrolinodoxorubicin.

This paper describes the synthesis and biological evaluation of a conjugate of the highly cytotoxic drug 2-pyrrolinodoxorubicin (p-DOX) with an N-(2-hydroxypropyl)methacrylamide copolymer (PHPMA) as a water-soluble biocompatible polymer carrier, utilizing the advantageous concept of polymer-drug conjugates. The conjugate of p-DOX with HPMA copolymer (PHPMA/p-DOX) was prepared by reacting the PHPMA/DOX conjugate, where the DOX was bound via a hydrazone bond, with 4-iodobutyraldehyde. The hydrazone bond between the polymer and drug is susceptible to pH-controlled hydrolysis, enabling prolonged stability in circulation and fast p-DOX release under conditions mimicking the intracellular environment. The in vitro cytostatic activity of free p-DOX was in accordance with literature, whereas its PHPMA conjugate exhibited a 1.3- to 5-fold lower cytotoxicity, depending on the cancer cell line, when compared to the free p-DOX. This is in qualitative agreement with the data obtained for DOX and its HPMA copolymer conjugates. On mice bearing T-cell EL4 lymphoma, no tumor suppression was observed from the free p-DOX at a subtoxic dose of 0.1 mg/kg, whereas the PHPMA/p-DOX conjugate significantly inhibited the initial tumor growth at approximately equitoxic doses of 0.4 and 0.8 mg p-DOX eq/kg. However, moderately elevated doses of the p-DOX equivalent in the conjugate caused toxic effects, making accurate dosage setting essential.