Multiple Myeloma-Specific Targeted Therapy: Use of the Tumor Specific Immunoglobulin Gene Sequence to Activate Drugs Only within Tumor Cells.
Authors: Li Zhi-Wei , Shalitin Dror , Finefield Jennifer , Leung Crystal , Hu Mengyin , Shen Jing , Li Mingjie , Wang Cathy S , Steinberg Jeffrey A , Sanchez Eric , Chen Haiming , Williams Robert M , Bonavida Benjamin , Berenson James R. 
Published: October 2019

Abstract
Abstract 1851
Poster Board I-877
Currently available drugs for multiple myeloma (MM) treatment show very little ability to distinguish MM cells from normal cells. This limits the dose of drugs with anti-MM activity that can be administered safely; and, thus, reduces their efficacy in eliminating the malignant plasma cell population. Therefore, novel strategies are needed that allow concentrations of higher levels of active drugs within tumor cells than in other healthy cells. One approach is to allow release of active drugs only within the tumor cells in these patients without affecting nonmalignant cells. MM is a malignancy of clonal antibody-secreting plasma cells with specific rearrangement of DNA that is transcribed into a unique mRNA sequence that is translated into the tumor specific monoclonal antibody. These tumor specific transcripts are abundant in all of the malignant cells in these patients. We have explored the possibility of using a unique sequence from this tumor specific transcript, the complementarity determining region (CDR) gene sequence, to direct drug release only within MM cells. First, we determined whether this type of tumor specific oligonucleotide could specifically recognize the tumor cell population. Using a quenched fluorescein-labeled oligonucleotide sequence complementary to the CDR3 gene sequence from the MM cell line RPMI8226 as a probe (designated as molecular beacon [MB] 8226), we demonstrated that this oligonucleotide specifically distinguished the RPMI8226 from other cell lines, including U266, another MM cell line. Second, in order to translate this approach into potentially therapeutically active anti-MM agents, we synthesized naphthyridine-modified (N) vorinostat, a FDA-approved histone deacetylase inhibitor, and N-melphalan. The modification allowed us to conjugate vorinostat or melphalan, two drugs currently used in MM treatment, with MB8226. Histone acetylation analysis demonstrated that the modification of vorinostat with naphthyridine did not change its function compared to the unmodified compound. Moreover, using cell viability and apoptosis assays, there was no reduction in the cytotoxic effects of N-vorinostat or N-melphalan compared to the parent drugs. In addition, induction of cell death occurred in a cell specific matter with N-melphalan conjugated to its tumor specific oligonucleotide. Upon transfection with N-melphalan-conjugated MB8226, only RPMI8226 but not U266 cells showed cytotoxic effects from exposure to this tumor specific cytotoxic construct. We are currently evaluating the specific efficacy of N-vorinostat-conjugated MB8226 as well as an oligonucleotide that specifically recognizes the CDR3 sequence of U266 cells conjugated with N-vorinostat or N-melphalan. We are also determining the efficacy of this approach in vivo using our severe combined immunodeficiency-hu mouse models of human MM. Our studies provide a novel targeted therapeutic approach for the treatment MM as well as other B cell malignancies that should specifically be active only within the malignant cell population and not impact nonmalignant cells. This type of treatment should allow delivery of higher concentrations of drugs that will be active only within tumor cells ultimately leading to both much more effective and better tolerated therapies for patients with MM and other B-cell malignancies.

Disclosures:
No relevant conflicts of interest to declare.