Phase II study of gemcitabine, oxaliplatin in combination with panitumumab in KRAS wild-type unresectable or metastatic biliary tract and gallbladder cancer.

BACKGROUND: Current data suggest that platinum-based combination therapy is the standard first-line treatment for biliary tract cancer. EGFR inhibition has proven beneficial across a number of gastrointestinal malignancies; and has shown specific advantages among KRAS wild-type genetic subtypes of colon cancer. We report the combination of panitumumab with gemcitabine (GEM) and oxaliplatin (OX) as first-line therapy for KRAS wild-type biliary tract cancer. METHODS: Patients with histologically confirmed, previously untreated, unresectable or metastatic KRAS wild-type biliary tract or gallbladder adenocarcinoma with ECOG performance status 0-2 were treated with panitumumab 6 mg kg(-1), GEM 1000 mg m(-2) (10 mg m(-2) min(-1)) and OX 85 mg m(-2) on days 1 and 15 of each 28-day cycle. The primary objective was to determine the objective response rate by RECIST criteria v.1.1. Secondary objectives were to evaluate toxicity, progression-free survival (PFS), and overall survival. RESULTS: Thirty-one patients received at least one cycle of treatment across three institutions, 28 had measurable disease. Response rate was 45% and disease control rate was 90%. Median PFS was 10.6 months (95% CI 5-24 months) and median overall survival 20.3 months (95% CI 9-25 months). The most common grade 3/4 adverse events were anaemia 26%, leukopenia 23%, fatigue 23%, neuropathy 16% and rash 10%. CONCLUSIONS: The combination of gemcitabine, oxaliplatin and panitumumab in KRAS wild type metastatic biliary tract cancer showed encouraging efficacy, additional efforts of genetic stratification and targeted therapy is warranted in biliary tract cancer.

A multicenter phase II trial of single-agent cetuximab in advanced esophageal and gastric adenocarcinoma.

BACKGROUND: Epidermal growth factor receptor (EGFR) is overexpressed in a significant proportion of esophageal and gastric carcinomas. Although previous studies have examined tyrosine kinase inhibitors of EGFR, there remains limited data regarding the role of EGFR-directed monoclonal antibody therapy in these malignancies. We carried out a multi-institutional phase II study of cetuximab, a monoclonal antibody against EGFR, in patients with unresectable or metastatic esophageal or gastric adenocarcinoma. PATIENTS AND METHODS: Thirty-five patients with previously treated metastatic esophageal or gastric adenocarcinoma were treated with weekly cetuximab, at an initial dose of 400 mg/m(2) followed by weekly infusions at 250 mg/m(2). Patients were followed for toxicity, treatment response, and survival. RESULTS: Treatment with cetuximab was well tolerated; no patients were taken off study due to drug-related adverse events. One (3%) partial treatment response was noted. Two (6%) patients had stable disease after 2 months of treatment. Median progression-free survival and overall survival were 1.6 and 3.1 months, respectively. CONCLUSION: Although well tolerated, cetuximab administered as a single agent had minimal clinical activity in patients with metastatic esophageal and gastric adenocarcinoma. Ongoing studies of EGFR inhibitors in combination with other agents may define a role for these agents in the treatment of esophageal and gastric cancer.

Outer segment phagocytosis by cultured retinal pigment epithelial cells requires Gas6.

The function and viability of vertebrate photoreceptors requires the daily phagocytosis of photoreceptor outer segments (OS) by the adjacent retinal pigment epithelium (RPE). We demonstrate here a critical role in this process for Gas6 and by implication one of its receptor protein tyrosine kinases (RTKs), Mertk (Mer). Gas6 specifically and selectively stimulates the phagocytosis of OS by normal cultured rat RPE cells. The magnitude of the response is dose-dependent and shows an absolute requirement for calcium. By contrast the Royal College of Surgeons (RCS) rat RPE cells, in which a mutation in the gene Mertk results in the expression of a truncated, non-functional receptor, does not respond to Gas6. These data strongly suggest that activation of Mertk by its ligand, Gas6, is the specific signaling pathway responsible for initiating the ingestion of shed OS. Moreover, photoreceptor degeneration in the RCS rat retina, which lacks Mertk, and in humans with a mutation in Mertk, strongly suggests that the Gas6/Mertk signaling pathway is essential for photoreceptor viability. We believe that this is the first demonstration of a specific function for Gas6 in the eye.

Further studies on the identification of the phagocytosis receptor of rat retinal pigment epithelial cells.

We have previously produced a polyclonal antiserum (R1S5) against a plasma membrane-enriched fraction of rat retinal pigment epithelial (RPE) cells which inhibits the phagocytosis of photoreceptor outer segments (OS) by these cells. This antiserum has now been used to purify a subset of RPE membrane glycoproteins. Using a combination of lectin affinity chromatography, and chromatography on an affinity column made with R1S5-IgG, we have enriched an RPE membrane extract about 100-fold. This enriched extract contains only 12 components, all of which are glycoproteins, and retains the ability to adsorb out the inhibitory activity of antiserum R1S5. This shows that one or more of these glycoproteins recognizes an inhibitory IgG in R1S5 and suggests that one or more of these glycoproteins may participate in the phagocytosis of OS by RPE cells, possibly as the phagocytosis receptor. We have performed N-terminal microsequencing of seven of these glycoproteins: four of the seven, with Mrs of 34, 36, 51 and 55 kDa, show no sequence homology to any known proteins.

Carbachol does not correct the defect in the phagocytosis of outer segments by Royal College of Surgeons rat retinal pigment epithelial cells.

PURPOSE: To investigate the effect of carbachol on the phagocytosis of photoreceptor outer segments (OS) in cultures of normal Long-Evans and dystrophic Royal College of Surgeons (RCS) rat retinal pigment epithelial (RPE) cells. METHODS: Retinal pigment epithelial cells from normal and RCS rats were grown in tissue culture. On reaching confluence, they were presented with OS suspended in Krebs-Henseleit buffer in the presence or absence of carbachol and LiCl. The number of bound and ingested OS was quantitated using double immunofluorescence staining. RESULTS: LiCl inhibited the ingestion of OS by more than 90% but had no effect on the binding of OS by Long-Evans RPE cells. The addition of carbachol further reduced OS ingestion. Carbachol alone decreased OS ingestion by normal RPE cells by 30% but had no effect on OS binding. The effect of LiCl and carbachol on RCS RPE cells was similar to their effect on normal RPE cells. CONCLUSIONS: Carbachol does not increase OS phagocytosis in normal or RCS rat RPE cells. The phagocytic defect in RCS rat RPE cannot be reversed or overcome by stimulation of the IP3 pathway by carbachol. LiCl strongly inhibits the ingestion of OS by normal and by RCS RPE cells, and this effect is enhanced by carbachol.

Isoproterenol inhibits rod outer segment phagocytosis by both cAMP-dependent and independent pathways.

PURPOSE: The authors studied the involvement of cAMP-dependent second messenger systems in the inhibition of rod outer segment (ROS) phagocytosis by isoproterenol (ISO) and forskolin (FSK) using two membrane-permeant analogs of cyclic adenosine monophosphate (cAMP), the Rp and Sp diastereoisomers of cyclic adenosine 3',5' monophosphothioate (cAMPS). Rp-cAMPS is a potent competitive inhibitor of cAMP-dependent protein kinase I and II (PKA I and II), whereas Sp-cAMPS is a potent activator of these enzymes. METHODS: ROS phagocytosis was quantitated in cultured rat RPE cells using a previously described double immunofluorescence assay. RESULTS: Sp-cAMPS showed a dose-dependent inhibition of ROS phagocytosis, whereas 100 microM Rp-cAMPS had no effect on this process. Rp-cAMPS fully prevented the inhibitory effect of Sp-cAMPS and FSK but was able to prevent only partially the inhibition of ROS phagocytosis induced by ISO. Isoproterenol plus FSK showed an additive effect on the inhibition of phagocytosis, suggesting that they act at two independent sites. However, ISO plus Sp-cAMPS or FSK plus Sp-cAMPS showed no additivity. CONCLUSIONS: Results suggest that FSK inhibits ROS phagocytosis by RPE cells through a cAMP-dependent pathway, whereas ISO inhibits ROS phagocytosis by RPE cells through cAMP-dependent and cAMP-independent pathways.

Stimulation of A2 adenosine receptors inhibits the ingestion of photoreceptor outer segments by retinal pigment epithelium.

PURPOSE: Recent studies have shown that A2 adenosine receptors are present in retinal pigment epithelium (RPE). In this study, the effect of adenosine and adenosine analogues on photoreceptor outer segment (ROS) phagocytosis by RPE was investigated. METHODS: Primary cultures of RPE cells were incubated with isolated outer segments in the presence of various adenosine derivatives. Changes in adenylyl cyclase activity was measured by cyclic adenosine monophosphate (cAMP) production using a radioimmunoassay detection system. RESULTS: Adenosine inhibited the ingestion phase of phagocytosis (IC50 = 50 microM), and this effect was potentiated 80-fold in the presence of dipyridamole (IC50 = 0.6 microM). In the presence of 10 microM 8-phenyltheophylline, the inhibitory effect of 100 microM adenosine was reduced from 80% inhibition of ROS ingestion to 33% inhibition. The rank order of potency of adenosine analogues to inhibit ROS ingestion by RPE was N6-cyclohexyladenosine/5'-[N-ethylcarboxamido]-adenosine (NECA) = NECA > adenosine >> [R]-N6-[2-phenylisopropyl]-adenosine. The greatest stimulation of cAMP production was observed with 33.3 microM NECA: The production of cAMP reached its maximum level after 2 minutes of incubation, and after 10 minutes the levels of cAMP were back to basal. CONCLUSIONS: These results suggest that adenosine and adenosine analogues modulate ROS ingestion by RPE via activation of adenosine A2b receptors, possibly through the cAMP intracellular signaling pathway.

The phagocytosis of rod outer segments is inhibited by drugs linked to cyclic adenosine monophosphate production.

PURPOSE: To study the effect of drugs that increase intracellular cyclic adenosine monophosphate on the ability of rat retinal pigment epithelial cells to phagocytize rod outer segments (ROS). METHODS: Cultured rat retinal pigment epithelial cells were treated with cholera toxin, forskolin, isoproterenol, or isobutylmethylxanthine and the phagocytosis of ROS by such treated cells was compared to that of control specimens. RESULTS: All of the drugs examined inhibited the ingestion, but not the binding of ROS by cultured retinal pigment epithelial cells. Cell viability was not compromised by the drug treatment because they rapidly recovered their ability to ingest ROS when the drug was removed. Dose-response curves for the inhibition of ROS phagocytosis by forskolin and isoproterenol demonstrated that this process is exquisitely sensitive to these agonists, with an IC50 for these drugs of 33 nmol/l. The results showed no measurable quantitative correlation between cyclic adenosine monophosphate levels and the inhibition of ROS phagocytosis. CONCLUSIONS: Results showed that the ingestion of ROS by retinal pigment epithelial cells was inhibited by agents that increase intracellular cyclic adenosine monophosphate, but seems to be independent of the level of this second messenger. Alternatively, ROS phagocytosis may be exquisitely sensitive to changes in the intracellular concentration of cyclic adenosine monophosphate, which are too small to measure by available methods.

cAMP production via the adenylyl cyclase pathway is reduced in RCS rat RPE.

cAMP production was investigated in retinal pigment epithelium (RPE) cells isolated from normal rats and from rats with an inherited retinal dystrophy (Rdy/p+). In normal RPE cells, 5'-[N-Ethylcarboxamido]-adenosine (A2 receptors) produced a fivefold increase in the level of cyclic adenosine monophosphate (cAMP) over basal levels. However, only a onefold increase in cAMP was observed in dystrophic cells. cAMP production by prostaglandins E1 and E2 (prostaglandin receptors) in dystrophic RPE cells was only 29-38% of the level observed in normal cells. Direct stimulation of adenylyl cyclase by 10 mumol/l forskolin increased cAMP levels in normal RPE cells by 90 fold over basal, but only by sixfold in the dystrophic cells. These data suggest there may be a defect in the adenylyl cyclase signaling pathway in dystrophic RPE cells.

The phagocytosis of ROS by RPE cells is not inhibited by mannose-containing ligands.

We have examined the ability of mannose and the mannose-rich ligands, mannan and mannosylated BSA, to inhibit the phagocytosis of rod outer segments (ROS) by cultured rat retinal pigment epithelial (RPE) cells. Mannose, at concentrations up to 0.25 M, had no effect on either the binding or the ingestion of ROS. At concentrations above 0.25 M, the cells were rounded and showed detachment from the substrate, and phagocytosis was markedly inhibited. Neither mannan (2 mg ml-1), nor mannosylated BSA(0.8 mg ml-1), affected the phagocytosis of ROS. These results suggest that the phagocytosis of ROS is probably not mediated by a mannose receptor on the surface of the RPE cells.

ROS ingestion by RPE cells is turned off by increased protein kinase C activity and by increased calcium.

The activation of protein kinase C (PKC) by phorbol myristate acetate (PMA) rapidly inhibits the phagocytosis of rod outer segments (ROS) by cultured rat retinal pigment epithelial (RPE) cells. PMA, at a concentration between 3.3 and 10 nM, blocks ROS ingestion by 50%, but does not inhibit the binding of ROS. The Ca2+ ionophore, A23187, also inhibits ROS phagocytosis, with an IC50 of about 0.5-1.0 microM and interferes with the ability of RPE cells to bind ROS. The effects of both of these drugs are reversible after drug washout. When PMA and A23187 are applied to cells consecutively, the effects are additive. These results suggest either that PMA and A23187, act upon the same proteins in the pathway which controls ROS ingestion, or that A23187 affects phagocytosis at the ROS binding level, while PKC affects steps further along the ingestion path. The effect of this process is to shut down the ingestion of ROS, as is seen during the prolonged feeding of ROS to RPE cells in culture.

RPE cells from normal rats do not secrete a factor which enhances the phagocytosis of ROS by dystrophic rat RPE cells.

Retinal pigment epithelial (RPE) cells from normal and dystrophic rats were grown separately and in mixed culture for 7 days, without a change of growth medium. Isolated rod outer segments (ROS) were suspended in the conditioned medium from these cells, and were fed to the mixed or pure RPE cell cultures. No increase or decrease in the phagocytosis of ROS by dystrophic or normal RPE cells, respectively, was observed. These results suggest that normal RPE cells do not secrete a diffusible factor(s) which enhances the phagocytosis of ROS by dystrophic RPE cells.