Release of peptides from sustained delivery systems (microcapsules and microparticles) in vivo. A histological and immunohistochemical study

Sustained delivery systems (microcapsules, microparticles, or implants) developed for once a month administration of peptides are efficacious and convenient. Long acting formulations of several bioactive peptides are based on microcapasules of a biodegradable polymer poly(DL-lactide-co-glycolide) (PLG), but a better understanding is required of the mechanism of the peptide release from the microcapsules, which is assumed to be primarily by diffusion through pores. In order to clarify this mechanism, microcapsules and microparticles of the agonist [D-Trp6]-LHRH and microcapsules of the LHRH antagonist SB-75 were given i.m. to rats 2 h and 1, 2, 4, 7, 14 and 21 days before histological and immunohistochemical investigation. Signs of biodegradation of the PLG matrix could be seen the first day after the injection, in a form of vacuole development in the interior of the particles and connected with the presence of macrophages within the matrix. The microcapsules showed excellent tissue-compatibility, and no significant foreign body reaction was detected. Immunohistochemical study on the microcapsules revealed no visible decrease in peptide concentration in the remnants of the matrix even 2 weeks after the injection. Evaluation of serum [D-Trp6]-LHRH showed that after an initial burst, both microcapsules and microparticles maintained elevated serum [D-Trp6]-LHRH levels for more than 3 weeks. Our results suggest that the previously proposed mechanisms do not reflect the experimental findings, particularly for the insoluble peptides. The peptide release from the PLG microcapsules or microparticles appears to be controlled mostly by the speed of the biodegradation of the polymer matrix and the diffusion of the peptides from the PGL is negligible.     

Biological activity and receptor binding characteristics to various human tumors of acetylated somatostatin analogs.

Several somatostatin analogs with recently synthesized acetylated N terminus were assayed in vivo for their effects on sodium pentobarbital-stimulated growth hormone (GH) levels in fed male rats and gastrin-releasing peptide (14-27)-stimulated gastrin levels in fasted male rats. The binding characteristics of these analogs to somatostatin receptors were also examined in various human tumors and normal tissues. The analog RC-101-I, injected at a dose of 0.1 micrograms/100 g body wt, significantly suppressed GH release (P less than 0.01) for at least 2 hr. Analog RC-160-II caused the longest inhibition of GH release, greater than that induced by nonacetylated parent analog RC-160, with GH levels showing significant suppression (P less than 0.01) for more than 3 hr. Analogs RC-160-II and RC-101-I and RC-160, injected at a dose of 1.0 micrograms/100 g body wt, significantly (P less than 0.01) suppressed gastrin-releasing peptide (14-27)-stimulated serum gastrin. Analog RC-101-I was active in this test at a dose of 0.1 micrograms/100 g body wt. RC-160-II showed significant binding to somatostatin-14 receptors in all investigated tissues (human colon, human colon cancer, breast cancer, human pancreas and pancreatic cancer, human prostate and prostate cancer, and rat cerebral cortex), but there were marked variations in binding affinities among various normal and cancerous tissues. The highest affinity was found in membranes of colon cancer (Ka = 18.4 nM-1) and breast cancer (Ka = 12.46 nM-1). The binding affinity of RC-160-II to somatostatin receptors in membranes of the breast cancer was similar to that of RC-160. RC-101-I showed higher binding affinity to somatostatin-14 receptors than RC-160 in human breast, pancreatic, and prostate cancer. With the exception of breast cancer tissue, the binding affinity of RC-101-I was significantly lower than that of RC-160-II in membranes of all investigated tissues. It can be concluded that acetylated somatostatin analogs RC-101-I and RC-160-II possess prolonged and enhanced biological activities in suppressing serum GH and gastrin in rats. Significant variations in binding affinities for these analogs in different tissues and various tumors suggest that differences may exist between somatostatin receptors in normal versus malignant tissues. This raises the possibility that some of these analogs could be used more selectively in the treatment of various neoplasms.     

L1 (LINE-1) retrotransposable elements provide a "fossil" record of the phylogenetic history of murid rodents

The single most difficult problem in phylogenetic analysis is deciding whether a shared taxonomic character is due to common ancestry or one that appeared independently due to convergence, parallelism, or reversion to an ancestral state. Mammalian L1 retrotransposons undergo periodic amplifications in which multiple copies of the elements are interspersed in the genome. Because these elements apparently are transmitted only by inheritance and are retained in the genome, a shared L1 amplification event can only be an inherited ancestral character. We propose that L1 amplification events can be an excellent tool for analyzing mammalian evolution and demonstrate here how we addressed several refractory problems in rodent systematics using L1 DNA as a taxonomic character.      

New approaches to the therapy of various tumors based on peptide analogues.

The discovery of hypothalamic hormones was briefly reviewed. The development of new hormonal methods for the therapy of various cancers based on analogues of hypothalmic hormones is then presented. My group isolated luteininzing hormone-releasing hormone (LH-RH), also known as Gn-RH, from pig hypothalmi, elucidated its amino acid sequence, and synthesized it in 1971. The interest in medical applications of LH-RH led to the synthesis of LH-RH analogues by various groups. LH-RH agonists substituted in positions 6 or 10 including Decapeptyl, Leuprolide and Zoladex are much more active than LH-RH and on continuous administration produce inhibition of pituitary and gonads. Chronic administration of LH-RH agonists is being utilized for the treatment of prostate and breast cancer. Octapeptide analogues of somatostatin have various applications in Oncology. In 1980 we developed a new endocrine therapy for advanced prostate cancer based on agonists of LH-RH, which is now preferred by 70-90% of prostate cancer patients for primary treatment. LH-RH antagonists such as Cetrorelix can be used for therapy of BPH. On the basis of the presence of specific receptors for hypothalamic peptides on human cancers, we developed targeted cytotoxic analogues of LH-RH, somatostatin, and bombesin/GRP linked to doxorubicin or 2-pyrrolinodoxorubicin. These analogues inhibit the growth of experimental human prostate, breast, ovarian and endometrial cancer, renal cell carcinoma, pancreatic, colorectal and gastric cancers, small cell lung carcinoma (SCLC) and non-SCLC, brain tumors, melanomas, and lymphomas. Cytotoxic LH-RH analogues are now in clinical trials. Recently we demonstrated that growth hormone-releasing hormone (GH-RH) also serves as an autocrine growth factor in many cancers. Antagonistic analogues of GH-RH synthesized in our laboratory inhibit the growth of diverse tumors. The discovery of LH-RH and somatostatin has led to clinical use of their analogues in the field of cancer treatment and GH-RH antagonists also show a great promise.     

Plant virus infection development as affected by heavy metal stress

The work was focused on the investigation of possible dependencies between the development of viral infection in plants and the presence of high heavy metal concentrations in soil. Field experiments have been conducted in order to study the development of systemic tobacco mosaic virus (TMV) infection in Lycopersicon esculentum L. cv. Miliana plants under effect of separate salts of heavy metals Cu, Zn and Pb deposited in soil. As it is shown, simultaneous effect of viral infection and heavy metals in tenfold maximum permissible concentration leads to decrease of total chlorophyll content in experiment plants mainly due to the degradation of chlorophyll a. The reduction of chlorophyll concentration under the combined influence of both stress factors was more serious comparing to the separate effect of every single factor. Plants' treatment with toxic concentrations of lead and zinc leaded to slight delay in the development of systemic TMV infection together with more than twofold increase of virus content in plants that may be an evidence of synergism between these heavy metal's and virus' effects. Contrary, copper although decreased total chlorophyll content but showed protective properties and significantly reduced amount of virus in plants.     

Luteinizing hormone-releasing hormone analogs lacking N-terminal pGlu ring structure

Six analogs of LH-RH lacking N-terminal pGlu ring structure, Gly¹-LH-RH, formyl Gly¹-LH-RH, acetyl Gly¹-LH-RH, propionyl Gly¹-LH-RH, palmitoyl Gly¹-LH-RH and acetyl Ala¹-LH-RH were synthesized. The Gly¹ analog was inactive, whereas acyl Gly¹ analogs except palmitoyl Gly¹ analog showed small but significant LH-RH activity in spite of the lack of the pyrrolidone ring structure. These findings suggest that the -CO-NHCHCO- group is the minimum necessary part of the pGlu residue to exhibit the biological activity.