Effective treatment of experimental U-87MG human glioblastoma in nude mice with a targeted cytotoxic bombesin analogue, AN-215

Magnetic and GRPR-targeted reduced graphene oxide/doxorubicin nanocomposite for dual-targeted chemo-photothermal cancer therapy

Herein, we design a rGO-based magnetic nanocomposite by decorating rGO with citrate-coated magnetic nanoparticles (CMNP). The magnetic rGO (mrGO) was modified by phospholipid-polyethylene glycol to prepare PEGylated mrGO, for conjugating with gastrin-releasing peptide receptor (GRPR)-binding peptide (mrGOG). The anticancer drug doxorubicin (DOX) was bound to mrGO (mrGOG) by π-π stacking for drug delivery triggered by the low pH value in the endosome. The mrGOG showed enhanced photothermal effect under NIR irradiation, endorsing its role for dual targeted DOX delivery. With efficient DOX release in the endosomal environment and heat generation from light absorption in the NIR range, mrGOG/DOX could be used for combination chemo-photothermal therapy after intracellular uptake by cancer cells. We characterized the physico-chemical as well as biological properties of the synthesized nanocomposites. The mrGOG is stable in biological buffer solution, showing high biocompatibility and minimum hemolytic properties. Using U87 glioblastoma cells, we confirmed the magnetic drug targeting effect in vitro for selective cancer cell killing. The peptide ligand-mediated targeted delivery increases the efficiency of intracellular uptake of both nanocomposite and DOX up to ~3 times due to the over-expressed GRPR on U87 surface, leading to higher cytotoxicity. The increased cytotoxicity using mrGOG over mrGO was shown from a decreased IC₅₀ value (0.70 to 0.48 μg/mL) and an increased cell apoptosis rate (19.8% to 47.1%). The IC₅₀ and apoptosis rate changed further to 0.19 μg/mL and 76.8% in combination with NIR laser irradiation, with the photothermal effect supported from upregulation of heat shock protein HSP70 expression. Using U87 tumor xenograft model created in nude mice, we demonstrated that magnetic guidance after intravenous delivery of mrGOG/DOX could significantly reduce tumor size and prolong animal survival over free DOX and non-magnetic guided groups. Augmented with NIR laser treatment for 5 min, the anti-cancer efficacy significantly improves with elevated cell apoptosis and reduced cell proliferation. Together with safety profiles from hematological as well as major organ histological analysis of treated animals, the mrGOG nanocomposite is an effective nanomaterial for combination chemo-photothermal cancer therapy.

Bombesin Receptor Family Activation and CNS/Neural Tumors: Review of Evidence Supporting Possible Role for Novel Targeted Therapy

G-protein-coupled receptors (GPCRs) are increasingly being considered as possible therapeutic targets in cancers. Activation of GPCR on tumors can have prominent growth effects, and GPCRs are frequently over-/ectopically expressed on tumors and thus can be used for targeted therapy. CNS/neural tumors are receiving increasing attention using this approach. Gliomas are the most frequent primary malignant brain/CNS tumor with glioblastoma having a 10-year survival <1%; neuroblastomas are the most common extracranial solid tumor in children with long-term survival<40%, and medulloblastomas are less common, but one subgroup has a 5-year survival <60%. Thus, there is an increased need for more effective treatments of these tumors. The Bombesin-receptor family (BnRs) is one of the GPCRs that are most frequently over/ectopically expressed by common tumors and is receiving particular attention as a possible therapeutic target in several tumors, particularly in prostate, breast, and lung cancer. We review in this paper evidence suggesting why a similar approach in some CNS/neural tumors (gliomas, neuroblastomas, medulloblastomas) should also be considered.

The aggressiveness of murine lymphomas selected in vivo by growth rate correlates with galectin-1 expression and response to cyclophosphamide

Although lymphomas account for almost half of blood-derived cancers that are diagnosed each year, the causes of new cases are poorly understood, as reflected by the relatively few risk factors established. Galectin-1, an immunoregulatory ß-galactoside-binding protein, has been widely associated with tumor-immune escape. The aim of the present work was to study the relationship between tumor growth rate, aggressiveness, and response to cyclophosphamide (Cy) therapy with regard to Gal-1 expression in murine T-cell lymphoma models. By means of a disruptive selection process for tumor growth rate, we generated two lymphoma variants from a parental T-cell lymphoma, which have unique characteristics in terms of tumor growth rate, spontaneous regression, metastatic capacity, Gal-1 expression and sensitivity to Cy therapy. Here, we show that Gal-1 expression strongly correlates with tumor growth rate, metastatic capacity and response to single-dose Cy therapy in T-cell lymphoma models; this association might have important consequences for evaluating prognosis and treatments of this type of tumors.

Multifunctionalized gold nanoparticles with peptides targeted to gastrin-releasing peptide receptor of a tumor cell line

Functionalization of gold nanoparticles (AuNPs) with both a targeting peptide (an analogue of the peptide Bombesin) and a drug peptide ligand (an analogue of the RAF peptide) with the aim of improving selectivity in the delivery of the conjugates as well as the antitumor activity is described. Studies on the internalization mechanism of peptide-AuNP conjugates and viability of cells were carried out. An enhancement of the activity and selectivity of the peptide multifunctionalized conjugates was observed.

Specific growth rate versus doubling time for quantitative characterization of tumor growth rate

Doubling time (DT) is widely used for quantification of tumor growth rate. DT is usually determined from two volume estimations with measurement time intervals comparable with or shorter than DT. Clinical data show that the frequency distribution of DT in patients is positively skewed, with some very long DT values compared with the average DT. Growth rate can also be quantified using specific growth rate (SGR; %/d), equal to ln2/DT. The aim of this work was to compare DT and SGR as growth rate variables. Growth rate calculations were computer simulated for a tumor with DT of 100 days, measurement time interval of 1 to 200 days, and volume estimation uncertainty of 5% to 20%. Growth rate variables were determined and compared for previously published clinical data. The study showed that DT is not a suitable variable for tumor growth rate because (a) for short measurement time intervals, or high volume uncertainties, mean DT can either overestimate or underestimate the average growth rate; (b) DT is not defined if the consecutively estimated volumes are equal; and (c) the asymmetrical frequency distribution of DT makes it unsuitable for common statistical testing. In contrast, mean SGR and its equivalent DT give the correct values for average growth rate, SGR is defined for all tumor volume changes, and it has a symmetrical frequency distribution. SGR is also more accurate to use when discussing, for example, growth fraction, cell loss rate, and growth rate heterogeneities within the tumor. SGR should thus be used, instead of DT, to quantify tumor growth rate.

Gastrin-releasing peptide and cancer

Over the past 20 years, abundant evidence has been collected to suggest that gastrin-releasing peptide (GRP) and its receptors play an important role in the development of a variety of cancers. In fact, the detection of GRP and the GRP receptor in small cell lung carcinoma (SCLC), and the demonstration that anti-GRP antibodies inhibited proliferation in SCLC cell lines, established GRP as the prototypical autocrine growth factor. All forms of GRP are generated by processing of a 125-amino acid prohormone; recent studies indicate that C-terminal amidation of GRP18-27 is not essential for bioactivity, and that peptides derived from residues 31 to 125 of the prohormone are present in normal tissue and in tumors. GRP receptors can be divided into four classes, all of which belong to the 7 transmembrane domain family and bind GRP and/or GRP analogues with affinities in the nM range. Over-expression of GRP and its receptors has been demonstrated at both the mRNA and protein level in many types of tumors including lung, prostate, breast, stomach, pancreas and colon. GRP has also been shown to act as a potent mitogen for cancer cells of diverse origin both in vitro and in animal models of carcinogenesis. Other actions of GRP relevant to carcinogenesis include effects on morphogenesis, angiogenesis, cell migration and cell adhesion. Future prospects for the use of radiolabelled and cytotoxic GRP analogues and antagonists for cancer diagnosis and therapy appear promising.

Targeted chemotherapy with cytotoxic bombesin analogue AN-215 inhibits growth of experimental human prostate cancers

We developed a powerful cytotoxic analogue of bombesin AN-215, in which the bombesin (BN)-like carrier peptide is conjugated to 2-pyrrolino doxorubicin (AN-201). Human prostate cancers express high levels of receptors for BN/gastrin releasing peptide (GRP) that can be used for targeted chemotherapy. The effects of targeted chemotherapy with cytotoxic BN analogue AN-215 were evaluated in nude mice bearing subcutaneous xenografts of DU-145, LuCaP-35, MDA-PCa-2b and intraosseous implants of C4-2 human prostate cancers. Intraosseous growth of C4-2 tumors was monitored by serum PSA. BN/GRP receptors were evaluated by 125I-[Tyr4]BN binding assays and RT-PCR. The effects of AN-215 on apoptosis and cell proliferation were followed by histology, and the expression of Bcl-2 and Bax protein was determined by Western blot analysis. Targeted analog AN-215 significantly inhibited growth of subcutaneously implanted DU-145, LuCaP-35 and MDA-PCa-2b prostate cancers by 81% to 91% compared to controls, while cytotoxic radical AN-201 was less effective and more toxic. Serum PSA levels of mice bearing intraosseous C4-2 prostate tumors were significantly reduced. In LuCaP-35 tumors administration of BN antagonist RC-3095 prior to AN-215 blocked the receptors for BN/GRP and inhibited the effects of AN-215. High affinity receptors for BN/GRP and their m-RNA were detected on membranes of all 4 tumor models. Therapy with AN-215, but not with AN-201, decreased the ratio of Bcl-2/Bax in DU-145 and the expression of antiapoptotic Bcl-2 in LuCaP-35 tumors. The presence of BN/GRP receptors on primary and metastatic prostate cancers makes possible targeted chemotherapy with AN-215 for the treatment of this malignancy.

Targeted chemotherapy with cytotoxic bombesin analogue AN-215 can overcome chemoresistance in experimental renal cell carcinomas

BACKGROUND

Multidrug resistance (MDR) mediated by membrane transporters, such as P-glycoprotein (MDR-1) and MDR-associated protein (MRP), remains a challenge in the therapy of renal cell carcinoma (RCC). Chemotherapy targeted to hormone receptors may provide a new approach to overcome chemoresistance. The cytotoxic analogue of bombesin/gastrin-releasing peptide (GRP), AN-215, consists of a superactive derivative of doxorubicin, AN-201, which is linked to a bombesin analogue carrier: RC-3094.

METHODS

The authors examined the expression of bombesin/GRP receptors in 3 human RCC cell lines (A-498, ACHN. and 786-0) by using reverse-transcriptase-polymerase chain reaction (RT-PCR) analysis and radioligand-binding assays. They also evaluated the effects of AN-215 and its cytotoxic radical AN-201 in the same RCC models in vivo, and they studied the effects of AN-215 and AN-201 on the expression levels of MDR-1 and subtype 1 of MRP (MRP-1) by using real-time PCR.

RESULTS

A N-215 significantly (P < 0.05) inhibited the growth of A-498, ACHN, and 786-0 RCC xenografted into nude mice by 59.2-67.6%, whereas the cytotoxic radical AN-201 alone had no significant antitumor effects. The efficacy of AN-215 was independent of the expression patterns of MDR-1 and MRP-1 in these RCC cell lines. The induction of MDR-1 by AN-215 was similar (Experiment 2) or weaker (Experiment 1) compared with AN-201. Both AN-215 and AN-201 caused only a minor induction of MRP-1.

CONCLUSIONS

The current findings indicated that targeted chemotherapy with cytotoxic bombesin/GRP analogue AN-215 can inhibit the growth of RCC, providing a new treatment modality for patients with advanced RCC.

Inhibition of growth of experimental human and hamster pancreatic cancers in vivo by a targeted cytotoxic bombesin analog

OBJECTIVES

Targeting anticancer agents to receptors for peptide hormones such as bombesin/gastrin-releasing peptide (GRP) on tumor cells increases the efficacy and lowers the toxicity of cancer therapy. We studied the expression of bombesin/GRP receptors in 6 experimental pancreatic cancers and evaluated tumor inhibition in vivo produced by targeted chemotherapy with the cytotoxic bombesin analog AN-215.

METHODS

Nude mice with xenografts of Panc-1, CFPAC-1, Capan-1, Capan-2, MiaPaCa-2, and SW-1990 human ductal pancreatic cancers, as well as hamsters with nitrosamine-induced pancreatic cancers, were treated with AN-215 or its cytotoxic radical 2-pyrrolinodoxorubicin (AN-201) for 7 to 12 weeks. Tumor growth reduction and survival were analyzed, and cell proliferation rate and apoptosis were examined by histologic methods. Bombesin/GRP receptors on the tumors were studied by ligand-binding assays and their mRNA expression was studied by reverse transcriptase-polymerase chain reaction.

RESULTS

All tumors expressed mRNA for subtype 1 bombesin/GRP receptor, but MiaPaCa-2, and in one experiment, SW-1990 tumors did not show binding sites for bombesin. AN-215 powerfully inhibited the growth of all pancreatic cancers that expressed functional receptors for bombesin/GRP. AN-201 was less effective on most tumors and somewhat more toxic than AN-215.

CONCLUSIONS

Bombesin/GRP receptors are expressed on most ductal pancreatic carcinoma cell lines and can be used for targeted chemotherapy with the cytotoxic bombesin analog AN-215.

Effective Inhibition of Experimental Human Ovarian Cancers with a Targeted Cytotoxic Bombesin Analogue AN-215

PURPOSE

To determine whether the cytotoxic analogue of bombesin/gastrin-releasing peptide (GRP) AN-215 can inhibit the in vivo growth of four human ovarian cancer cell lines. AN-215 consists of 2-pyrrolinodoxorubicin (AN-201), a superactive derivative of doxorubicin linked to a bombesin antagonist carrier des-D-Tpi-RC-3095. This conjugate binds strongly to receptors for bombesin/GRP and can be targeted to tumors that express these receptors. Bombesin/GRP receptors are found in 77% of human ovarian cancer specimens.

EXPERIMENTAL DESIGN

Nude mice bearing xenografts of ES-2, SKOV-3, OV-1063, and UCI-107 human ovarian carcinomas were treated with AN-215. The antitumor effects and the toxicity were determined. The expression of bombesin receptor subtypes was measured by reverse-transcriptase PCR analysis, and the presence of bombesin/GRP receptors was determined by radioligand binding assays.

RESULTS

AN-215 significantly (P < 0.05) inhibited growth of ES-2, OV-1063, and UCI-107 tumors, prevented the metastatic spread of ES-2 cancers, and prolonged the survival of nude mice bearing i.p. ES-2 xenografts. Cytotoxic radical AN-201, the unconjugated mixture of bombesin antagonist RC-3095 and AN-201 or RC-3095 alone had no significant effects. Blockade of bombesin/GRP receptors abolished the effect of AN-215. The expression of bombesin/GRP receptors was not changed after repeated treatment with AN-215.

CONCLUSIONS

Our findings indicate that targeted chemotherapy with cytotoxic bombesin/GRP analogue AN-215 can inhibit ovarian tumors, which express bombesin/GRP receptors. AN-215 might provide a new treatment modality for women with advanced ovarian carcinoma.

Synthesis and Evaluation of Bombesin Derivatives on the Basis of Pan-Bombesin Peptides Labeled with Indium-111, Lutetium-177, and Yttrium-90 for Targeting Bombesin Receptor-Expressing Tumors

Bombesin receptors are overexpressed on a variety of human tumors like prostate, breast, and lung cancer. The aim of this study was to develop radiolabeled (Indium-111, Lutetium-177, and Yttrium-90) bombesin analogues with affinity to the three bombesin receptor subtypes for targeted radiotherapy. The following structures were synthesized: diethylenetriaminepentaacetic acid-gamma-aminobutyric acid-[D-Tyr6, beta-Ala11, Thi13, Nle14] bombesin (6-14) (BZH1) and 1,4,7,10-tetraazacyclododecane-N,N',N",N"' -tetraacetic acid-gamma-aminobutyric acid-[D-Tyr6, beta-Ala11, Thi13, Nle14] bombesin (6-14) (BZH2). [111In]-BZH1 and in particular [90Y]-BZH2 were shown to have high affinity to all three human bombesin receptor subtypes with binding affinities in the nanomolar range. In human serum metabolic cleavage was found between beta-Ala11 and His12 with an approximate half-life of 2 hours. The metabolic breakdown was inhibited by EDTA and beta-Ala11-His12 (carnosine) indicating that carnosinase is the active enzyme. Both 111In-labeled peptides were shown to internalize into gastrin-releasing peptide-receptor-positive AR4-2J and PC-3 cells with similar high rates, which were independent of the radiometal. The biodistribution studies of [111In]-BZH1 and [111In]-BZH2 ([177Lu]-BZH2) in AR4-2J tumor-bearing rats showed specific and high uptake in gastrin-releasing peptide-receptor-positive organs and in the AR4-2J tumor. A fast clearance from blood and all of the nontarget organs except the kidneys was found. These radiopeptides were composed of the first pan-bombesin radioligands, which show great promise for the early diagnosis of tumors bearing not only gastrin-releasing peptide-receptors but also the other two bombesin receptor subtypes and may be of use in targeted radiotherapy of these tumors.

Chemotherapy targeted to cancers through tumoral hormone receptors

Work on cytotoxic analogs of luteinizing hormone-releasing hormone (LH-RH), somatostatin and bombesin, designed for targeting chemotherapy to peptide receptors on various cancers, is reviewed here as the project is at advanced stages of development and clinical trials are pending. Cytotoxic analogs of LH-RH, AN-152 and AN-207, containing doxorubicin (DOX) or 2-pyrrolino-DOX (AN-201), respectively, target LH-RH receptors and can be used for the treatment of prostatic, breast, ovarian and endometrial cancers and melanomas. AN-201 was also incorporated into the cytotoxic analog of somatostatin, AN-238, which can be targeted to receptors for somatostatin in prostatic, renal, mammary, ovarian, gastric, colorectal and pancreatic cancers as well as glioblastomas and lung cancers, suppressing the growth of these tumors and their metastases. A cytotoxic analog of bombesin AN-215, containing 2-pyrrolino-DOX, was likewise synthesized and successfully tested in experimental models of prostate cancer, small cell lung carcinoma, gastrointestinal cancers and brain tumors expressing receptors for bombesin/gastrin-releasing peptide. This new class of targeted cytotoxic peptide analogs might provide a more effective therapy for various cancers.

New approaches to treatment of various cancers based on cytotoxic analogs of LHRH, somatostatin and bombesin

The development of targeted cytotoxic analogs of hypothalamic peptides for the therapy of various cancers is reviewed and various oncological studies on experimental tumors are summarized. Novel therapeutic modalities for breast, prostate and ovarian cancer consist of the use of targeted cytotoxic analogs of LH-RH containing doxorubicin (DOX) or 2-pyrrolino-DOX. The same radicals have been incorporated into cytotoxic analogs of somatostatin which can be also targeted to receptors for this peptide in prostatic, mammary, ovarian, renal and lung cancers, brain tumors and their metastases. A targeted cytotoxic analog of bombesin containing 2-pyrrolino-DOX has also been synthesized and successfully tried in experimental models of prostate cancer, small cell lung carcinoma and brain tumors. The development of these new classes of peptide analogs should lead to a more effective treatment for various cancers.