In Vitro Cytotoxicity and in Vivo Distribution after Direct Delivery of PEG−Camptothecin Conjugates to the Rat Brain

Abstract

Low water solubility and rapid elimination from the brain inhibits local delivery via implants and other delivery systems of most therapeutic drugs to the brain. We have conjugated the chemotherapy drug, camptothecin (CPT), to poly(ethylene glycol) (PEG) of molecular weight 3400 using previously established protocols. These new conjugates are very water-soluble and hydrolyze at a pH-dependent rate to release the active parent drug. We have studied the uptake of these conjugates by cells in vitro and quantified their cytotoxicity toward gliosarcoma cells. These conjugates were loaded into biodegradable polymeric controlled-release implants, and their release characteristics were studied in vitro. We implanted similar polymeric disks into rat brains and used a novel sectioning scheme to determine the concentration profile of CPT in comparison to conjugated CPT in the brain after 1, 7, 14, and 28 days. We have found that PEGylation greatly increases the maximum achievable drug concentration and greatly enhances the distribution properties of CPT, compared to corelease of CPT with PEG. Although only one percent of CPT in the conjugate system was found in the hydrolyzed, active form, drug concentrations were still significantly above cytotoxic levels over a greater distance for the conjugate system. On the basis of these results, we believe that PEGylation shows great promise toward increasing drug distribution after direct, local delivery in the brain for enhanced efficacy in drug treatment.

Conjugation to Increase Treatment Volume during Local Therapy: A Case Study with PEGylated Camptothecin

“…Diffusion and elimination properties in brain tissue have previously been reported for a variety of compounds, including our recent measurements for camptothecin (5). These drugs have low molecular weights (below 500, except for paclitaxel), and are fairly hydrophobic (except sucrose), making them susceptible to rapid elimination through capillaries.…”

“…Conjugation extends circulation time in the bloodstream, and additional attachment of protease-specific sequences can target release of the free drug. Recently, we have shown that conjugation of camptothecin to PEG can dramatically improve solubility and penetration through tissue (5).…”

10-Hydroxycamptothecin (HCPT) nanosuspensions stabilized by mPEG₁₀₀₀-HCPT conjugate: high stabilizing efficiency and improved antitumor efficacy

“…There are two hydroxyl groups in the structure of HCPT: one aromatic (10-OH) and one aliphatic . Although the 20-OH could be grafted by PEG derivatives, [18][19][20][21][22][23] its reactivity is much less than 10-OH due to the steric hindrance. 24 The HCPT spot by TLC plate was yellow at 365 nm.…”

“…[15][16][17] PEGylated CPT [18][19][20] or mPEG 1000 -HCPT 21 have been synthesized and evaluated in vitro and in vivo. So far, only a few studies have used a PEGylated drug as carrier to further encapsulate drugs, but the drug payload was limited (20%) in the resultant liposome-like structure.…”

Improving aqueous solubility and antitumor effects by nanosized gambogic acid-mPEG2000 micelles

“…Several chemotherapeutic agents have been conjugated to PEG with covalent bonds, including a PEG-curcumin conjugate, a PEGpaclitaxel conjugate, and a PEG-camptothecin conjugate, resulting in homogeneous water-soluble prodrugs with an extended circulatory life and altered biodistribution. [26][27][28][29] Tang et al 30 reported that using PEG as a water-solubilizing unit was a useful strategy for increasing the water solubility of gambogic acid, which is hydrophobic. Ding et al 31 synthesized a series of gambogic acid-PEG conjugates with different amino acid and dipeptide spacers, which showed satisfactory water solubility compared with gambogic acid, and the circulatory retention time, biodistribution, and bioavailability of the conjugates were remarkably improved.…”