Optimization of an Imidazo[1,2-a]pyridine Series to Afford Highly Selective Type I1/2 Dual Mer/Axl Kinase Inhibitors with In Vivo Efficacy

Inhibition of Mer and Axl kinases has been implicated as a potential way to improve the efficacy of current immuno-oncology therapeutics by restoring the innate immune response in the tumor microenvironment. Highly selective dual Mer/Axl kinase inhibitors are required to validate this hypothesis. Starting from hits from a DNA-encoded library screen, we optimized an imidazo[1,2-a]pyridine series using structure-based compound design to improve potency and reduce lipophilicity, resulting in a highly selective in vivo probe compound 32. We demonstrated dose-dependent in vivo efficacy and target engagement in Mer- and Axl-dependent efficacy models using two structurally differentiated and selective dual Mer/Axl inhibitors. Additionally, in vivo efficacy was observed in a preclinical MC38 immuno-oncology model in combination with anti-PD1 antibodies and ionizing radiation.

Abstract 3769: Continuous, low intensity systemic dosing maximizes the therapeutic margin of Eg5/KSP inhibition in an orthotopic model of urothelial cell carcinoma

Urothelial Cell Carcinoma (UCC) is the fifth most common cancer, but no new generation molecularly targeted therapies have been registered to treat this disease. Non muscle-invasive bladder cancer can be treated by systemic or intravesical dosing routes. However, the urothelium is one of the most formidable permeability barriers in nature, and may limit the penetration of small molecules into tumour tissue from the intravesical location. Inhibitors of mitosis, including spindle proteins such as Eg5, are attractive targets for cancer therapy, but their efficacy when dosed systemically is severely limited by bone marrow toxicities such as neutropenia and thrombocytopenia. AZ9814, a very potent and selective small molecule inhibitor of Eg5, induces apoptosis and inhibits proliferation of UCC cells in culture with a GI50 of < 1 nM. We have developed an orthotopic model of bladder cancer in the nude rat coupled with a programmable mini-pump system to continuously infuse AZ9814 into the bladder, and compared the therapeutic index of this delivery route with systemic dosing schedules using intraperitoneal injection and continuous subcutaneous infusion using an osmotic mini-pump. Continuous intravesical infusion resulted in severe bladder toxicity including hydropic degeneration and ulceration of urothelium, mucosal erosion and bilateral hydronephrosis, with limited penetration of compound into the tumour, and no significant impact on tumour pharmacodynamics and growth. In contrast, continuous low intensity systemic dosing resulted in significant tumour pharamacodynamic activity and control of tumour growth, albeit with significant but non-lethal effects on bone marrow toxicity. Daily intraperitoneal injection of AZ9814 resulted in very modest anti-tumour effects which were limited by bone marrow toxicity. It is concluded that Eg5 inhibitors have potential to treat UCC, but continuous systemic infusion is the best dosing schedule to maximize therapeutic index.

Citation Format: Leigh Williams, Rebecca Ellston, Dawn Trueman, Helen Musgrove, Linette Ruston, Brian Aquila, Elizabeth Pease, Stephanie Klein, Barry R. Davies. Continuous, low intensity systemic dosing maximizes the therapeutic margin of Eg5/KSP inhibition in an orthotopic model of urothelial cell carcinoma. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 3769.

Prevention of fostamatinib-induced blood pressure elevation by antihypertensive agents

Fostamatinib is a tyrosine kinase inhibitor with activity against spleen tyrosine kinase which has completed clinical trials for patients with rheumatoid arthritis. In clinical studies fostamatinib treatment was associated with a small elevation of systemic arterial blood pressure (BP), a similar finding to that seen with other kinase inhibitors, especially those that inhibit VEGFR2 signaling. We have investigated the link between fostamatinib-induced blood pressure elevation and plasma levels of the fostamatinib-active metabolite R940406 in conscious rats and found the time course of the BP effect correlated closely with changes in R940406 plasma concentration, indicating a direct pharmacological relationship. Free plasma levels of R940406 produced in these studies (up to 346 nmol/L) span the clinically observed mean peak free plasma concentration of 49 nmol/L. We have demonstrated that the blood pressure elevation induced by fostamatinib dosing can be successfully controlled by a variety of methods, notably simple drug withdrawal or codosing with a range of standard antihypertensive agents such as atenolol, captopril, and nifedipine. These findings support potential methods of maintaining patient safety while on fostamatinib therapy. Furthermore, we have demonstrated, using nifedipine as an example agent, that this blood pressure control was not achieved by reduction in plasma exposure of R940406, suggesting that potential benefits from the pharmacology of the investigational drug can be maintained while blood pressure control is managed by use of standard comedications.

Abstract 5146: Establishment of an orthotopic bladder cancer model to evaluate continuous intravesical delivery of small molecule inhibitors in the nude rat

Bladder cancer is a disease with high unmet need, with no new treatments being registered in the last two decades. Intravesical delivery is an attractive option for organ-confined bladder cancer; indeed, non-muscle invasive disease is currently treated by intravesical administration of agents such as bacillus Calmette-Guerin (BCG) and mitomycin C, and neoadjuvant intravesical therapy has the potential to preserve the bladder and improve survival in M0 muscle invasive disease. Intravesical delivery has the potential to increase the therapeutic index compared with systemic dosing routes, particularly if the duration of exposure can be extended. In order to explore this concept, we have developed an orthotopic model of bladder cancer and a drug delivery method to administer gemcitabine into the nude rat bladder for one week. An orthotopic model of bladder cancer was established by serial passaging of MGH-U3 human bladder cancer cells into the muscle wall. Tumor take-rate and growth was monitored by ultrasound imaging. Serial ex vivo - in vivo passaging increased growth and take rate of the tumors in both orthotopic and subcutaneous locations. Orthotopic implantation of cells following two previous passages in vivo resulted in reproducible tumor growth and take rates of >90%. Immunohistochemistry analysis showed that the orthotopic tumors were stably epithelial in phenotype after three serial in vivo passages. Principal component analysis of gene expression (GE) data from RNA sequencing of the parental cell line, sequentially passaged cells growing ex vivo, and both subcutaneous and orthotopically implanted tumours after various numbers of passages revealed three clusters; two distinct but closely related clusters representing the orthotopic and subcutaneously growing tumors, and another distinct cluster representing the various cell lines. This analysis showed that in vitro/in vivo location of growth is a more important determinant of global GE than the process of serial passaging in vivo. We have used the iPRECIO programmable infusion pump system to continuously infuse gemcitabine into the bladders of rats with orthotopic bladder tumors. Infusion of 2.5 mg/day at a flow rate of 5 ul/h for 7 days resulted in urine concentrations in the range of 1- 10 mM (∼ 1000-fold greater than systemic plasma drug concentrations), a 4-fold increase of γH2AX and induction of both necrosis and apoptosis (10-fold induction of cleaved casapse 3) in the orthotopic tumors. This model system holds considerable potential for evaluation of intravesical small molecule therapies that are potentially translatable to patients.

Citation Format: Leigh J. Williams, Stephanie K. Klein, Danielle Greenawalt, Dawn Trueman, Helen Musgrove, Helen Jones, Linette Ruston, Barry R. Davies. Establishment of an orthotopic bladder cancer model to evaluate continuous intravesical delivery of small molecule inhibitors in the nude rat. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 5146. doi:10.1158/1538-7445.AM2015-5146

The contribution of VEGF signalling to fostamatinib-induced blood pressure elevation

BACKGROUND AND PURPOSE

Fostamatinib is an inhibitor of spleen tyrosine kinase (TK). In patients, fostamatinib treatment was associated with increased BP. Some TK inhibitors cause BP elevation, by inhibiting the VEGF receptor 2 (VEGFR2). Here, we have assessed the mechanistic link between fostamatinib-induced BP elevation and inhibition of VEGF signalling.

EXPERIMENTAL APPROACH

We used conscious rats with automated blood sampling and radio telemetry and anaesthetized rats to measure cardiovascular changes. Rat isolated aorta and isolated hearts, and human resistance vessels in vitro were also used. NO production by human microvascular endothelial cells was measured with the NO-dependent probe, DAF-FM and VEGFR2 phosphorylation was determined in mouse lung, ex vivo.

KEY RESULTS

In conscious rats, fostamatinib dose-dependently increased BP. The time course of the BP effect correlated closely with the plasma concentrations of R406 (the active metabolite of fostamatinib). In anaesthetized rats, infusion of R406 increased BP and decreased femoral arterial conductance. Endothelial function was unaffected, as infusion of R406 did not inhibit hyperaemia- or ACh-induced vasodilatation in rats. R406 did not affect contraction of isolated blood vessels. R406 inhibited VEGF-stimulated NO production from human endothelial cells in vitro, and treatment with R406 inhibited VEGFR2 phosphorylation in vivo. R406 inhibited VEGF-induced hypotension in anaesthetized rats.

CONCLUSIONS AND IMPLICATIONS

Increased vascular resistance, secondary to reduced VEGF-induced NO release from endothelium, may contribute to BP increases observed with fostamatanib. This is consistent with the elevated BP induced by other drugs inhibiting VEGF signalling, although the contribution of other mechanisms cannot be excluded.

Comparison of plasma and tissue levels of ZD1694 (Tomudex), a highly polyglutamatable quinazoline thymidylate synthase inhibitor, in preclinical models

ZD1694 (Tomudex, raltitrexed) is a specific quinazoline antifolate thymidylate synthase inhibitor that relies on polyglutamation for high potency. Antibodies to ZD1694 have been used to establish a sensitive radioimmunoassay as an alternative to high-performance liquid chromatography (HPLC). The radioimmunoassay is reproducible, accurate and provides a means of determining low levels of ZD1694 in plasma (< 1 nM). By virtue of the high cross-reactivity of the antibodies with polyglutamated forms of ZD1694, it is also possible to measure the total concentration of drug in tissues. Results obtained in L1210 mouse leukaemia cells and in mouse tissues were similar to those previously determined using radiolabelled drug. Pharmacokinetic studies in mice have confirmed that the compound is rapidly eliminated from the plasma and that there is a prolonged terminal elimination phase. ZD1694 was measured in plasma (0.56 ng ml(-1); 1.2 pmol ml(-1)) up to 7 days after a single i.p. dose of 100 mg kg(-1) ZD1694. Liver, kidney and gut epithelium had a substantially higher level of ZD1694 immunoreactivity than plasma. For example, 24 h after a single i.p. dose at 1, 10 and 100 mg kg(-1), total drug levels in the liver were 480, 325 and 152 times higher than plasma levels respectively. In kidney and gut epithelium, total drug levels at these doses were approximately 55 and 34 times those of plasma. The high tissue to plasma ratios were maintained for at least 7 days after administration. Similarly, high tissue to plasma ratios (> 100) were found in dogs treated with a clinically relevant dose of ZD1694. These were maintained for 4 weeks in liver and kidney tissue (> 100). Total gastrointestinal concentrations of ZD1694 were approximately 10 times higher than plasma 3 days after administration, but levels were near to the limit of detection at 4 weeks. These results are consistent with extensive polyglutamation of ZD1694 within tissues in both mice and dog and provide further support for the infrequent schedule that has been used clinically. Although it has not been possible to measure individual polyglutamated forms of ZD1694, the radioimmunoassay provides a convenient means of assessing total drug levels in tissues and is currently the only method suitable for measuring the extent of drug retention in normal tissue and tumour biopsies obtained from patients treated with ZD1694.