Integrin-αvβ6 targeted peptide-toxin therapy in a novel αvβ6-expressing immunocompetent model of pancreatic cancer

Previously we reported that a novel αvβ6-specific peptide-drug conjugate (SG3299) could eliminate established human pancreatic ductal adenocarcinoma (PDAC) xenografts. However the development of effective therapies for PDAC, which is an essential need, must show efficacy in relevant immunocompetent animals. Previously we reported that the KPC mouse transgenic PDAC model that closely recapitulates most stages of development of human PDAC, unlike in humans, failed to express αvβ6 on their tumours or metastases. In this study we have taken the KPC-derived PDAC line TB32043 and engineered a variant line (TB32043mb6S2) that expresses mouse integrin αvβ6. We report that orthotopic implantation of the αvβ6 over-expressing TB32043mb6S2 cells promotes shorter overall survival and increase in metastases. Moreover, systemic treatment of mice with established TB32043mb6S2 tumours in the pancreas with SG2399 lived significantly longer (p < 0.001; mean OS 48d) compared with PBS or control SG3511 (mean OS 25.5d and 26d, respectively). Thus SG3299 is confirmed as a promising candidate therapeutic for the therapy of PDAC.

Opposing roles for ADAMTS2 and ADAMTS14 in myofibroblast differentiation and function

Crosstalk between cancer and stellate cells is pivotal in pancreatic cancer, resulting in differentiation of stellate cells into myofibroblasts that drives tumour progression. To assess cooperative mechanisms in a 3D context, we generated chimeric spheroids using human and mouse cancer and stellate cells. Species-specific deconvolution of bulk-RNA sequencing data revealed cell type-specific transcriptomes underpinning invasion. This dataset highlighted stellate-specific expression of transcripts encoding the collagen-processing enzymes ADAMTS2 and ADAMTS14. Strikingly, loss of ADAMTS2 reduced, while loss of ADAMTS14 promoted, myofibroblast differentiation and invasion independently of their primary role in collagen-processing. Functional and proteomic analysis demonstrated that these two enzymes regulate myofibroblast differentiation through opposing roles in the regulation of transforming growth factor β availability, acting on the protease-specific substrates, Serpin E2 and fibulin 2, for ADAMTS2 and ADAMTS14, respectively. Showcasing a broader complexity for these enzymes, we uncovered a novel regulatory axis governing malignant behaviour of the pancreatic cancer stroma. © 2023 The Authors. The Journal of Pathology published by John Wiley & Sons Ltd on behalf of The Pathological Society of Great Britain and Ireland.

Disruption of pancreatic stellate cell myofibroblast phenotype promotes pancreatic tumor invasion

In pancreatic ductal adenocarcinoma (PDAC), differentiation of pancreatic stellate cells (PSCs) into myofibroblast-like cancer-associated fibroblasts (CAFs) can both promote and suppress tumor progression. Here, we show that the Rho effector protein kinase N2 (PKN2) is critical for PSC myofibroblast differentiation. Loss of PKN2 is associated with reduced PSC proliferation, contractility, and alpha-smooth muscle actin (α-SMA) stress fibers. In spheroid co-cultures with PDAC cells, loss of PKN2 prevents PSC invasion but, counter-intuitively, promotes invasive cancer cell outgrowth. PKN2 deletion induces a myofibroblast to inflammatory CAF switch in the PSC matrisome signature both in vitro and in vivo. Further, deletion of PKN2 in the pancreatic stroma induces more locally invasive, orthotopic pancreatic tumors. Finally, we demonstrate that a PKN2KO matrisome signature predicts poor outcome in pancreatic and other solid human cancers. Our data indicate that suppressing PSC myofibroblast function can limit important stromal tumor-suppressive mechanisms, while promoting a switch to a cancer-supporting CAF phenotype.

Abstract 958: Effective targeting of pancreatic ductal adenocarcinoma metastases with an integrin αvβ6-targeting peptide-drug conjugate

Pancreatic ductal adenocarcinoma (PDAC) exhibits an extremely poor prognosis, with 5 year-survival rates &lt;5%. This is due to a lack of effective therapies for the majority of patients, 65% of whom present with metastatic disease. Integrin αvβ6 is expressed in &gt;80% of human PDAC tumors including their paired metastases but is not significantly expressed by healthy pancreas tissue. Thus, αvβ6 represents a promising therapeutic target. We previously developed the αvβ6-specific peptide-drug conjugate (PDC) SG3299, composed of the DNA-binding pyrrolobenzodiazepine (PBD)-based compound tesirine conjugated to the αvβ6-targeting peptide A20FMDV2. Relative to the non-targeting PDC SG3511, SG3299 showed anti-tumor efficacy against αvβ6-positive human PDAC xenografts in immunodeficient mouse models. The present study aimed to evaluate the efficacy of αvβ6-targeted therapy on primary tumors and metastases in an immunocompetent murine model of PDAC. We have previously reported that KPC (Kras-G12D P53-R172H Pdx1-Cre) transgenic mouse PDAC tumors do not express αvβ6, so we ectopically expressed murine integrin-β6 in the TB32043 KPC-derived PDAC cell line, creating the αvβ6-expressing line TB32043mb6S2. When injected orthotopically into immunocompetent C57BL/6 mice, TB32043mb6S2 cells produced primary pancreatic tumors with αvβ6-positive metastases to the liver, peritoneum, and lung. Mice injected orthotopically with TB32043mb6S2 cells exhibited increased primary tumor desmoplasia, increased incidence of peritoneal metastases (100% vs 20%, p&lt;0.05) and decreased survival (median survival 27 vs 37.5 days, p=0.0233) relative to mice injected with αvβ6-negative TB32043 cells. When injected into the tail vein of C57BL/6 mice, αvβ6-positive TB32043mb6S2 cells exhibited significantly increased colonisation of the lungs relative to TB32043 cells (p&lt;0.0001). These data indicate that αvβ6 expression increases PDAC cell metastatic propensity. SG3299 was 17-fold more effective (p&lt;0.0001) for TB32043mb6S2 cells versus TB32043 cells in vitro, indicating αvβ6-selective killing of PDAC cells by our αvβ6-targeting PDC. Moreover, treatment of αvβ6-positive orthotopic tumors with the αvβ6-specific PDC SG3299 significantly increased survival relative to the non-targeting PDC SG3511 or saline control (median survival 48 days vs 26 days vs 25.5 days, p&lt;0.0001). When mice bearing αvβ6-positive TB32043b6S2 lung metastases generated by tail vein injection were treated with SG3299 or SG3511, the SG3299 therapy significantly reduced metastatic tumor burden relative to SG3511 (p&lt;0.05). Together, these data indicate that the peptide-drug conjugate SG3299 shows efficacy against both αvβ6-positive primary and αvβ6-positive secondary tumors in immunocompetent animals, providing a molecular-specific drug for the effective therapy of pancreatic cancer.

Citation Format: Elizabeth R. Murray, Nicholas F. Brown, Philip Howard, Luke Masterson, Francesca Zammarchi, Patrick H. van Berkel, John F. Marshall. Effective targeting of pancreatic ductal adenocarcinoma metastases with an integrin αvβ6-targeting peptide-drug conjugate [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 958.

Integrin αvβ6-specific therapy for pancreatic cancer developed from foot-and-mouth-disease virus

Goals of investigation: The 5-year survival rate for pancreatic ductal adenocarcinoma (PDAC) has remained at <5% for decades because no effective therapies have been identified. Integrin αvβ6 is overexpressed in most PDAC and represents a promising therapeutic target. Thus, we attempted to develop an αvβ6-specific peptide-drug conjugate (PDC) for therapy of PDAC. Methodology: We conjugated the DNA-binding pyrrolobenzodiazepine (PBD)-based payload SG3249 (tesirine) to an αvβ6-specific 20mer peptide from the VP1 coat protein of foot-and-mouth-disease virus (FMDV) (forming conjugate SG3299) or to a non-targeting peptide (forming conjugate SG3511). PDCs were tested for specificity and toxicity on αvβ6-negative versus-positive PDAC cells, patient-derived cell lines from tumor xenografts, and on two different in vivo models of PDAC. Immunohistochemical analyses were performed to establish therapeutic mechanism. Results: The αvβ6-targeted PDC SG3299 was significantly more toxic (up to 78-fold) for αvβ6-expressing versus αvβ6-negative PDAC cell lines in vitro, and achieved significantly higher toxicity at equal dose than the non-targeted PDC SG3511 (up to 15-fold better). Moreover, SG3299 eliminated established (100mm3) Capan-1 PDAC human xenografts, extending the lifespan of mice significantly (P=0.005). Immunohistochemistry revealed SG3299 induced DNA damage and apoptosis (increased γH2AX and cleaved caspase 3, respectively) associated with significant reductions in proliferation (Ki67), β6 expression and PDAC tumour growth. Conclusions: The FMDV-peptide drug conjugate SG3299 showed αvβ6-selectivity in vitro and in vivo and can specifically eliminate αvβ6-positive cancers, providing a promising new molecular- specific therapy for pancreatic cancer.

Phase I study of the checkpoint kinase 1 inhibitor GDC-0575 in combination with gemcitabine in patients with refractory solid tumors

BACKGROUND

Checkpoint kinase 1 (Chk1) inhibition following chemotherapy-elicited DNA damage overrides cell cycle arrest and induces mitotic catastrophe and cell death. GDC-0575 is a highly-selective oral small-molecule Chk1 inhibitor that results in tumor shrinkage and growth delay in xenograft models. We evaluated the safety, tolerability, and pharmacokinetic properties of GDC-0575 alone and in combination with gemcitabine. Antitumor activity and Chk1 pathway modulation were assessed.

PATIENTS AND METHODS

In this phase I open-label study, in the dose escalation stage, patients were enrolled in a GDC-0575 monotherapy Arm (1) or GDC-0575 combination with gemcitabine Arm (2) to determine the maximum tolerated dose. Patients in arm 2 received either i.v. gemcitabine 1000 mg/m2 (arm 2a) or 500 mg/m2 (arm 2b), followed by GDC-0575 (45 or 80 mg, respectively, as RP2D). Stage II enrolled disease-specific cohorts.

RESULTS

Of 102 patients treated, 70% were female, the median age was 59 years (range 27-85), and 47% were Eastern Cooperative Oncology Group PS 0. The most common tumor type was breast (37%). The most frequent adverse events (all grades) related to GDC-0575 and/or gemcitabine were neutropenia (68%), anemia (48%), nausea (43%), fatigue (42%), and thrombocytopenia (35%). Maximum concentrations of GDC-0575 were achieved within 2 hours of dosing, and half-life was ∼23 hours. No pharmacokinetic drug-drug interaction was observed between GDC-0575 and gemcitabine. Among patients treated with GDC-0575 and gemcitabine, there were four confirmed partial responses, three occurring in patients with tumors harboring TP53 mutation. Pharmacodynamic data were consistent with GDC-0575 inhibition of gemcitabine-induced expression of pCDK1/2.

CONCLUSION

GDC-0575 can be safely administered as a monotherapy and in combination with gemcitabine; however, overall tolerability with gemcitabine was modest. Hematological toxicities were frequent but manageable. Preliminary antitumor activity was observed but limited to a small number of patients with a variety of refractory solid tumors treated with GDC-0575 and gemcitabine.

CLINICAL TRIAL NUMBER

NCT01564251.

Uncoupling TORC2 from AGC kinases inhibits tumour growth

Mammalian target of rapamycin (mTOR) is a central regulator of growth and metabolism. mTOR resides in two distinct multi-protein complexes - mTORC1 and mTORC2 - with distinct upstream regulators and downstream targets. While it is possible to specifically inhibit mTORC1 with rapamycin, or inhibit both mTOR complexes together with ATP pocket directed mTOR kinase inhibitors, it is not possible to assess the specific roles for mTORC2 pharmacologically. To overcome this, we have developed a novel, inducible, dominant negative system for disrupting substrate recruitment to mTORC2. Previously we identified the mTORC2 specific subunit Sin1 as a direct binding partner for AGC kinases Akt and PKC. Sin1 mutants, which retain the ability to bind Rictor and mTOR, but fail to recruit their AGC client kinases, inhibit AKT and PKC priming and block cell growth. In this study, we demonstrate that uncoupling mTORC2 from AGC kinases in DLD1 colon cancer cells inhibits Akt activation and blocks tumour growth in vivo. Further we demonstrate, using time resolved two-site amplified FRET (A-FRET) analysis of xenograft tumours, that inhibition of tumour growth correlates with the degree of mTORC2 uncoupling from its downstream targets, as demonstrated for Akt. These data add weight to the body of evidence that mTORC2 represents a pharmacological target in cancer independently of mTORC1.

Measurement of IR laser backscatter spectra from sulfuric acid and ammonium sulfate aerosols

An optical system employing a tunable carbon dioxide laser has been used to investigate backscatter signatures of aerosols as a function of wavelength. Submicron sulfuric acid or ammonium sulfate aerosols are produced with a vapor-condensation aerosol generator. The aerosol is contained in a 1-m long windowless aerosol chamber, and laser radiation backscattered from the irradiated aerosol is collected and measured as the laser is tuned from 9.2 to 10.8 microm. The volume backscatter coefficient is calculated from the lidar equation to yield the theoretical IR spectrum of the aerosol. The measured spectral signature is compared with the theoretical signature, which is computed from Mie theory. Backscatter signatures show excellent agreement with calculated signatures. The spectral signature of ammonium sulfate is readily distinguished from that of sulfuric acid for the conditions of the experiment. Because of vapor pressure characteristics of sulfuric acid, it is possible to concentrate the acid in the generator over time and look for a change in the acid concentration in the aerosol. Not only has this concentration process been observed optically, but under these experimental conditions the acid concentration in the aerosol can be determined by observing backscatter at just two wavelengths.

Measurement of average atmospheric temperature using a CO(2) laser radar

A single-ended CO(2) lidar system has been used to measure the average temperature over a path between the lidar and the foothills located 5 km away. The CO(2) lidar was used to measure the ratio of transmission of the P(38) to the P(20) lines in the 10-microm band of CO(2). This ratio of transmission is directly related to temperature. Good correlation was obtained between the lidar-measured temperature and the thermometermeasured values.

Remote measurement of ethylene using a CO(2) differential-absorption lidar

Ethylene has been monitored with a single-ended CO(2) lidar using topographical scattering. Foliage on the foothills 5 km away provided the backscattered signal. Interference due to water vapor was found to be equivalent to 7.6 ppb of ethylene, and this correction was applied to the data. The total measurement uncertainty was found to average 1.6 ppb. The lidar-measured concentrations agree with point monitor samples over a wide range of ambient concentrations.

Single-ended measurement of infrared extinction using lidar

The goal of this study was to investigate the feasibility of single-ended measurement of the total extinction coefficient using an ir lidar system. Extinction was measured using a CO(2) laser radar system at four wavelengths near 10.3 microm. The measured results agree with theoretical estimates of extinction over a wide range. Single-ended measurements of extinction appear feasible to a horizontal range of 10 km using commercially available components. The system could potentially generate extinction data in a 3-D grid, enabling one to determine ir transmission between any two points in the field.

Remote measurement of HCI, CH(4), and N(2)O using a single-ended chemical-laser lidar system

The applicability of the high energy discretely tuned DF laser for remote measurement of HCl, CH(4), and N(2)O has been investigated. A single-ended or monostatic lidar system using radiation backscattered from topographical targets was tested. Selective absorption of the backscattered signal was used to infer concentration of gaseous species. Good agreement was obtained between the lidar measurements and the concentrations determined by in situ measurements in the remotely positioned sample chamber. The lowest measurable material concentration for each gas was inferred from random fluctuations in the measured concentration. Sensitivity of the existing system to HCl, CH(4), and N(2)O was found to be 0.05 ppm-km, 6.0 ppm-km, and 0.24 ppm-km, respectively. An N(2)O plume was also measured in the open atmosphere between the lidar system and a foliage target to demonstrate system capabilities under typical field conditions. Performance predictions indicate that total burden and range-resolved species concentration measurements are feasible to a range of 10 km or more with commercially available components.