Pilot Study To Evaluate The Prevalence Of Actionable Oncogenic Mutations In Patients With Relapsed Refractory Multiple Myeloma

Patients with multiple myeloma (MM) have realized improved survival with the development of multi-drug combinations using immunomodulatory drugs (IMiDs), proteasome inhibitors, and alkylating agents. Nevertheless, all MM patients eventually become refractory to available therapies, underscoring the importance of identifying additional rational therapeutic targets. Recent genomic studies using exome/copy number analysis have demonstrated that, at presentation, multiple myeloma is characterized by a dominant plasma cell clone and a heterogeneous group of subclones, with resistance emerging due to altered clonal dominance driven by therapeutic selective pressure or clonal evolution through the acquisition of additional mutational events. This suggests oncogenic mutations in dominant plasma cell clones in multiply relapsed disease may not only be involved in resistance, but should also be prioritized for further clinical development.

We performed a pilot study by sequencing DNA from cryopreserved whole bone marrow aspirate samples obtained pre-treatment from 28 patients with newly diagnosed myeloma (Cohort A) and 27 heavily pre-treated patients enrolled on a phase II clinical study of infusional carfilzomib (NCT01351623), a selective 2^nd generation proteasome inhibitor (Cohort B). Genomic DNA and total RNA was isolated from all patient samples. Adaptor ligated sequencing libraries were captured by solution hybridization using two custom baitsets targeting 374 cancer-related genes and 24 genes frequently rearranged for DNA-seq, and 258 genes frequently rearranged for RNA-seq. All captured libraries were sequenced to high depth (Illumina HiSeq), averaging 712X for DNA and >20,000,000 total pairs for RNA, to enable the sensitive and specific detection of genomic alterations.

Median follow-up for both cohorts was 21 months (26.3m for A; 15.6m for B). Cohort B patients were treated with a median of 5 prior therapies, with 74% refractory to the non-selective 1^st generation proteasome inhibitor bortezomib, 70% refractory to IMiD therapy, and 55% refractory to both therapies. 44% had high-risk cytogenetics. Responses to initial therapy in Cohort A demonstrated that 21%, 7%, and 7%, respectively harbored bortezomib--resistant, IMiD-resistant, or double-resistant myeloma at presentation. 28% of cohort A patients had high risk cytogenetics. We obtained high coverage, high quality sequence data for 54/55 cases and examined alteration prevalence in the 35 samples with sufficient plasma cell content. We observed a high frequency of mutations in the MAPK pathway, including mutually exclusive mutations in NRAS and KRAS in 48% of cases and BRAF V600E mutation in 3%. 14% of cases had TET2 frameshift/nonsense mutations or IDH2 mutations, suggesting the DNA hydroxymethylation pathway is targeted by recurrent somatic mutations in MM. Given that MEK/RAF inhibition has demonstrated efficacy in a spectrum of human tumors and that there are emerging data that epigenetic (decitabine and 5-azacytadine) and targeted (IDH2) therapies offer significant benefit in patients with TET2/IDH mutations, these data demonstrate that mutational profiling can identify patients with actionable mutations that can lead to novel therapies, including mechanism-based clinical trials.

Taken together, we identified mutations in epigenetic modifiers in 41% of the patients in our cohort, including mutations in TET2/IDH, in chromatin modifying enzymes/scaffolds (ARID1A, ASXL1), and DNA methyltransferases (DNMT3A). Moreover, we identified novel mutations in DNA repair pathways (ATM, FANCA, FANCD2) and in FAT3, suggesting there are novel disease alleles, which require functional investigation for their role in MM pathogenesis. No differences in mutation frequency were found between bortezomib sensitive vs resistant MM cases present in either cohort. We did not identify mutations, which impacted progression free and overall survival in this small sample set.

We demonstrate next generation sequencing of unsorted bone marrow samples is feasible in MM and can rapidly identify actionable mutations based on genetic profiling of limited clinical isolates. These include the identification of mutations, which can guide therapeutic trials of clinically targeting specific oncogenic pathways (ex, MAPK or TET2/IDH) on an individual patient level.

Lesokhin:Janssen Pharmaceuticals, Inc: Research Funding; Bristol-Myers Squibb: Consultancy, Research Funding; Foundation Medicine, inc: Consultancy. Brennan:Foundation Medicine, Inc: Employment. Wang:Foundation Medicine, Inc: Employment. Sanford:Foundation Medicine, Inc: Employment. Brennan:Foundation Medicine, Inc: Employment. Otto:Foundation Medicine, Inc: Employment. Nahas:Foundation Medicine, Inc: Employment. Lipson:Foundation Medicine, Inc: Employment. Stephens:Foundation Medicine, Inc: Employment. Yelensky:Foundation Medicine, Inc: Employment. Miller:Foundation Medicine, Inc: Employment. Levine:Foundation Medicine, Inc: Consultancy. Dogan:Foundation Medicine, Inc: Consultancy.