Improved in vivo antitumor effect of a daunorubicin - GnRH-III bioconjugate modified by apoptosis inducing agent butyric acid on colorectal carcinoma bearing mice.

Compared to classical chemotherapy, peptide-based drug targeting is a promising therapeutic approach for cancer, which can provide increased selectivity and decreased side effects to anticancer drugs. Among various homing devices, gonadotropin-releasing hormone-III (GnRH-III) peptide represents a suitable targeting moiety, in particular in the treatment of hormone independent tumors that highly express GnRH receptors (e.g. colon carcinoma). We have previously shown that GnRH-III[(4)Lys(Ac),(8)Lys(Dau = Aoa)] bioconjugate, in which daunorubicin was attached via oxime linkage to the (8)Lys of a GnRH-III derivative, exerted significant in vivo antitumor effect on subcutaneously developed HT-29 colon tumor. In contrast, results of the study reported here indicated that this compound was not active on an orthotopically developed tumor. However, if Lys in position 4 was acylated with butyric acid instead of acetic acid, the resulting bioconjugate GnRH-III[(4)Lys(Bu),(8)Lys(Dau = Aoa)] had significant tumor growth inhibitory effect. Furthermore, it prevented tumor neovascularization, without detectable side effects. Nevertheless, the development of metastases could not be inhibited by the bioconjugate; therefore, its application in combination with a metastasis preventive agent might be necessary in order to achieve complete tumor remission. In spite of this result, the treatment with GnRH-III[(4)Lys(Bu),(8)Lys(Dau = Aoa)] bioconjugate proved to have significant benefits over the administration of free daunorubicin, which was used at the maximum tolerated dose.

[Studying the tumor growth inhibitory effect of modified GnRH-III-anthracycline bioconjugates in subcutaneous vs. orthotopic models in vivo]. / Módosított GnRH-III-antraciklin biokonjugátumok daganatnövekedést gátló hatásának tanulmányozása in vivo szubkután vs. ortotopikus rendszerekben.

Targeted tumor therapy is a perspective procedure to specifically destroy the cancer tissues with eliminating or at least decreasing the side effects of anticancer drugs. For this purpose the drug molecule is attached to a targeting moiety (e.g. peptide hormones) that recognizes tumor specific or overexpressed receptors on cancer cells. The in vitro cytostatic or cytotoxic assays do not give proper information whether the tumor growth inhibitory effect of the conjugate is better than the activity of the free drug. Only in vivo studies are adequate to answer this question. However, the selection of the appropriate tumor model is important to eliminate the false positive results. In our studies a gonadotropin-releasing hormone analog (GnRH-III) was applied as targeting moiety in drug conjugates. The in vivo antitumor activity of these conjugates was investigated on mice bearing subcutaneously or orthotopically szigdeveloped tumors. The subcutaneously implanted tumor model which is isolated from its surroundings may provide false results in tumor growth inhibition. In contrast, the orthotopically developed tumor is a better model representing appropriate anatomical and clinical status of cancer. Therefore, the orthotopical colon cancer developed in our laboratory is a suitable model for the study of the antitumor activity of the conjugates prepared for targeted tumor therapy.

A mixture of amino acids and other small molecules present in the serum suppresses the growth of murine and human tumors in vivo.

Previously we have hypothesized that the small molecules which are selectively accumulated in cancer cells might participate in a non-immunological antitumor surveillance mechanism. We demonstrated earlier that a mixture of experimentally selected substances ("active mixture", AM: L-arginine, L-histidine, L-methionine, L-phenylalanine, L-tyrosine, L-tryptophan, L-ascorbate, D-biotin, pyridoxine, riboflavin, adenine, L(-)malate) possesses a selective toxic effect in vitro on a variety of tumor cell lines, and we have shown that the AM selectively induces apoptosis of cancer cells in vitro. To explore the in vivo significance of our earlier findings we examined the antitumor effect of AM in Colon 26 murine colorectal adenocarcinoma, B16 murine melanoma, MXT murine mammary carcinoma, S180 murine sarcoma, P388 murine lymphoid leukemia, HL-60 human promyeloid leukemia, PC-3 human prostate carcinoma, and HT-29 human colon carcinoma tumor models. Treatment of tumor bearing mice with AM inhibited the growth of the tumors investigated, with an inhibitory effect ranging from 40 to 69%. The AM had a comparable antitumor effect with 5-fluorouracil and cisplatin in the Colon-26 tumor model, and combined treatment with AM and 5-fluorouracil or cisplatin resulted in an enhanced tumor growth inhibitory effect. The AM induced apoptosis through the mitochondrial pathway and induced G1 arrest in PC-3 cells and increased the number of apoptotic cells in PC-3 xenografts. These findings suggest that the AM might offer an interesting perspective in the treatment of cancer and in combination with other treatments may offer hope for a more effective cancer therapy.

In-vivo antitumour effect of daunorubicin-GnRH-III derivative conjugates on colon carcinoma-bearing mice.

Targeted cancer chemotherapy is a novel approach developed for the specific delivery of anticancer drugs. Tumour targeting can be achieved by combining a chemotherapeutic agent with a targeting moiety that recognizes tumour-specific or highly expressed receptors on cancer cells. We used the gonadotropin-releasing hormone-III (GnRH-III) as a targeting moiety to which the chemotherapeutic agent daunorubicin (Dau) was attached through an oxime bond either directly or by inserting a GFLG tetrapeptide spacer. The in-vivo toxicity of Dau-GnRH-III derivative conjugates was evaluated on healthy BDF-1 female mice, and their tumour growth inhibitory effect was determined on C26 murine and HT-29 human colon carcinoma-bearing mice. Both oxime bond-containing conjugates were well tolerated and exerted significant antitumour activity on C26 colon carcinoma-bearing mice at a dose of 30 mg Dau content in conjugate/kg body weight. Furthermore, the conjugates inhibited the tumour growth more than the free drug at a dose that was still not toxic. Similar tumour growth inhibitory effects were obtained on HT-29 human colon carcinoma-bearing mice using three treatments with 15 mg Dau content in conjugate/kg. The tumour growth inhibitions according to the tumour volume and the tumour weight were 44/41% and 58/50%, respectively. Considering the results, both of the investigated Dau-GnRH-III derivative conjugates were well tolerated and had significant antitumour effect on colon carcinoma-bearing mice.

Enhanced enzymatic stability and antitumor activity of daunorubicin-GnRH-III bioconjugates modified in position 4.

Here, we report on the synthesis, enzymatic stability, and antitumor activity of novel bioconjugates containing the chemotherapeutic agent daunorubicin attached through an oxime bond to various gonadotropin-releasing hormone-III (GnRH-III) derivatives. In order to increase the enzymatic stability of the bioconjugates (in particular against chymotrypsin), (4)Ser was replaced by N-Me-Ser or Lys(Ac). A compound in which (4)Lys was not acetylated was also prepared, with the aim of investigating the influence of the free ε-amino group on the biochemical properties. The in vitro cytostatic effect of the bioconjugates was determined on MCF-7 human breast, HT-29 human colon, and LNCaP human prostate cancer cells by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay. Their stability/degradation (1) in human serum, (2) in the presence of rat liver lysosomal homogenate, and (3) in the presence of digestive enzymes (trypsin, chymotrypsin, and pepsin) was analyzed by liquid chromatography in combination with mass spectrometry. The results showed that (1) all synthesized bioconjugates had in vitro cytostatic effect, (2) they were stable in human serum at least for 24 h, and (3) they were hydrolyzed in the presence of lysosomal homogenate. All compounds were stable in the presence of (1) pepsin and (2) trypsin (except for the (4)Lys containing bioconjugate). In the presence of chymotrypsin, all bioconjugates were digested; the degradation rate strongly depending on their structure. The bioconjugates in which (4)Ser was replaced by N-Me-Ser or Lys(Ac) had the highest enzymatic stability, making them potential candidates for oral administration. In vivo tumor growth inhibitory effect of two selected bioconjugates was evaluated on orthotopically developed C26 murine colon carcinoma bearing mice. The results indicated that the compound containing Lys(Ac) in position 4 had significantly higher antitumor activity than the parent bioconjugate.