Targeting Molecular Measurable Residual Disease and Low-Blast Relapse in AML With Venetoclax and Low-Dose Cytarabine: A Prospective Phase II Study (VALDAC)

PURPOSE

A prospective phase II study examined the safety and efficacy of venetoclax combined with low-dose cytarabine (LDAC) in AML at first measurable residual disease (MRD) or oligoblastic relapse.

METHODS

Patients with either MRD (≥1 log10 rise) or oligoblastic relapse (blasts 5%-15%) received venetoclax 600 mg once daily D1-28 plus LDAC once daily D1-10 in 28-day cycles. The primary objective was MRD response in the MRD relapse cohort or complete remission (CR/CRh/CRi) in the oligoblastic relapse cohort.

RESULTS

Forty-eight adults with either MRD (n = 26) or oligoblastic (n = 22) relapse were enrolled. Median age was 67 years (range, 18-80) and 94% had received previous intensive chemotherapy. Patients received a median of four cycles of therapy; 17% completed ≥12 cycles. Patients with oligoblastic relapse had more grade ≥3 anemia (32% v 4%; P = .02) and infections (36% v 8%; P = .03), whereas grade 4 neutropenia (32 v 23%) or thrombocytopenia (27 v 15%) were comparable with the MRD relapse cohort. Markers of molecular MRD relapse included mutant NPM1 (77%), CBFB::MYH11 (4%), RUNX1::RUNX1T1 (4%), or KMT2A::MLLT3 (4%). Three patients with a log10 rise in IDH1/2 (12%) were included. By cycle 2 in the MRD relapse cohort, a log10 reduction in MRD was observed in 69%; 46% achieved MRD negative remission. In the oligoblastic relapse cohort, 73% achieved CR/CRh/CRi. Overall, 21 (44%) underwent hematopoietic cell transplantation. Median overall survival (OS) was not reached in either cohort. Estimated 2-year OS rate was 67% (95% CI, 50 to 89) in the MRD and 53% (95% CI, 34 to 84) in the oligoblastic relapse cohorts.

CONCLUSION

For AML in first remission and either MRD or oligoblastic relapse, venetoclax plus LDAC is well tolerated and highly effective.

Combining BH3-mimetics to target both BCL-2 and MCL1 has potent activity in pre-clinical models of acute myeloid leukemia

Improving outcomes in acute myeloid leukemia (AML) remains a major clinical challenge. Overexpression of pro-survival BCL-2 family members rendering transformed cells resistant to cytotoxic drugs is a common theme in cancer. Targeting BCL-2 with the BH3-mimetic venetoclax is active in AML when combined with low-dose chemotherapy or hypomethylating agents. We now report the pre-clinical anti-leukemic efficacy of a novel BCL-2 inhibitor S55746, which demonstrates synergistic pro-apoptotic activity in combination with the MCL1 inhibitor S63845. Activity of the combination was caspase and BAX/BAK dependent, superior to combination with standard cytotoxic AML drugs and active against a broad spectrum of poor risk genotypes, including primary samples from patients with chemoresistant AML. Co-targeting BCL-2 and MCL1 was more effective against leukemic, compared to normal hematopoietic progenitors, suggesting a therapeutic window of activity. Finally, S55746 combined with S63845 prolonged survival in xenograft models of AML and suppressed patient-derived leukemia but not normal hematopoietic cells in bone marrow of engrafted mice. In conclusion, a dual BH3-mimetic approach is feasible, highly synergistic, and active in diverse models of human AML. This approach has strong clinical potential to rapidly suppress leukemia, with reduced toxicity to normal hematopoietic precursors compared to chemotherapy.

Abstract 5283: Elucidating a novel role for inositol polyphosphate 4-phosphatase type II (INPP4B) in mediating chemoresistance in acute myeloid leukemia

Acute myeloid leukaemia (AML) is an aggressive blood cancer that is usually fatal within weeks without effective therapy. Treatment currently involves standard chemotherapy agents such as cytarabine (Ara-C) and anthracyclines but these drugs fail to elicit complete clinical responses in 20-30% of cases. An understanding of the mechanisms in AML mediating resistance to chemotherapy may uncover new oncoproteins amenable to medicinal targeting. Activation of the phosphoinositide 3-kinase (PI3-K)/AKT pathway is prevalent in AML and linked to chemotherapy failure and poor outcomes. Homeostatic regulation of PI3K activity is orchestrated by a triad of lipid phosphatases, categorized functionally as 3-, 4-, or 5-phosphoinositide phosphatases (PIPs). We screened for pathological expression of 3-, 4-, or 5-PIPs in AML using a quantitative multiplexed MassArray platform (Sequenom®) and found marked overexpression of inositol polyphosphate 4-phosphatase II (INPP4B) in a subset of primary AMLs compared to normal bone marrow. Immunohistochemical staining of 120 primary AML bone marrow samples showed INPP4B was overexpressed (>20% blasts positive) in 16% of cases. INPP4B overexpression was associated with an inferior complete response rate to intensive chemotherapy (33%), compared to AMLs low (5-20%; CR 66%) or negative (<5%; CR 93%) for INPP4B. Ectopic overexpression of INPP4B in MV4;11 and HEL AML cells conferred resistance to in vitro cell death (flow-based viability and colony forming capacity) when exposed to standard agents used to treat AML, including cytarabine, daunorubicin and etoposide. High levels of INPP4B in AML also limited the cytotoxic efficacy of drugs such as cytarabine in vivo using human xenograft models of AML. Although INPP4B phosphatase function was proven to be catalytically active in primary AML, expression of a phosphatase inactive mutant (INPP4B C842A) did not abrogate chemoresistance. Conversely, siRNA-mediated knockdown of endogenous INPP4B expression in KG1 and OCI-AML3 AML increased leukemic sensitivity to cytarabine. These findings infer 1) the presence of a novel phosphatase-independent function for this protein and 2) a previously unsuspected role for INPP4B overexpression in mediating chemoresistance and poor clinical outcome in a subset of patients with AML.

Citation Format: Sewa Rijal, Nhu-Y Nugyen, Tse-Chieh Teh, Natalie K. Rynkiewicz, Nik Cummings, Lisa Ooms, Sharon Avery, Julie Mcmanus, Mark A. Guthridge, Catriona Mclean, Christina A. Mitchell*, Andrew Wei*. Elucidating a novel role for inositol polyphosphate 4-phosphatase type II (INPP4B) in mediating chemoresistance in acute myeloid leukemia. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 5283. doi:10.1158/1538-7445.AM2014-5283