Preclinical efficacy of a PSMA-targeted actinium-225 conjugate (225Ac-macropa-pelgifatamab) - a targeted alpha therapy for prostate cancer

PURPOSE

Initially, prostate cancer responds to hormone therapy but eventually resistance develops. Beta emitter-based PSMA (prostate-specific membrane antigen)-targeted radionuclide therapy is approved for the treatment of metastatic castration-resistant prostate cancer. Here we introduce a targeted alpha therapy (TAT) consisting of the PSMA antibody pelgifatamab covalently linked to a macropa chelator and labeled with actinium-225 and compare its efficacy and tolerability with other TATs.

EXPERIMENTAL DESIGN

The in vitro characteristics and in vivo biodistribution, antitumor efficacy, and tolerability of 225Ac-macropa-pelgifatamab (225Ac-pelgi) and other TATs were investigated in cell line- and patient-derived prostate cancer xenograft models. The antitumor efficacy of 225Ac-pelgi was also investigated in combination with the androgen receptor inhibitor darolutamide.

RESULTS

Actinium-225-labeling of 225Ac-pelgi was efficient already at room temperature. Potent in vitro cytotoxicity was seen in PSMA-expressing (LNCaP, MDA-PCa-2b, and C4-2) but not in PSMA-negative (PC-3 and DU-145) cell lines. High tumor accumulation was seen for both 225Ac-pelgi and 225Ac-DOTA-pelgi in the MDA-PCa-2b xenograft model. In the C4-2 xenograft model, 225Ac-pelgi showed enhanced antitumor efficacy with a T/Cvolume (treatment/control) ratio of 0.10 compared with 225Ac-DOTA-pelgi, 225Ac-DOTA-J591, and 227Th-HOPO-pelgifatamab (227Th-pelgi) (all at 300 kBq/kg) with T/Cvolume ratios of 0.37, 0.39, and 0.33, respectively. 225Ac-pelgi was less myelosuppressive than 227Th-pelgi. 225Ac-pelgi showed dose-dependent treatment efficacy in the patient-derived KuCaP-1 model and strong combination potential with darolutamide in both cell line- (22Rv1) and patient-derived (ST1273) xenograft models.

CONCLUSIONS

These results provide a strong rationale to investigate 225Ac-pelgi in patients with prostate cancer. A clinical phase 1 study has been initiated (NCT06052306).

Targeted thorium-227 conjugates as treatment options in oncology

Targeted alpha therapy (TAT) is a promising approach for addressing unmet needs in oncology. Inherent properties make α-emitting radionuclides well suited to cancer therapy, including high linear energy transfer (LET), penetration range of 2-10 cell layers, induction of complex double-stranded DNA breaks, and immune-stimulatory effects. Several alpha radionuclides, including radium-223 (²²³Ra), actinium-225 (²²⁵Ac), and thorium-227 (²²⁷Th), have been investigated. Conjugation of tumor targeting modalities, such as antibodies and small molecules, with a chelator moiety and subsequent radiolabeling with α-emitters enables specific delivery of cytotoxic payloads to different tumor types. ²²³Ra dichloride, approved for the treatment of patients with metastatic castration-resistant prostate cancer (mCRPC) with bone-metastatic disease and no visceral metastasis, is the only approved and commercialized alpha therapy. However, ²²³Ra dichloride cannot currently be complexed to targeting moieties. In contrast to ²²³Ra, ²²⁷Th may be readily chelated, which allows radiolabeling of tumor targeting moieties to produce targeted thorium conjugates (TTCs), facilitating delivery to a broad range of tumors. TTCs have shown promise in pre-clinical studies across a range of tumor-cell expressing antigens. A clinical study in hematological malignancy targeting CD22 has demonstrated early signs of activity. Furthermore, pre-clinical studies show additive or synergistic effects when TTCs are combined with established anti-cancer therapies, for example androgen receptor inhibitors (ARI), DNA damage response inhibitors such as poly (ADP)-ribose polymerase inhibitors or ataxia telangiectasia and Rad3-related kinase inhibitors, as well as immune checkpoint inhibitors.

Abstract 3311: Darolutamide potentiates the antitumor efficacy of a PSMA-targeted thorium-227 conjugate (PSMA-TTC) in a hormone-independent prostate cancer model

Androgen receptor (AR) inhibitors are standard of care for the treatment of advanced prostate cancer. Despite an initial response to treatment, patients eventually progress, and novel therapeutic approaches are required. Prostate-specific membrane antigen (PSMA; FOLH1) is an integral membrane glycoprotein that is highly expressed in prostate cancer but has limited expression in normal tissues. PSMA-TTC (227Th-pelgifatamab corixetan; BAY 2315497) consists of the alpha emitter thorium-227 complexed to a 3,2-HOPO chelator conjugated to a PSMA targeting antibody. PSMA-TTC delivers potent radiation to PSMA expressing cells. Here we evaluated the efficacy of PSMA-TTC in combination with darolutamide, a novel AR inhibitor in a hormone insensitive prostate cancer model and investigated the mode of action of the combination treatment. In vitro, darolutamide induced the expression of PSMA in the androgen-independent cell lines C4-2 and 22Rv1 more than 3-fold and 2-fold, respectively. Expression of the apoptosis marker CDKN1A was significantly induced in the PSMA-TTC alone and in the combination group compared to vehicle. Expression of the DNA repair genes BRCA1, XRCC2 and XRCC3 were significantly reduced in PSMA-TTC alone and in the combination group compared to vehicle. In vivo, a single i.v. injection of PSMA-TTC at 300 kBq/kg resulted in a tumor/control (T/C) ratio of 0.44 on day 19 in the 22Rv1 hormone-insensitive prostate cancer model while a twice daily oral treatment with 100 mg/kg darolutamide showed a T/C ratio of 0.82. The combination of darolutamide and PSMA-TTC resulted in a higher efficacy with a T/C ratio of 0.27. Tumor area on day 19 after treatment was significantly reduced in the PSMA-TTC alone group and more so in the combination group, compared to vehicle. As expected, darolutamide alone was not efficacious in this hormone insensitive model. Nine out of 10 mice showed disease control (CR, PR or SD) in the combination group whereas no animals showed disease control in either of the monotherapy groups. This difference was significant by Fisher’s exact test analysis. Treatments were well tolerated with no significant changes in body weight in any of the treatment groups. Using the tumor dissociation kit Miltenyi individual tumor cells were isolated from darolutamide treated and untreated 22Rv1 xenograft tumors. FACS analysis showed a 50fold increase in PSMA expression in the darolutamide treated 22Rv1 tumors compared to vehicle treated animals. These data indicate that darolutamide induces PSMA expression in the hormone independent 22Rv1 model, which may have contributed to the stronger efficacy observed when combined with PSMA-TTC. Altogether these results support the further evaluation of darolutamide combination with PSMA radionuclides.

Citation Format: Christoph Schatz, Urs Hagemann, Sabine Zitzmann-Kolbe, Bernard Haendler, Hartwig Hennekes, Stefanie Hammer, Arne Scholz. Darolutamide potentiates the antitumor efficacy of a PSMA-targeted thorium-227 conjugate (PSMA-TTC) in a hormone-independent prostate cancer model [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 3311.

Immunostimulatory effects of targeted thorium-227 conjugates as single agent and in combination with anti-PD-L1 therapy

Background

Targeted thorium-227 conjugates (TTCs) are an emerging class of targeted alpha therapies (TATs). Their unique mode of action (MoA) is the induction of difficult-to-repair clustered DNA double-strand breaks. However, thus far, their effects on the immune system are largely unknown. Here, we investigated the immunostimulatory effects of the mesothelin-targeted thorium-227 conjugate (MSLN-TTC) in vitro and in vivo in monotherapy and in combination with an inhibitor of the immune checkpoint programmed death receptor ligand 1 (PD-L1) in immunocompetent mice.

Methods

The murine cell line MC38 was transfected with the human gene encoding for MSLN (hMSLN) to enable binding of the non-cross-reactive MSLN-TTC. The immunostimulatory effects of MSLN-TTC were studied in vitro on human cancer cell lines and MC38-hMSLN cells. The efficacy and MoA of MSLN-TTC were studied in vivo as monotherapy or in combination with anti-PD-L1 in MC38-hMSLN tumor-bearing immunocompetent C57BL/6 mice. Experiments were supported by RNA sequencing, flow cytometry, immunohistochemistry, mesoscale, and TaqMan PCR analyses to study the underlying immunostimulatory effects. In vivo depletion of CD8+ T cells and studies with Rag2/Il2Rg double knockout C57BL/6 mice were conducted to investigate the importance of immune cells to the efficacy of MSLN-TTC.

Results

MSLN-TTC treatment induced upregulation of DNA sensing pathway transcripts (IL-6, CCL20, CXCL10, and stimulator of interferon genes (STING)-related genes) in vitro as determined by RNASeq analysis. The results, including phospho-STING activation, were confirmed on the protein level. Danger-associated molecular pattern molecules were upregulated in parallel, leading to dendritic cell (DC) activation in vitro. MSLN-TTC showed strong antitumor activity (T:C 0.38, p<0.05) as a single agent in human MSLN-expressing MC38 tumor-bearing immunocompetent mice. Combining MSLN-TTC with anti-PD-L1 further enhanced the efficacy (T:C 0.08, p<0.001) as evidenced by the increased number of tumor-free surviving animals. MSLN-TTC monotherapy caused migration of CD103+ cDC1 DCs and infiltration of CD8+ T cells into tumors, which was enhanced on combination with anti-PD-L1. Intriguingly, CD8+ T-cell depletion decreased antitumor efficacy.

Conclusions

These in vitro and in vivo data on MSLN-TTC demonstrate that the MoA of TTCs involves activation of the immune system. The findings are of relevance for other targeted radiotherapies and may guide clinical combination strategies.

Darolutamide Potentiates the Antitumor Efficacy of a PSMA-targeted Thorium-227 Conjugate by a Dual Mode of Action in Prostate Cancer Models

PURPOSE

Androgen receptor (AR) inhibitors are well established in the treatment of castration-resistant prostate cancer and have recently shown efficacy also in castration-sensitive prostate cancer. Although most patients respond well to initial therapy, resistance eventually develops, and thus, more effective therapeutic approaches are needed. Prostate-specific membrane antigen (PSMA) is highly expressed in prostate cancer and presents an attractive target for radionuclide therapy. Here, we evaluated the efficacy and explored the mode of action of the PSMA-targeted thorium-227 conjugate (PSMA-TTC) BAY 2315497, an antibody-based targeted alpha-therapy, in combination with the AR inhibitor darolutamide.

EXPERIMENTAL DESIGN

The in vitro and in vivo antitumor efficacy and mode of action of the combination treatment were investigated in preclinical cell line-derived and patient-derived prostate cancer xenograft models with different levels of PSMA expression.

RESULTS

Darolutamide induced the expression of PSMA in androgen-sensitive VCaP and LNCaP cells in vitro, and the efficacy of darolutamide in combination with PSMA-TTC was synergistic in these cells. In vivo, the combination treatment showed synergistic antitumor efficacy in the low PSMA-expressing VCaP and in the high PSMA-expressing ST1273 prostate cancer models, and enhanced efficacy in the enzalutamide-resistant KUCaP-1 model. The treatments were well tolerated. Mode-of-action studies revealed that darolutamide induced PSMA expression, resulting in higher tumor uptake of PSMA-TTC, and consequently, higher antitumor efficacy, and impaired PSMA-TTC-mediated induction of DNA damage repair genes, potentially contributing to increased DNA damage.

CONCLUSIONS

These results provide a strong rationale to investigate PSMA-TTC in combination with AR inhibitors in patients with prostate cancer.

Thorium-227-Labeled Anti-CD22 Antibody (BAY 1862864) in Relapsed/Refractory CD22-Positive Non-Hodgkin Lymphoma: A First-in-Human, Phase I Study

Background: BAY 1862864 is an α-particle emitting thorium-227-labeled CD22-targeting antibody. This first-in-human dose-escalation phase I study evaluated BAY 1862864 in patients with CD22-positive relapsed/refractory B cell non-Hodgkin lymphoma (R/R-NHL). Materials and Methods: BAY 1862864 intravenous injections were administered at the starting thorium-227 radioactivity dose of 1.5 MBq (2 or 10 mg antibody), and the radioactivity dose escalated in ∼1.5 MBq increments (10 mg antibody) until the maximum tolerated dose (MTD) was reported. The primary objective was to determine the safety, tolerability, and MTD. Results: Twenty-one patients received BAY 1862864. Two dose-limiting toxicities (grade 3 febrile neutropenia and grade 4 thrombocytopenia) were reported in one patient in the 4.6 MBq (10 mg antibody) cohort. The MTD was not reached. Ten (48%) patients reported grade ≥3 treatment-emergent adverse events, with the most common being neutropenia, thrombocytopenia, and leukopenia, each occurring in 3 (14%) patients. Pharmacokinetics demonstrated the dose proportionality and stability of BAY 1862864 in the blood. The objective response rate (ORR) was 25% (5/21 patients) according to the LUGANO 2014 criteria, including 1 complete and 4 partial responses. The ORR was 11% (1/9) and 30% (3/10) in patients with relapsed high- and low-grade lymphomas, respectively. Conclusions: BAY 1862864 was safe and tolerated in patients with R/R-NHL. The Clinical Trial Registration numbers: NCT02581878 and EudraCT 2014-004140-36.

Abstract 2257: Targeted thorium-227 conjugates demonstrate synergistic activity in combination with PD-L1 inhibitors

Targeted thorium-227 conjugates (TTCs) represent a new class of targeted alpha therapy (TAT). TTCs consist of an antigen targeting moiety, which is covalently attached to a 3,2-HOPO chelator, enabling specific complexation and delivery of the alpha particle emitter thorium-227 to tumor cells. TTCs have demonstrated potent preclinical in vivo activity in monotherapy and in combination with DNA damage inhibitors. In the present work, the immunostimulatory effects of the mesothelin (MSLN) targeted thorium-227 conjugate (MSLN-TTC) was studied in immunocompetent mice, bearing human MSLN-transfected MC38 cells, in monotherapy and in combination with the PD-L1 inhibitor (PD-L1i) atezolizumab. Surface expression of DAMPs (calreticulin, HMGB1, HSP70 and HSP90), immunoinhibitory markers (PD-L1 and CTLA-4) and immunostimulatory markers (IFNAR, B7H2 and ICOS-L) was analyzed on murine, human MSLN-transfected MC38 colorectal cancer cells (MC38-hMSLN cells) after a 3-day exposure to MSLN-TTC. In vivo, C57/Bl6 mice were inoculated s.c. with MC38-hMSLN cells and treated with a single i.v. dose of non-radiolabeled MSLN-conjugate (0.14 mg/kg), isotype control-TTC (250 kBq/kg; 0.14 mg/kg), MSLN-TTC (250 kBq/kg; 0.14 mg/kg), PD-L1i (1.5 mg/kg; Q3D4; i.p.) or MSLN-TTC/PD-L1i combination. Tumors, lymph nodes, spleen and plasma were analyzed for MSLN and molecular markers. Tumor-free survivors were re-challenged with MC38-hMSLN or vector cells 125 d post-treatment. In a parallel arm of the experiment, CD8+ T cells were depleted using YTS169.4 antibody. MSLN-TTC treatment resulted in a specific dose-dependent increase of IFNAR, PD-L1 and HMGB1 in MC38-hMSLN cells in vitro. MSLN-TTC (T/C 0.38; Day 22) and PD-L1i (T/C 0.0.42; Day 22) monotherapies showed specific antitumor activity (T/C of radiolabeled isotype control was 0.76, Day 22) and their combination was synergistic (T/C 0.08; Day 22) with increased numbers of tumor free survivors. All three treatments increased HMGB1 levels in plasma. Induction of DSBs was observed in MSLN-TTC (+/- PD-L1i) treated tumors. Re-challenge of tumor-free survivors treated with MSLN-TTC, PD-L1i or MSLN-TTC/PD-L1i resulted in rejection of MC38-hMSLN, but not vector-cells. Infiltration of CD8+ T cells into tumors and their increase in tumor-draining lymph nodes were observed in MSLN-TTC, PD-L1i and MSLN-TTC/PD-L1i-treated groups but not in the vehicle group. Depletion of CD8+ T cells decreased the efficacy of PD-L1i and to a lower extent, MSLN-TTC and MSLN-TTC/PD-L1i. These results suggest that the efficacy of MSLN-TTC may involve activation of CD8+ T cells. These findings support the hypothesis that upon binding to antigen-positive cancer cells, TTC treatment induces DNA double strand breaks, leading to apoptosis and potentially immunogenic cell death, resulting in activation of the adaptive immune system.

Citation Format: Urs B. Hagemann, Pascale Lejeune, Lisa Bartnitzky, Kathleen Stadelmann, Veronique Cruciani, Roger M. Bjerke, Sandra Berndt, Claudia Kamfenkel, Manuela Brand, Manuela Steinbach, Stefan Stargard, Christoph A. Schatz, Jenny Karlsson, Hartwig Hennekes, Alan S. Cuthbertson, Dominik Mumberg. Targeted thorium-227 conjugates demonstrate synergistic activity in combination with PD-L1 inhibitors [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 2257.

Abstract 5355: MSLN-targeted thorium-227 conjugate demonstrates increased antitumor activity in combination with bevacizumab and regorafenib

Mesothelin-targeted thorium-227 conjugate (MSLN-TTC) is a targeted alpha therapeutic consisting of a MSLN-targeting antibody anetumab covalently attached to a 3,2-HOPO chelator complexed with the alpha emitter thorium-227. It has potent in vivo activity in cell and patient-derived xenograft (PDX) models in monotherapy and in combination with DNA damage repair inhibitors. We evaluated the antitumor efficacy of MSLN-TTC in a mesothelin overexpressing ovarian PDX model (ST206B) in monotherapy and in combination bevacizumab or the multikinase inhibitor regorafenib which both have anti-angiogenic activity. The biodistribution of MSLN-TTC was studied in parallel. Athymic mice were transplanted s.c. with ST206B-derived tumor fragments and treated with MSLN-TTC (250 kBq/kg, Q7Dx2, 0.43 mg/kg) alone or in combination with bevacizumab (1.25 or 5 mg/kg, i.p., Q5D; or 5 mg/kg, single dose) or regorafenib (7.5, 15, or 30 mg/kg, QD, p.o. for 28 days). The biodistribution of the respective treatment groups was analyzed using a germanium detector. For molecular analyses, tumors were stained for γ-H2AX, Ki67, CD31 and α-SMA. MSLN-TTC monotherapy showed high in vivo potency at 2 × 250 kBq/kg with a Treated/Control (T/C) ratio of 0.28 (n=5) on day 29. Monotherapy treatment with bevacizumab and regorafenib showed dose-dependent antitumor activity with T/C ratios ranging from 0.31 (regorafenib 30 mg/kg) to 0.33 (bevacizumab 5 mg/kg, single dose). The in vivo efficacy of MSLN-TTC was further enhanced by combination therapy with bevacizumab (T/C 0.21; n=5) or regorafenib (T/C 0.15; n=5). Combination of MSLN-TTC and regorafenib (30 mg/kg) resulted in more complete and partial responses (3/4 CRs; 1/4 PR) as compared to MSLN-TTC (2/3 PRs; 1/3 PD) at day 141. All treatments were well-tolerated based on body weight assessment; a reversible myelosuppression of white blood cells was observed for MSLN-TTC monotherapy and combination with bevacizumab or regorafenib did not worsen it. In the biodistribution study, tumor-specific accumulation of MSLN-TTC was observed over 336 h (14 days) with lower accumulation in the MSLN-TTC + bevacizumab group (1.25 mg/kg, Q5D, p&lt;0.05; 5 mg/kg, single dose, p&lt;0.05). On the molecular level, MSLN-TTC- and MSLN-TTC/ regorafenib (15 and 30 mg/kg) -treated tumors showed an increase in the DNA damage marker γ-H2AX compared to vehicle. The endothelial cell marker CD31 was decreased in tumors treated with MSLN-TTC and bevacizumab (1.25 mg/kg, Q5D; 5 mg/kg, single dose), but not in MSLN-TTC monotherapy (p&lt;0.05). In summary, MSLN-TTC effectively reduced the growth of primary tumors in the ST206B ovarian cancer model which was further enhanced by addition of bevacizumab and regorafenib. Further studies are needed to investigate the underlying molecular mechanisms.

Citation Format: Urs B. Hagemann, Christine Ellingsen, Claudia Kamfenkel, Dieter Zopf, Jesper Fonslet, Carsten Nielsen, Hartwig Hennekes, Alan S. Cuthbertson, Dominik Mumberg. MSLN-targeted thorium-227 conjugate demonstrates increased antitumor activity in combination with bevacizumab and regorafenib [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 5355.

Advances in Precision Oncology: Targeted Thorium-227 Conjugates As a New Modality in Targeted Alpha Therapy

Targeted α therapy (TAT) offers the potential for the targeted delivery of potent α-particle-emitting radionuclides that emit high linear energy transfer radiation. This leads to a densely ionizing radiation track over a short path. Localized radiation induces cytotoxic, difficult-to-repair, clustered DNA double-strand breaks (DSBs). To date, radium-223 (²²³Ra) is the only TAT approved for the treatment of patients with metastatic castration-resistant prostate cancer. Thorium-227 (²²⁷Th), the progenitor nuclide of ²²³Ra, offers promise as a wider-ranging alternative due to the availability of efficient chelators, such as octadentate 3,2-hydroxypyridinone (3,2-HOPO). The 3,2-HOPO chelator can be readily conjugated to a range of targeting moieties, enabling the generation of new targeted thorium-227 conjugates (TTCs). This review provides a comprehensive overview of the advances in the preclinical development of TTCs for hematological cancers, including CD22-positive B cell cancers and CD33-positive leukemia, as well as for solid tumors overexpressing renal cell cancer antigen CD70, membrane-anchored glycoprotein mesothelin in mesothelioma, prostate-specific membrane antigen in prostate cancer, and fibroblast growth factor receptor 2. As the mechanism of action for TTCs is linked to the formation of DSBs, the authors also report data supporting combinations of TTCs with inhibitors of the DNA damage response pathways, including those of the ataxia telangiectasia and Rad3-related protein, and poly-ADP ribose polymerase. Finally, emerging evidence suggests that TTCs induce immunogenic cell death through the release of danger-associated molecular patterns. Based on encouraging preclinical data, clinical studies have been initiated to investigate the safety and tolerability of TTCs in patients with various cancers.

Preclinical Efficacy of a PSMA-Targeted Thorium-227 Conjugate (PSMA-TTC), a Targeted Alpha Therapy for Prostate Cancer

PURPOSE

Prostate-specific membrane antigen (PSMA) is an attractive target for radionuclide therapy of metastatic castration-resistant prostate cancer (mCRPC). PSMA-targeted alpha therapy (TAT) has shown early signs of activity in patients with prostate cancer refractory to beta radiation. We describe a novel, antibody-based TAT, the PSMA-targeted thorium-227 conjugate PSMA-TTC (BAY 2315497) consisting of the alpha-particle emitter thorium-227 complexed by a 3,2-HOPO chelator covalently linked to a fully human PSMA-targeting antibody.

EXPERIMENTAL DESIGN

PSMA-TTC was characterized for affinity, mode of action, and cytotoxic activity in vitro. Biodistribution, pharmacokinetics, and antitumor efficacy were investigated in vivo using cell line and patient-derived xenograft (PDX) models of prostate cancer.

RESULTS

PSMA-TTC was selectively internalized into PSMA-positive cells and potently induced DNA damage, cell-cycle arrest, and apoptosis in vitro. Decrease in cell viability was observed dependent on the cellular PSMA expression levels. In vivo, PSMA-TTC showed strong antitumor efficacy with T/C values of 0.01 to 0.31 after a single injection at 300 to 500 kBq/kg in subcutaneous cell line and PDX models, including models resistant to standard-of-care drugs such as enzalutamide. Furthermore, inhibition of both cancer and cancer-induced abnormal bone growth was observed in a model mimicking prostate cancer metastasized to bone. Specific tumor uptake and efficacy were demonstrated using various PSMA-TTC doses and dosing schedules. Induction of DNA double-strand breaks was identified as a key mode of action for PSMA-TTC both in vitro and in vivo.

CONCLUSIONS

The strong preclinical antitumor activity of PSMA-TTC supports its clinical evaluation, and a phase I trial is ongoing in mCRPC patients (NCT03724747).

Abstract 3937: MSLN-TTC (BAY 2287411) demonstrates increased activity in comparison to standard of care chemotherapy in models of acquired drug resistance

Mesothelin (MSLN)-targeted thorium conjugate (MSLN-TTC; BAY 2287411) is a targeted alpha therapy consisting of the MSLN-targeting antibody anetumab, covalently attached to a 3,2-HOPO chelator complexing the alpha-emitter thorium-227. We previously demonstrated the potent in vivo activity of MSLN-TTC in cell line and patient-derived xenograft models, and further, demonstrated its combination potential with DNA damage repair inhibitors. MSLN-TTC is currently in clinical development for the treatment of patients with MSLN-positive mesothelioma and ovarian cancer (NCT03507452). Development of cellular resistance mechanisms are often co-evolutionary to the treatment regimen given to the respective individual. As such, it is well described that ovarian cancer patients have a decreased overall survival when tested positive for markers of acquired drug resistance (ADR), e.g. phospho-glycoprotein (P-gp) (Herzog TJ et al; Oncotarget 2016). However, MSLN-TTC should also be effective independent of P-gp expression, as the major mode of action of MSLN-TTC is the induction of irreparable DNA double-strand breaks upon alpha decay by thorium-227, resulting in apoptotic cell death. To confirm this hypothesis, we first determined the involvement of P-gp in cellular resistance mechanisms in ovarian cancer. To this end, immunohistochemical staining of ovarian cancer patient samples for P-gp was performed. Expression of P-gp was observed in 15% (7/48) primary and relapsing specimens. We then evaluated the potency of MSLN-TTC in MSLN-expressing cell line models in vitro using the isogenic cell line pair OVCAR-8 (P-gp negative) and NCI-RES-ADR (P-gp positive) in comparison to the standard of care (SOC) therapies cisplatin, paclitaxel, doxorubicin and vinorelbine. Whereas paclitaxel and doxorubicin showed a 100- and 10-fold decrease in in vitro potency on the P-gp positive cell line NCI-RES-ADR vs the P-gp negative cell line OVCAR-8, the potency of MSLN-TTC on the two isogenic cell lines remained unaffected.

To further confirm and explore these observations, in vivo xenograft models were conducted. Similar to the in vitro results, the in vivo efficacy of MSLN-TTC was not affected by the P-gp status in the OVCAR-8 vs NCI-RES-ADR xenograft model. In contrast, limited efficacy of paclitaxel and doxorubicin was observed in the P-gp-positive MSLN-expressing NCI-RES-ADR and Hela-MATU-ADR models. Similar, vinorelbine showed no efficacy in the Hela-MATU-ADR xenograft. In summary, these data demonstrate that the efficacy of MSLN-TTC is independent of the P-gp status. Further, these data suggest that MSLN-TTC may be active in patients relapsing after standard therapy.

Citation Format: Urs B. Hagemann, Sabine Zitzmann-Kolbe, Alexander Kristian, Carolyn Sperl, Christoph A. Schatz, Roger M. Bjerke, Alan S. Cuthbertson, Hartwig Hennekes, Karl Ziegelbauer, Dominik Mumberg. MSLN-TTC (BAY 2287411) demonstrates increased activity in comparison to standard of care chemotherapy in models of acquired drug resistance [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 3937.

Abstract 3926: MSLN-TTC (BAY 2287411) induces immunogenic cell death and secretion of pro-inflammatory cytokines in vitro and triggers an immune memory effect against a mouse tumor model

Mesothelin (MSLN)-targeted thorium conjugate (MSLN-TTC; BAY 2287411) is the first targeted alpha therapy in clinical development for the treatment of patients suffering from MSLN-positive mesothelioma and ovarian cancer (NCT03507452). It consists of the MSLN-targeting antibody anetumab, covalently attached to a 3,2-HOPO chelator complexing the alpha-emitter thorium-227. The main mode of action of MSLN-TTC is the induction of clustered DNA double-strand breaks upon alpha decay of thorium-227, resulting in cell death. The preclinical efficacy of MSLN-TTC has been demonstrated previously. The tumor control achieved by external beam radiation is partly driven by immune-stimulatory effects (Vatner et al; Frontiers in Oncology 2014). The essential mechanisms can be attributed to different pathways, including (a) induction of immunogenic cell death and (b) activation of the STING-pathway resulting in the secretion of pro-inflammatory cytokines (Vanpouille-Box C et al; NatComm 2017). We therefore investigated whether the targeted alpha therapy MSLN-TTC is also able to induce both of these pathways in vitro. The human ovarian cancer MSLN-expressing cell line OVCAR-3 was exposed to MSLN-TTC resulting in a dose dependent upregulation of markers of immunogenic cell death, e.g. calreticulin and HMGB-1. Further, exposure of OVCAR-3 cells to MSLN-TTC resulted in the secretion of pro-inflammatory cytokines, including IFN-β, IL-6 and IP-10. The efficacy of MSLN-TTC was evaluated in a syngeneic subcutaneous tumor model. As MSLN-TTC is not cross-reactive to murine MSLN, an MC38 cell line stably transfected with human MSLN was established (MC38-hMSLN). In vitro, MSLN-TTC induced specific reduction of MC38-hMSLN cell viability. Following single dose administration to MC38-hMSLN tumor-bearing mice, MSLN-TTC induced dose dependent antitumor activity with complete tumor eradication in 10 out of 36 treated animals. Interestingly, when tumor-free animals were re-inoculated with MC38-hMSLN cells 121 days post treatment, no tumor growth was observed. In contrast, tumors grew in animals inoculated with B16F10 cells, suggesting the development of an immune memory response against MC38-hMSLN cells. In summary, the data presented demonstrate that MSLN-TTC is able to induce immunogenic cell death and secretion of pro-inflammatory cytokines in vitro. Further, MSLN-TTC monotherapy evokes an immune-stimulatory effect in vivo.

Citation Format: Urs B. Hagemann, Pascale LeJeune, Jenny Karlsson, Christoph A. Schatz, Alan S. Cuthbertson, Hartwig Hennekes, Karl Ziegelbauer, Dominik Mumberg. MSLN-TTC (BAY 2287411) induces immunogenic cell death and secretion of pro-inflammatory cytokines in vitro and triggers an immune memory effect against a mouse tumor model [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 3926.

Abstract 1141: Preclinical analysis of biodistribution and PET imaging of a zirconium-89 labeled PSMA-targeted antibody-chelator conjugate

The PSMA targeted thorium-227 conjugate PSMA-TTC (BAY 2315497) is a targeted alpha therapy approach for metastatic castration resistant prostate cancer that has shown strong anti-tumor activity in PSMA-positive prostate cancer models (Hammer et al. AACR 2017/2018/2019). PSMA-TTC consists of a fully human IgG1 PSMA-targeted antibody covalently linked to a 3,2-HOPO chelator moiety, stably complexing the alpha emitter thorium-227. As this chelator can also complex zirconium-89, positron emission tomography (PET) imaging using the zirconium-89 labeled variant of the PSMA antibody-chelator conjugate could support clinical development of PSMA-TTC by enabling monitoring of organ distribution.

Herein, we describe radiolabeling of the PSMA antibody-chelator conjugate with zirconium-89 and its quality control using bioanalytical assays. In addition, the zirconium-89 labeled PSMA antibody-chelator conjugate was injected into mice bearing LNCaP xenograft tumors and biodistribution was assessed by measurement of radioactivity in tumor and organs as well as PET imaging at different time points after injection.

The PSMA antibody-chelator conjugate was successfully labeled with zirconium-89 at high yield, purity and specific activity. Target binding was confirmed by determination of the immunoreactive fraction. Biodistribution experiments revealed high, long lasting uptake of zirconium-89 in PSMA-positive LNCaP tumors after single injection of the zirconium-89 labeled conjugate. An uptake of 40-50% of the injected dose per gram of tumor was measured at 24, 48, 72, 168 and 240h after injection. The PET images showed that the zirconium-89 labeled PSMA antibody-chelator conjugate provided an excellent image contrast for the delineation of LNCaP xenografts between 48 and 168 h after administration. Other organs showed only very little background and tumor-to-heart ratio was greater than 10 when PET imaging was performed between 48 and 168 h after injection.

These results indicate that the zirconium-89 labeled PSMA antibody-chelator conjugate shows promise for PET imaging studies. These properties may allow its use to support clinical development of PSMA-TTC.

Citation Format: Stefanie Hammer, Sabine Zitzmann-Kolbe, Felix Oden, Joerg Jannsen, Eva Bickel, Andre Mueller, Lothar Everz, Urs B. Hagemann, Jenny Karlsson, Olav B. Ryan, Hartwig Hennekes, Patricia E. Cole, Dominik Mumberg. Preclinical analysis of biodistribution and PET imaging of a zirconium-89 labeled PSMA-targeted antibody-chelator conjugate [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 1141.

Meeting report from the Prostate Cancer Foundation PSMA-directed radionuclide scientific working group

INTRODUCTION

The Prostate Cancer Foundation (PCF) convened a PSMA-Directed Radionuclide Scientific Working Group on November 14, 2017, at Weill Cornell Medicine, New York, NY.

METHODS

The meeting was attended by 35 global investigators with expertise in prostate cancer biology, radionuclide therapy, molecular imaging, prostate-specific membrane antigen (PSMA)-targeted agents, drug development, and prostate cancer clinical trials. The goal of this meeting was to discuss the potential for using PSMA-targeted radionuclide agents for the treatment of advanced prostate cancer and to define the studies and clinical trials necessary for validating and optimizing the use of these agents.

RESULTS

Several major topic areas were discussed including the overview of PSMA biology, lessons and applications of PSMA-targeted PET imaging, the nuances of designing PSMA-targeted radionuclide agents, clinical experiences with PSMA-targeted radionuclides, PCF-funded projects to accelerate PSMA-targeted radionuclide therapy, and barriers to the use of radionuclide treatments in widespread clinical practice.

DISCUSSION

This article reviews the major topics discussed at the meeting with the goal of promoting research that will validate and optimize the use of PSMA-targeted radionuclide therapies for the treatment of advanced prostate cancer.

Abstract 844: Preclinical activity of PSMA-TTC, a targeted alpha therapeutic in patient-derived prostate cancer models

Targeted alpha therapy (TAT) agents deliver high linear energy transfer (LET) alpha-radiation selectively to tumors. The first TAT to be approved is radium-223 which prolongs overall survival in metastatic castration resistant prostate cancer (mCRPC) patients with symptomatic bone metastasis. Radium-223 shows a selective uptake in newly formed bone matrix such as bone metastasis and binds to hydroxyapatite. The PSMA targeted thorium-227 conjugate PSMA-TTC represents another TAT approach in mCRPC. It consists of a fully human PSMA IgG antibody covalently linked to the chelator moiety (3,2 HOPO). This antibody-chelator conjugate is radiolabeled with thorium-227, which decays with a half-life of 18.7 days to radium-223 via alpha-particle emission.

Herein we describe tumor targeting and anti-tumor activity of PSMA-TTC in two PSMA positive patient derived xenograft (PDx) models of prostate cancer with different characteristics. In vivo biodistribution and anti-tumor efficacy were analyzed after i.v. injection of PSMA-TTC at radioactive doses from 75-500 kBq/kg and protein doses of either 0.14 or 0.43 mg/kg to tumor bearing mice.

Initially, the PDx model KuCap1 (provided by Prof. O. Ogava, University of Kyoto, Japan), a prostate cancer model resistant to the second generation antiandrogen enzalutamide, was analyzed. In this model PSMA-TTC showed strong dose dependent tumor growth inhibition starting at a single dose of 75 kBq/kg. Moreover, after a single i.v. administration of PSMA-TTC at 300 kBq/kg 9 out of 10 mice (90%) showed either stable disease or tumor regression for at least 33 days after treatment. The observed activity was highly selective, as injection of a radiolabeled control conjugate at 300 kBq/kg showed only limited tumor growth inhibition.

Next, PSMA-TTC was tested in the hormone- and enzalutamide-sensitive prostate cancer PDx model ST1273 (South Texas Accelerated Research Therapeutics, San Antonio, Texas). A single i.v. injection of PSMA-TTC resulted in significant tumor accumulation of thorium-227 for more than 3 weeks, whereas a radiolabeled isotype control conjugate did not show tumor uptake. In addition, single i.v. administration of PSMA-TTC showed strong dose dependent anti-tumor activity while limited tumor growth inhibition was observed for a radiolabeled isotype control conjugate. Single doses of either 250 or 500 kBq/kg resulted in a 100 % response rate 4 weeks after treatment, with all animals showing partial or even complete regression of tumor growth. No significant effects on body weight were detected compared to vehicle treated animals.

In summary, PSMA-TTC shows strong anti-tumor activity in patient derived prostate cancer models which were either sensitive or resistant to standard of care drugs. These data warrant further clinical investigation of this targeted alpha pharmaceutical investigational agent.

Citation Format: Stefanie Hammer, Urs B. Hagemann, Sabine Zitzmann-Kolbe, Aasmund Larsen, Christine Ellingsen, Oliver von Ahsen, Jenny Karlsson, Roger M. Bjerke, Olav B. Ryan, Pascale Lejeune, Hartwig Hennekes, Alan Cuthbertson, Karl Ziegelbauer, Dominik Mumberg. Preclinical activity of PSMA-TTC, a targeted alpha therapeutic in patient-derived prostate cancer models [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 844.

Abstract 850: Mesothelin targeted thorium-227 conjugate (MSLN-TTC): Preclinical evaluation of a new targeted alpha therapeutic in mesothelin-positive cancers

Targeted Thorium-227 Conjugates (TTCs) represent a new class of targeted alpha therapy. In this compound family a 3,2-HOPO chelator, which binds thorium-227 with high affinity, is covalently attached to an antibody. This enables the specific delivery of the alpha particle emitter thorium-227 to tumor cells. Thorium-227 has a half-life of 18.7 days and decays via emission of an alpha particle to radium-223 (half-life of 11.4 days), a calcium-mimetic used in the treatment of CRPC [Henriksen et al. J Nucl Med, 2003]. The high linear energy transfer from the alpha-emitter thorium-227 induces clustered DNA double-strand breaks. Its short penetration range of 2-10 cell diameters limits the damage to the normal tissue surrounding the tumor. We present the preclinical evaluation of a mesothelin targeted thorium-227 conjugate (MSLN-TTC), the first TTC that will enter clinical development in MSLN-positive solid tumor indications, based on the fully human anti-MSLN monoclonal antibody anetumab. MSLN is a 40 kDa membrane-anchored glycoprotein with prominent overexpression in mesothelioma, ovarian, pancreatic, lung and breast cancer. In normal tissue, MSLN is confined mainly to the mesothelial cells of pleura, peritoneum and pericardium. In vitro, the mode of action of MSLN-TTC in cellular assays was demonstrated to induce DNA double strand breaks, leading to cell cycle arrest and subsequent reduced cell viability. In vivo, MSLN-TTC demonstrated potent tumor growth inhibition administered as a single-dose in cell- and patient-derived xenograft tumor models. Similar anti-tumor activity to single dose application was observed when the MSLN-TTC was applied at fractionated doses. A trend for dependence of anti-tumor activity on MSLN expression levels in preclinical tumor models was observed. Biodistribution studies evaluated the tumor accumulation of MSLN-TTC in xenograft models. These studies served to develop a mechanistic PK/PD model, which was used to predict the efficacious dose in humans. The initiation of clinical investigation of the MSLN-TTC in mesothelin positive cancers' is planned for 2018.

Citation Format: Urs B. Hagemann, Alexander Kristian, Christine Ellingsen, Katrine Wickstroem, Anne Mobergslien, Jenny Karlsson, Roger M. Bjerke, Christoph Schatz, Christoph Kneip, Joachim Schuhmacher, Liv-Ingrid Oedegaardstuen, Hartwig Hennekes, Anna Tafuri, Dominik Mumberg, Hanno Wild, Karl Ziegelbauer, Alan S. Cuthbertson. Mesothelin targeted thorium-227 conjugate (MSLN-TTC): Preclinical evaluation of a new targeted alpha therapeutic in mesothelin-positive cancers [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 850.

Dissociation of transactivation from transrepression by a selective glucocorticoid receptor agonist leads to separation of therapeutic effects from side effects

Glucocorticoids (GCs) are the most commonly used antiinflammatory and immunosuppressive drugs. Their outstanding therapeutic effects, however, are often accompanied by severe and sometimes irreversible side effects. For this reason, one goal of research in the GC field is the development of new drugs, which show a reduced side-effect profile while maintaining the antiinflammatory and immunosuppressive properties of classical GCs. GCs affect gene expression by both transactivation and transrepression mechanisms. The antiinflammatory effects are mediated to a major extent via transrepression, while many side effects are due to transactivation. Our aim has been to identify ligands of the GC receptor (GR), which preferentially induce transrepression with little or no transactivating activity. Here we describe a nonsteroidal selective GR-agonist, ZK 216348, which shows a significant dissociation between transrepression and transactivation both in vitro and in vivo. In a murine model of skin inflammation, ZK 216348 showed antiinflammatory activity comparable to prednisolone for both systemic and topical application. A markedly superior side-effect profile was found with regard to increases in blood glucose, spleen involution, and, to a lesser extent, skin atrophy; however, adrenocorticotropic hormone suppression was similar for both compounds. Based on these findings, ZK 216348 should have a lower risk, e.g., for induction of diabetes mellitus. The selective GR agonists therefore represent a promising previously undescribed class of drug candidates with an improved therapeutic index compared to classical GCs. Moreover, they are useful tool compounds for further investigating the mechanisms of GR-mediated effects.

SEGRAs: a novel class of anti-inflammatory compounds

Dissociated GCs show a separation between anti-inflammatory effects and certain side effects. This renders them as attractive compounds with better effect/side-effect profile as promising drug candidates and tool compounds for analyzing the molecular mechanisms of single side effects. A number of the GC-mediated side effects (e.g., osteoporosis, skin atrophy) are regulated in a very complex manner and use more than one molecular mechanism of the GR. Thus, theoretical predictions about the behavior of selective GR agonists regarding these effects are very difficult to make. Investigations of SEGRA compounds in relevant animal models will be the only way to get this important information. By availability of these tool compounds we now are in the advantageous situation to test them in vivo and to learn more about the possibilities and even the limitations of the selective GR agonists. Considering that the compounds have a non-steroidal structure, i.e., totally unrelated to steroids or other hormones at all, displaying only partially the molecular effects of GCs and are dissociated in their clinical profile, they should not be considered as GCs. Therefore, we introduced the term selective glucocorticoid receptor agonists (SEGRAs). These SEGRAs seem to represent a useful novel therapeutic modality which may complement existing therapeutic principles for the topical and especially the systemic treatment of inflammatory diseases. In summary, we and others are convinced that dissociated GCs are therapeutic compounds that exert many of the anti-inflammatory and immunosuppressive effects of standard GCs, while their potential to induce side effects is reduced. Whereas the in vitro dissociated profile of other compound classes (Belvisi et al. 2001) was not translated into a separation between anti-inflammatory activity and the induction of side effects in in vivo models, we could demonstrate this for the SEGRA compounds. Regarding the diversity of molecular mechanisms involved in mediating the complex side effects of GCs, it might be that only some of these unwanted effects can be reduced. However, as GCs are one of the most important anti-inflammatory therapeutics in the treatment of severe and chronic inflammatory diseases, even a partial reduction of side effect induction would be a great advantage for many patients.

The role of isoprenylation in membrane attachment of nuclear lamins. A single point mutation prevents proteolytic cleavage of the lamin A precursor and confers membrane binding properties

Mature A- and B-type lamins differ in the extent to which they interact with the nuclear membrane and thus represent an interesting model for studying the role of isoprenylation and carboxyl-methylation in membrane attachment. Both A- and B-type lamins are isoprenylated and carboxyl-methylated shortly after synthesis, but A-type lamins undergo a further proteolytic cleavage which results in the loss of the hydrophobically modified C terminus. Here, we have constructed mutants of chicken lamin A that differ in their abilities to serve as substrates for different post-translational processing events occurring at the C terminus of the wild-type precursor. In addition to studying full-length proteins, we have analyzed C-terminal end domains of lamin A, either alone or after fusion to reporter proteins. Mutant proteins were expressed in mammalian cells, and their membrane association was analyzed by immunofluorescence microscopy and subcellular fractionation. Our results provide information on the substrate specificity and subcellular localization of the lamin-A-specific protease. Moreover, they indicate that hydrophobic modifications of the C-terminal end domains account for the differential membrane-binding properties of A- and B-type lamins. Thus, some of the integral membrane proteins implicated in anchoring B-type lamins to the membrane may function as receptors for the isoprenylated and carboxyl-methylated C terminus.

Phosphorylation on protein kinase C sites inhibits nuclear import of lamin B2

The nuclear lamina is a karyoskeletal structure at the nucleoplasmic surface of the inner nuclear membrane. Its assembly state is regulated by phosphorylation of the intermediate filament type lamin proteins. Strong evidence has been obtained for a causal link between phosphorylation of lamins by the p34cdc2 protein kinase and disassembly of the nuclear lamina during mitosis. In contrast, no information is currently available on the role of lamin phosphorylation during interphase of the cell cycle. Here, we have identified four protein kinase C phosphorylation sites in purified chicken lamin B2 as serines 400, 404, 410, and 411. In vivo, the tryptic peptide containing serines 400 and 404 is phosphorylated throughout interphase, whereas serines 410 and 411 become phosphorylated specifically in response to activation of protein kinase C by phorbol ester. Prompted by the close proximity of serines 410/411 to the nuclear localization signal of lamin B2, we have studied the influence of phosphorylation of these residues on nuclear transport. Using an in vitro assay, we show that phosphorylation of lamin B2 by protein kinase C strongly inhibits transport to the nucleus. Moreover, phorbol ester treatment of intact cells leads to a substantial reduction of the rate of nuclear import of newly synthesized lamin B2 in vivo. These findings have implications for the dynamic structure of the nuclear lamina, and they suggest that the modulation of nuclear transport rates by cytoplasmic phosphorylation may represent a general mechanism for regulating nuclear activities.

Phosphorylation of Na,K-ATPase alpha-subunits in microsomes and in homogenates of Xenopus oocytes resulting from the stimulation of protein kinase A and protein kinase C

The phosphorylation of the alpha-subunit of Na+/K(+)-transporting ATPase (Na,K-ATPase) by cAMP-dependent protein kinase (PKA) and protein kinase C (PKC) was characterized in purified enzyme preparations of Bufo marinus kidney and duck salt gland and in microsomes of Xenopus oocytes. In addition, we have examined cAMP and phorbol esters, which are stimulators of PKA and PKC, respectively, for their ability to provoke the phosphorylation of alpha-subunits of Na,K-ATPase in homogenates of Xenopus oocytes. In the enzyme from the duct salt gland, phosphorylation by PKA and PKC occurs on serine and threonine residues, whereas in the enzyme from B. marinus kidney and Xenopus oocytes, phosphorylation by PKA occurs only on serine residues. Phosphopeptide analysis indicates that a site phosphorylated by PKA resides in a 12-kDa fragment comprising the C terminus of the polypeptide. Studies of phosphorylation performed on homogenates of Xenopus oocytes show that not only endogenous oocyte Na,K-ATPase but also exogenous Xenopus Na,K-ATPase expressed in the oocyte by microinjection of cRNA can be phosphorylated in response to stimulation of oocyte PKA and PKC. In conclusion, these data are consistent with the possibility that the alpha-subunit of Na,K-ATPase can serve as a substrate for PKA and PKC in vivo.

Coding sequence and flanking regions of the mouse vimentin gene

Using a polyclonal antibody, a cDNA clone coding for part of mouse vimentin was identified in a lambda gt11 expression library. DNA from this clone was used to screen a genomic library from Ehrlich Ascites Tumor cells for the mouse vimentin gene. A clone was found which contained the whole coding sequence and a large part of the 5'- and 3'-untranslated sequences. It was used to prepare a construct equivalent to a full-length cDNA clone. Extensive homologies to the vimentin sequence from other species were found for the coding and 3'-untranslated sequences and the promoter region.

Control of pulsed field gel electrophoresis at short switching intervals by a microcomputer

Pulsed field gel electrophoresis allows not only the separation of very large DNA molecules (up to 10 megabase pairs) but also gives an enhanced resolution in separations of DNA in the size range of 10-100 kilobase pairs (kbp). For this application, rapid alternation of the electrical field polarity is required. Here we describe equipment for the delivery of short switching pulses that is easy and inexpensive to build and is controlled by a standard microcomputer. It has proved to be useful in the separation of lambda DNA and its fragments. Parameters for enhanced separation of 23- and 48-kbp DNA molecules at high voltage gradients (15 V/cm) are presented and shown to provide superior resolution when compared to those for conventional electrophoresis at both high and low voltage gradients.