PHILADELPHIA—A drug that targets the ribosome may be active in a broad range of hematologic malignancies, researchers say.
The drug, CX-5461, inhibits the protein RNA polymerase I (Pol I), which is consistently upregulated in hematologic and other cancers.
CX-5461 significantly prolonged survival in mouse models of refractory acute myeloid leukemia (AML) and multiple myeloma (MM). It also synergized with everolimus to extend survival in mice with B-cell lymphoma.
Furthermore, the drug did not elicit severe adverse effects.
“We were excited to find that therapeutic doses of CX-5461 had little effect on normal cells in our experiments,” said Ross D. Hannan, PhD, of the Peter MacCallum Cancer Centre in Melbourne, Australia,
“Prior to these studies, few people would have guessed that such a therapeutic window could be obtained by targeting a so-called house-keeping protein that is essential to all cells for survival.”
Dr Hannan and his colleagues presented these findings in a poster at the AACR conference Hematologic Malignancies: Translating Discoveries to Novel Therapies.
The researchers previously showed that cancer cells are much more dependent on ribosome biogenesis than normal cells. And blocking the accelerated reading of ribosomal genes in mice—using CX5461—can cause lymphoma and leukemia cells to die, while sparing normal cells.
With their latest research, the group expanded upon these findings by testing CX-5461 in MLL-driven AML, V*κ-Myc-driven MM, and Eμ-Myc lymphoma.
They found that CX-5461 improved overall survival in MLL/ENL Nras leukemic mice, compared to placebo and standard therapy. The median survival was 17 days for vehicle-treated mice, 21 days for mice treated with cytarabine and doxorubicin, and 36 days for mice that received CX-5461 (P<0.0001 for vehicle vs CX-5461).
CX-5461 treated MLL-driven AML by inducing apoptosis, delaying cell-cycle progression, and promoting differentiation.
The researchers also found the therapeutic benefit of CX-5461 is not p53-dependent, which contradicts their previous findings. Human AML cell lines and primary patient samples were sensitive to CX-5461 independent of p53 status.
And MLL/ENL Nras p53-/- leukemic mice had significantly prolonged survival when treated with CX-5461, compared to vehicle-treated controls. The median survival was 11 days and 24 days, respectively (P<0.0001).
Likewise, CX-5461 significantly prolonged survival in mice bearing V*κ-Myc MM. The median survival was 103.5 days for controls and 175 days for mice that received CX-5461 (P<0.0001).
Finally, the researchers showed that CX-5461 synergizes with everolimus to treat Eμ-Myc lymphoma. The median survival was 15 days in control mice, 18 days in mice that received everolimus, 32 days in mice treated with CX-5461, and 54 days in mice that received both drugs (P<0.0001 for CX-5461 vs the combination).
“These results provide further rationale for the first-in-human phase 1 clinical trial that we initiated in July 2013 testing CX-5461 for patients with advanced hematological malignancies, including AML and multiple myeloma,” Dr Hannan said.
His group’s preclinical research was funded by the National Health and Medical Research Council, Australia; the Leukaemia Foundation of Australia; and Cancer Council Victoria, Melbourne, Australia. Senhwa Biosciences, the makers of CX-5461, provided the drug.
