Targeting of EGFR tyrosine kinase by ZD1839 ("Iressa") in androgen-responsive prostate cancer in vitro

Linc00963 Promote Cell Proliferation and Tumor Growth in Castration-Resistant Prostate Cancer by Modulating miR-655/TRIM24 Axis

Previous studies have shown that both long intergenic non-coding RNA 00963 (Linc00963) and tripartite motif containing 24 (TRIM24) are activators of the PI3K/AKT pathway, and both are involved in the carcinogenesis and progression of prostate cancer. However, the regulatory mechanisms between Linc00963 and TRIM24 are still unclear. In this study, we aimed to elucidate the underlying relationship between Linc00963 and TRIM24 in castration-resistant prostate cancer (CRPC). We found that TRIM24, an established oncogene in CRPC, was positively correlated with Linc00963 in prostate cancer tissues. In addition, TRIM24 was positively regulated by Lin00963 in CRPC cells. Mechanistically, TRIM24 was the direct target of microRNA-655 (miR-655) in CRPC cells, and Linc00963 could competitively bind miR-655 and upregulate TRIM24 expression. Using gain- and loss-of- function assays and rescue assays, we identified that miR-655 inhibits TRIM24 expression and cell proliferation and colony forming ability in CRPC, and that Linc00963 promotes TRIM24 expression, cell proliferation, and colony forming ability of CRPC cells by directly suppressing miR-655 expression. We further identified that Linc00963 could promote tumor growth of CRPC cells by inhibiting miR-655 and upregulating TRIM24 axis in vivo. Taken together, our study reveals a new mechanism for the Linc00963/miR-655/TRIM24 competing endogenous RNA (ceRNA) network in accelerating cell proliferation in CRPC in vitro and in vivo, and suggests that Linc00963 could be considered a novel therapeutic target for CRPC.

Kinase-Inactivated EGFR Is Required for the Survival of Wild-Type EGFR-Expressing Cancer Cells Treated with Tyrosine Kinase Inhibitors

Inhibiting the tyrosine kinase activity of epidermal growth factor receptor (EGFR) using small molecule tyrosine kinase inhibitors (TKIs) is often ineffective in treating cancers harboring wild-type EGFR (wt-EGFR). TKIs are known to cause dimerization of EGFR without altering its expression level. Given the fact that EGFR possesses kinase-independent pro-survival function, the role of TKI-inactivated EGFR in cancer cell survival needs to be addressed. In this study, using wt-EGFR-expressing cancer cells A549 (lung), DU145 (prostate), PC3 (prostate), and MDA-MB-231 (breast), we characterized the TKI-induced dimerization status of EGFR and determined the dependency of cells on kinase-inactivated EGFR for survival. We report that TKI-induced EGFR dimerization is dependent on palmitoylation and independent of its kinase activity, and that mutations of the cysteine residues known to be critical for EGFR’s palmitoylation abolished TKI-induced EGFR dimerization. Furthermore, TKI-induced EGFR dimerization is persistent in TKI-resistant cells, and inhibition of palmitoylation by 2-bromopalmitate, or targeted reduction of the kinase-inactivated EGFR by siRNA or by an EGFR-downregulating peptide, are lethal to TKI-resistant cancer cells. This study suggests that kinase-inactivated EGFR remains to be a viable therapeutic target for wt-EGFR cancers and that inhibiting palmitoylation or downregulating EGFR may overcome TKI resistance.

Prostate cancer health disparities: An immuno-biological perspective

Prostate cancer (PCa) is the most commonly diagnosed malignancy in males, and, in the United States, is the second leading cause of cancer-related death for men older than 40 years. There is a higher incidence of PCa for African Americans (AAs) than for European-Americans (EAs). Investigations related to the incidence of PCa-related health disparities for AAs suggest that there are differences in the genetic makeup of these populations. Other differences are environmentally induced (e.g., diet and lifestyle), and the exposures are different. Men who immigrate from Eastern to Western countries have a higher risk of PCa than men in their native countries. However, the number of immigrants developing PCa is still lower than that of men in Western countries, suggesting that genetic factors are involved in the development of PCa. Altered genetic polymorphisms are associated with PCa progression. Androgens and the androgen receptor (AR) are involved in the development and progression of PCa. For populations with diverse racial/ethnic backgrounds, differences in lifestyle, diet, and biology, including genetic mutations/polymorphisms and levels of androgens and AR, are risk factors for PCa. Here, we provide an immuno-biological perspective on PCa in relation to racial/ethnic disparities and identify factors associated with the disproportionate incidence of PCa and its clinical outcomes.

Amphiregulin stimulates liver regeneration after small-for-size mouse liver transplantation

This study investigated whether amphiregulin (AR), a ligand of the epidermal growth factor receptor (EGFR), improves liver regeneration after small-for-size liver transplantation. Livers of male C57BL/6 mice were reduced to ~50% and ~30% of original sizes and transplanted. After transplantation, AR and AR mRNA increased in 50% but not in 30% grafts. 5-Bromodeoxyuridine (BrdU) labeling, proliferating cell nuclear antigen (PCNA) expression and mitotic index increased substantially in 50% but not 30% grafts. Hyperbilirubinemia and hypoalbuminemia occurred and survival decreased after transplantation of 30% but not 50% grafts. AR neutralizing antibody blunted regeneration in 50% grafts whereas AR injection (5 μg/mouse, iv) stimulated liver regeneration, improved liver function and increased survival after transplantation of 30% grafts. Phosphorylation of EGFR and its downstream signaling molecules Akt, mTOR, p70S6K, ERK and JNK increased markedly in 50% but not 30% grafts. AR stimulated EGFR phosphorylation and its downstream signaling pathways. EGFR inhibitor PD153035 suppressed regeneration of 50% grafts and largely abrogated stimulation of regeneration of 30% grafts by AR. AR also increased cyclin D1 and cyclin E expression in 30% grafts. Together, liver regeneration is suppressed in small-for-size grafts, as least in part, due to decreased AR formation. AR supplementation could be a promising therapy to stimulate regeneration of partial liver grafts.

Induced apoptosis in human prostate cancer cells by blocking of vascular endothelial growth factor by siRNA

INTRODUCTION

Vascular endothelial growth factor (VEGF) regulates several cell functions including; proliferation, differentiation, permeability, vascular tone, and the production of vasoactive molecules. The purpose of this study was to evaluate the potency of specific short-interfering RNA (siRNA) to suppress human VEGF expression by siRNA and investigate the effects of VEGF down-regulation on the cell proliferation and apoptosis of the human prostate cancer cell lines DU-145.

METHODS

Transfection was performed using X-tremeGENE siRNA transfection reagent. At different time intervals, transfected cells were harvested and total RNA was extracted for RT-PCR. The VEGF content in supernatants were measured by ELISA. Inhibition of cell growth by hVEGF-siRNA was measured by using cell proliferation ELISA BrdU assay. Apoptotic cells were evaluated by using annexin-V-FITC apoptotic detection method.

RESULTS

Transfection of hVEGF-siRNA resulted in statistically significant inhibition of hVEGF-mRNA that in turn caused a marked reduction in the expression of hVEGF. The cell growth was assessed every 24 h for 4 days after siRNA treatment resulted in a marked inhibition of cell proliferation as compared to scramble siRNA. The results of apoptosis showed that approximately 15 % of the cells treated with control-siRNA manifested evident apoptotic changes after 24 hpt, whereas DU-145 cells treated with hVEGF-siRNA significantly were positive, that is to say, 53 % at 72 hpt 23.9 ± 2.78 % (P < 0.001) and 13 ± 1.57 % at 96 hpt.

CONCLUSION

Our findings indicate that siRNA are effective in eliciting the RNAi pathway in cancerous cells and that specific siRNA efficiently down-regulate VEGF expression. They could decrease VEGF production and induce apoptosis, which may also be linked to the inhibition of cancerous cell proliferation. Therefore, it can be concluded that siRNA-mediated suppression of VEGF represents a powerful tool against prostate cancer cell proliferation. VEGF down-regulation exerts a direct anti-apoptotic function in the DU-145 cell lines and promises the development of drugs for cancer therapy.

177Lu-DO3A-HSA-Z EGFR:1907: characterization as a potential radiopharmaceutical for radionuclide therapy of EGFR-expressing head and neck carcinomas

Epidermal growth factor receptor 1 (EGFR) is an attractive target for radionuclide therapy of head and neck carcinomas. Affibody molecules against EGFR (Z(EGFR)) show excellent tumor localizations in imaging studies. However, one major drawback is that radiometal-labeled Affibody molecules display extremely high uptakes in the radiosensitive kidneys which may impact their use as radiotherapeutic agents. The purpose of this study is to further explore whether radiometal-labeled human serum albumin (HSA)-Z(EFGR) bioconjugates display desirable profiles for the use in radionuclide therapy of EGFR-positive head and neck carcinomas. The Z(EFGR) analog, Ac-Cys-Z(EGFR:1907), was site-specifically conjugated with HSA. The resulting bioconjugate 1,4,7,10-tetraazacyclododecane-1,4,7-triacetic acid (DO3A)-HSA-Z(EGFR:1907) was then radiolabeled with either (64)Cu or (177)Lu and subjected to in vitro cell uptake and internalization studies using the human oral squamous carcinoma cell line SAS. Positron emission tomography (PET), single photon emission computed tomography (SPECT), and biodistribution studies were conducted using SAS-tumor-bearing mice. Cell studies revealed a high (8.43 ± 0.55 % at 4 h) and specific (0.95 ± 0.09 % at 4 h) uptake of (177)Lu-DO3A-HSA-Z(EGFR:1907) as determined by blocking with nonradioactive Z(EGFR:1907). The internalization of (177)Lu-DO3A-HSA-Z(EGFR:1907) was verified in vitro and found to be significantly higher than that of (177)Lu-labeled Z(EFGR) at 2-24 h of incubation. PET and SPECT studies showed good tumor imaging contrasts. The biodistribution of (177)Lu-DO3A-HSA-Z(EGFR:1907) in SAS-tumor-bearing mice displayed high tumor uptake (5.1 ± 0.44 % ID/g) and liver uptake (31.5 ± 7.66 % ID/g) and moderate kidney uptake (8.5 ± 1.08 % ID/g) at 72 h after injection. (177)Lu-DO3A-HSA-Z(EGFR:1907) shows promising in vivo profiles and may be a potential radiopharmaceutical for radionuclide therapy of EGFR-expressing head and neck carcinomas.

The combi-targeting concept: mechanism of action of the pleiotropic combi-molecule RB24 and discovery of a novel cell signaling-based combination principle

RB24 (NSC 741279), a 3-methyltriazene termed "combi-molecule" designed to possess mixed epidermal growth factor receptor (EGFR) targeting and DNA methylating properties showed over a 100-fold greater antiproliferative activity than Temodal(®) (TEM), a 4-fold greater potency than gefitinib and a 5-fold stronger activity than an equi-effective combination of gefitinib+TEM against the O(6)-alkylguanine transferase (AGT)-proficient DU145 cell line that co-expresses EGFR. Investigation of the mechanisms underlying the unique potency of RB24 revealed that cell exposure to TEM was accompanied by activation of p38MAPK and concomitant elevation of the levels of X-ray repair cross-complementing group 1 (XRCC1) protein. Levels of phospho-p38MAPK and XRCC1 were increased by 2-fold in EGF-stimulated cells. In contrast, EGF-stimulation did not alter the status of these proteins in RB24-treated cells and this translated into a 2-fold lower level of XRCC1 when compared with those exposed to TEM+EGF. These effects correlated with significantly delayed DNA repair activity in combi-molecule-treated cells when compared with TEM-exposed ones. Further analysis demonstrated that in contrast to TEM, RB24 could block Bad phosphorylation at serine 136 in a dose-dependent manner and induced significantly higher levels of apoptosis than the former molecule. Tandem depletion of XRCC1 and Bad activation through alternative pathways using the MEK1 inhibitor, PD98059, led to substantial levels of apoptosis in RB24-treated cells. The results in toto indicate that the superior activity of the combi-molecule may be attributed to its ability to down-regulate DNA repair proteins such as XRCC1 and to alleviate anti-apoptotic signaling through blockade of EGFR-mediated signaling while inflicting high levels of DNA lesions to the cells.

Vasoactive intestinal peptide (VIP) induces transactivation of EGFR and HER2 in human breast cancer cells

We analyzed the cross-talk between receptors for vasoactive intestinal peptide (VIP) and the human epidermal growth factor family of tyrosine kinase receptors (HER) in oestrogen-dependent (T47D) and oestrogen-independent (MDA-MB-468) human breast cancer cells. VIP treatment slowly increased the expression levels of EGFR but it rapidly augmented phosphorylation of EGFR and HER2 in both cell lines. This pattern of HERs transactivation was blocked by the specific VIP antagonist JV-1-53, supporting the direct involvement of VIP receptors in formation of P-EGFR and P-HER2. VIP-induced transactivation was also abolished by H89 (protein kinase A inhibitor), PP2 (Src inhibitor) or TAPI-1 (inhibitor of matrix metalloproteases), following a differential pattern. These results shed a new light on the specific signalling pathways involved in EGFR/HER2 transactivation by VPAC receptors and suggest the potential usefulness of VIP receptor antagonists together with current antibodies against EGFR/HER2 and/or tyrosine kinase inhibitors for breast cancer therapy.

The effect of tyrosine kinase inhibitors, tyrphostins: AG1024 and SU1498, on autocrine growth of prostate cancer cells (DU145)

It is well established that autocrine growth of human prostate cancer cell line DU145 is dependent on TGF (EGF)/EGFR loop. However, the participation of several other growth factors in proliferation of DU145 cells has been also proposed. We employed two selective tyrosine kinase inhibitors (tyrphostins): AG1024 (an IGFIR inhibitor) and SU1498 (a VEGFR2 inhibitor) for growth regulation of DU145 cells, cultured in chemically defined DMEM/F12 medium. Both the tested compounds inhibited autocrine growth of DU145 cells at similar concentration values (IC50 approximately 2.5 microM). The tyrphostins arrested cell growth of DU145 in G1 phase, similarly as inhibitors of EGFR. However, in contrast to selective inhibitors of EGFR, neither AG1024, nor SU1498 (at concentration < or =10 microM) decreased the viability of the investigated cells. These results strongly suggest that autocrine growth of DU145 cells is stimulated by, at least, three autocrine loops: TGFalpha(EGF)/EGFR, IGFII/IGFIr and VEGF/VEGFR2(VEGFR1). These data support the hypothesis of multi-loops growth regulation of metastatic prostate cancer cell lines.

The epidermal growth factor receptor (EGFR) is proteolytically modified by the Matriptase-Prostasin serine protease cascade in cultured epithelial cells

Prostasin is expressed at the apical surface of normal epithelial cells and suppresses in vitro invasion of cancer cells. Prostasin re-expression in the PC-3 prostate carcinoma cells down-regulated the epidermal growth factor receptor (EGFR) protein expression and EGF-induced phosphorylation of the extracellular signal-regulated kinases (Erk1/2). We report here that prostasin and its activating enzyme matriptase are capable of inducing proteolytic cleavages in the EGFR extracellular domain (ECD) when co-expressed in the FT-293 cells, generating two amino-terminally truncated fragments EGFR135 and EGFR110, at 135 and 110 kDa. Prostasin's role in EGFR cleavage is dependent on the serine active-site but not the GPI-anchor. The modifications of EGFR were confirmed to be on the primary structure by deglycosylation. EGFR135 and EGFR110 are not responsive to EGF stimulation, indicating loss of the ligand-binding domains. EGFR110 is constitutively phosphorylated and in its presence Erk1/2 phosphorylation is increased in the absence of EGF. The protease-induced EGFR cleavages are not dependent on EGFR phosphorylation. The EGFR ECD proteolytic modification by matriptase-prostasin is also observed in the BEAS-2B normal lung epithelial cells, the BPH-1 benign prostate hyperplasia and the MDA-MB-231 breast cancer cell lines; and represents a novel mechanism for epithelial cells to modulate EGF-EGFR signaling.

Effect of lipid mimetics of GM3 and lyso-GM3 dimer on EGF receptor tyrosine kinase and EGF-induced signal transduction

The tyrosine kinase activity associated with epidermal growth factor receptor (EGFR) has been a target in studies of pharmacological reagents to inhibit growth of cancer cells, which are mostly of epidermal origin. Lyso-GM3 dimer showed stronger inhibitory effect on the tyrosine kinase of EGFR than GM3, with minimal cytotoxicity [Y. Murozuka, et al. Lyso-GM3, its dimer, and multimer: their synthesis, and their effect on epidermal growth factor-induced receptor tyrosine kinase. Glycoconj. J. 24 (2007) 551-563]. Synthesis of lipids with sphingosine requires many steps, and the yield is low. A biocombinatory approach overcame this difficulty; however, products required a C(12) aliphatic chain, rather than the sphingosine head group [Y. Murozuka, et al. Efficient sialylation on azidododecyl lactosides by using B16 melanoma cells. Chemistry & Biodiversity 2 (2005) 1063-1078]. The present study was to clarify the effects of these lipid mimetics of GM3 and lyso-GM3 dimer on EGFR tyrosine kinase activity, and consequent changes of the A431 cell phenotype, as follows. (i) A lipid mimetic of lyso-GM3 dimer showed similar strong inhibitory effect on EGF-induced EGFR tyrosine kinase activity, and similar low cytotoxicity, as the authentic lyso-GM3 dimer. (ii) A lipid mimetic of lyso-GM3 dimer inhibited tyrosine phosphorylation of EGFR or its dimer to a level similar to that of the authentic lyso-GM3 dimer, but more strongly than GM3 or a lipid mimetic of GM3. (iii) Associated with the inhibitory effect of a lipid mimetic of lyso-GM3 dimer on EGF-induced EGFR kinase activity, only Akt kinase activity was significantly inhibited, but kinases associated with other signal transducers were not affected. (iv) The cell cycle of A431 cells, and the effects of GM3 and a lipid mimetic of lyso-GM3 dimer, were studied by flow cytometry, measuring the rate of DNA synthesis with propidium iodide. Fetal bovine serum greatly enhanced S phase and G(2)/M phase. Enhanced G(2)/M phase was selectively inhibited by pre-incubation of A431 cells with a lipid mimetic of lyso-GM3 dimer, whereas GM3 had only a minimal effect.

Lyso-GM3, its dimer, and multimer: their synthesis, and their effect on epidermal growth factor-induced receptor tyrosine kinase

Glycosphingolipids, particularly gangliosides, are known to modulate growth factor receptor tyrosine kinase. A well-documented example is the inhibitory effect of GM3 on kinase associated with epidermal growth factor receptor (EGFR) in human epidermoid carcinoma A431 cells. Lyso-GM3 was detected as a minor component in A431 cells, and may function as an auxiliary factor in GM3-dependent inhibition of EGFR. We studied the inhibitory effect of chemically synthesized GM3, lyso-GM3, and its derivatives, on EGFR function, based on their interaction in membrane microdomain, with the following major findings: (1) GM3, EGFR, and caveolin coexist, but tetraspanins CD9 and CD82 are essentially absent, within the same low-density membrane fraction, separated by sucrose density gradient ultracentrifugation. (2) Strong interaction between EGFR and GM3 was indicated by increasing binding of EGFR to GM3-coated polystyrene beads, in a GM3 dose-dependent manner. Confocal microscopy results suggested that three components in the microdomain (GM3, EGFR, and caveolin) are closely associated. (3) Lyso-GM3 or lyso-GM3 dimer strongly inhibited EGFR kinase activity, in a dose-dependent manner, while lyso-GM3 trimer and tetramer did not. >50 microM lyso-GM3 was cytolytic, while >50 microM lyso-GM3 dimer was not cytolytic, yet inhibited EGFR kinase strongly. Thus, lyso-GM3 and its dimer exert an auxiliary effect on GM3-induced inhibition of EGFR kinase and cell growth, and lyso-GM3 dimer may be a good candidate for pharmacological inhibitor of epidermal tumor growth.