Preclinical toxicology of a novel polymeric antitumour agent: HPMA copolymer-doxorubicin (PK1)

Thermally Targeted p50 Peptide Inhibits Proliferation and Induces Apoptosis of Breast Cancer Cell Lines

The application of rationally designed therapeutic peptides (TP) may improve outcomes in cancer treatment. These peptides hold the potential to directly target proliferative pathways and stimulate cell arrest or death pathways. Elastin-like polypeptide (ELP) is an elastin derived biopolymer that undergoes a thermally mediated phase transition. This study employs p50, a nuclear localization sequence derived peptide that inhibits the activation of NFκB and is implicated in cancer cell survival and metastasis. In order to effectively delivery p50, it is conjugated to SynB1-ELP1, a thermally responsive macromolecular carrier. By applying an external heat source, mild hyperthermic conditions (41 °C) induce aggregation and therefore can be used to specifically target ELP to solid tumors in cancer therapy. The addition of a cell penetrating peptide (CPP) to the N-terminus of the macromolecular carrier enhances the cellular uptake and directs the subcellular localization of the bioactive peptide. The novel TP, p50, inhibits proliferation and induces apoptosis of breast cancer cells by blocking the intranuclear import of NFκB. By expanding the repertoire of oncogenic targets, CPPs, and ELP carrier sizes, ELP-based polypeptides may be modulated to optimize the delivery of these novel therapies and allow for the flexibility to create individualized cancer therapies.

Hemodynamic effects of HPMA copolymer based doxorubicin conjugate: A randomized controlled and comparative spectral study in conscious rats

Conjugation of Doxorubicin (DOX) to N-(2-hydroxypropyl) methylacrylamide copolymer (HPMA) has significantly reduced the DOX-associated cardiotoxicity. However, the reports on the impact of HPMA–DOX conjugates on the cardiovascular system such as blood pressure (BP) and heart rate (HR) were in restrained animals using tail cuff and/or other methods that lacked the resolution and sensitivity. Herein, we employed radiotelemetric-spectral-echocardiography approach to further understand the in vivo cardiovascular hemodynamics and variability post administration of free DOX and HPMA–DOX. Rats implanted with radio-telemetry device were administered intravenously with DOX (5 mg/kg), HPMA–DOX (5 mg DOX equivalent/kg) and HPMA copolymer and subjected to continuous cardiovascular monitoring and echocardiography for 140 days. We found that DOX-treated rats had ruffled fur, reduced body weight (BW) and a low survival rate. Although BP and HR were normal, spectral analysis indicated that their BP and HR variabilities were reduced. All rats exhibited typical signs of cardiotoxicity at histopathology. In contrast, HPMA–DOX rats gained weight over time and survived. Although BP, HR and related variabilities were unaffected, the left ventricular end diastolic volume (EDV) of these rats, as well as of the HPMA copolymer-treated rats, was found increased at the end of observation period. Additionally, HPMA copolymer caused microscopic injury of the heart tissue. All of these suggest the necessity of caution when employing HPMA as carrier for prolonged drug delivery. The current study also indicates the potential of radiotelemetric-spectral-echocardiography approach for improved preclinical cardiovascular risk assessment of polymer–drug conjugate and other nano-sized-drug constructs.

Intracellular Cleavable CpG Oligodeoxynucleotide-Antigen Conjugate Enhances Anti-tumor Immunity

Conjugation of a vaccine adjuvant to an antigen enhances anti-tumor immune responses. Direct chemical conjugation, however, may limit their processing by the antigen-presenting cell for immune stimulation. To test this hypothesis, antigen-adjuvant conjugates were designed to be cleaved by an intracellular trigger to release antigen and adjuvant from each other. The different reductive environment inside and outside antigen-presenting cells was used as a trigger for targeted intracellular release. Two redox-responsive disulphide linkers were used to conjugate the model antigen ovalbumin to CpG. In vitro stability assays with the reductant glutathione showed that one conjugate (SS) was cleaved by glutathione concentrations of the extra- and intracellular compartments. A second conjugate (HYN-SS) was only cleaved at the higher intracellular glutathione concentration. In vitro cell culture studies showed that high T cell responses were generated by the HYN-SS and the stable conjugate HYN. The SS conjugate induced a lower T cell response similar to a mixture of CpG and ovalbumin. An in vivo therapeutic tumor trial demonstrated a superior survival rate of 9/10 for mice vaccinated with HYN-SS conjugate compared to HYN (6/10), SS (2/10), and the mixture (2/10). This intracellular cleavable conjugation strategy represents a promising approach to improve cancer immunotherapy of soluble vaccines.

Biodegradable multiblock poly(N-2-hydroxypropyl)methacrylamide gemcitabine and paclitaxel conjugates for ovarian cancer cell combination treatment

The synthesis, characterization, and in vitro evaluation of a combination delivery of multiblock poly(N-2-hydroxypropyl)methacrylamide (HPMA), gemcitabine (GEM) and paclitaxel (PTX) conjugates is described in this study. Multiblock copolymer conjugates of a large molecular weight (Mw>200 kDa) were studied and compared to traditional, small molecular weight (Mw<45 kDa) conjugates. Stability of the conjugates in different pH was assessed, and their cytotoxicity in combination toward A2780 human ovarian cancer cells was evaluated by combination index analysis. Treatment duration (4 and 72 h) and sequence of addition were explored. In addition, an HPMA copolymer conjugate with both GEM and PTX in the side chains was evaluated in a similar manner and compared to a physical mixture of individual conjugates. Conjugates with narrow molecular weight distribution (Mw/Mn<1.1) were obtained via RAFT polymerization, and drug loadings of between 5.5 and 9.2 wt% were achieved. Conjugates demonstrated moderate stability with less than 65% release over 24h at pH 7.4, and near complete drug release in the presence of the lysosomal enzyme cathepsin B in 3h. In combination, the cytotoxic effects of a mixture of the conjugates were primarily additive. Synergistic effects were observed when A2780 human ovarian cancer cells were treated simultaneously for 4h with multiblock conjugates (CI<0.7). When both GEM and PTX were conjugated to the same copolymer backbone, moderate antagonism (CI 1.3-1.6) was observed. These results demonstrate that multiblock HPMA copolymer-GEM and -PTX conjugates, when delivered as a mixture of individual agents, are promising for the treatment of ovarian cancer.

Protease-activated drug development

In this extensive review, we elucidate the importance of proteases and their role in drug development in various diseases with an emphasis on cancer. First, key proteases are introduced along with their function in disease progression. Next, we link these proteases as targets for the development of prodrugs and provide clinical examples of protease-activatable prodrugs. Finally, we provide significant design considerations needed for the development of the next generation protease-targeted and protease-activatable prodrugs.

Targetable HPMA copolymer-aminohexylgeldanamycin conjugates for prostate cancer therapy

PURPOSE

This study focuses on the synthesis and characterization of N-(2-hydroxypropyl)methacrylamide (HPMA) copolymer-cyclo-RGD (Arg-Gly-Asp) conjugates for delivery of geldanamycin to prostate tumors.

MATERIALS AND METHODS

HPMA copolymers containing aminohexylgeldanamycin (AH-GDM) with and without the targeting peptide RGDfK were synthesized and characterized. Drug release from copolymers was evaluated using cathepsin B. Competitive binding of copolymer conjugates to alpha(v)beta(3) integrin was evaluated in prostate cancer (PC-3) and endothelial (HUVEC) cell lines and in vitro growth inhibition was assessed. The maximum tolerated dose for single i.v. injections of free drug and the conjugates was established in nude mice.

RESULTS

HPMA copolymers containing AH-GDM and RGDfK showed active binding to the alpha(v)beta(3) integrin similar to that of free peptide. Similarly, growth inhibition of cells by conjugates was comparable to that of the free drug. Single intravenous doses of HPMA copolymer-AH-GDM-RGDfK conjugates in mice were tolerated at 80 mg/kg drug equivalent, while free drug caused morbidity at 40 mg/kg. No signs of toxicity were present in mice receiving HPMA copolymer-AH-GDM-RGDfK over the 14-day evaluation period.

CONCLUSION

Results of in vitro activity and in vivo tolerability experiments hold promise for the utility of HPMA copolymer-AH-GDM-RGDfK conjugates for treatment of prostate cancer with greater efficacy and reduced toxicity.

L-histidine-based pH-sensitive anticancer drug carrier micelle: reconstitution and brief evaluation of its systemic toxicity

A doxorubicin (DOX)-carrier micellar system consisting of poly(histidine)(5K)-b-poly(ethylene glycol)(2K) and poly(l-lactic acid)(3K)-b-PEG(2K)-folate has been developed targeting the early endosomal pH and it have been convincingly proved that intracellular high dose strategy using such micelles is effective in overcoming multidrug resistance (MDR) of cancer cells. Due to the low DOX concentrations in the micelle solution obtained by dialysis and the lack of long-term stability of the micelles, stable and lyophilized micelle formulations were the subject of investigation reported here by using excipients of sucrose, PEG or Pluronic. The reconstituted micelle solutions were examined by particle size, pH sensitivity, and cytotoxicity for MDR cells and the results were compared with the non-lyophilized micelles. Among tested excipients, Pluronic F127 (33 wt%) added to the polymer/drug solution prior to dialysis resulted in a reconstituted product stable for a week and presented equivalent benefits as the fresh micelle formulation. The blank micelles did not present any apparent systemic toxicity in mice up to 2400 mg/kg i.v. injection (800 mg/kg day) for 3 days). The brief toxicity of reconstituted DOX loaded micelles was examined by the maximum tolerated dose (MTD), which was approximately 7.5-fold higher than free DOX and guaranteeing further animal toxicity and efficacy study.

A thermally targeted elastin-like polypeptide-doxorubicin conjugate overcomes drug resistance

The ability of cancer cells to become simultaneously resistant to different drugs, a trait known as multidrug resistance, remains a major obstacle for successful anticancer therapy. One major mechanism of resistance involves cellular drug efflux by expression of P-glycoprotein (P-gp), a membrane transporter with a wide variety of substrates. Anthracyclines are especially prone to induction of resistance by the P-gp mechanism. P-gp mediated resistance is often confronted by use of P-gp inhibitors, synthesis of novel analogs, or conjugating drugs to macromolecular carriers in order to circumvent the efflux mechanism. In this report, the effect of free and Elastin-like polypeptide (ELP) bound doxorubicin (Dox) on the viability of sensitive (MES-SA and MCF-7) and multidrug resistant (MES-SA/Dx5 and NCI/ADR-RES) human carcinoma cells was studied in vitro. The resistant MES-SA/Dx5 cells demonstrated about 70 times higher resistance to free Dox than the sensitive MES-SA cells, and the NCI/ADR-RES cells were about 30 fold more resistant than the MCF-7 cells. However, the ELP-bound Dox was equally cytotoxic in both sensitive and resistant cell lines. The ELP-bound Dox was shown to accumulate in MES-SA/Dx5 cells, as opposed to free Dox, which was rapidly pumped out by the P-gp transporter. Since ELP is a thermally responsive carrier, the effect of hyperthermia on the cytotoxicity of the ELP-Dox conjugate was investigated. Both cytotoxicity and apoptosis were enhanced by hyperthermia in the Dox resistant cells. The results suggest that ELP-Dox conjugates may provide a means to thermally target solid tumors and to overcome drug resistance in cancer cells.

Phase I dose escalation and pharmacokinetic study of pluronic polymer-bound doxorubicin (SP1049C) in patients with advanced cancer

SP1049C is a novel anticancer agent containing doxorubicin and two nonionic pluronic block copolymers. In preclinical studies, SP1049C demonstrated increased efficacy compared to doxorubicin. The objectives of this first phase I study were to determine the toxicity profile, dose-limiting toxicity, maximum tolerated dose and pharmacokinetic profile of SP1049C, and to document any antitumour activity. The starting dose was 5 mg m⁻² (doxorubicin content) as an intravenous infusion once every 3 weeks for up to six cycles. A total of 26 patients received 78 courses at seven dose levels. The dose-limiting toxicity was myelosuppression and DLT was reached at 90 mg m⁻². The maximum tolerated dose was 70 mg m⁻² and is recommended for future trials. The pharmacokinetic profile of SP1049C showed a slower clearance than has been reported for conventional doxorubicin. Evidence of antitumour activity was seen in some patients with advanced resistant solid tumours. Phase II trials with this agent are now warranted to further define its antitumour activity and safety profile.