Apoptotic Effects of Drug Targeting Conjugates Containing Different GnRH Analogs on Colon Carcinoma Cells

Lajkó Lajkó,Hegedüs Hegedüs,Mező Mező,Kőhidai Kőhidai

doi:10.3390/ijms20184421

Abstract

The wide range of cellular target reactions (e.g., antitumor) of gonadotropin-releasing hormone (GnRH) variants provides the possibility to develop multifunctional GnRH conjugates. The aim of our work was to compare the cytotoxic/apoptotic activity of different GnRH-based, daunorubicin (Dau)-linked conjugates with or without butyrated Lys in position 4 (4Lys(Bu)) at a molecular level in a human colorectal carcinoma cell line. Cell viability was measured by impedimetry, cellular uptake and apoptosis were studied by flow cytometry, and the expression of apoptosis-related genes was analyzed by qRT-PCR. The modification with 4Lys(Bu) resulted in an increased cytotoxic and apoptotic effects and cellular uptake of the GnRH-I and GnRH-III conjugates. Depending on the GnRH isoform and the presence of 4Lys(Bu), the conjugates could regulate the expression of several apoptosis-related genes, especially tumor necrosis factor (TNF), tumor protein p53 (TP53) and the members of growth-factor signaling. The stronger cytotoxicity of GnRH-I and GnRH-III conjugates containing 4Lys(Bu) was associated with a stronger inhibitory effect on the expression of growth-factor signaling elements in comparison with their 4Ser counterparts, in which the upregulation of TP53 and caspases (e.g., CASP9) seemed to play a more important role. We were able to provide further evidence that targeting the GnRH receptor could serve as a successful therapeutic approach in colon cancer, and GnRH-III-[4Lys(Bu),8Lys(Dau=Aoa)] proved to be the best candidate for this purpose.

Highlights

Targeted tumor therapy represents a promising strategy to improve the selectivity and efficacy of chemotherapy by delivering a cytotoxic drug covalently linked to a targeting unit which is selective to a tumor’s overexpressed receptors
In our previous work concerning the in vitro biological effects of different gonadotropin-releasing hormone (GnRH)-I and GnRH-II-based conjugates, where daunorubicin (Dau) as an anticancer drug was attached directly or through an enzyme labile spacer (GFLG) to GnRH-I-[6D-Lys] or GnRH-II-[6D-Lys] via an oxime bound, we demonstrated that they have similar antiproliferative and apoptotic effects as well as receptor binding affinity [12]
Receptors for various peptide hormones have been demonstrated in colorectal carcinomas, and these receptors could be utilized for both therapeutic and diagnostic purposes [47,48]

Summary

Introduction

Targeted tumor therapy represents a promising strategy to improve the selectivity and efficacy of chemotherapy by delivering a cytotoxic drug covalently linked to a targeting unit which is selective to a tumor’s overexpressed receptors. Due to controversial findings of the existence of a functional GnRH-II receptor, it is highly suggested that the type-I GnRH-R (GnRH-IR) mediates the effects of the GnRH isoforms [4,7]. Their affinity and effects proved to be tissue/cell-dependent. GnRH-II exhibits the ability to inhibit the proliferation of both GnRH-IR positive and negative tumor cells These findings imply the possibility of other types of binding partners on the tumor cell membrane [11,12]

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