Roneparstat (SST0001), an Innovative Heparanase (HPSE) Inhibitor for Multiple Myeloma (MM) Therapy: First in Man Study

Background: HPSE is an endo-ß-d-glucuronidase that trims the heparan sulfate (HS) chains of proteoglycans, releasing biologically active fragments of HS. HPSE activity impacts cell signaling, gene expression and promotes extracellular matrix remodeling within the tumor microenvironment; high HPSE expression is associated with enhanced tumor growth, angiogenesis and metastases in several cancer types. As a result of its tumor promoting activities, HPSE is a promising new and unexploited target for anti-cancer therapy. There is a single enzymatically active HPSE in humans and HPSE knockout mice appear to be healthy, thus therapeutic neutralization of HPSE activity would likely have limited negative side effects. In MM preclinical models HPSE was shown to be a master regulator of aggressive tumor behavior. Preclinical evidence also indicates that HPSE promotes chemoresistance suggesting it plays a pivotal role in regulating myeloma response to therapy (Ramani VPC et al., AACR 2014, Abstract nr. 1708). In preclinical studies, bortezomib or melphalan were found to enhance HPSE expression and secretion. High HPSE expressing MM cells were less susceptible to the cytotoxic effects of those drugs. Likewise, a very significant increase in HPSE gene expression following chemotherapy was observed in patient-derived tumor samples, indicating a potential role for HPSE in regulating myeloma response to therapy. Roneparstat (SST0001), a 100% N-acetylated and glycol split heparin, is a potent HPSE inhibitor devoid of any significant anticoagulant activity. In an in vivo model of disseminated myeloma, Roneparstat in combination with either bortezomib or melphalan, significantly decreased both the number of animals with detectable tumor and the tumor burden when compared with animals treated with either of these drugs alone. In addition, studies in animal models of MM indicated that the mechanism of action of Roneparstat was consistent with it having anti-HPSE activity in vivo (reduced angiogenesis and diminished expression of HGF, VEGF and MMP-9 and diminished HPSE induced shedding of syndecan-1, a HS proteoglycan known to be a potent promoter of myeloma growth).

Patients and Methods: A First in Man, multicenter, international, phase I clinical study is currently ongoing in advanced heavily pre-treated refractory MM patients (pts) who have exhausted all available anti-MM therapies. Roneparstat is administered subcutaneously, with a starting flat dose defined according to ICH S9 guidelines. A schedule DX5W1,W2 Q28D is being tested. Each cohort plans 3 + 3 pts. A direct fluorescence method (Heparin Red assay) is used in pharmacokinetic studies along with aPTT, used as a surrogate (indirect) measurement of Roneparstat plasma concentration. The pharmacodynamic effect of the drug on the coagulation cascade and any antitumor effect are also evaluated.

Results: 15 pts have been enrolled to date. 5 cohorts (doses ranging from 25 to 200 mg/day) have been evaluated, while a 400 mg cohort has just been opened. Five pts have received 1 cycle of therapy, six pts 2 cycles, one 3 cycles, one 5 cycles, one 9 cycles; one patient is currently on treatment, one is not evaluable. Roneparstat administration was found to be safe with only minimal transient side effects. No DLTs and no bleeding complications have been observed. Roneparstat has been well tolerated both systemically and locally. The only side effect observed was minor reactions (redness, bruising) at the injection site (in 6 pts, all grade 1). A decrease > 50% in the serum monoclonal component was observed in one patient, lasting for 6 cycles.

Conclusions: Preclinical studies in MM lines and animal models have demonstrated Roneparstat as a potent anti-myeloma compound, particularly when used in combination with other drugs. In the ongoing Phase I escalating dose study (n. pts = 15), Roneparstat administration (at a dose of up to 200 mg/day) was found to be safe with only minimal local side effects. Based on these results, Roneparstat, at a defined dose, in combination with other anti-myeloma agents, will be evaluated in relapsed/resistant MM pts.