PG545, a dual heparanase and angiogenesis inhibitor, induces potent anti-tumour and anti-metastatic efficacy in preclinical models

Abstract

Background: PG545 is a heparan sulfate (HS) mimetic that inhibits tumour angiogenesis by sequestering angiogenic growth factors in the extracellular matrix (ECM), thus limiting subsequent binding to receptors. Importantly, PG545 also inhibits heparanase, the only endoglycosidase which cleaves HS chains in the ECM. The aim of the study was to assess PG545 in various solid tumour and metastasis models.

Methods: The anti-angiogenic, anti-tumour and anti-metastatic properties of PG545 were assessed using in vivo angiogenesis, solid tumour and metastasis models. Pharmacokinetic (PK) data were also generated in tumour-bearing mice to gain an understanding of optimal dosing schedules and regimens.

Results: PG545 was shown to inhibit angiogenesis in vivo and induce anti-tumour or anti-metastatic effects in murine models of breast, prostate, liver, lung, colon, head and neck cancers and melanoma. Enhanced anti-tumour activity was also noted when used in combination with sorafenib in a liver cancer model. PK data revealed that the half-life of PG545 was relatively long, with pharmacologically relevant concentrations of radiolabeled PG545 observed in liver tumours.

Conclusion: PG545 is a new anti-angiogenic clinical candidate for cancer therapy. The anti-metastatic property of PG545, likely due to the inhibition of heparanase, may prove to be a critical attribute as the compound enters phase I clinical trials.

Figure 1

The structure of PG545.

Figure 2

PG545 inhibits angiogenesis in vivo. (A) PG545 treatment was shown to possess anti-angiogenic activity in the AngioSponge model following evaluation of CD31/PECAM-1 positive endothelial cells after immunohistochemical staining of blood vessels. ^##P<0.01 vs vehicle control without FGF-2; ^**P<0.01 vs vehicle control and FGF-2. (B) Treatment with PG545 at 20 and 40 mg kg⁻¹ once-weekly (s.c.) resulted in a significant (P<0.001) decrease in CD31 endothelial staining in tumours by 30 and 22%, respectively.

Figure 3

The anti-tumour activity of PG545 in the orthotopic HCC model Hep3b2.1-7 can be enhanced by addition of sorafenib and exhibits favourable PK profiles in blood and tumour tissue. (A) Efficacy of PG545 when administered at 20 mg kg⁻¹ twice-weekly. (B) Efficacy of PG545 alone and in combination with sorafenib, when administered using a loading dose of 20 mg kg⁻¹ followed by a twice-weekly maintenance dose of 10 mg kg⁻¹. (C) Actual and estimated mean concentration vs time curve data for [³H]-PG545 in blood following administration of three bolus doses of [³H]-PG545 at 20 mg kg⁻¹ at 96 h intervals. (D) Actual and estimated mean concentration vs time curve data in tumour tissue of mice treated with three doses of [³H-PG545] at 20 mg kg⁻¹, 96 h apart. ^*P<0.05 vs vehicle control (unpaired t-test or ANOVA followed by Dunnett's test).

Figure 4

PG545 significantly inhibits solid tumour progression in (A) breast (MDA-MB-231), (B) prostate (PC3), (C) liver (HepG2) and (D) head and neck (Cal27) cancer models. Treatment commenced once tumours reached 100–200 mm³. ^*P<0.05 vs vehicle control, ^**P<0.01 vs vehicle control (repeated measures ANOVA followed by Dunnett's post hoc test, n=8–10 per group depending on study). TGI values are also shown.

Figure 5

PG545 significantly inhibits metastases in the B16 experimental metastasis model for melanoma and the spontaneous metastasis model HT-29 (colon). (A) PG545 administered on days indicated either before or after tumour cell inoculation (Day 0) reduced metastatic development in the lungs of mice in the B16 model. (B) PG545 treatment once-weekly over 8 weeks completely prevented metastasis to the liver in the HT-29 model. (C) PG545 treatment once-weekly over 8 weeks significantly reduced metastasis to the colon in the HT-29 model. Data are presented as mean number of lung, liver or colon metastases with s.e. ^*P<0.05, ^**P<0.01 vs vehicle control (one-way ANOVA followed by Dunnett's test for B16 model or t-test for HT-29 model).

Figure 6

PG545 significantly inhibits solid tumour progression and spontaneous metastasis in the Lewis Lung Carcinoma model (LL/2). (A) PG545 treatment once-weekly (total 3 weeks) significantly inhibited solid tumour growth. (B) Either a single injection or weekly dosing inhibited metastasis, which was significant in the 20 mg kg⁻¹ 1 × week group and the 40 mg kg⁻¹ single dose group, whereas sorafenib had no effect on metastasis. Data are presented as mean number of lung metastases with s.e. (C) PG545 plasma concentration vs time curves following a once-weekly dose of PG545 in week 1 and week 2. ^*P<0.05 vs vehicle control (one-way ANOVA followed by Holm-Sidak test or Dunnett's test).