L-DOS47 Elevates Pancreatic Cancer Tumor pH and Enhances Response to Immunotherapy

Acidosis is an important immunosuppressive mechanism that leads to tumor growth. Therefore, we investigated the neutralization of tumor acidity to improve immunotherapy response. L-DOS47, a new targeted urease immunoconjugate designed to neutralize tumor acidity, has been well tolerated in phase I/IIa trials. L-DOS47 binds to CEACAM6, a cell-surface protein that is highly expressed in gastrointestinal cancers, allowing urease to cleave endogenous urea into two NH4+ and one CO2, thereby raising local pH. To test the synergetic effect of neutralizing tumor acidity with immunotherapy, we developed a pancreatic orthotopic murine tumor model (KPC961) expressing human CEACAM6. Using chemical exchange saturation transfer-magnetic resonance imaging (CEST-MRI) to measure the tumor extracellular pH (pHe), we confirmed that L-DOS47 raises the tumor pHe from 4 h to 96 h post injection in acidic tumors (average increase of 0.13 units). Additional studies showed that combining L-DOS47 with anti-PD1 significantly increases the efficacy of the anti-PD1 monotherapy, reducing tumor growth for up to 4 weeks.

L-DOS47 enhances response to immunotherapy in pancreatic cancer tumor

Acidosis is an important immunosuppressive mechanism that leads to tumor growth. Therefore, we investigated the neutralization of tumor acidity to improve immunotherapy response. L-DOS47, a new targeted urease immunoconjugate designed to neutralize tumor acidity, has been well tolerated in phase I/IIa trials. L-DOS47 binds CEACAM6, a cell surface protein highly expressed in gastrointestinal cancers, allowing urease to cleave endogenous urea into two NH4+ and one CO2, thereby raising local pH. To test the synergetic effect of neutralizing tumor acidity with immunotherapy, we developed a pancreatic orthotopic murine tumor model (KPC961) expressing human CEACAM6. Our results demonstrate that combining L DOS47 with anti-PD1 significantly increases the efficacy of anti-PD1 monotherapy, reducing tumor growth for up to 4 weeks.

In vivo and in silico pharmacokinetics and biodistribution of a melanocortin receptor 1 targeted agent in preclinical models of melanoma

The melanocortin 1 receptor (MC1R) is overexpressed in most melanoma metastases, making it a promising target for imaging of melanomas. In this study, the expression of MC1R in a large fraction of patients with melanoma was confirmed using mRNA and tissue microarray. Here, we have characterized the in vivo tumor and tissue distribution and pharmacokinetics (PK) of uptake and clearance of a MC1R specific peptidomimetic ligand conjugated to a near-infrared fluorescent dye. We propose an interdisciplinary framework to bridge the different time and space scales of ligand-tumor-host interactions: intravital fluorescence microscopy to quantify probe internalization at the cellular level, a xenograft tumor model for whole body pharmacokinetics, and a computational pharmacokinetic model for integration and interpretation of experimental data. Administration of the probe into mice bearing tumors with high and low MC1R expression demonstrated normalized image intensities that correlated with expression levels (p < 0.05). The biodistribution study showed high kidney uptake as early as 30 min postinjection. The PK computational model predicted the presence of receptors in the kidneys with a lower affinity, but at higher numbers than in the tumors. As the mouse kidney is known to express the MC5R, this hypothesis was confirmed by both coinjection of a ligand with higher MC5R affinity compared to MC1R and by injection of lower probe concentrations (e.g., 1 nmol/kg), both leading to decreased kidney accumulation of the MC1R ligand. In addition, through this interdisciplinary approach we could predict the rates of ligand accumulation and clearance into and from organs and tumors, and the amount of injected ligand required to have maximum specific retention in tumors. These predictions have potential to aid in the translation of a targeted agent from lab to the clinic. In conclusion, the characterized MC1R-specific probe has excellent potential for in vivo detection of melanoma metastases. The process of cell-surface marker validation, targeted imaging probe development, and in vitro, in vivo, and in silico characterization described in this study can be generally applied to preclinical development of targeted agents.

Abstract 4557: Development of a melanocortin receptor 1 targeted probe for molecular imaging of melanoma

Melanoma is curable by means of surgical excision if diagnosed in early stages, but once the metastatic stage is reached, prognosis is poor because the tumor is resistant to most cures. Therefore, a melanoma targeted probe that can deliver therapy to metastases at high dosages could increase the chances of treatment. Melanocortin 1 receptor (MC1R) is overexpressed in most human melanoma metastases, thus making it a promising target for imaging and therapy of melanomas. To confirm that MC1R is a specific melanoma marker, mRNA and protein expression was confirmed and quantified in tumor and normal unaffected patient tissue samples. MC1R mRNA expression was highly and generally expressed among melanoma samples surveyed. In contrast, MC1R expression was not elevated in other skin cancers, normal skin and organs involved in toxicity and clearance, i.e. heart, spleen, liver and kidney. To determine MC1R protein expression in patient samples, immunohistochemistry was performed on a melanoma tissue microarray containing 267 samples. None of the normal skin samples (n = 19) had staining with a pathology score of α4. Benign lesions (n = 65), samples of local invasion to regional lymph nodes (n = 35) and metastatic melanoma (n=40) had moderate to high staining in 15, 33 and 47% of the samples, respectively. We have previously reported the development of a peptidomimetic ligand with high specificity and affinity for MC1R. In this study, we have conjugated this ligand to an infrared dye to generate a MC1R specific optical probe (named ML-800). Our whole-cell binding assay using A375/MC1R human melanoma engineered cells was used to determine the high binding affinity of ML-800 (0.4± 0.1 nM Ki). The cellular uptake of the probe was studied in A375/MC1R cells by fluorescence microscopy both in vitro and in vivo using a dorsal skin-fold window-chamber mouse model. The in vivo tumor targeting of ML-800 was evaluated by intravenous injection of probe into nude mice bearing bilateral subcutaneous tumors of A375 with low number of MC1R receptors and A375/MC1R with high expression of MC1Rs. Fluorescence imaging showed that the agent has higher uptake values in A375/MC1R tumors than those in A375M tumors (P, 0.05), demonstrating differentiation of probe retention in tumors with different levels of expression. In conclusion, the imaging probe designed in this study demonstrates the potential for the development of agents that can deliver imaging contrast and therapy to melanoma metastases that express MC1R. Since radiopeptides have proven their usefulness for diagnostic imaging and radiotherapy, in the future, this ligand could be developed as a targeted delivery vehicle for non-invasive nuclear imaging to detect regional lymph node involvement, or delivery of radiotherapy. Furthermore, by attachment to the MC1R ligand with a cleavable linker, cytotoxins may also be targeted to tumor cells for receptor mediated endocytosis and intracellular release.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 4557. doi:1538-7445.AM2012-4557

Abstract 53: Exploiting heterogeneity to develop better treatment strategies using an evolutionary multiscale mathematical model of tumor-vessel interactions

Tumor heterogeneity in cancer is an observed fact, both genetically and phenotypically. Cell-cell variation is seen in almost all aspects of cancer from early development all the way through to invasion and subsequent metastasis. The tumor microenvironment is also very heterogeneous and dynamic with multiple zones of hypoxia, normoxia, acidosis and necrosis. Central to our understanding of this heterogeneity is how the tumor cells interact with each other and with their microenvironment. Since the microenvironment is modulated by the tumor itself, as well as the surrounding stroma and the vasculature supply, these interactions rapidly become complex. In order to better understand these complex interactions, we have developed an integrated approach utilizing a hybrid multiscale mathematical model in parallel with an experimental murine window chamber model. This study aims to understand the development of the vasculature in response to a growing tumor, the effects of a heterogeneous microenvironment, and how interactions between the tumor and its vasculature modulate tumor progression and treatment resistance. By incorporating phenotypic heterogeneity into the model, a range of tumor phenotypes emerges due to the heterogeneous microenvironment. The response of the tumor to a treatment will depend on the distribution of phenotypes as well as the local conditions. At the same time, treatment will alter the phenotypic distribution and the microenvironment, so that subsequent tumor progression will be profoundly different than it was prior to treatment. By using the spatial and temporal projections of the mathematical model, optimal treatment strategies are derived and classified based on tumor and microenvironmental parameters. One particularly intriguing result is that tumor control, as opposed to eradication, may be more readily achieved by modulation of the tumor heterogeneity via treatment-mediated microenvironmental selection.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 53. doi:10.1158/1538-7445.AM2011-53

Lysophosphatidic acid induction of urokinase plasminogen activator secretion requires activation of the p38MAPK pathway

Lysophosphatidic acid (LPA) is an important intercellular signaling molecule involved in a myriad of biological responses. Elevated concentrations of LPA are present in the ascites and plasma of ovarian cancer patients suggesting a role for LPA in the pathophysiology of ovarian cancer. We have demonstrated previously that oleoyl (18:1) LPA at concentrations present in ascites induces the secretion of urokinase plasminogen activator (uPA) from ovarian cancer cells, possibly linking LPA to cellular invasion. In this study we sought to elucidate which signaling pathway(s) are involved in LPA-mediated secretion of uPA from ovarian cancer cells. Specific inhibitors were utilized to determine if interference with the p38(MAPK), p42/44(MAPK), and PI3K pathways functionally blocked LPA-mediated uPA secretion. LPA stimulation of ovarian cancer cells markedly increased the phosphorylation and activity of p38(MAPK), p42/p44(MAPK), and PI3K. Both tyrosine phosphorylation and Src kinase activity were required for optimal activation of signaling by LPA including phosphorylation of p38(MAPK). Inhibition of p38(MAPK) signaling by SB202190 completely abrogated LPA-induced uPA secretion, while inhibition of the p42/44(MAPK) or PI3K pathways with PD98059 or wortmannin and LY294002, respectively, decreased but did not completely block uPA secretion. In contrast, inhibitors of phospholipase D or the p70S6 kinase pathway did not alter LPA-induced uPA secretion. Further, tyrosine phosphorylation and functional Src were required for optimal uPA secretion. Finally, LPA induces uPA secretion from ovarian cancer cells predominantly through the LPA2 receptor, with LPA3 contributing to this process. These results indicate that the p38(MAPK) signaling pathway is required for optimal LPA-dependent uPA secretion from ovarian cancer cells.

Activated SRC protein tyrosine kinase is overexpressed in late-stage human ovarian cancers

OBJECTIVE

The objective of this study was to determine if the Src tyrosine kinase is overexpressed and activated in late-stage human ovarian cancers.

METHODS

Western analysis and immune complex kinase assays were performed on a panel of human ovarian cancer cell lines and normal ovarian epithelial cell cultures, and immunohistochemical analysis for Src and activated Src were performed on a panel of late-stage human ovarian tumors.

RESULTS AND CONCLUSIONS

Src is overexpressed and activated in a majority of late-stage ovarian tumors as well as in a panel of cultured malignant human ovarian epithelium grown in vitro, but not in normal ovarian epithelium (NOE) or immortalized NOE. Src overexpression was found to be frequently, but not always, associated with HER-2/neu overexpression, but no statistical association between Src and Her-2/neu overexpression could be demonstrated.