PDGFR Inhibition Results in Pericyte Depletion and Hemorrhage into the Corpus Luteum of the Rat Ovary.

The growth plate, ovary, adrenal gland, and rodent incisor tooth are sentinel organs for antiangiogenic effects since they respond reliably, quantitatively, and sensitively to inhibition of the vascular endothelial growth factor receptor (VEGFR). Here we report that treatment of rats with platelet-derived growth factor receptor beta (PDGFRß) inhibitors that target pericytes results in severe ovarian hemorrhage with degeneration and eventual rupture of the corpus luteum. Evaluation of the growth plate, adrenal gland, and incisor tooth that are typical target organs for antiangiogenic treatment in the rodent revealed no abnormalities. Histologically, the changes in the ovary were characterized by sinusoidal dilatation, increased vessel fragility, and hemorrhage into the corpus luteum. Immunocytochemical staining of vessels with alpha smooth muscle actin and CD31 that recognize pericytes and vascular endothelium, respectively, demonstrated that this effect was due to selective pericyte deficiency within corpora lutea. Further experiments in which rats were treated concurrently with both PDGFRß and VEGFR inhibitors ablated the hemorrhagic response, resulting instead in corpus luteum necrosis. These changes are consistent with the notion that selective pericyte loss in the primitive capillary network resulted in increased vessel fragility and hemorrhage, whereas concomitant VEGFR inhibition resulted in vessel regression and reduced vascular perfusion that restricted development of the hemorrhagic vessels. These results also highlight the utility of the rodent ovary to respond differentially to VEGFR and PDGFR inhibitors, which may provide useful information during routine safety assessment for determining target organ toxicity.

AZD9291, an irreversible EGFR TKI, overcomes T790M-mediated resistance to EGFR inhibitors in lung cancer.

UNLABELLED: First-generation EGFR tyrosine kinase inhibitors (EGFR TKI) provide significant clinical benefit in patients with advanced EGFR-mutant (EGFRm(+)) non-small cell lung cancer (NSCLC). Patients ultimately develop disease progression, often driven by acquisition of a second T790M EGFR TKI resistance mutation. AZD9291 is a novel oral, potent, and selective third-generation irreversible inhibitor of both EGFRm(+) sensitizing and T790M resistance mutants that spares wild-type EGFR. This mono-anilino-pyrimidine compound is structurally distinct from other third-generation EGFR TKIs and offers a pharmacologically differentiated profile from earlier generation EGFR TKIs. Preclinically, the drug potently inhibits signaling pathways and cellular growth in both EGFRm(+) and EGFRm(+)/T790M(+) mutant cell lines in vitro, with lower activity against wild-type EGFR lines, translating into profound and sustained tumor regression in EGFR-mutant tumor xenograft and transgenic models. The treatment of 2 patients with advanced EGFRm(+) T790M(+) NSCLC is described as proof of principle. SIGNIFICANCE: We report the development of a novel structurally distinct third-generation EGFR TKI, AZD9291, that irreversibly and selectively targets both sensitizing and resistant T790M(+) mutant EGFR while harboring less activity toward wild-type EGFR. AZD9291 is showing promising responses in a phase I trial even at the first-dose level, with first published clinical proof-of-principle validation being presented.

Inhibition of vascular endothelial growth factor-a signaling induces hypertension: examining the effect of cediranib (recentin; AZD2171) treatment on blood pressure in rat and the use of concomitant antihypertensive therapy.

PURPOSE: Inhibition of vascular endothelial growth factor-A (VEGF) signaling is a key therapeutic approach in oncology given the role of VEGF in angiogenesis and vascular permeability in solid tumors. Clinical trials examining VEGF signaling inhibitors commonly report hypertension. We examined the effect of cediranib, a highly potent VEGF signaling inhibitor, on the blood pressure of rats and the ability of standard antihypertensive agents to modulate the consequences of VEGF signaling inhibition. EXPERIMENTAL DESIGN: The ability of cediranib to induce hypertensive changes and the effect of giving antihypertensive therapy were investigated in conscious, unrestrained telemetered rats. Two antihypertensive agents were studied: captopril, an angiotensin-converting enzyme inhibitor, and nifedipine, a dihydropyridine calcium channel blocker. The antitumor activity of cediranib, alone and in combination with nifedipine, was also evaluated in a LoVo human colorectal tumor xenograft model in nude rats. All treatments were given orally. RESULTS: Administration of 0.1 to 1.5 mg/kg/d of cediranib for 4 consecutive days induced a relatively mild hypertensive effect, elevating diastolic blood pressure by 10 to 14 mmHg. Dosing 3 mg/kg/d cediranib for 4 days induced a marked hypertension of 35 to 50 mmHg. Captopril (30 mg/kg, qd) was effective at lowering a 10 mmHg increase in blood pressure but not a 35 to 50 mmHg increase. However, the latter was rapidly reversed by administration of nifedipine (10 mg/kg, bd). Coadministration of nifedipine did not negatively affect the antitumor activity of cediranib (1.5 mg/kg/d). CONCLUSIONS: Hypertension is a direct consequence of inhibiting VEGF signaling but can be controlled with appropriately selected, standard antihypertensive medication.

AZD2171: a highly potent, orally bioavailable, vascular endothelial growth factor receptor-2 tyrosine kinase inhibitor for the treatment of cancer.

Inhibition of vascular endothelial growth factor-A (VEGF) signaling is a promising therapeutic approach that aims to stabilize the progression of solid malignancies by abrogating tumor-induced angiogenesis. This may be accomplished by inhibiting the kinase activity of VEGF receptor-2 (KDR), which has a key role in mediating VEGF-induced responses. The novel indole-ether quinazoline AZD2171 is a highly potent (IC50 < 1 nmol/L) ATP-competitive inhibitor of recombinant KDR tyrosine kinase in vitro. Concordant with this activity, in human umbilical vein endothelial cells, AZD2171 inhibited VEGF-stimulated proliferation and KDR phosphorylation with IC50 values of 0.4 and 0.5 nmol/L, respectively. In a fibroblast/endothelial cell coculture model of vessel sprouting, AZD2171 also reduced vessel area, length, and branching at subnanomolar concentrations. Once-daily oral administration of AZD2171 ablated experimental (VEGF-induced) angiogenesis in vivo and inhibited endochondral ossification in bone or corpora luteal development in ovary; physiologic processes that are highly dependent upon neovascularization. The growth of established human tumor xenografts (colon, lung, prostate, breast, and ovary) in athymic mice was inhibited dose-dependently by AZD2171, with chronic administration of 1.5 mg per kg per day producing statistically significant inhibition in all models. A histologic analysis of Calu-6 lung tumors treated with AZD2171 revealed a reduction in microvessel density within 52 hours that became progressively greater with the duration of treatment. These changes are indicative of vascular regression within tumors. Collectively, the data obtained with AZD2171 are consistent with potent inhibition of VEGF signaling, angiogenesis, neovascular survival, and tumor growth. AZD2171 is being developed clinically as a once-daily oral therapy for the treatment of cancer.

ZD6474 inhibits vascular endothelial growth factor signaling, angiogenesis, and tumor growth following oral administration.

ZD6474 [N-(4-bromo-2-fluorophenyl)-6-methoxy-7-[(1-methylpiperidin-4-yl)methoxy]quinazolin-4-amine]is a potent, p.o. active, low molecular weight inhibitor of kinase insert domain-containing receptor [KDR/vascular endothelial growth factor receptor (VEGFR) 2] tyrosine kinase activity (IC(50) = 40 nM). This compound has some additional activity versus the tyrosine kinase activity of fms-like tyrosine kinase 4 (VEGFR3;IC(50) = 110 nM) and epidermal growth factor receptor (EGFR/HER1; IC(50) = 500 nM) and yet demonstrates selectivity against a range of other tyrosine and serine-threonine kinases. The activity of ZD6474 versus KDR tyrosine kinase translates into potent inhibition of vascular endothelial growth factor-A (VEGF)-stimulated endothelial cell (human umbilical vein endothelial cell) proliferation in vitro (IC(50) = 60 nM). Selective inhibition of VEGF signaling has been demonstrated in vivo in a growth factor-induced hypotension model in anesthetized rat: administration of ZD6474 (2.5 mg/kg, i.v.) reversed a hypotensive change induced by VEGF (by 63%) but did not significantly affect that induced by basic fibroblast growth factor. Once-daily oral administration of ZD6474 to growing rats for 14 days produced a dose-dependent increase in the femoro-tibial epiphyseal growth plate zone of hypertrophy, which is consistent with inhibition of VEGF signaling and angiogenesis in vivo. Administration of 50 mg/kg/day ZD6474 (once-daily, p.o.) to athymic mice with intradermally implanted A549 tumor cells also inhibited tumor-induced neovascularization significantly (63% inhibition after 5 days; P < 0.001). Oral administration of ZD6474 to athymic mice bearing established (0.15-0.47 cm(3)), histologically distinct (lung, prostate, breast, ovarian, colon, or vulval) human tumor xenografts or after implantation of aggressive syngeneic rodent tumors (lung, melanoma) in immunocompetent mice, produced a dose-dependent inhibition of tumor growth in all cases. Statistically significant antitumor activity was evident in each model with at least 25 mg/kg ZD6474 once daily (P < 0.05, one-tailed t test). Histological analysis of Calu-6 tumors treated with 50 mg/kg/day ZD6474 for 24 days showed a significant reduction (>70%) in CD31 (endothelial cell) staining in nonnecrotic regions. ZD6474 also restrained growth of much larger (0.9 cm(3) volume) Calu-6 lung tumor xenografts and induced profound regression in established PC-3 prostate tumors of 1.4 cm(3) volume. ZD6474 is currently in Phase I clinical development as a once-daily oral therapy in patients with advanced cancer.