Barriers to Successful Implementation of Precision Medicine to the Treatment of Refractory AML: Lessons Learned

Tremendous genomic heterogeneity has been reported for patients with acute myeloid leukemia (AML), as well as variability in gene expression. We have developed a custom high throughput drug sensitivity (HTS) assay enabling testing of ~150 drugs and combinations, both FDA approved and investigational, including chemotherapy agents and targeted inhibitors. We enrolled advanced relapsed/refractory AML patients (pts) on two successive trials, NCT01872819 "Treatment for Relapsed / Refractory AML Based on a High Throughput Drug Sensitivity Assay" and NCT NCT02551718 "Individualized Treatment for Relapsed/Refractory Acute Leukemia Based on Chemosensitivity and Genomics/Gene Expression Data." The first trial enrolled 16 AML pts (3-5 prior regimens) of whom 14 received single agent study directed treatment, and the second trial (2-6 prior regimens) enrolled 25 AML pts of whom 14 received study directed therapy including drug combinations. We were able to choose chemotherapy drugs for all pts that had IC50's of ≤ 0.1 µM, or regimens that demonstrated synergy for drugs in combination. We have established feasibility as defined by the study, in that HTS assay results were reported at an average of 5.6 days (range 4-10), mutation analysis for 194 genes by MyAML™ reported in 12.5 days (range 9-17) with turnaround from receipt median 8 days (range 7-12) and treatment started at 7.8 (mean), 8 (median) days (range 4-11).

In the first trial, 1 pt (5prior regimens), achieved complete remission with incomplete count recovery (CRi) with the single chosen drug, and 1 achieved CR, 1 CRi with subsequent regimens of additional drugs based on screening and published combinations. Median overall survival (OS) was 88 days for all patients, range 7 to 411. For the 2^nd trial, where combinations were used, there were 2 CRs, 1 CRi and 3 partial responses. Median OS was 122 days, range 19-379. Of the patients in the 1^st trial who had therapy that could have been directed by mutation analysis, there were 4 with FLT3, 1 KIT, 1 IDH2, 1 TP53, 1 FLT3+KIT, 2 FLT3+ IDH2 mutations (10/12 tested). For the 2^nd trial there were 2 pts with FLT3D835, 2 TP53, 2 translocations involving FLT3, 1 IDH2 + FLT3-ITD, 1 FLT3-ITD + IDH1, 1 IDH1, 1 FLT3D839, 1 FLT3-ITD + TP53, 1 IDH2, 1 BCR-ABL (13/17 tested), and one patient received imatinib for BCR-ABL, 2 sorafenib for Flt3 mutations, and 1 with a TP53 mutation received decitabine. We had a number of logistical difficulties, including very advanced disease , poor performance status, inability to obtain the drugs with the lowest IC50's or as directed by mutations due to investigational status or lack of insurance approval, and inability to treat pts who returned home to their local physicians. We observed a higher response rate in pts who received drug combinations (8) vs. single agents (1). Although these were just feasibility trials, we also tried to compare their outcomes to a historical control group. We selected 2 matches for each of our pts, total of 50. They were matched to age, length of CR1, prior HCT, prior intense salvage and prior number of total salvages. One limitation was to find controls that had received ≥3 salvages like some of our studied population. Most of the patients in our clinical trial received single drug therapy (64 vs 24%) and non-intense therapy (4 vs 44%), when compared to our historical control group. Although these were very important treatment differences, the median OS did not differ statistically between both groups (88 vs 115 days, p: 0.327).

We have gathered clinical data, and data on mutation analysis, gene expression, and drug sensitivity testing, that have been analyzed to determine correlations of specific features with drug resistance. Moreover, we have the ability to confirm functional drug sensitivity to the targeted inhibitors based on mutation data. All these data can contribute to future algorithms to assist in optimizing drug choices.

In conclusion, our future iterations of this approach will include 1) only drug combinations, 2) study of pts with only 2 prior regimens, and 3) earlier incorporation of targeted inhibitors such as midostaurin and the new IDH2 inhibitor, enasidenib, into combination regimens. The current salvage options for relapsed/refractory AML have dismal results, as exhibited by our historical control group; only 10% were alive at 1 year. We will therefore pursue alternative approaches for this population, including the optimization of precision medicine methodology.