Potent EMT and CSC Phenotypes Are Induced By Oncostatin-M in Pancreatic Cancer

Pancreatic ductal adenocarcinoma (PDAC) is referred to as a silent killer due to the lack of clear symptoms, a lack of early detection methods, and a high frequency of metastasis at diagnosis. In addition, pancreatic cancer is remarkably resistant to chemotherapy, and clinical treatment options remain limited. The tumor microenvironment (TME) and associated factors are important determinants of metastatic capacity and drug resistance. Here, oncostatin M (OSM), an IL6 cytokine family member, was identified as an important driver of mesenchymal and cancer stem cell (CSC) phenotypes. Furthermore, the generation of cells that harbor mesenchymal/CSC properties following OSM exposure resulted in enhanced tumorigenicity, increased metastasis, and resistance to gemcitabine. OSM induced the expression of ZEB1, Snail (SNAI1), and OSM receptor (OSMR), engaging a positive feedback loop to potentiate the mesenchymal/CSC program. Suppression of JAK1/2 by ruxolitinib prevented STAT3-mediated transcription of ZEB1, SNAI1 and OSMR, as well as the emergence of a mesenchymal/CSC phenotype. Likewise, ZEB1 silencing, by shRNA-mediated knockdown, in OSM-driven mesenchymal/CSC reverted the phenotype back to an epithelial/non-CSC state. Importantly, the generation of cells with mesenchymal/CSC properties was unique to OSM, and not observed following IL6 exposure, implicating OSMR and downstream effector signaling as a distinct target in PDAC. Overall, these data demonstrate the capacity of OSM to regulate an epithelial-mesenchymal transition (EMT)/CSC plasticity program that promotes tumorigenic properties.Implications: Therapeutic targeting the OSM/OSMR axis within the TME may prevent or reverse the aggressive mesenchymal and CSC phenotypes associated with poor outcomes in patients with PDAC. Mol Cancer Res; 15(4); 478-88. ©2017 AACR.

Identification of PAM4 (clivatuzumab)-reactive epitope on MUC5AC: a promising biomarker and therapeutic target for pancreatic cancer

PAM4 is a monoclonal antibody showing high specificity for pancreatic ductal adenocarcinoma (PDAC). Humanized PAM4 labeled with ⁹⁰Y in combination with low-dose gemcitabine has shown promising therapeutic activity, and is being evaluated in a phase III clinical trial. Prior efforts have suggested that PAM4 potentially reacts with MUC5AC, a secretory mucin expressed de novo in early pancreatic neoplasia and retained throughout disease progression. In present study, we provide further evidence validating MUC5AC as the PAM4 antigen, and locate PAM4-reactive epitope within the N-terminal cysteine-rich subdomain 2 (Cys2), thus differentiating PAM4 from most anti-MUC5AC antibodies known to-date. Specifically, we show (i) PAM4-antigen and MUC5AC were co-localized in multiple human cancer cell lines, including Capan-1, BxPC-3, and CFPAC-1; (ii) MUC5AC-specific siRNA prominently reduced the expression of both MUC5AC and PAM4-antigen in CFPAC-1 cells; (iii) PAM4 preferentially binds to the void-volume fractions from Sepharose-CL2B chromatography of Capan-1 culture supernatants, which were revealed by Western blot to display the ladder pattern characteristic of oligomeric MUC5AC; and (iv) the N-terminal Cys2 within several recombinant MUC5AC fragments is essential for binding to PAM4. These findings shed light on the mechanism of PAM4-based diagnosis and treatment for pancreatic cancer, and guide further exploration of its clinical utility.

Differentiation of pancreatic ductal adenocarcinoma from chronic pancreatitis by PAM4 immunohistochemistry

CONTEXT

PAM4 is a monoclonal antibody that shows high specificity for pancreatic ductal adenocarcinoma (PDAC) and its neoplastic precursor lesions. A PAM4-based serum immunoassay is able to detect 71% of early-stage patients and 91% with advanced disease. However, approximately 20% of patients diagnosed with chronic pancreatitis (CP) are also positive for circulating PAM4 antigen. The specificity of the PAM4 antibody is critical to the interpretation of the serum-based and immunohistochemical assays for detection of PDAC.

OBJECTIVE

To determine whether PAM4 can differentiate PDAC from nonneoplastic lesions of the pancreas.

DESIGN

Tissue microarrays of PDAC (N = 43) and surgical specimens from CP (N = 32) and benign cystic lesions (N = 19) were evaluated for expression of the PAM4 biomarker, MUC1, MUC4, CEACAM5/6, and CA19-9.

RESULTS

PAM4 and monoclonal antibodies (MAbs) to MUC1, MUC4, CEACAM5/6, and CA19-9 were each reactive with the majority of PDAC cases; however, PAM4 was the only monoclonal antibody not to react with adjacent, nonneoplastic parenchyma. Although PAM4 labeled 19% (6 of 32) of CP specimens, reactivity was restricted to pancreatic intraepithelial neoplasia associated with CP; inflamed tissues were negative in all cases. In contrast, MUC1, MUC4, CEACAM5/6, and CA19-9 were detected in 90%, 78%, 97%, and 100% of CP, respectively, with reactivity also present in nonneoplastic inflamed tissue.

CONCLUSIONS

PAM4 was the only monoclonal antibody able to differentiate PDAC (and pancreatic intraepithelial neoplasia precursor lesions) from benign, nonneoplastic tissues of the pancreas. These results suggest the use of PAM4 for evaluation of tissue specimens, and support its role as an immunoassay for detection of PDAC.

Mapping PAM4 (clivatuzumab), a monoclonal antibody in clinical trials for early detection and therapy of pancreatic ductal adenocarcinoma, to MUC5AC mucin

BACKGROUND

PAM4, an antibody that has high specificity for pancreatic ductal adenocarcinoma (PDAC), compared to normal pancreas, benign lesions of the pancreas, and cancers originating from other tissues, is being investigated as a biomarker for early detection, as well as antibody-targeted imaging and therapy. Therefore, the identity of the antigen bound by this monoclonal antibody (MAb) can provide information leading to improved use of the antibody. Prior results suggested the antigen is a mucin-type glycoprotein rich in cysteine disulfide bridges that provide stable conformation for the PAM4-epitope.

METHODS

Indirect and sandwich enzyme immunoassays (EIA) were performed to compare and contrast the reactivity of PAM4 with several anti-mucin antibodies having known reactivity to specific mucin species (e.g., MUC1, MUC4, MUC5AC, etc.). Studies designed to block reactivity of PAM4 with its specific antigen also were performed.

RESULTS

We demonstrate that MAbs 2-11 M1 and 45 M1, each reactive with MUC5AC, are able to provide signal in a heterologous sandwich immunoassay where PAM4 is the capture antibody. Further, we identify MAbs 21 M1, 62 M1, and 463 M1, each reactive with MUC5AC, as inhibiting the reaction of PAM4 with its specific epitope. MAbs directed to MUC1, MUC3, MUC4, MUC16 and CEACAM6 are not reactive with PAM4-captured antigen, nor are they able to block the reaction of PAM4 with its antigen.

CONCLUSIONS

These data implicate MUC5AC as a specific mucin species to which PAM4 is reactive. Furthermore, this realization may allow for the improvement of the current PAM4 serum-based immunoassay for detection of early-stage PDAC by the application of anti-MUC5AC MAbs as probes in this sandwich EIA.

Diagnostic and therapeutic implications of a novel immunohistochemical panel detecting duodenal mucosal invasion by pancreatic ductal adenocarcinoma

BACKGROUND

We investigated a series of pancreaticoduodenectomy and duodenal biopsies with a panel of immunohistochemical markers to identify duodenal mucosal invasion by pancreatic ductal adenocarcinoma (PDAC), including markers of poor prognosis and targets of promising novel immunotherapies.

MATERIALS AND METHODS

Eighteen consecutive pancreaticoduodenectomy specimens with duodenal mucosal invasion by PDAC were examined for expression of MUC1, MUC4, MUC5AC, MUC6, mesothelin, MUC2, CDX2, and DPC4 on formalin-fixed, paraffin-embedded sections of duodenal-ampullary-pancreatic junctions. Expression of all but MUC6 was also assessed in duodenal biopsies from 12 patients with duodenal mucosal invasion by PDAC.

RESULTS

The duodenal mucosa expressed MUC1 (crypts), MUC2 (goblet cells), MUC6 (Brunner glands), CDX2, and DPC4. PDACs in the duodenal mucosa from the resection (n=16-18) and biopsy (n=12) specimens were marked as follows: MUC1 100% (30/30), MUC4 83% (24/29), MUC5AC 83% (25/30), mesothelin 82% (23/28), MUC2 7% (2/30), and CDX2 36% (10/28). Loss of DPC4 expression was seen in 16 of 29 (55%) cases. Reactive mucosa adjacent to PDAC expressed MUC4, MUC5AC and mesothelin in 65% (17/26), 19% (5/27), and 19% (5/26) of cases, respectively. While MUC5AC and mesothelin had high diagnostic accuracy for detection of PDAC, MUC2, CDX2 and DPC4 expression demonstrated negative correlation with PDAC, with absent expression being highly specific for PDAC.

CONCLUSION

Immunohistochemical labeling for PDAC biomarkers may aid the diagnosis of PDAC in duodenal biopsy, especially in situations where diagnosis of a pancreatic mass is challenging.

Abstract 1630: Cell-cell fusion in vivo transfers genes for human malignancy, metastasis, and the donor tumors’ organoid phenotype to stromal hamster cells

Cell-cell fusion in vitro has been a method for investigating oncogenesis, gene mapping, and gene regulation. Whether such mechanisms occur in vivo requires similar studies with in-vivo cell fusion, particularly whether genes for malignancy, metastasis, and organoid features can be transmitted horizontally to adjacent stromal cells. We describe our experiences with the transplantation of a human glioblastoma multiforme and two Hodgkin lymphomas from patient specimens directly to the hamster cheek pouch, resulting in highly malignant tumors that metastasize in their rodent hosts within the initial transplantation passage and subsequently over passage for many years. The resulting glioblastoma cell line, GB-749, showed heterosynkaryon formation between the tumor and hamster host cells by karyology and FISH, and the retention of 7 human genes, VIM, CD74, CXCR4, TP53, PLAGL2, GFAP, and EGFR, by PCR, of which 3 showed protein translation in vivo by immunohistochemistry; namely, CD74, CXCR4, and PLAGL2. These 3 genes have been implicated with malignancy or, particularly, glioblastoma.

In the second example of two Hodgkin lymphomas grafted to hamsters, FISH again demonstrated stable human-hamster heterosynkaryons, while PCR showed the retention of 7 human genes in the GW-532 and GW-584 cell lines propagated for 5-6 years in-vivo (VIM, CD74, CXCR4, CD19, CD20, CD71, and CD79b). Thus, the glioblastoma and Hodgkin tumor hybrids retained different genes after cell-cell fusion with hamster cells, but VIM, CD74, and CXCR4 were common, surprisingly, to all three tumor hybrid lines. The hybrid transplants also retained the morphological appearance of their original donor tumors, thus retaining their organoid genes providing the tumor's morphological phenotype. In the glioblastoma, GB-749, these included PLAGL2, GFAP, and EGFR, while in the Hodgkin lymphoma lines, GW-532 and GW-584, the B-cell-lineage genes, CD19, CD20, CD79b, were retained. We believe these are the first examples of in-vivo cell-cell fusion between human tumor and rodent host cells showing stable heterosynkaryon formation and propagation over many years, and with the retention of select human genes implicated in the malignant phenoytype, metastasis, and organoid gene signatures. Thus, at least in this model, human cancer cells can transmit malignant and organoid genes to stromal cells in their microenvironment, perhaps representing a basic mechanism for the tumor heterogeneity observed clinically. Whether such fusion events occur during the progression of cancers in patients remains to be determined.

Citation Format: David M. Goldenberg, Donglin Liu, Meiyu Loo, David V. Gold, Chien-Hsing Chang, Elaine S. Jaffe. Cell-cell fusion in vivo transfers genes for human malignancy, metastasis, and the donor tumors’ organoid phenotype to stromal hamster cells. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 1630. doi:10.1158/1538-7445.AM2013-1630

Abstract 1141: MAb-PAM4 can differentiate between pancreatic ductal adenocarcinoma and chronic pancreatitis

Background: Due to the asymptomatic nature of pancreatic ductal adenocarcinoma (PDAC) in its early stages of growth, and its relatively low incidence, screening methods have not received high attention. However, with recent studies providing the ability to identify specific patient groups at high risk for PDAC, a rationale exists for longitudinal surveillance as a means to improve early detection specifically in these high-risk settings. Individuals with a family history of PDAC, those patients with long-standing chronic pancreatitis (CP), patients with new-onset diabetes who meet certain other conditions, or those with FAMMM syndrome, etc., could be evaluated on a long-term basis for the detection of early malignant changes by use of a MAb-PAM4-based immunoassay procedure.

Methods: We have developed and validated (in over 600 patient specimens) an enzyme immunoassay (EIA) based upon use of MAb-PAM4 for quantitation of antigen in the serum of patients diagnosed with pancreatic ductal adenocarcinoma. In addition, the antibody has been used for immunohistochemical evaluation of malignant, benign, and normal pancreatic tissues.

Results: 71% of patients with confirmed early-stage disease and 91% with advanced disease were positive by EIA for circulating PAM4-antigen. Overall specificity was 81% with respect to benign pancreatic disease. Of 126 patients diagnosed with benign conditions of the pancreas, 24 (19%) were positive for the PAM4-antigen, with the majority of these cases being diagnosed with chronic pancreatitis [18 of 80 positive (23%)], all of whom had surgical resection performed for severity and/or duration of disease activity. ROC curve analyses of PAM4 assays revealed a statistically significant difference between the PDAC and CP groups (P<0.0001), with an area under the curve of 0.84 ± 0.02 (95% CI: 0.79-0.89). The positive likelihood ratio for differentiating PDAC from benign conditions of the pancreas was 4.00, which was significant (P<0.001). It is very important to emphasize that the “true” specificity of this assay is likely underestimated. Immunohistochemistry data have shown the PAM4-biomarker is absent from normal pancreas and benign, non-neoplastic lesions of the pancreas. In over 50 surgical specimens of CP, the PAM4-biomarker was identified only within PanIN lesions that are associated with long-term CP, and not by the inflamed tissue.

Conclusions: Our results suggest that PAM4-positive CP patients (and likely other PAM4-positive patients diagnosed with benign conditions of the pancreas) may very likely have pancreatic neoplasia (invasive and/or precursor lesions), and therefore should be followed closely. Indeed, such studies might reveal new cutoff values or kinetic changes that would support early surgical intervention. (Supported in part by NIH grant CA096924.)

Citation Format: David V. Gold, Chanjuan Shi, Guy Newsome, David M. Goldenberg. MAb-PAM4 can differentiate between pancreatic ductal adenocarcinoma and chronic pancreatitis. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 1141. doi:10.1158/1538-7445.AM2013-1141

Milatuzumab-SN-38 conjugates for the treatment of CD74+ cancers

CD74 is an attractive target for antibody-drug conjugates (ADC), because it internalizes and recycles after antibody binding. CD74 mostly is associated with hematologic tumors but is expressed also in solid cancers. Therefore, ADCs of the humanized anti-CD74 antibody, milatuzumab, were examined for the therapy of CD74-expressing solid tumors. Milatuzumab-doxorubicin and two milatuzumab-SN-38 conjugates with cleavable linkers, differing in their stability in serum and how they release SN-38 in the lysosome, were prepared. CD74 expression was determined by flow cytometry and immunohistology. In vitro cytotoxicity and in vivo therapeutic studies were conducted in the human cancer cell lines A-375 (melanoma), HuH-7 and Hep-G2 (hepatoma), Capan-1 (pancreatic), NCI-N87 (gastric), and Raji Burkitt lymphoma. The milatuzumab-SN-38 ADC was compared with SN-38 ADCs prepared with anti-Trop-2 and anti-CEACAM6 antibodies in xenografts expressing their target antigens. Milatuzumab-doxorubicin was most effective in the lymphoma model, whereas in A-375 and Capan-1 solid tumors, only milatuzumab-SN-38 showed a therapeutic benefit. Despite much lower surface expression of CD74 than Trop-2 or CEACAM6, milatuzumab-SN-38 had similar efficacy in Capan-1 as anti-Trop-2-SN-38, but in NCI-N87, anti-CEACAM6 and anti-Trop-2 conjugates were superior. Studies in two hepatoma lines at a single dose level showed significant benefit over saline controls but not against an irrelevant immunoglobulin G conjugate. CD74 is a suitable target for ADCs in some solid tumor xenografts, with efficacy largely influenced by uniformity of CD74 expression and with SN-38 conjugates providing the best therapeutic responses; SN-38 conjugates were preferable in solid cancers, whereas doxorubicin ADC was better in lymphoma tested.

Horizontal transmission of malignancy: in-vivo fusion of human lymphomas with hamster stroma produces tumors retaining human genes and lymphoid pathology

We report the in-vivo fusion of two Hodgkin lymphomas with golden hamster cheek pouch cells, resulting in serially-transplanted (over 5-6 years) GW-532 and GW-584 heterosynkaryon tumor cells displaying both human and hamster DNA (by FISH), lymphoma-like morphology, aggressive metastasis, and retention of 7 human genes (CD74, CXCR4, CD19, CD20, CD71, CD79b, and VIM) out of 24 tested by PCR. The prevalence of B-cell restricted genes (CD19, CD20, and CD79b) suggests that this uniform population may be the clonal initiating (malignant) cells of Hodgkin lymphoma, despite their not showing translation to their respective proteins by immunohistochemical analysis. This is believed to be the first report of in-vivo cell-cell fusion of human lymphoma and rodent host cells, and may be a method to disclose genes regulating both organoid and metastasis signatures, suggesting that the horizontal transfer of tumor DNA to adjacent stromal cells may be implicated in tumor heterogeneity and progression. The B-cell gene signature of the hybrid xenografts suggests that Hodgkin lymphoma, or its initiating cells, is a B-cell malignancy.

PAM4 enzyme immunoassay alone and in combination with CA 19-9 for the detection of pancreatic adenocarcinoma

BACKGROUND

The monoclonal antibody PAM4 has high specificity for pancreatic ductal adenocarcinoma (PDAC), as well as its precursor lesions, but has not been found to be reactive with normal and benign pancreatic tissues. The objective of the current study was to evaluate a PAM4-based serum enzyme immunoassay alone and in combination with the carbohydrate antigen (CA) 19-9 assay for the detection of PDAC, with particular attention to early stage disease.

METHODS

Sera from patients with confirmed PDAC (N = 298), other cancers (N = 99), benign disease of the pancreas (N = 120), and healthy adults (N = 79) were evaluated by a specific enzyme immunoassay for the concentration of PAM4 and CA 19-9 antigen levels by blinded analyses. All tests for statistical significance were 2-sided.

RESULTS

The overall sensitivity for PAM4 detection of PDAC was 76%, with 64% of patients with stage I disease also identified. The detection rate was considerably higher (85%) for patients with advanced disease. The assay demonstrated high specificity compared with benign pancreatic disease (85%), with a positive likelihood ratio of 4.93. CA 19-9 provided an overall sensitivity of 77%, and was positive in 58% of patients with stage I disease; however, the specificity was significantly lower for CA 19-9 (68%), with a positive likelihood ratio of 2.85 (P = .026 compared with PAM4). It is important to note that a combined PAM4 and CA 19-9 biomarker serum assay demonstrated an improved sensitivity (84%) for the overall detection of PDAC without a significant loss of specificity (82%) compared with either arm alone.

CONCLUSIONS

The PAM4 enzyme immunoassay identified approximately two-thirds of patients with stage I PDAC with high discriminatory power with respect to benign, nonneoplastic pancreatic disease. These results provide a rationale for testing patient groups considered to be at high risk for PDAC with a combined PAM4 and CA 19-9 biomarker serum assay for the detection of early stage PDAC.

Phase I/II study of 90Y-clivatuzumab tetraxetan (90Y-hPAM4) combined with gemcitabine (Gem) in advanced pancreatic cancer (APC): Final results

4043

Background: A Phase I/II trial evaluated single and repeated cycles of fractionated radioimmunotherapy (RAIT) with 90Y-labeled humanized mAb (90Y-hPAM4) plus Gem as first-line therapy in Stage 3-4 APC. Methods: Cycles of Gem once-weekly x 4 with 90Y-hPAM4 on wks 2, 3 and 4 were repeated until progression, withdrawal or unacceptable toxicity. In Part I, 90Y doses were escalated with Gem fixed at 200 mg/m2. In Part II, Gem was increased up to 1000 mg/m2, with 90Y fixed at 12 mCi/m2 for cycle 1 and lowered for retreatment. Results: Of 100 pts entered, 10 withdrew early, while 90 (73 stage IV) received 1-4 cycles. In Part I, 38 pts received 90Y-hPAM4 weekly x 3 at 6.5, 9, 12, or 15 mCi/m2, with the same cycle repeated 1-3 times in 13 pts. By CT-RECIST criteria, 6 pts (16%) had PRs and 16 (42%) had stabilization as best response (58% disease control). After cycle 1, 52% (13/25) with PET-avid images had >25% SUV reduction, and 33% (9/27) with elevated CA19-9 levels decreased by >50%. The median OS was 7.7 mo., but 11.8 mo. for retreated pts [46% (6/13) survived ≥1 yr.], and with improved efficacy at higher 90Y doses. NCI-CTCv3 Grade 3-4 platelets or ANC developed in 20/38 (53%) after cycle 1 (all reversible to Grade 1) and in all retreated pts (irreversible in 4/9 pts at 12 or 15 mCi/m2). In Part II, 52 pts received increased Gem without evidence of improved efficacy, while 13 pts were retreated with more acceptable toxicity at lower 90Y doses of 6.5 or 9 mCi/m2. Treatment was well tolerated with no infusion reactions. Infections requiring IV antibiotics occurred at a low rate and responded to appropriate coverage (bacteremia/sepsis, 7%; febrile neutropenia, 4%; ascending cholangitis, 3%; pneumonia, 2%; others 1%). One case of bleeding occurred, due to rectal tumor invasion. Anecdotal reports of good performance and decreased pain medication requirements require further validation. Conclusions: Fractionated RAIT with 90Y-hPAM4 combined with low-dose 200 mg/m2 GEM appears promising as a treatment regimen for APC. Hematologic toxicity was dose limiting. A 90Y-hPAM4 dose of 12 mCi/m2 for cycle 1 and 6.5 mCi/m2 for cycle 2 have been selected as suitable for further clinical development in the first-line setting.

Therapy of human solid tumor xenografts with CD74-targeted milatuzumab-SN-38 immunoconjugates

3091

Background: CD74 is commonly considered to be an antigen present in hematopoietic cancers, but it is also expressed in a number of solid tumors. The humanized anti-CD74 antibody, milatuzumab (hLL1), was previously shown to have exquisite internalization properties, making it an attractive carrier for drug delivery. In this study, we evaluated hLL1 conjugates of a potent topo I inhibitor, SN-38, for treating solid tumors. Methods: Two hLL1-SN-38 conjugates, possessing either a pH-sensitive linker (‘CL2A’ form) or a cathepsin-B-cleavable linker ("CL2E" form), were examined. In vitro analyses were carried out in the A-375 human melanoma cell line, and therapy experiments were performed in female athymic nude mice bearing established s.c. A-375 or s.c. human pancreatic adenocarcinoma (Capan-1) xenografts using specified doses (i.p.) at a twice weekly × 4 wks schedule; animals were sacrificed when tumor volumes (TVs) reached 1 cm3. Results: Both A-375 and Capan-1 cell lines tested positive for CD74 expression by IHC. In vitro, both SN-38 derivatives liberated free drug at the same rate when exposed to cathepsin-B at pH 5, while serum stabilities for CL2A and CL2E forms of the conjugates were ~ 1 d and >10 d, respectively. In the A-375 melanoma cell line, IC50 for the hLL1-SN-38 conjugates of CL2A and CL2E forms were 5 nM and 34 nM, respectively. In the aggressive A-375 s.c. model of melanoma, in nude mice (n =8; TV: 0.23 ± 0.06 cm3) treated with 12.5 mg/kg protein dose (total 1.7 mg/kg SN-38 eq.) of specific or non-specific SN-38 conjugates of CL2A and CL2E forms, only hLL1-CL2A-SN-38 conjugate was efficacious (Log-rank: P<0.009 vs. all controls), with a median survival time of 28 d vs. 10.5 d for untreated. Likewise, in mice bearing Capan-1 xenografts (n = 8-10; TV=0.27 ± 0.05 cm3), two low doses of hLL1-CL2A-SN-38 (12.5 or 5 mg/kg) significantly improved survival in comparison to saline control mice (p<0.035), whereas the CL2E form and a non-specific control demonstrated no efficacy. Conclusions: These results indicate the therapeutic potential of hLL1-CL2A-SN-38 conjugate and the importance of linker chemistry, and encourage additional testing in other CD74-positive solid cancers.

Fractionated radioimmunotherapy with (90) Y-clivatuzumab tetraxetan and low-dose gemcitabine is active in advanced pancreatic cancer: A phase 1 trial

BACKGROUND

It has been demonstrated that the humanized clivatuzumab tetraxetan (hPAM4) antibody targets pancreatic ductal carcinoma selectively. After a trial of radioimmunotherapy that determined the maximum tolerated dose of single-dose yttrium-90-labeled hPAM4 ((90) Y-hPAM4) and produced objective responses in patients with advanced pancreatic ductal carcinoma, the authors studied fractionated radioimmunotherapy combined with low-dose gemcitabine in this disease.

METHODS

Thirty-eight previously untreated patients (33 patients with stage IV disease and 5 patients with stage III disease) received gemcitabine 200 mg/m(2) weekly for 4 weeks with (90) Y-hPAM4 given weekly in Weeks 2, 3, and 4 (cycle 1), and the same cycle was repeated in 13 patients (cycles 2-4). In the first part of the study, 19 patients received escalating weekly (90) Y doses of 6.5 mCi/m(2) , 9.0 mCi/m(2) , 12.0 mCi/m(2) , and 15.0 mCi/m(2) . In the second portion, 19 additional patients received weekly doses of 9.0 mCi/m(2) or 12.0 mCi/m(2) .

RESULTS

Grade 3/4 thrombocytopenia or neutropenia (according to version 3.0 of the National Cancer Institute's Common Terminology Criteria for Adverse Events) developed in 28 of 38 patients after cycle 1 and in all retreated patients; no grade >3 nonhematologic toxicities occurred. Fractionated dosing of cycle 1 allowed almost twice the radiation dose compared with single-dose radioimmunotherapy. The maximum tolerated dose of (90) Y-hPAM4 was 12.0 mCi/m(2) weekly for 3 weeks for cycle 1, with ≤9.0 mCi/m(2) weekly for 3 weeks for subsequent cycles, and that dose will be used in future trials. Six patients (16%) had partial responses according to computed tomography-based Response Evaluation Criteria in Solid Tumors, and 16 patients (42%) had stabilization as their best response (58% disease control). The median overall survival was 7.7 months for all 38 patients, including 11.8 months for those who received repeated cycles (46% [6 of 13 patients] ≥1 year), with improved efficacy at the higher radioimmunotherapy doses.

CONCLUSIONS

Fractionated radioimmunotherapy with (90) Y-hPAM4 and low-dose gemcitabine demonstrated promising therapeutic activity and manageable myelosuppression in patients with advanced pancreatic ductal carcinoma.

Evaluation of a non-viral vaccine in smallpox-vaccinated individuals and immunized HLA-transgenic mice

The current poxvirus vaccine is associated with rare, but serious adverse events. Therefore, we investigated a non-replicating approach to vaccine design. Peptides encoding potential HLA-binding motifs were derived from the orthopoxvirus genes, D8L, A27L, and C12L (the IL-18-binding protein [vIL18BP105]), all of which are preserved among poxviruses that infect humans, and which may be a target of host immunity. The peptides were tested with poxvirus-vaccinated human PBMC and serum for eliciting memory responses, as well as with splenocytes and serum from peptide-immunized, human HLA-DR04 transgenic (HLA tg) mice. vIL18BP105 induced 5-fold proliferation of vaccinated-donor PBMC over non-vaccinated (P<0.001), including IL-2-producing CD8+ cells. Serum IgG recognizing vIL18BP105 was detected (P<0.002 vs non-vaccinated) by ELISA. Viral peptides were conjugated to the HLA-targeting mAb, L243, for immunization of HLA tg mice. Splenocytes from vIL18BP105-L243-immunized mice proliferated upon exposure to vIL18BP105 (P<0.001). Proliferating splenocytes were interferon-γ-producing CD4(+)CD45RA(neg). vIL18BP105-L243-immunized mice generated IgG more rapidly than free-peptide-immunized mice. Peptide-specific antibody was also detected when different L243-peptide conjugates were combined. vIL18BP, by eliciting human memory responses, is a viable antigen for inclusion in a virus-free vaccine. The immunogenicity of peptides was boosted by conjugation to L243, whether administered alone or combined.

Combination of the PAM4 and CA19-9 biomarkers to improve the detection of pancreatic adenocarcinoma

164

Background: Pancreatic ductal adenocarcinoma (PDAC) is almost universally lethal, due mainly to the inability to detect early-stage disease. Thus, identification of biomarkers that can identify patients with early-stage PDAC may improve overall survival.

Methods: In a blinded study, PAM4 and CA19-9 immunoassays were performed on sera from 480 patients, including those with confirmed PDAC (N=234), other cancers (N=84), benign diseases of the pancreas (N=89), and healthy adults (N=50).

Results: Overall sensitivity for PDAC was similar, 74% and 77% for PAM4 and CA19-9, respectively. Sensitivity for detection of early, stage-1 disease (N=26), although somewhat higher for the PAM4-antigen, was also statistically similar, 65% and 58% for PAM4 and CA19-9, respectively (P = 0.5775). However, specificity was significantly lower for CA19-9, particularly with respect to chronic pancreatitis (CP): 68% vs.86% for the PAM4 assay (P = 0.014). Furthermore, CA19-9 results showed considerably higher detection rates for non-PDAC neoplasia, including patients with other cancers that metastasized to the pancreas. Thus, positive likelihood ratios (+LR) were lower for CA19-9 (+LR = 2.41) than for the PAM4 assay (+LR = 5.29). PAM4 and CA19-9 antigen levels in PDAC were independent of each other (r2 = 0.003, P=0.410); however, the positive and negative interpretations were concordant in 68% of the cases. Thus, we used a combined biomarker analysis that ultimately improved the overall PDAC detection rate (84%), without a significant decrease in specificity (83%). Comparison of the ROC curves for PDAC vs. CP and PDAC vs. benign disease demonstrated a statistically significant improvement for the combined immunoassay, as compared to either assay alone (P < 0.0001 in both comparisons), to detect and discriminate PDAC from benign disease.

Conclusions: While the PAM4-immunoassay provides high sensitivity and specificity for detection and diagnosis of PDAC, inclusion of the CA19-9 biomarker significantly enhanced positive identification of PDAC patients, from 74% to 84%. Further studies are needed to confirm these results. (Supported in part by NIH grants CA096924, CA120432 and CA62924, and the Turpin Foundation.)

Detection of early-stage pancreatic ductal adenocarcinoma (PDAC): Sensitivity, specificity, and discriminatory properties of the serum-based PAM4-immunoassay

151

Background: We recently reported that a serum-based enzyme immunoassay employing the PAM4 antibody was able to correctly identify 82% of patients with known PDAC and, importantly, that this assay had promising sensitivity for detecting early-stage disease. We now extend these findings in a much larger patient population that includes over 600 sera from both malignant and benign diseases of the pancreas and surrounding tissues.

Methods: In a blinded analysis, sera from patients with confirmed PDAC (N=298), other cancers (N=99), benign disease of the pancreas (N=126), and healthy adults (N=79) were evaluated by enzyme immunoassay for concentration of PAM4-antigen levels.

Results: Overall sensitivity for detection of PDAC was 76%, with 64% of stage-1 patients testing positive and a higher sensitivity (85%) for advanced disease. For the most part, sera from patients with neuroendocrine tumors of the pancreas or cancers of other origin (squamous, GIST, etc.) did not have elevated levels of the PAM4-antigen. Approximately half of the patients with ampullary (48%) and extrahepatic biliary (50%) adenocarcinomas had positive levels of circulating PAM4-antigen. Of 126 patients diagnosed with benign conditions of the pancreas, only 24 (19%) were positive and, in particular, 18 of 80 (23%) patients with chronic pancreatitis (CP) were positive. ROC curve analysis demonstrated a statistically significant difference between the PDAC and CP groups (P < 0.0001), with an area under the curve of 0.84 ± 0.02 (95% CI: 0.79 – 0.89). The positive- and negative-likelihood ratios for differentiating PDAC from benign conditions of the pancreas were 4.00 and 0.30, respectively.

Conclusions: The PAM4-immunoassay detects nearly two-thirds of stage-1 PDAC patients, and does so with high discriminatory power with respect to benign pancreatic disease. Our results provide a rationale for longitudinal surveillance of patients considered at high-risk for PDAC (e.g., familial pancreatic cancer, new-onset diabetes, etc.) with the PAM4 assay. (Supported in part by NIH grants CA096924, CA120432 and CA62924, and the Turpin Foundation.)

Use of the monoclonal antibody PAM4 to differentiate pancreatic ductal adenocarcinoma (PDAC) from chronic pancreatitis and benign nonmucinous cysts of the pancreas

188

Background: Previous studies have demonstrated that anti-mucin monoclonal antibody (mAb) PAM4 is highly specific for PDAC and its precursor lesions. To investigate specificity further, we examined the expression of PAM4-reactive mucin in chronic pancreatitis and benign non-mucinous cystic lesions of the pancreas.

Methods: A tissue microarray of PDAC (N=14), as well as surgical specimens from chronic pancreatitis (N=32) and benign non-mucinous cystic lesions of the pancreas (N=19), were assessed by immunohistochemistry for expression of the PAM4-reactive mucin, as well as MUC1 (mAb-MA5), MUC4 (mAb-8G7), and CEACAM6 (mAb-MN-15).

Results: PAM4-reactive mucin, MUC1, MUC4 and CEACAM6 were expressed in 79% (11/14), 100% (14/14), 86% (12/14) and 100% (14/14) of invasive pancreatic adenocarcinoma. PAM4 only weakly labeled 6% (1/19) of benign non-mucinous cystic lesions, 1 of 15 serous cystadenomas (SCAs) and 0 of 4 cysts with squamous epithelial lining (2 lymphoepithelial cysts, and 2 retention cysts with squamous metaplasia). However, the expression of MUC1, MUC4 and CEACAM6 was detected in 53% (8/15), 0% (0/15) and 13% (2/15) of SCAs, and in 4, 3 and 3 of the 4 cysts with squamous epithelial lining, respectively. PAM4 labeled 19% (6/32) of chronic pancreatitis specimens; however, this PAM4 reactivity was restricted to the PanIN precursor lesions associated with chronic pancreatitis. Inflamed tissue was negative. The expression of MUC1, MUC4 and CEACAM6 was detected in 90% (27/30), 78% (25/32), and 97% (31/32) of chronic pancreatitis. In all of the positively-labeled specimens, the reactivity was present in non-neoplastic inflamed pancreatic tissue in addition to PanIN.

Conclusions: The expression of PAM4 was detected in only 6% of benign non-mucinous cystic lesions and in the precursor lesions associated with chronic pancreatitis. These results suggest that PAM4, in contrast to MUC1, MUC4, and CEACAM6, may be useful to differentiate benign non-mucinous cystic lesions of the pancreas and chronic pancreatitis from PDAC. (Supported in part by NIH grant CA096924.)

Activity of fractionated radioimmunotherapy (RAIT) with 90Y clivatuzumab tetraxetan (90Y-hPAM4) plus gemcitabine (Gem) in advanced pancreatic cancer (APC): Final results from a two-part study

227

Background: A Phase I/II trial was undertaken to evaluate repeated cycles of 90Y-labeled anti-mucin humanized mAb (90Y-hPAM4) plus Gem as first-line therapy in Stage 3-4 APC.

Methods: Pts received Gem once-weekly x 4 with 90Y-hPAM4 on wks 2, 3 and 4, with cycles repeated until progression or unacceptable toxicity. In Part I, pts were treated in cohorts with escalating 90Y doses and Gem fixed at a low 200 mg/m2 dose for radiosensitization. In Part II, the Gem doses were increased up to standard levels, with 90Y doses fixed for first cycle, but decreased for subsequent cycles. Tumor responses were assessed by CT, FDG/PET and serum CA19-9; safety by NCI-CTCv3.

Results: Of 100 untreated pts enrolled, 10 withdrew early, while 90 (73 stage IV) received 1-4 cycles. In Part I, 38 pts received 90Y-hPAM4 weekly x 3 at 90Y doses of 6.5 (N=4), 9 (N=12), 12 (N=17) or 15 (N=5) mCi/m2, with the same cycle repeated 1-3 times in 13 pts. Grade 3-4 platelets or ANC developed in 20/38 (53%) after cycle 1 (all reversible to Grade 1) and in all retreated pts (irreversible in 4/9 pts at 12 or 15 mCi/m2). There were 3 febrile neutropenias, 4 other infections treated with IV antibiotics, but no major bleeding or other AEs. By CT-RECIST criteria, 6 pts (16%) had PRs and 16 (42%) had stabilization as best response (58% disease control). After cycle 1, 52% (13/25) with PET-avid images became negative or had >25% SUV reduction, and 33% (9/27) with elevated CA19-9 levels decreased by >50%. The median overall survival was 7.7 mo., but 11.8 mo. for retreated pts [46% (6/13) survived ≥1 yr.], with improved efficacy at higher 90Y doses. In Part II, 52 pts received 12 mCi/m2 90Y-hPAM4 x 3 with Gem doses of 200 (N=17), 600 (N=8) or 1000 mg/m2 (N=27), with 13 pts now retreated at 90Y doses of 6.5 or 9 mCi/m2. Results so far indicate no advantage to giving higher doses of Gem with RAIT. Toxicity, response and survival data for this group will be presented at the conference.

Conclusions: Fractionated RAIT with 90Y-hPAM4 combined with low-dose gemcitabine appears to be a manageable and active first-line therapy for APC. It may provide comparable efficacy yet less toxicity compared to other regimens.

Horizontal transmission and retention of malignancy, as well as functional human genes, after spontaneous fusion of human glioblastoma and hamster host cells in vivo

Cell fusion in vitro has been used to study cancer, gene mapping and regulation, and the production of antibodies via hybridomas. However, in-vivo heterosynkaryon formation by cell-cell fusion has received less attention. This investigation describes the spontaneous fusion of a human glioblastoma with normal hamster cells after xenogeneic transplantation, resulting in malignant cells that express both human and hamster genes and gene products, and retention of glioblastoma traits with an enhanced ability to metastasize. Three of 7 human genes found showed translation of their proteins during serial propagation in vivo or in vitro for years; namely, CD74, CXCR4 and PLAGL2, each implicated with malignancy or glioblastoma. This supports the thesis that genetic hybridization of cancer and normal cells can transmit malignancy and also, as first described herein, regulatory genes involved in the tumor's organotypic morphology. Evidence also is increasing that even cell-free human cancer DNA can induce malignancy and transfer genetic information to normal cells. Hence, we posit that the transfer of genetic information between tumor and stromal cells, whether by cell-cell fusion or other mechanisms, is implicated in the progression of malignancy, and may further define the crosstalk between cancer cells and their stromal neighbors.

Treatment of advanced pancreatic carcinoma with 90Y-Clivatuzumab Tetraxetan: a phase I single-dose escalation trial

PURPOSE

Humanized antibody hPAM4 specifically binds a mucin glycoprotein expressed in pancreatic adenocarcinomas. This phase I study evaluated a single dose of (90)Y-clivatuzumab tetraxetan ((90)Y-labeled hPAM4) in patients with advanced pancreatic cancer.

EXPERIMENTAL DESIGN

Twenty-one patients (4 stage III; 17 stage IV) received (111)In-hPAM4 for imaging and serum sampling before (90)Y-hPAM4. Study procedures evaluated adverse events, safety laboratories, computed tomography (CT) scans, biomarkers, pharmacokinetics, radiation dosimetry, and immunogenicity (HAHA).

RESULTS

(111)In-hPAM4 showed normal biodistribution with radiation dose estimates to red marrow and solid organs acceptable for radioimmunotherapy and with tumor targeting in 12 patients. One patient withdrew before (90)Y-hPAM4; otherwise, 20 patients received (90)Y doses of 15 (n = 7), 20 (n = 9), and 25 mCi/m(2) (n = 4). Treatment was well tolerated; the only significant drug-related toxicities were (NCI CTC v.3) grade 3 to 4 neutropenia and thrombocytopenia increasing with (90)Y dose. There were no bleeding events or serious infections, and most cytopenias recovered to grade 1 within 12 weeks. Three patients at 25 mCi/m(2) encountered dose-limiting toxicity with grade 4 cytopenias more than 7 days, establishing 20 mCi/m(2) as the maximal tolerated (90)Y dose. Two patients developed HAHA of uncertain clinical significance. Most patients progressed rapidly and with CA19-9 levels increasing within 1 month of therapy, but 7 remained progression-free by CT for 1.5 to 5.6 months, including 3 achieving transient partial responses (32%-52% tumor diameter shrinkage).

CONCLUSION

(90)Y-Clivatuzumab tetraxetan was well tolerated with manageable hematologic toxicity at the maximal tolerated (90)Y dose, and is a potential new therapeutic for advanced pancreatic cancer.

Enhanced expression of CD74 in gastrointestinal cancers and benign tissues

CD74, a transmembrane glycoprotein that associates with MHC II, is an important chaperone that regulates antigen presentation for immune response. In addition, CD74 is the receptor for macrophage migration-inhibitory factor which, when bound to CD74, initiates survival pathways and cell proliferation. Formalin fixed, paraffin embedded clinical specimens were evaluated by immunohistochemical procedures for expression of CD74. Overall, expression of CD74 within gastrointestinal carcinomas showed a statistically greater expression than in the normal tissue counterparts (P<0.001 or better). CD74 expression was observed in 95% of pancreatic carcinomas with the majority of cases presenting a mostly intense, diffuse labeling pattern. The results suggested a trend towards greater expression within the higher grade carcinomas (P=0.06). Colorectal and gastric carcinomas gave similar results with 60% and 86%, respectively, positive for CD74 with an intense, diffuse staining pattern. We hypothesized that precursor lesions would express levels of CD74 as high, or higher, than their respective carcinomas, since activation of survival pathways would be of particular importance at the early stages of neoplastic development. For PanIN lesions there was greater expression of CD74 within higher grade, PanIN-3 lesions, whereas the colonic adenomas showed no such trend, but overall, a higher frequency and intensity of CD74 labeling than was observed within the colon carcinomas. These findings are supportive of a role for CD74 in the development and maintenance of gastrointestinal neo-plasia, and provide a rationale for development of therapeutic agents that are able to block CD74 function, specifically within the tumor cell.

Detection of early-stage pancreatic adenocarcinoma

BACKGROUND

Pancreatic adenocarcinoma is an almost universally lethal disease, in large part, due to our inability to detect early-stage disease. Monoclonal antibody PAM4 is reactive with a unique biomarker expressed by >85% of pancreatic adenocarcinomas. In this report, we examined the ability of a PAM4-based immunoassay to detect early-stage disease.

MATERIALS AND METHODS

The PAM4-based immunoassay was used to quantitate antigen in the serum of healthy volunteers (n = 19), patients with known pancreatic adenocarcinoma (n = 68), and patients with a primary diagnosis of chronic pancreatitis (n = 29).

RESULTS

Sensitivity for detection of pancreatic adenocarcinoma was 82%, with a false-positive rate of 5% for healthy controls. Patients with advanced disease had significantly higher antigen levels than those with early-stage disease (P < 0.01), with a diagnostic sensitivity of 91%, 86%, and 62% for stage 3/stage 4 advanced disease, stage 2, and stage 1, respectively. We also evaluated chronic pancreatitis sera, finding 38% positive for antigen; however, this was discordant with immunohistochemical findings that suggest the PAM4 antigen is not produced by inflamed pancreatic tissue. Furthermore, several of the serum-positive pancreatitis patients, for whom tissue specimens were available for pathologic interpretation, had evidence of neoplastic precursor lesions.

CONCLUSIONS

These results suggest the use of the PAM4 serum assay to detect early-stage pancreatic adenocarcinoma and that positive levels of PAM4 antigen are not derived from inflamed pancreatic tissues but rather may provide evidence of subclinical pancreatic neoplasia. EFFECT: The ability to detect pancreatic adenocarcinoma at an early stage could provide for early therapeutic intervention with potentially improved patient outcomes.

Abstract 5341: Sensitivity of NHL to killing by anti-HLA-DR and anti-CD74 mAbs is increased by interferon-gamma

Background: HLA-DR and CD74 are similarly, but not identically, expressed and induced by interferons on a variety of cells. Expression of both antigens on hematological malignancies led to their development as targets for antibody-based therapy. The humanized anti-CD74 monoclonal antibody (mAb), milatuzumab (Immunomedics Inc, Morris Plains, NJ), is in clinical evaluation for therapy of NHL, multiple myeloma (MM), and CLL after preclinical evidence of activity in these tumor types. A humanized anti-HLA-DR mAb, hL243γ4P (IMMU-114, Immunomedics) has demonstrated anti-tumor activity in vitro and in vivo, and clinical evaluation is planned. In addition to expression in hematologic cancers, these antigens are expressed on the surface of other tumor types, including melanoma and renal cell carcinoma, and in the cytoplasm of others, including pancreatic and colonic carcinomas, and glioblastomas (GBM).

Methods: We examined whether the ability of anti-HLA-DR and anti-CD74 mAbs to kill cancer cells can be increased by using IFNγ as an inducer of antigen expression. Using a panel of diverse cancer cell lines (including NHL, MM, GBM, and pancreatic and colonic carcinomas), we examined IFNγ-induced changes in surface and cytoplasmic HLA-DR and CD74 expression. Sensitivity of malignant cells to milatuzumab and hL243γ4P was assessed with and without INFγ by cytotoxicity assays.

Results: Without IFNγ surface expression of HLA-DR and CD74 were present on 2/2 NHL, 2/2 MM, and only weakly positive on 2/2 GBM cell lines. Surface CD74 and HLA-DR were weak or undetectable on 4/4 colon and 4/4 pancreatic carcinomas. Cytoplasmic CD74 and HLA-DR were seen in NHL, MM, GBM, and 1/4 colon and 1/4 pancreatic (CD74 only) carcinomas. Two-day incubation with IFNγ increased surface and cytoplasmic expression of both HLA-DR and CD74 in all the NHL and GBM, and 3/4 pancreatic cancer lines, but not MM cell lines. In all 4 colon lines, IFNγ increased cytoplasmic expression of both antigens, and surface expression of HLA-DR in 3/4 and CD74 in 2/4. Upregulation of HLA-DR and CD74 ranged from 23-3700%. Increased killing by both hL243γ4P (58%) and milatuzumab (33%) was seen in vitro after INFγ exposure in WSU-FSCCL NHL cells. No cell killing was observed using these mAbs in vitro on U118 (GBM), Capan-1 (pancreatic carcinoma), or LoVo (colon carcinoma), despite upregulation of the antigens in these cell lines. A CD74-transfected version of the U118 GBM cell line has been prepared for comparison of milatuzumab sensitivity based on antigen density only.

Conclusions: Cell surface and cytoplasmic expression of CD74 and HLA-DR are increased on cell lines from a variety of cancer types after INFγ exposure. This increased expression correlates with increased toxicity of anti-HLA-DR and anti-CD74 mAbs in a NHL cell line, and is under evaluation in other cancer types. These studies could prove useful in predicting the potential benefit of combined INFγ and mAb therapies.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 5341.

Pretargeted radioimmunotherapy of pancreatic cancer xenografts: TF10-90Y-IMP-288 alone and combined with gemcitabine

Pancreatic cancer is a silent disease that most commonly presents in an already metastatic form. Current treatment options provide little survival benefit. Radiolabeled PAM4 IgG, a monoclonal antibody that recognizes a unique epitope associated with a mucin found almost exclusively in pancreatic cancer, has shown encouraging therapeutic effects in animal models and in early clinical testing ((90)Y-humanized PAM4 IgG, (90)Y-clivatuzumab tetraxetan). The studies reported herein examine a new pretargeting procedure for delivering therapeutic radionuclides.

METHODS

We prepared a humanized, recombinant tri-Fab bispecific monoclonal antibody (bsmAb) (TF10) using specificity for targeting pancreatic cancer of PAM4 and another Fab binding to a hapten (histamine-succinyl-glycine [HSG]) and tested this in a pretargeting setting with a (90)Y-1,4,7,10-tetraazacyclododecane-N,N',N'',N'''-tetraacetic acid-di-HSG-peptide (pretargeted radioimmunotherapy [PT-RAIT]). Nude mice bearing established Capan-1 human pancreatic cancer xenografts were given TF10 and then received the (90)Y peptide as a single bolus dose 19 h later, or the therapy cycle was fractionated weekly. Other studies examined different combinations with gemcitabine.

RESULTS

PT-RAIT of 18.5 MBq ( approximately 50% of its maximum tolerated dose [MTD]) was as effective as the MTD of (90)Y-PAM4 IgG (5.55 MBq). Three monthly doses of 9.25 MBq of PT-RAIT combined with a monthly cycle of gemcitabine (3 weekly, 6-mg doses) significantly enhanced survival, compared with PT-RAIT alone. Adding gemcitabine as a radiosensitizer to 9.25 MBq of PT-RAIT enhanced objective responses. Weekly fractionation of the PT-RAIT, as compared with a single treatment, improved responses.

CONCLUSION

PAM4-based PT-RAIT with (90)Y hapten peptide is an effective treatment for pancreatic cancer, with less toxicity than (90)Y-PAM4 IgG, in this model. Combinations with gemcitabine and dose fractionation of the PT-RAIT enhanced therapeutic responses.

Ceramide regulates gemcitabine-induced senescence and apoptosis in human pancreatic cancer cell lines

Bioactive sphingolipids are potent intracellular signaling molecules having profound effects on cell death, growth, and differentiation. Pharmacologic manipulation of sphingolipid levels could have a significant effect on the induction of apoptosis by anticancer agents, and thus, improve treatment efficacy. We observed that gemcitabine cannot completely kill AsPc1 and Panc1 human pancreatic cancer cells in culture; even at high concentrations of gemcitabine, 30% to 40% of the cells remain viable. By adding sphingomyelin to the culture medium, gemcitabine-induced cell death increased synergistically to >90%. Panc1 cells that survived high concentrations of gemcitabine had an increase in beta-galactosidase activity, a marker of senescence. The inclusion of sphingomyelin with gemcitabine reduced beta-galactosidase activity, as compared with cells treated with gemcitabine alone. Expression of p21(waf1/cip1) in both cell lines exposed to sphingomyelin, gemcitabine, and gemcitabine + sphingomyelin varied relative to the untreated group. C(8)-ceramide induced both cell death and senescence in a dose-dependent manner. These results indicate that gemcitabine induces senescence in pancreatic cancer cells and that sphingomyelin-enhanced chemosensitivity is achieved through reducing the induction of senescence by redirecting the cell to enter the apoptotic pathway. Ceramide levels seem to be critical to this decision, with cell cycle progression being uninhibited at low ceramide levels, senescence induced at moderate levels, and apoptosis initiated at high levels. Our results provide further evidence that targeting the sphingolipid metabolism is a means of enhancing the efficacy of chemotherapeutic agents.

A novel bispecific, trivalent antibody construct for targeting pancreatic carcinoma

Preclinical and clinical studies have demonstrated the application of radiolabeled mAb-PAM4 for nuclear imaging and radioimmunotherapy of pancreatic carcinoma. We have now examined the ability of a novel PAM4-based, bispecific monoclonal antibody (mAb) construct, TF10, to pretarget a radiolabeled peptide for improved imaging and therapy. TF10 is a humanized, bispecific mAb, divalent for mAb-PAM4 and monovalent for mAb-679, reactive against the histamine-succinyl-glycine hapten. Biodistribution studies and nuclear imaging of the radiolabeled TF10 and/or TF10-pretargeted hapten-peptide (IMP-288) were conducted in nude mice bearing CaPan1 human pancreatic cancer xenografts. (125)I-TF10 cleared rapidly from the blood, with levels decreasing to <1% injected dose per gram (ID/g) by 16 hours. Tumor uptake was 3.47 +/- 0.66% ID/g at this time point with no accumulation in any normal tissue. To show the utility of the pretargeting approach, (111)In-IMP-288 was administered 16 hours after TF10. At 3 hours postadministration of radiolabeled peptide, imaging showed intense uptake within the tumors and no evidence of accretion in any normal tissue. No targeting was observed in animals given only the (111)In-peptide. Tumor uptake of the TF10-pretargeted (111)In-IMP-288 was 24.3 +/- 1.7% ID/g, whereas for (111)In-IMP-288 alone it was only 0.12 +/- 0.002% ID/g at 16 hours. Tumor/blood ratios were significantly greater for the pretargeting group ( approximately 1,000:1 at 3 hours) compared with (111)In-PAM4-IgG ( approximately 5:1 at 24 hours; P < 0.0003). Radiation dose estimates suggested that TF10/(90)Y-peptide pretargeting would provide a greater antitumor effect than (90)Y-PAM4-IgG. Thus, the results suggest that TF10 pretargeting may provide improved imaging for early detection, diagnosis, and treatment of pancreatic cancer as compared with directly radiolabeled PAM4-IgG.

PAM4-reactive MUC1 is a biomarker for early pancreatic adenocarcinoma

PURPOSE

The anti-MUC1 monoclonal antibody (MAb), PAM4, has a high specificity for pancreatic adenocarcinoma compared with other cancers, normal tissues, or pancreatitis. In order to assess its role in early pancreatic cancer development, we examined the expression of the PAM4-reactive MUC1 in the noninvasive precursor lesions, pancreatic intraepithelial neoplasia (PanIN) and intraductal papillary mucinous neoplasia (IPMN).

EXPERIMENTAL DESIGN

Tissue microarrays prepared from formalin-fixed, paraffin-embedded specimens were assessed by immunohistology for expression of the PAM4-reactive, non-variable number of tandem repeats (VNTR), MUC1 epitope, and the VNTR epitope bound by the MA5 MAb.

RESULTS

The PAM4-reactive MUC1 epitope was not detected in normal pancreas but was expressed in 87% (48 of 55) of invasive pancreatic adenocarcinomas, including early stage 1 disease: PAM4 labeled 94% (44 of 47) of the earliest PanIN lesions, PanIN-1A and 1B, along with 91% (10 of 11) of PanIN-2, 40% (2 of 5) of PanIN-3, and 86% (31 of 36) of intraductal papillary mucinous neoplasia lesions. A mostly diffuse pattern of labeling was observed. A second, unrelated, anti-MUC1 MAb, MA5, showed considerably less sensitivity with early PanIN-1 lesions; only 61% (25 of 41) were positive and the labeling did not differentiate normal pancreas from PanINs.

CONCLUSIONS

The results suggest that expression of the PAM4-reactive antigen may represent an early event in the development of invasive pancreatic adenocarcinoma, and is unrelated to the VNTR peptide core epitopes of MUC1. Detection of this biomarker using immunohistology, in vitro immunoassays, and in vivo antibody-based imaging may provide new opportunities for the early detection and improved diagnosis of pancreatic cancer.

Sphingolipid targets in cancer therapy

Considerable progress has been made recently in our understanding of the role of ceramide in the induction of apoptotic cell death. Ceramide is produced by cancer cells in response to exposure to radiation and most chemotherapeutics and is an intracellular second messenger that activates enzymes, leading to apoptosis. Because of its central role in apoptosis, pharmacologic manipulation of intracellular ceramide levels should result in attenuation or enhancement of drug resistance. This may be achieved through direct application of sphingolipids or by the inhibition/activation of the enzymes that either produce or use ceramide. In addition, attention should be given to the subcellular location of ceramide generation, because this has been shown to affect the biological activity of sphingolipids. This review summarizes the sphingolipid biosynthetic pathway, as it relates to the identification of important targets for drug discovery, and the development of novel agents capable of enhancing chemotherapy.

New MUC1 serum immunoassay differentiates pancreatic cancer from pancreatitis

PURPOSE

To evaluate a new immunoassay for identification and quantitation of MUC1 in the sera of patients with pancreatic cancer or pancreatitis. The sensitivity and specificity of the assay are examined and compared to results from a CA19-9 immunoassay.

METHODS

An in vitro enzyme immunoassay was established with monoclonal antibody PAM4 as the capture reagent, and a polyclonal anti-MUC1 antibody as the probe. Patient sera were obtained from healthy, adult patients with acute and chronic pancreatitis, and those with pancreatic and other forms of cancer, and were measured for PAM4-reactive MUC1.

RESULTS

At a cutoff of 10.2 units/mL, 41 (77%) of 53 pancreatic cancer patients, none of the healthy individuals (n = 43), and only four (5%) of 87 patients with pancreatitis were positive above this value. Among nonpancreatic cancers investigated, colorectal cancers gave the highest percentage of positives (14%; five of 36). Overall, the sensitivity and specificity of the immunoassay for pancreatic cancer were 77% and 95%, respectively. Receiver operator characteristic analyses for discrimination of pancreatic cancer from pancreatitis provided an area under the curve of 0.89 (95% CI, 0.82 to 0.93), with a specificity of 95.4% and a positive likelihood ratio of 16.8. A direct pair-wise comparison of PAM4 and CA19-9 immunoassays for discrimination of pancreatic cancer and pancreatitis resulted in a significant difference (P < .003), with the PAM4 immunoassay demonstrating superior sensitivity and specificity. CONCLUSION The high sensitivity and specificity observed suggest that the PAM4-based immunoassay of circulating MUC1 may be useful in the diagnosis of pancreatic cancer.

Identification of a Mu-9 (anti-colon-specific antigen-p)-reactive peptide having homology to CA125 (MUC16)

Mu-9, an anti-colon specific antigen-p (CSAp) monoclonal antibody (MAb), has shown excellent gastrointestinal cancer targeting in both pre-clinical and clinical trials. With the recent development of the humanized version of this MAb, Mu-9 will receive further attention as a potential therapeutic agent for colorectal cancer. Hence, we have undertaken studies to examine the nature of the CSAp antigen and the structure of the Mu-9 epitope. M13 phage displaying random 12-mer peptides were used to isolate a peptide that binds both murine and humanized Mu-9 MAbs. The peptide, Mu-9-p16, was synthesized and found to inhibit binding of Mu-9 to CSAp with a Ka for the humanized antibody of 4.28 x 10(-7) +/- 0.91 x 10(-7) M. Control peptides did not bind Mu-9, nor did they inhibit the Mu-9-CSAp interaction. Three overlapping peptides were synthesized and used to demonstrate that the last six residues were sufficient to inhibit the Mu-9-CSAp interaction. A search of GenBank revealed that the peptide sequence IHPRP, was also present within CA125, a very high molecular weight ovarian cancer-associated antigen. The sequence is present outside of the known antigenic regions identified by the Oc125, M-11 and Ov197 anti-CA125 antibodies. To demonstrate that CSAp and CA125 may be the same protein, a heterologous sandwich enzyme immunoassay was developed with anti-CA125 MAbs used as capture reagents and Mu-9 as probe. By use of this ELISA system, we were able to specifically identify CSAp. In conclusion, our results indicate that the Mu-9-p16 peptide isolated through our screen identifies a peptide epitope shared by CSAp and CA125 and suggest that these proteins are related.

Synergistic interaction between sphingomyelin and gemcitabine potentiates ceramide-mediated apoptosis in pancreatic cancer

We have examined the mechanism by which sphingomyelin (SM) enhances chemotherapy in human pancreatic cancer cells, focusing on the correlation between ceramide metabolism and apoptosis. Dose response curves for gemcitabine in the absence or presence of 0.2 mg/mL SM provided IC(50) values of 78.3 +/- 13.7 and 13.0 +/- 3.0 nmol/L, respectively. The cytotoxic effect of the combined treatment was synergistic (combination index = 0.36). Using annexin-V staining, the percentage of apoptotic cells was 3.6 +/- 2.6% for the untreated cells, 6.5 +/- 3.8% for the 0.2 mg/mL SM-treated cells, and 19.9 +/- 12.9% for the 100 nmol/L gemcitabine-treated cells, but increased significantly to 42.1 +/- 12.7% with the combined treatment (P < 0.001, compared with gemcitabine-treated group). The percentage of cells losing mitochondrial membrane potential followed a similar trend. The ceramide content of untreated and gemcitabine-treated cells was not significantly different (0.46 +/- 0.29 and 0.59 +/- 0.34 pmol ceramide/nmole PO(4)). However, when 0.2 mg/mL SM was added, ceramide levels were 1.09 +/- 0.42 and 1.58 +/- 0.55 pmol ceramide/nmol PO(4), for the SM alone and SM with gemcitabine-treated cells, respectively (P = 0.038). Acidic SMase was activated by exposure to gemcitabine but not SM, whereas the activities of neutral SMase and glycosylceramide synthase did not change with either gemcitabine or SM. The data are consistent with gemcitabine-induced activation of acidic SMase and indicate that the addition of SM can yield increased production of ceramide, mitochondrial depolarization, apoptosis, and cell death. Because SM by itself is relatively nontoxic, addition of this lipid to agents that induce apoptosis may prove useful to enhance apoptosis and increase cytotoxicity in cancer cells.

Improved targeting of pancreatic cancer: experimental studies of a new bispecific antibody, pretargeting enhancement system for immunoscintigraphy

PURPOSE

The early detection and diagnosis of pancreatic cancer remains a major clinical challenge in which imaging procedures have a central role. The purpose of this study was to evaluate a pretargeting method with a bispecific PAM4 (bsPAM4; anti-MUC1) antibody for radioimmunoscintigraphy of experimental human pancreatic cancer.

EXPERIMENTAL DESIGN

A bispecific F(ab')(2) antibody was generated from chimeric PAM4 Fab' and murine 734 (anti-indium-diethylenetriaminepentaacetic acid) Fab' fragments and then used in conjunction with 2 peptide haptens ((111)In-IMP-156 and (99m)Tc-IMP-192). Biodistribution studies and radioimmunoscintigraphic imaging properties of the radiolabeled bsPAM4, and pretargeted, radiolabeled peptides were examined in the CaPan1 human pancreatic tumor grown as s.c. xenografts in athymic nude mice. Tumor uptake and tumor:nontumor ratios were compared with a nontargeting irrelevant anti-CD20, bispecific rituximab, radiolabeled peptides alone, and with directly labeled PAM4.

RESULTS

Biodistribution results indicated significantly greater tumor uptake of radiolabeled peptides at 3 h after injection when pretargeting was performed with bsPAM4 as compared with the bispecific rituximab [20.2 +/- 5.5 percentage of injected dose per gram of tissue (%ID/g) versus 0.9 +/- 0.1%ID/g, respectively, for (111)In-IMP-156, and 16.8 +/- 4.8%ID/g versus 1.1 +/- 0.2%ID/g, respectively, for (99m)Tc-IMP-192]. Similar results were obtained at the 24-h time point. Tumor:nontumor ratios were >30 for all of the tissues except the kidneys, where a ratio of 7.8 +/- 2.8 was observed. By immunoscintigraphy, tumors could be visualized as early as 30 min after injection of the radiolabeled peptide.

CONCLUSIONS

These studies demonstrate the feasibility of using the pretargeted, bispecific antibody technology for nuclear imaging of pancreatic cancer. The advantage of pretargeted bsPAM4 antibody as an imaging platform is the high specificity for pancreatic cancer as compared with the physicochemical parameters identified by current imaging technologies.

CD74 Is Expressed by Multiple Myeloma and Is a Promising Target for Therapy

PURPOSE

CD74 (HLA-DR-associated invariant chain) plays a role in antigen presentation. In addition to its expression on antigen-presenting cells, it is expressed by carcinomas of renal, lung, gastric, and thymic origin and by certain sarcomas. The restricted expression of CD74 by normal tissues and its very rapid internalization make CD74 an attractive therapeutic target for both cancer and immunologic diseases. Preclinical efficacy of anti-CD74 monoclonal antibody (mAb) therapy has been demonstrated in B-lymphoma models. Because there are few validated antigenic targets in multiple myeloma, CD74 expression was examined.

EXPERIMENTAL DESIGN

CD74 expression was assessed by immunohistochemistry in bone marrow biopsies of known multiple myeloma cases. Its expression was measured by flow cytometry in multiple myeloma lines, and CD74 mRNA expression was determined by reverse transcription-PCR. In addition, the in vitro antiproliferative effect of LL1 mAb was evaluated on a CD74+ multiple myeloma cell line using a [3H]thymidine incorporation assay.

RESULTS

CD74 expression was observed in 19 of 22 cases of multiple myeloma, with most expressing moderate to high levels in the majority of malignant plasma cells. CD74 was expressed by most multiple myeloma cell lines, as was CD74 mRNA, at levels mirroring CD74 protein. Also, unlabeled LL1 mAb mediated in vitro growth inhibition of a CD74+ multiple myeloma cell line.

CONCLUSIONS

CD74 expression is frequent in multiple myeloma, with predominant expression by the malignant plasma cells. Because anti-CD74 mAbs internalize very rapidly and LL1 mAb has shown efficacy in B-lymphoma models, CD74 represents a novel and promising target for treatment of multiple myeloma. Therefore, LL1 mAb is well suited as a carrier of radionuclides, drugs, or toxins, and also has activity as an unlabeled mAb, thereby supporting its development for this unmet need in cancer therapy.

Combined 90Yttrium-DOTA-labeled PAM4 antibody radioimmunotherapy and gemcitabine radiosensitization for the treatment of a human pancreatic cancer xenograft

We have examined the application of (90)Y-DOTA-cPAM4, anti-MUC1 IgG, in combination with the front-line drug gemcitabine as a potential therapeutic for pancreatic cancer. Athymic nude mice bearing CaPan1 human pancreatic cancer xenografts were administered 2 mg of gemcitabine on days 0, 3, 6, 9 and 12 with concurrent (90)Y-DOTA-cPAM4 (100 microCi) provided on day 0. A second group of mice received a second cycle of treatment 5 weeks after the start of the first cycle. Control groups of mice included those that received either treatment arm alone, the combined modality treatment employing a nontargeting control antibody (hLL2, anti-B-cell lymphoma) and a final group that was left untreated. Gemcitabine administered as a single agent provided no antitumor effect. A single cycle of the combined (90)Y-DOTA-cPAM4 and gemcitabine treatment provided greater inhibition of tumor growth than was observed for any of the other treatment procedures. Tumor growth was delayed for a period of 7 weeks. Two cycles of gemcitabine with concomitant (90)Y-DOTA-cPAM4 yielded significant tumor regression and increased median survival to 21 weeks vs. 12 weeks for mice receiving a single cycle of therapy (p<0.024). Median tumor volume doubling-times were 18 weeks in mice treated with 2-cycles of therapy vs. 7 weeks in mice given only 1-cycle (p<0.001), and 3.5 weeks for the group that received 2-cycles of gemcitabine concomitant with equitoxic nontargeting (90)Y-DOTA-hLL2 (p<0.001). These data suggest that addition of (90)Y-DOTA-cPAM4 RAIT to a gemcitabine treatment regimen may provide enhanced antitumor efficacy for the treatment of pancreatic cancer.

Low-dose radioimmunotherapy ((90)Y-PAM4) combined with gemcitabine for the treatment of experimental pancreatic cancer

PURPOSE

Monoclonal antibody PAM4 is reactive with the MUC1 mucin as expressed by >85% of human pancreatic cancers. Significant antitumor effects have been demonstrated using radiolabeled PAM4 for radioimmunotherapy (RAIT) of experimental pancreatic cancer. The goal of the present study was to determine whether the addition of low-dose (90)Y-PAM4 RAIT to a clinically relevant regimen of gemcitabine chemotherapy would provide enhanced antitumor efficacy over that observed by chemotherapy alone without the addition of significant toxicity to normal tissues.

EXPERIMENTAL DESIGN

Mice bearing human pancreatic tumor xenografts (CaPan1) were administered three cycles of gemcitabine chemotherapy (1000 mg/m(2)/week for 3 weeks with 1 week off) concomitant with (90)Y-labeled PAM4 RAIT (25 micro Ci; 10% of the single agent MTD) given at weeks 0, 4, and 7. Control groups of mice received chemotherapy alone, (90)Y-PAM4 RAIT alone, or an equidose of (90)Y-labeled nontargeting control antibody with and without gemcitabine.

RESULTS

Mice that received (90)Y-PAM4 RAIT with gemcitabine had tumors that were significantly smaller in size than all of the other treatment groups (P < 0.005). A median survival of 24 weeks was achieved in mice that received the combined treatment versus 10 weeks for mice that received only gemcitabine (P < 0.001) and 16 weeks for mice that received only (90)Y-PAM4 RAIT (P < 0.040). The combined treatment regimen was well tolerated.

CONCLUSIONS

A combined chemoimmunotherapy and RAIT approach using gemcitabine and low-dose (90)Y-PAM4 provided significantly increased antitumor efficacy than was observed for each treatment arm given alone. Importantly, the enhanced antitumor efficacy was achieved with minimal toxicity to normal tissues. These studies provide justification for clinical trials using the combined modality treatment for patients with pancreatic cancer.

Interferon-gamma upregulates MUC1 expression in haematopoietic and epithelial cancer cell lines, an effect associated with MUC1 mRNA induction

Epithelial mucin-1 (MUC1) is an important target antigen that it is overexpressed in both epithelial and haematological cancers including multiple myeloma (MM) and some lymphomas and leukaemias. MUC1 has adhesive and immunosuppressive properties, which may promote cancer progression. These studies evaluated the effect of IFNs on MUC1 expression, since these agents are widely used in clinical cancer therapy. MUC1 and interferon (IFN) receptor expression were measured by radioligand binding. Changes in MUC1 mRNA levels in response to IFN-gamma were assessed by semi-quantitative reverse transcriptase-polymerase chain reaction (RT-PCR). IFN-gamma was found to be a more potent inducer of MUC1 expression than IFN-alpha. 125I-IFN binding studies indicated that both IFN receptors were expressed in most of the cell lines. With IFN-gamma treatment, there was upregulation of MUC1 mRNA. IFN-gamma has a more consistent and more potent effect upon MUC1 induction than IFN-alpha. The ability to upregulate MUC1 across a broad range of cancer types by a clinically available cytokine, IFN-gamma, has important implications for enhancing immunotherapeutic approaches targeting MUC1.

Colonic tumor CEA, CSAp and MUC-1 expression following radioimmunotherapy or chemotherapy

Understanding the changes in tumor biology following cytotoxic therapy may lead to a better understanding of the properties of surviving tumor cell populations and to an improved ability to target and treat these cells. This report addressed the time-dependent dynamic alterations in the expression of three tumor-associated antigens: carcinoembryonic antigen (CEA), colon-specific antigen (CSAp) and mucin-1 (MUC-1) following chemotherapy with 5-fluorouracil (5-FU) or radioimmunotherapy (RAIT; (131)I-labeled anti-CEA IgG) in human colonic tumor xenografts. Immunoassay results show that CEA and MUC-1 expression all increase rapidly after either 5-FU or RAIT. GW-39 tumors show a 2.7-fold increase in CEA expression after a maximum tolerated dose of RAIT, being highest after 21 days, while LS174T and HT-29 tumors maximally increase expression 8.3- and 2.6-fold on day 7 after RAIT, respectively. The change in LS174T is short-term, whereas the change in HT-29 is maintained for at least 4 weeks. Serum CEA levels in these tumor- bearing mice also increase in parallel to the changes observed in tumor. MUC-1 increases 2.5-fold by day 5-7 following RAIT in LS174T tumors and 6-fold by day 14 following RAIT in GW-39 tumors, with a corresponding increase in serum MUC-1. Dramatic increases in CSAp after RAIT were also demonstrated in GW-39 tissue by immunohistochemistry. Thus, these data indicate that the response of tumor cells to low-dose-rate radiation from RAIT or to chemotherapy is associated with an increase of CEA, MUC-1 and CSAp.

Monoclonal antibody G47 engineered to be reactive with colorectal tumor mucin

We have previously shown that the normal adult colon produces a sialomucin containing the core trisaccharide 1,3 N-acetylgalactosamine. This structure was shown to be the epitope for a polyclonal antiserum that demonstrated colon "specific" activity. Antiserum binding is dependent upon the presence of O-acetylated sialic acids present at high concentrations in normal adult colon tissue. However, O-acetylation of sialic acids is decreased in colorectal cancer. Indeed, approximately 50% of colorectal carcinomas are nonreactive with this antiserum. In the current work, we used a de-O-acetylated, normal colon mucin as immunogen to generate monoclonal antibody (MAb) G47. Untreated normal colon mucins having a high O-acetylated sialic acid content were essentially nonreactive with G47. Removal of O-acetyl groups by saponification generated a reactive mucin derivative while subsequent treatment with neuraminidase abolished reactivity. By immunoperoxidase procedures MAb-G47 was reactive with approximately 85% of colorectal tumors while exhibiting relatively low reactivity with normal colon tissue. Mucins isolated from normal colon had on average less than 10% of the specific epitope as compared with mucins derived from colorectal tumors (p < 0.01). Initial immunohistochemical studies on tumors of noncolonic origin revealed few positive cases. The potential of MAb-G47 to assist in the diagnosis and/or prognosis of colorectal cancer is now being studied.

Combined gemcitabine and radioimmunotherapy for the treatment of pancreatic cancer

MAb-PAM4 is an anti-MUC1 antibody that has been shown to be reactive with 85% of pancreatic adenocarcinomas with no reactivity with normal pancreas or other tissues. Initial clinical studies have shown excellent targeting with high tumor/nontumor ratios. Gemcitabine, an analog of deoxycytidine, is currently a frontline treatment for pancreatic cancer. Acting via a number of metabolic pathways, gemcitabine is also a powerful radiosensitizer. Combined-modality, chemo/radiosensitization with gemcitabine and low dose (131)I-PAM4 radioimmunotherapy was performed to determine if a more effective treatment procedure could be developed. Athymic nude mice bearing large (1 cm(3)) CaPan1 human pancreatic tumors were given a single treatment cycle consisting of gemcitabine, 333 mg/m(2) administered on Days 0, 3, 6, 9 and 12 by intraperitoneal injection, along with either 100 or 200 microCi, (131)I-PAM4 administered on Day 0 by intravenous injection. Gemcitabine did not interfere with the biodistribution of radiolabeled antibody. Specific tumor targeting was observed for (131)I-PAM4, with a tumor/blood radiation dose ratio of 2.6 over the first 14 days. Gemcitabine alone and low dose radioimmunotherapy alone, each had no affect upon tumor growth; no statistical differences were noted in comparison to the untreated group. When combined, however, a statistically significant (p = 0.0324), synergistic anti-tumor effect was observed. Median survival time doubled for the combined treatment regimen compared to single modality treatment groups. The combined treatment modality was well tolerated by the mice. Our data show that combined gemcitabine with radioimmunotherapy may provide an improved alternative for the treatment of pancreatic cancer, achieving successful anti-tumor effects with low toxicity.

Therapeutic advantage of (90)yttrium- versus (131)iodine-labeled PAM4 antibody in experimental pancreatic cancer

OBJECTIVES

Radioimmunotherapy studies using (131)I-PAM4 have demonstrated significant antitumor effects in mice bearing human pancreatic cancer xenografts. For several reasons (90)Y has been proposed as a more effective radionuclide for radioimmunotherapy of pancreatic cancer. The present study examined whether one radionuclide was more efficacious than the other in tumor-bearing mice.

METHODS

Athymic nude mice bearing CaPan1 xenograft tumors ( approximately 1.0 cm(3)) were given increasing doses of either (90)Y-PAM4 or (131)I-PAM4 up to their respective maximal tolerated doses [MTDs (260 and 700 microCi, respectively)].

RESULTS

(90)Y-PAM4 provided significantly greater growth inhibition than the (131)I-PAM4 (P < 0.035). Median survival time for the untreated mice was 6 weeks, whereas median survival times for the (131)I-treated mice and (90)Y-treated mice at their respective MTDs were 17.5 weeks and >26 weeks (the end of the study period), respectively. Within the (131)I-PAM4-treated group, two of eight mice were responders (>50% decrease in tumor size) for a median of 14 weeks. At the end of the study (26 weeks), 1 mouse was alive with no sign of tumor. All of the (90)Y-PAM4-treated mice were responders with a median duration of response of 20 weeks. Six of the seven mice were alive at week 26, with four mice having no evidence of disease.

CONCLUSIONS

These data demonstrate the advantage of (90)Y over (131)I as the radionuclide for PAM4-targeted radioimmunotherapy of xenografted pancreatic cancer. Furthermore, the duration and extent of the antitumor response suggests that multiple treatment cycles of (90)Y-PAM4 may provide an effective therapeutic for the control of pancreatic cancer.

Localization of pancreatic cancer with radiolabeled monoclonal antibody PAM4

Experimental animal studies were performed with (111)In-labeled PAM4 anti-MUC1 antibody along with (111)In-labeled control antibody. Tumor uptake of radiolabeled PAM4 was significantly higher than for the control antibody at all time points. When normalized to a blood dose of 1500 cGy as an estimate of myelotoxicity, (90)Y-labeled PAM4 would provide 5344 cGy to the tumor, whereas an equitoxic dose of (90)Y-labeled control antibody would provide only 862 cGy to the tumor. In addition to the animal studies, five patients with proven pancreatic cancer were administered either (131)I-PAM4 IgG (n=2) or 99mTc-PAM4 Fab' (n=3). Tumor targeting was observed in four out of five patients. By immunohistochemistry, PAM4 was non-reactive with tumor from the one patient not targeted. Dosimetry from the patients given (131)I-PAM4 predicted that tumors would receive 10-20 cGy/mCi with tumor/red marrow dose ratios ranging from 3 to 10. Based upon these results, we have established a phase-I (111)In-labeled PAM4 imaging and (90)Y-labeled PAM4 therapy trial.

Epithelial mucin-1 (MUC1) expression and MA5 anti-MUC1 monoclonal antibody targeting in multiple myeloma

Multiple myeloma (MM) is the second most common hematological cancer in the United States. It is typically incurable, even with myeloablative chemotherapy and stem-cell transplantation. The epithelial mucin-1 (MUC1) glycoprotein is expressed by normal and malignant epithelial cells but has also been shown to be expressed by MM cells. MUC1 is a useful antigenic target in solid tumors for clinical diagnostic and therapeutic monoclonal antibody (mAb)-based approaches. The MA5 mAb, as well as other anti-MUC1 mAbs reactive with the MUC1 variable number tandem repeat domain, exhibited moderate to strong reactivity with both MM cell lines and clinical samples. To explore the biochemical nature and potential of MUC1 as an antigenic target in MM, studies were performed to: (a) compare the mRNA and the MUC1 glycoprotein species between epithelial cancer and MM cell lines; and (b) develop and use a human MM tumor xenograft model system to study the biodistribution of the MA5 mAb. MA5 mAb was strongly reactive with six of eight human MM cell lines by flow cytometry. In seven of eight MM patient samples (bone marrow and/or peripheral blood) reactivity was found in 10-90% of the cells, whereas normal control (n = 5) and leukemia and lymphoma (n = 5) cells showed only 0-6% reactivity. 125I-labeled MA5 whole-cell binding studies showed quantitatively similar amounts of binding between strongly positive MM lines and high-MUC1-expressing breast carcinoma lines. mRNA expression was assessed by Northern blotting and reverse transcription-PCR. MM cell lines were positive by both methods, with strong similarity in the sizes of the mRNAs and cDNAs that were obtained. Finally, biodistribution experiments were carried out with 131I-labeled MA5 versus a nonbinding control 125I-labeled mAb in a s.c. MM xenograft model. Selective MM tumor uptake of the MA5 mAb was demonstrated, with a potential for delivering a tumor radiation absorbed dose of 8540 cGy/mCi of injected dose compared with 3099 cGy/mCi of tumor-absorbed dose delivered by nonspecific antibody.

Co-secretion of two distinct kappa light chains by the mu-9 hybridoma

Mu-9 is a monoclonal antibody (MAb) specific for the CSAp antigen (Ag) expressed by colorectal cancers. By using variable (V)-region-specific primers, the respective VH and VL sequences of Mu-9 were polymerase chain reaction (PCR)-amplified. However, chimeric Ab (cMu-9-1) constructed from these PCR-amplified V sequences failed to bind the CSAp Ag. Although the light chain of murine Mu-9 was not glycosylated, that of cMu-9-1 was found to be O-glycosylated, as confirmed by reducing SDS-PAGE analyses, glycoprotein blotting and O-linked specific deglycosylation studies. Removal of O-linked oligosaccharides either by enzymatic digestion or by blocking O-glycosylation with a specific inhibitor did not restore the immunoreactivity of cMu-9-1, indicating that light chain O-glycosylation was not the cause for lack of immunoreactivity. We reported earlier that screening of a Mu-9 cDNA library uncovered the presence of an additional light chain sequence that was later proven to be the authentic light chain of Mu-9. Analyses of the cDNA sequence encoding the nonimmunoreactive light chain, however, revealed no defects that would preclude the sequence from being translated and secreted by the murine hybridoma. By adapting the Mu-9 hybridoma culture to serum-free conditions, we confirmed the secretion of low levels of O-glycosylated light chain. The biological significance of the O-glycosylation as well as the cosecretion of both light chains with respect to allelic exclusion are discussed.

Radioimmunotherapy of experimental pancreatic cancer with 131I-labeled monoclonal antibody PAM4

We examined the therapeutic efficacy of 131I-labeled murine monoclonal antibody (MAb) PAM4 against human pancreatic cancers carried as xenografts in athymic nude mice. Animals bearing the CaPan1 tumor (0.2 cm3) were either untreated or were given, 131I-labeled nonspecific Ag8 antibody. By week 7 mean tumor size had grown 16.5 +/- 8.4-fold and 4.2 +/- 2.5-fold for the untreated and 131I-Ag8-treated animals, respectively. In contrast, animals administered 131I-PAM4 exhibited marked regression of tumors to an average of 15% of initial tumor volume. Since most pancreatic cancer patients present with large tumor burdens, the limitation of 131I-PAM4 treatment with respect to initial tumor size was investigated in animals bearing tumors of approximately 0.5 cm3, 1.0 cm3 and 2.0 cm3. Significant extension of survival time (>3-fold increase) was noted for both the 0.5 cm3 and 1.0 cm3 131I-PAM4-treated groups, compared to their respective untreated controls. Even in the group bearing large 2.0-cm3 tumors, survival was increased 2-fold over the control group. To further improve anti-tumor effects in large tumors, 2 injections of 131I-PAM4 were administered at a 4-week interval to animals bearing tumors of approximately 1.0 cm3. Significant extended survival was noted for the group receiving 2 doses when compared to the group receiving only 1 dose.

Factors influencing the pharmacokinetics, dosimetry, and diagnostic accuracy of radioimmunodetection and radioimmunotherapy of carcinoembryonic antigen-expressing tumors

The aim of this study was to examine factors that may influence the pharmacokinetics, diagnostic accuracy, and dosimetry in radioimmunodetection and radioimmunotherapy with anti-carcinoembryonic antigen (CEA) monoclonal antibodies (mAbs). Data from 275 patients with CEA expressing tumors were analyzed retrospectively. Of these, 69 patients devoid of human antimouse antibody (i.e., 31 colorectal, 9 lung, 7 breast, 4 ovarian, 6 pancreatic, 9 medullary thyroid, 1 gallbladder, and 1 salivary gland cancer, and 1 primary tumor of unknown origin) underwent a low-protein-dose diagnostic study (0.3-2.6 mg of protein; 6.8-28.8 mCi 131I-labeled IgG or fragments), followed within 4 weeks by a high-protein-dose therapy injection (4.0-27.5 mg of protein; 29.8-238.9 mCi). The anti-CEA antibodies NP-4 (Ka=10(8)M-1) and MN-14 (ka=10(9)M-1) were used. Plasma clearance, the molecular composition of radioactivity in the plasma, and the cumulated activity in organs and tumors were determined. Radiation doses were derived from the Medical Internal Radiation Dose scheme. At a low-protein dose and over a similar range of plasma CEA, a significantly higher percentage of MN-14 than of NP-4 was complexed with circulating CEA, consistent with its higher affinity. Complexation was reduced with increasing protein doses. However, the targeting sensitivity was not affected. Profound differences were found in the clearance of the antibody between different types of cancer. Colorectal cancer patients cleared the antibody significantly faster from blood (T1/2=17.6+/-12.6 versus 44.2 +/- 23.7 h) and whole body (t1/2= 53.2 +/- 30.1 versus 114.6+/-59.7 h) than all other tumor types (P <0.001). Consequently, significantly lower red marrow (2.1 +/- 1.0 cGy/mCi versus 4.3 +/- 1.6 cGy/mCi) and whole-body doses (0.5 +/- 0.3 cGy/mCi versus 1.0 +/- 0.4 cGy/mCi) were seen in colorectal cancer patients as compared with other tumor types (P < 0.001). This clearance is probably due to hepatic metabolism of the immune complexes. Clearance rates were especially high in patients with colorectal cancer having large liver metastases and elevated liver enzymes (rapid hepatic clearance with liberation of free I-). In contrast, a disease-stage and plasma CEA-matched cohort of colorectal cancer patients, examined with the 131 I-labeled anti-colon-specific antigen p mAb Mu-9, showed normal murine IgG pharmacokinetics (n=22;3 of them compared intraindividually to MN-14). Only in colorectal cancer patients did complexes between mAb and CEA tend to clear rapidly, whereas Mu-9 had normal kinetics in these patients. This suggests that different CEA-expressing cancer types may produce heterogeneous CEA molecules and that the variability in mAb clearance is due to varying clearance rates of these different circulating CEA subspecies. Disease-related alterations in antibody metabolism are unlikely, given that only anti-CEA antibodies exhibit this phenomenon.

Initial studies of monoclonal antibody PAM4 targeting to xenografted orthotopic pancreatic cancer

To resemble the clinical presentation of pancreatic cancer in an animal model more closely, we developed an orthotopic xenograft of CaPan-1 human pancreatic cancer in athymic nude mice. Within 3 weeks after implantation into the body and head of the pancreas, animals had palpable tumors. By 8 weeks, metastases to the liver and spleen were observed, and at 10-14 weeks, ascites formation, with and without seeding of the diaphragm, and jaundice were evident. Thus, this tumor model exhibited many of the most common features of human pancreatic cancer. Radiolabeled monoclonal antibody PAM4 showed specific localization of the primary orthotopic and metastatic tumors. On day 3, PAM4 accumulation within the primary tumor (0.5 g) was 11.3 +/- 5.1% injected dose/g with a localization index of 11.3 +/- 4.0. The estimated tumor:blood radiation dose ratio for PAM4 was 4:1, whereas a nonspecific antibody (Ag8) would provide only 40% of the blood dose to the tumor. Based on these observations, animals bearing 4-week-old orthotopic tumors (estimated volume, 0.25 cm3) were administered either 131I-labeled PAM4, 350 microCi, or nonspecific Ag8, 350 microCi, and compared with an untreated control group. Radiolabeled PAM4 provided a significant (P < 0.001) increase in survival time with less morbidity compared with the untreated control group, whereas nonspecific Ag8 was not significantly different from the control group. These studies provide a rationale for initiating a Phase I clinical study for detection and therapy of pancreatic cancer with PAM4.

Initial tumor targeting, biodistribution, and pharmacokinetic evaluation of the monoclonal antibody PAM4 in patients with pancreatic cancer

This pharmacokinetic study was performed to assess the potential usefulness of the murine monoclonal antibody (MoAb) PAM4-IgG1 as an immunotargeting agent for pancreatic cancer imaging or therapy. This MoAb reacts specifically with mucin purified from human pancreatic cancer. 131I-labeled PAM4-IgG1 was injected i.v. into five patients with suspected pancreatic cancer. Whole-body scans and spot views of the abdominal area were recorded with a computerized gamma camera, and specific regions of interest were drawn over the liver and spleen to define the kinetics of activity in these organs. Blood samples taken from 0.1-144 h after injection served to define the kinetics of plasma distribution and removal of activity from the body. Surgery confirmed pancreatic cancer in four of the five patients, whereas chronic pancreatitis was present in the fifth patient; in all four pancreatic cancer patients, immunostaining with the MoAb PAM4 demonstrated the presence of the specific antigen, with a cytoplasmic and endoluminal/secretory pattern of distribution. Nonspecific radioactivity accumulation in the liver, spleen, and bone marrow was low, linked essentially to the blood pool effect of circulating activity in these organs. The overall quality of scintigraphic maps recorded over the abdomen was quite satisfactory due to the low liver and spleen activity, with good scintigraphic demonstration of the pancreatic cancers (either primary or metastatic); the patient subsequently found to have pancreatitis failed to show PAM4 targeting. Except in one patient with widespread peritoneal metastases (in whom these tumor implants were detected scintigraphically already 24-48 hours after tracer injection), scintigraphic evidence of the tumor lesions was usually late, starting at about 72-96 h after tracer injection. The results obtained in this preliminary study indicate the potential usefulness of MoAb PAM4 for immunoscintigraphy in patients with either primary and/or recurrent pancreatic cancer while also suggesting that the use of the faster-clearing Fab fragments of this MoAb probably would result in improved immunoscintigraphic properties.

Targeting of xenografted pancreatic cancer with a new monoclonal antibody, PAM4

We have examined the ability of murine monoclonal antibody PAM4, directed against a pancreatic cancer-derived mucin, to target human pancreatic cancers carried as xenografts in athymic nude mice. Four tumor lines were used representing the range of expected differentiation; CaPan1, AsPc1, Hs766T, and BxPc3. In each case tumor uptake of PAM4 (range, 21-48% injected dose/g on day 3) was significantly higher than concomitantly administered, nonspecific, isotype-matched Ag8 antibody (range, 3.6-9.3% injected dose/g on day 3). Based upon the biodistribution data the estimated potential radiation dose delivered to the tumors when normalized to the blood dose as an estimate of dose-limiting myelotoxicity would be 13.1-, 2.2-, 3.4-, and 3.3-fold higher than to blood, respectively. PAM4 showed no evidence of targeting to normal tissues, except within the CaPan1 tumor model, where a small but consistent splenic uptake was observed. Splenic targeting was abolished by use of an increased PAM4 protein dose. Targeting of PAM4 to other normal tissues was not affected by the increased protein dose; however, tumor uptake of PAM4 (percentage of injected dose/g) was significantly increased by as much as 3-fold. The ability of PAM4 to target the CaPan1 tumor compared favorably to that of MN14, an anti-carcinoembryonic antigen murine monoclonal antibody. Tumor uptake of PAM4 was much greater than that for MN14 at days 1 and 3, whereas at later time points equivalent accumulations of activity were noted. Estimates of potential radiation doses to the tumor when normalized to the blood dose were 3.0 for MN14 and 9.6 for PAM4. These studies have shown that PAM4 is able to target pancreatic cancer with high specificity, achieving high concentrations at the tumor site. A rationale exists, then, for the performance of a clinical trial of radiolabeled PAM4 in the detection and localization of pancreatic cancer.