PEG−Doxorubicin Conjugates:  Influence of Polymer Structure on Drug Release, in Vitro Cytotoxicity, Biodistribution, and Antitumor Activity

Abstract

Polymer-drug conjugates (polymer therapeutics) are finding increasing use as novel anticancer agents. Here a series of poly(ethylene glycol) PEG-doxorubicin (Dox) conjugates were synthesized using polymers of linear or branched architecture (molecular weight 5000-20000 g/mol) and with different peptidyl linkers (GFLG, GLFG, GLG, GGRR, and RGLG). The resultant conjugates had a drug loading of 2.7-8.0 wt % Dox and contained <2.0% free drug (% total drug). All conjugates containing a GFLG linker showed approximately 30% release of Dox at 5 h irrespective of PEG molecular weight or architecture. The GLFG linker was degraded more quickly (approximately 57% Dox release at 5 h), and the other linkers more slowly (<16% release at 5 h), by lysosomal enzymes in vitro. In vitro there was no clear relationship between cytotoxicity toward B16F10 cells and the observed Dox release rate. All PEG conjugates were more than 10-fold less toxic (IC50 values > 2 microg/mL) than free Dox (IC50 value = 0.24 microg/mL). Biodistribution in mice bearing sc B16F10 tumors was assessed after administration of PEGs (5000, 10000, or 20000 g/mol) radioiodinated using the Bolton and Hunter reagent or PEG-Dox conjugates by HPLC. The 125I-labeled PEGs showed a clear relationship between Mw and blood clearance and tumor accumulation. The highest Mw PEG had the longest plasma residence time and consequently the greatest tumor targeting. The PEG-Dox conjugates showed a markedly prolonged plasma clearance and greater tumor targeting compared to free Dox, but there was no clear molecular weight-dependence on biodistribution. This was consistent with the observation that the PEG-Dox conjugates formed micelles in aqueous solution comprising 2-20 PEG-Dox molecules depending on polymer Mw and architecture. Although PEG-Dox showed greater tumor targeting than free Dox, PEG conjugation led to significantly lower anthracycline levels in heart. Preliminary experiments to assess antitumor activity against sc B16F10 in vivo showed the PEG5000linear (L)-GFLG-Dox and PEG10000branched (B)-GLFG-Dox (both 5 mg/kg Dox-equiv) to be the most active with T/C values of 146 and 143%, respectively. Free Dox did not show significant activity in this model (T/C = 121%). Dose escalation of PEG5000(L)-GFLG-Dox to 10 mg/kg Dox-equiv prolonged further animal survival (T/C = 161%). Using the Dox-sensitive model ip L1210 (where Dox displayed a T/C = 150% after single ip dose), the PEG5000(L)-GFLG-Dox displayed a maximum T/C of 141% (10 mg/kg Dox-equiv) using a once a day (x3) schedule. Further studies are warranted with PEG5000(L)-GFLG-Dox to determine its spectrum of antitumor activity and also the optimum dosing schedule before clinical testing.

Noninvasive Visualization of in Vivo Drug Delivery of Poly(l-glutamic acid) Using Contrast-Enhanced MRI

“…Polymeric conjugates with high molecular weights had a prolonged blood circulation and higher tumor accumulation than low molecular weight conjugate, which is consistent to the results obtained with conventional pharmacokinetic studies [28,29]. The conjugate with 28 KDa eliminated rapidly from both blood pool and major organs due to its small size and fast excretion through renal filtration and had a relatively low tumor accumulation with short duration time.…”

Highly Active Analogs of α-Factor and Their Activities Against Saccharomyces cerevisiae

“…It has been reported that the physiological activity of α-factor pheromone is closely correlated with affinity for the phospholipid membrane. [36][37][38] Since the target of α-factor is a membrane-associated protein, Ste2p receptor, a certain type of hydrophobic moiety attached to α-factor could aid pheromone localization to the target cell membrane, as do many other hormone such as Ras protein, 29,36-38 thereby leading to increased probability of binding. However, integration of a pheromone into the cellular lipid bilayer depends on the type of modification applied.…”

Tumor pH-responsive flower-like micelles of poly(l-lactic acid)-b-poly(ethylene glycol)-b-poly(l-histidine)

“…In tumor treatment the micelles system has proven effective in regression of tumor size while minimizing damage to the healthy tissues [4] and is being actively investigated in conjunction with hyperthermia [5], ultrasound [6], specific enzyme-induced cleavable bonds [7][8][9], and specific ligands or antibodies [10][11][12][13] for active targeting purposes.…”