TARGETING OF STIMULI RESPONSIVE ELASTIN LIKE POLYPEPTIDE DRUG CONJUGATES TO OVARIAN CANCER R. DEEPTHI and M.J.N CHANDRASEKAR Department of Pharmaceutical Chemistry, JSS College of Pharmacy, Udhagamandalam, JSS Academy of Higher Education & Research, Tamil Nadu, India. Email: deepthiramamurthi@gmail.com
ABSTRACT Conventionally, antitumour agents are designed to have a balance between hydrophobicity and hydrophilicity and to be of relatively low molecular weight. These properties allow the drug to partition across lipoidal membranes relatively easily, but yet to be sufficiently water soluble to dissolve in the aqueous compartments where they usually exert their action. In essence this means that low molecular weight drugs can distribute rapidly within most cells. Being below the renal filtration threshold, they are not only rapidly eliminated by renal filtration but can also diffuse out of tissues just as rapidly. Due to this, their residence times at the active site are relatively short. In contrast, high molecular weight polymer drug conjugates do not partition across membranes and tend to be retained within different compartments of the body, thus redistributing the drug slowly. Conjugation of antitumour drugs to biocompatible/biodegradable polymers thus provides us the opportunity to solubilise poorly water soluble drugs, improve tumor targeting and reduce drug toxicity. Polymeric drug conjugates improve the drug pharmacokinetics and lead to increased tumor accumulation over free drugs due to passive targeting [also called Enhanced Permeability and Retention, (EPR effect)]. Recently a new class of polymers called thermally-responsive polymers, has been developed, which undergo abrupt reversible changes in volume in response to minor changes in the environment such as temperature. These polymers suddenly shrink as the temperature increases above a certain level, which is approximately the lower critical solution temperature (LCST) of the corresponding linear polymer. The release mechanisms of a drug entrapped in these hydrogels when the temperature is cycled above and below the LCST is determined by a cycle of swelling and deswelling. In other words such temperature sensitive polymers suck up the drug on cooling and squeeze it out on heating. One could take advantage of both these phenomena namely, enhanced permeability effect (EPR) and hyperthermia exhibited by some polymeric materials for targeting anticancer drugs. It is proposed, therefore, to synthesize and characterize some thermally-responsive polymers, attach anticancer drugs to these, to develop different pharmaceutical acceptable formulations and evaluate their potential, both ‘in vivo’ and ‘in vitro’, to deliver anticancer drugs to solid tumors.
STAGE 3: IN VIVO STUDIES IN SOLID TUMOR 1. Implant athymic mice with dorsal skin fold window chambers containing a small piece of human ovarian tumor placed near the center of the window and the tumor is allowed to grow for a week. 2. The window chamber connected to a temperature controlled water bath will be maintained either at 34°C, the physiologic subcutaneous temperature in mice or at 42°C. 3. Anesthetize the mice and select the region of the tumor containing clearly visible tumor microvasculature and 4. Quantify the accumulation of the carriers in the tumors by the fluorescence intensity using fluorescence microscope.
ELASTIN-LIKE POLYPEPTIDE –DRUG CONJUGATE Elastin like polypeptide (ELP) is a pentapeptide repeat and genetically designed as VPGXG where X can be any amino acid except proline because it neutralizes the characteristic properties of ELP.
V
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INTRODUCTION Ovarian cancer is a common gynecologic cancer that decreases the lifespan and is one of the leading causes of death worldwide. The polymers show excellent properties of low cytotoxicity, high functionalizability and good protein-resistance towards the applications like drug delivery, tissue engineering and polymer therapeutics. In drug delivery, polymerdrug conjugates have been considered as a promising approach. Drug delivery systems (DDS) deliver drugs to the tumor site leading to reduced exposure of drugs to healthy cells and hence reduce side effects. So efforts have been made to develop biodegradable, inexpensive and effective DDS using stimuli responsive polymers like thermosensitive, pH sensitive etc,. Elastin-like polypeptides (ELP) a thermal responsive polymers were identified to be a drug carrier in several kinds of cancer therapy. ELP-drug conjugates have the potential and can be used effectively in combination with hyperthermia for targeting drugs to solid tumors.
CONCLUSION Polymer chemistry has been widely investigated to develop the concept of targetable polymericdrug conjugates for site-specific delivery. In this context, thermally responsive ELPs as polymeric carriers have attracted the attention of researchers in recent times.
AIM AND OBJECTIVES AIM: To synthesize and characterize ELP – Drug conjugates to target the ovarian solid tumors OBJECTIVES: 1. Synthesize and characterize elastin like polypeptides containing pentapeptide (Val-ProGly-Val-Gly) repeat unit, capable of preferentially increasing the permeability of tumor vasculature 2. Conjugate anticancer drug to the polymer 3. Evaluate its in vitro release parameters and in vivo potential to deliver anticancer drugs to solid tumors
METHODOLOGY STAGE 1: SYNTHESIS OF THE POLYMER-DRUG CONJUGATE 1. Synthesize and characterize elastin like polypeptides containing pentapeptide (Val-ProGly-Val-Gly) to obtain (Val-Pro-Gly-Val-Gly)n with LCST from 37-42 °C. 2. Label the thermo-sensitive polymers with rhodamine dye at the amino terminal to facilitate visualization by fluorescence microscopy. 3. Attach antitumour drug covalently to the carboxyl terminal polymer backbone. STAGE 2: IN VITRO CYTOTOXIC STUDIES 1. Estimate the inhibition rate of cell proliferation after continuous exposure of the polymer-drug conjugates for 48-72h by MTT or SRB assay using SK-OV-3 (Ovarian cancer cells).
This study tries to investigate the feasibility of using soluble, thermally-responsive polymer ELP conjugates for targeted delivery to solid tumors in combination with focused hyperthermia of tumors. This aspect of the study is of critical significance, because significant transport barriers exist in solid tumors that limit the delivery of drugs. Hence, investigating a new drug delivery modality in a clinically relevant animal model is critical to evaluating its feasibility
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