P-202: SLAMF1-derived peptide P7N4-Pen as anti-myeloma treatment

Introduction: Multiple myeloma (MM) is one of the most common hematological cancers. Despite advances in treatment, most patients relapse, and MM is still considered an incurable disease. Thus, there is a need to identify new targets for treatment and new therapeutic approaches for the development of new drugs.
In human macrophages it has been demonstrated that Signaling lymphocytic activation molecule family member 1 (SLAMF1) amplifies signaling downstream Toll-like receptor 4. A synthetic peptide derived from a motif of SLAMF1 (P7), strongly inhibits production of inflammatory cytokines initiated by Nuclear factor kappa B (NFκB) activation. A total of 41 different variants of the SLAMF1-derived peptide have been synthesized, differing in one amino acid from the original peptide P7. Because NFκB has been found to be constitutively active in MM, we hypothesized that SLAMF1-derived peptides could inhibit proliferation and survival of MM cells.

Methods: Cytotoxic and cytostatic effects of SLAMF1-derived peptides alone, or in combination with melphalan were assessed in a panel of human MM cell lines, including sublines resistant to proteasome inhibitors, and primary MM human tumor cells (CD138-positive). Toxicity testing was evaluated in healthy peripheral blood mononuclear cells (PBMCs). Cell death was assessed by investigation of cell membrane integrity, co-treatment by pan-caspase-inhibitor, caspase-3 and PARP cleavage (apoptosis readout), and H2AX phosphorylation (DNA fragmentation). The effect on protein stability and phosphorylation state of key oncogenes in MM tumor cells was also evaluated by WB analysis in various settings.

Results: Screening of 39 SLAMF1-derived peptides; variants in a human MM cell line revealed several peptides with striking anti-cancer potential. One of these peptides, P7N4, linked to Penetratin for intracellular delivery (P7N4-Pen), was shown to efficiently inhibit the viability and proliferation of both IL-6 dependent (INA-6, ANBL-6, OH-2, IH-1, KJON) and IL-6 independent (U266, JJN3, AMO-1) human MM cell lines. Additionally, P7N4-Pen induced cell death of primary CD138+ tumor cells from patients with MM (obtained with patient consent and REC approval). At the same time, P7N4-Pen showed no toxicity towards human PBMCs from healthy donors. Further, P7N4-Pen strongly inhibited the viability of human MM cells resistant to proteasome inhibitors and showed resilient potential together with the alkylating drug melphalan. The latter allows for a marked dose-reduction of melphalan, which could have strong benefits for patients’ well-being. At the protein level P7N4-Pen induces cleavage of caspase-3 and PARP, H2AX phosphorylation and reduced levels of pro-survival proteins such as c-Myc, β-catenin and IRF4.

Conclusions: Altogether, with the ability to induce cell death and inhibit several central MM survival factors, P7N4-Pen is a promising novel drug-candidate for treatment of MM, which could be tested in the future as monotherapy or in combination with other drugs.