Inhibition of PlGF as a potential therapy against hepatocellular carcinoma

Background: Inhibition of angiogenesis is currently hot topic in the search for an effective treatment against hepatocellular carcinoma (HCC). Placental growth factor (PlGF) is a VEGF analogue only involved in pathologic angiogenesis and its inhibition has the potential to restrain tumour growth, without affecting healthy organs. Therefore, we assessed whether administration of PlGF-antibodies could serve as a potential therapy for HCC in mice.\n\nMethods: 5-week-old male mice received intraperitoneal injections with diethylnitrosamine (35 mg/kg bodyweight, 1x/week) leading to HCC after 25W. At 26W mice were treated with murine PlGF-antibodies (20 mg/kg aPlGF, 2x/week) or IgG for 5W. Tumour vasculature was assessed with endoglin staining. As a marker for vessel abnormality the number of cords without lumen, tortuous vessels and intercapillary distances were quantified. Arterialisation was assessed (aSMA staining) and the number and size of unpaired arteries (i.e. large SMA+ vessels not accompanied by a bile duct) determined. Stainings for HIF2alpha and PCNA were used to identify hypoxia and proliferation. \n\nResults: treatment with aPlGF caused a significant decrease in mortality (45% in IgG vs 23% aPlGF mice; P< 0.05) and lowered (p< 0,05) tumour burden. The vascular network decreased around the PlGF-treated tumours (P< 0,01) ; fewer (p< 0,05) and smaller (p< 0,001) unpaired arteries were present and PlGF-blockage partially normalized the vasculature. These changes were functionally relevant, as PlGF-blocked HCC nodules expressed lower levels of HIF2 (p< 0,05) and showed less proliferation (p< 0,05).\n\nConclusion: Inhibition of PlGF has a positive effect on survival in mice with HCC. aPlGF treatment decreased the tumour induced vascularisation and arterialisation, without effecting healthy tissue. Furthermore, the normalised vasculature and reduced hypoxia, decreases the proliferation of malignant cells. Given that VEGF-inhibitors enhance metastasis by evoking hypoxia, the anti-abnormalization activity of aPlGF may offer promising target to combat HCC.\n\nMethods: 5-week-old male mice received intraperitoneal injections with diethylnitrosamine (35 mg/kg bodyweight, 1x/week) leading to HCC after 25W. At 26W mice were treated with murine PlGF-antibodies (20 mg/kg aPlGF, 2x/week) or IgG for 5W. Tumour vasculature was assessed with endoglin staining. As a marker for vessel abnormality the number of cords without lumen, tortuous vessels and intercapillary distances were quantified. Arterialisation was assessed (aSMA staining) and the number and size of unpaired arteries (i.e. large SMA+ vessels not accompanied by a bile duct) determined. Stainings for HIF2alpha and PCNA were used to identify hypoxia and proliferation. \n\nResults: treatment with aPlGF caused a significant decrease in mortality (45% in IgG vs 23% aPlGF mice; P< 0.05) and lowered (p< 0,05) tumour burden. The vascular network decreased around the PlGF-treated tumours (P< 0,01) ; fewer (p< 0,05) and smaller (p< 0,001) unpaired arteries were present and PlGF-blockage partially normalized the vasculature. These changes were functionally relevant, as PlGF-blocked HCC nodules expressed lower levels of HIF2 (p< 0,05) and showed less proliferation (p< 0,05).\n\nConclusion: Inhibition of PlGF has a positive effect on survival in mice with HCC. aPlGF treatment decreased the tumour induced vascularisation and arterialisation, without effecting healthy tissue. Furthermore, the normalised vasculature and reduced hypoxia, decreases the proliferation of malignant cells. Given that VEGF-inhibitors enhance metastasis by evoking hypoxia, the anti-abnormalization activity of aPlGF may offer promising target to combat HCC.