Strategy could reduce myelosuppression in AML

Lab mouse

Researchers believe they may have found a way to prevent chemotherapy-induced myelosuppression in acute myeloid leukemia (AML).

The team found that priming mice with the FLT3 inhibitor quizartinib protected multipotent progenitor cells (MPPs) from subsequent treatment with fluorouracil (5-FU) or gemcitabine.

And treatment with quizartinib followed by 5-FU proved more effective against AML than standard induction with cytarabine and doxorubicin.

Samuel Taylor, of the University of Western Australia in Crawley, Australia, and his colleagues reported these results in Science Translational Medicine.

The researchers first found that quizartinib induced “rapid and transient” quiescence of MPPs in C57BL/6 mice.

Quizartinib also provided MPPs with “marked protection” from 5-FU. In these experiments, a 10 mg/kg dose of quizartinib was given to mice at the same time as a 150 mg/kg dose of 5-FU. This treatment provided MPPs with 4- to 5-fold greater protection than vehicle control.

Subsequent experiments revealed the optimal dose and schedule for quizartinib. A priming dose of 30 mg/kg given 6 hours before 5-FU provided “slightly greater” protection to hematopoietic stem and progenitor cells than a 10 mg/kg dose, with significantly greater protection observed for short-term hematopoietic stem cells.

The researchers then showed that priming with quizartinib allowed for “rapid recovery of bone marrow cellularity” after treatment with 5-FU. Bone marrow cells were fully restored by day 8 after treatment in quizartinib-primed mice but not in vehicle-primed mice.

Quizartinib priming also protected mice from multiple rounds of treatment with 5-FU (15 cycles in some mice) and from myelosuppression induced by gemcitabine.

Finally, the researchers tested quizartinib followed by 5-FU in mouse models of AML. They found the treatment was more effective than treatment with cytarabine and doxorubicin in both FLT3-ITD(F692L)/NPM1c AML and NPM1c/Nras^G12D AML.

FLT3-ITD(F692L)/NPM1c AML

The researchers transplanted 15 non-irradiated B6.CD45.1 mice with 3 × 10⁵ spleen cells each from a FLT3-ITD(F691L)/NPM1c mouse that succumbed to AML at 6 weeks of age. Sixteen days after transplant, the mice were given one of the following:

• No treatment
• 10-day cycles of quizartinib (30 mg/kg) followed 6 hours later by 5-FU (150 mg/kg)
• Cytarabine plus doxorubicin (5+3).

All 5 of the untreated mice died within 30 days of transplantation, exhibiting high white blood cell (WBC) counts and splenomegaly.

The 5+3 mice received 2 cycles of treatment (days 16 to 21 and 36 to 41). All 5 had died by day 56 after transplantation, with high WBC counts and splenomegaly.

One the other hand, 4 of the 5 mice in the quizartinib/5-FU arm were still healthy at 176 days after transplantation and 80 days after stopping treatment. There were no detectable CD45.2+ AML cells when the mice were last bled on day 160, and they had normal WBC counts. There were no AML cells detectable in the animals’ bone marrow after they were killed at day 176.

The quizartinib/5-FU mouse that died before day 176 is believed to have developed resistance to 5-FU. This animal died 121 days after transplantation.

NPM1c/ Nras^G12D AML

For another AML model, the researchers crossed NPM1c-mutant mice with Nras^G12D-mutant mice. The team transplanted spleen cells from NPM1c/Nras^G12D leukemic mice into 15 non-irradiated B6.CD45.1 recipient mice.

Fifteen days after transplantation, the NPM1c/ Nras^G12D mice received one of the following:

• No treatment
• Quizartinib and 5-FU as above
• Cytarabine plus doxorubicin (5+3).

All 5 untreated mice died by day 32 after transplantation, and all 5 mice that received 5+3 died by day 35. Both groups of mice had high WBC counts and splenomegaly.

Mice in the quizartinib/5-FU arm initially received 4 cycles of treatment, starting on days 15, 25, 35, and 45 after transplantation. On day 53, they had minimal or undetectable numbers of CD45.2+ AML cells, and WBC counts were normal or slightly below normal.

At day 81—a month after stopping treatment—4 of the mice had detectable CD45.2+ AML cells in their blood. So they restarted treatment the next day. After 4 additional cycles, AML cells were undetectable in all 5 mice. At day 146—a month after stopping the second round of treatment—AML cells again became detectable in the blood.

The mice did not receive any additional treatment. One died at day 196, and 1 was killed at day 197 due to weight loss related to feeding difficulties (but this mouse did not show signs of AML).

The other 3 mice were “active and healthy” until they were killed at day 214. However, they had “high proportions” of CD45.2+ myeloid cells in their blood since day 183. And 2 of the mice had increased WBC counts from day 197.

Lab mouse

Researchers believe they may have found a way to prevent chemotherapy-induced myelosuppression in acute myeloid leukemia (AML).

The team found that priming mice with the FLT3 inhibitor quizartinib protected multipotent progenitor cells (MPPs) from subsequent treatment with fluorouracil (5-FU) or gemcitabine.

And treatment with quizartinib followed by 5-FU proved more effective against AML than standard induction with cytarabine and doxorubicin.

Samuel Taylor, of the University of Western Australia in Crawley, Australia, and his colleagues reported these results in Science Translational Medicine.

The researchers first found that quizartinib induced “rapid and transient” quiescence of MPPs in C57BL/6 mice.

Quizartinib also provided MPPs with “marked protection” from 5-FU. In these experiments, a 10 mg/kg dose of quizartinib was given to mice at the same time as a 150 mg/kg dose of 5-FU. This treatment provided MPPs with 4- to 5-fold greater protection than vehicle control.

Subsequent experiments revealed the optimal dose and schedule for quizartinib. A priming dose of 30 mg/kg given 6 hours before 5-FU provided “slightly greater” protection to hematopoietic stem and progenitor cells than a 10 mg/kg dose, with significantly greater protection observed for short-term hematopoietic stem cells.

The researchers then showed that priming with quizartinib allowed for “rapid recovery of bone marrow cellularity” after treatment with 5-FU. Bone marrow cells were fully restored by day 8 after treatment in quizartinib-primed mice but not in vehicle-primed mice.

Quizartinib priming also protected mice from multiple rounds of treatment with 5-FU (15 cycles in some mice) and from myelosuppression induced by gemcitabine.

Finally, the researchers tested quizartinib followed by 5-FU in mouse models of AML. They found the treatment was more effective than treatment with cytarabine and doxorubicin in both FLT3-ITD(F692L)/NPM1c AML and NPM1c/Nras^G12D AML.

FLT3-ITD(F692L)/NPM1c AML

The researchers transplanted 15 non-irradiated B6.CD45.1 mice with 3 × 10⁵ spleen cells each from a FLT3-ITD(F691L)/NPM1c mouse that succumbed to AML at 6 weeks of age. Sixteen days after transplant, the mice were given one of the following:

• No treatment
• 10-day cycles of quizartinib (30 mg/kg) followed 6 hours later by 5-FU (150 mg/kg)
• Cytarabine plus doxorubicin (5+3).

All 5 of the untreated mice died within 30 days of transplantation, exhibiting high white blood cell (WBC) counts and splenomegaly.

The 5+3 mice received 2 cycles of treatment (days 16 to 21 and 36 to 41). All 5 had died by day 56 after transplantation, with high WBC counts and splenomegaly.

One the other hand, 4 of the 5 mice in the quizartinib/5-FU arm were still healthy at 176 days after transplantation and 80 days after stopping treatment. There were no detectable CD45.2+ AML cells when the mice were last bled on day 160, and they had normal WBC counts. There were no AML cells detectable in the animals’ bone marrow after they were killed at day 176.

The quizartinib/5-FU mouse that died before day 176 is believed to have developed resistance to 5-FU. This animal died 121 days after transplantation.

NPM1c/ Nras^G12D AML

For another AML model, the researchers crossed NPM1c-mutant mice with Nras^G12D-mutant mice. The team transplanted spleen cells from NPM1c/Nras^G12D leukemic mice into 15 non-irradiated B6.CD45.1 recipient mice.

Fifteen days after transplantation, the NPM1c/ Nras^G12D mice received one of the following:

• No treatment
• Quizartinib and 5-FU as above
• Cytarabine plus doxorubicin (5+3).

All 5 untreated mice died by day 32 after transplantation, and all 5 mice that received 5+3 died by day 35. Both groups of mice had high WBC counts and splenomegaly.

Mice in the quizartinib/5-FU arm initially received 4 cycles of treatment, starting on days 15, 25, 35, and 45 after transplantation. On day 53, they had minimal or undetectable numbers of CD45.2+ AML cells, and WBC counts were normal or slightly below normal.

At day 81—a month after stopping treatment—4 of the mice had detectable CD45.2+ AML cells in their blood. So they restarted treatment the next day. After 4 additional cycles, AML cells were undetectable in all 5 mice. At day 146—a month after stopping the second round of treatment—AML cells again became detectable in the blood.

The mice did not receive any additional treatment. One died at day 196, and 1 was killed at day 197 due to weight loss related to feeding difficulties (but this mouse did not show signs of AML).

The other 3 mice were “active and healthy” until they were killed at day 214. However, they had “high proportions” of CD45.2+ myeloid cells in their blood since day 183. And 2 of the mice had increased WBC counts from day 197.

Lab mouse

Researchers believe they may have found a way to prevent chemotherapy-induced myelosuppression in acute myeloid leukemia (AML).

The team found that priming mice with the FLT3 inhibitor quizartinib protected multipotent progenitor cells (MPPs) from subsequent treatment with fluorouracil (5-FU) or gemcitabine.

And treatment with quizartinib followed by 5-FU proved more effective against AML than standard induction with cytarabine and doxorubicin.

Samuel Taylor, of the University of Western Australia in Crawley, Australia, and his colleagues reported these results in Science Translational Medicine.

The researchers first found that quizartinib induced “rapid and transient” quiescence of MPPs in C57BL/6 mice.

Quizartinib also provided MPPs with “marked protection” from 5-FU. In these experiments, a 10 mg/kg dose of quizartinib was given to mice at the same time as a 150 mg/kg dose of 5-FU. This treatment provided MPPs with 4- to 5-fold greater protection than vehicle control.

Subsequent experiments revealed the optimal dose and schedule for quizartinib. A priming dose of 30 mg/kg given 6 hours before 5-FU provided “slightly greater” protection to hematopoietic stem and progenitor cells than a 10 mg/kg dose, with significantly greater protection observed for short-term hematopoietic stem cells.

The researchers then showed that priming with quizartinib allowed for “rapid recovery of bone marrow cellularity” after treatment with 5-FU. Bone marrow cells were fully restored by day 8 after treatment in quizartinib-primed mice but not in vehicle-primed mice.

Quizartinib priming also protected mice from multiple rounds of treatment with 5-FU (15 cycles in some mice) and from myelosuppression induced by gemcitabine.

Finally, the researchers tested quizartinib followed by 5-FU in mouse models of AML. They found the treatment was more effective than treatment with cytarabine and doxorubicin in both FLT3-ITD(F692L)/NPM1c AML and NPM1c/Nras^G12D AML.

FLT3-ITD(F692L)/NPM1c AML

The researchers transplanted 15 non-irradiated B6.CD45.1 mice with 3 × 10⁵ spleen cells each from a FLT3-ITD(F691L)/NPM1c mouse that succumbed to AML at 6 weeks of age. Sixteen days after transplant, the mice were given one of the following:

• No treatment
• 10-day cycles of quizartinib (30 mg/kg) followed 6 hours later by 5-FU (150 mg/kg)
• Cytarabine plus doxorubicin (5+3).

All 5 of the untreated mice died within 30 days of transplantation, exhibiting high white blood cell (WBC) counts and splenomegaly.

The 5+3 mice received 2 cycles of treatment (days 16 to 21 and 36 to 41). All 5 had died by day 56 after transplantation, with high WBC counts and splenomegaly.

One the other hand, 4 of the 5 mice in the quizartinib/5-FU arm were still healthy at 176 days after transplantation and 80 days after stopping treatment. There were no detectable CD45.2+ AML cells when the mice were last bled on day 160, and they had normal WBC counts. There were no AML cells detectable in the animals’ bone marrow after they were killed at day 176.

The quizartinib/5-FU mouse that died before day 176 is believed to have developed resistance to 5-FU. This animal died 121 days after transplantation.

NPM1c/ Nras^G12D AML

For another AML model, the researchers crossed NPM1c-mutant mice with Nras^G12D-mutant mice. The team transplanted spleen cells from NPM1c/Nras^G12D leukemic mice into 15 non-irradiated B6.CD45.1 recipient mice.

Fifteen days after transplantation, the NPM1c/ Nras^G12D mice received one of the following:

• No treatment
• Quizartinib and 5-FU as above
• Cytarabine plus doxorubicin (5+3).

All 5 untreated mice died by day 32 after transplantation, and all 5 mice that received 5+3 died by day 35. Both groups of mice had high WBC counts and splenomegaly.

Mice in the quizartinib/5-FU arm initially received 4 cycles of treatment, starting on days 15, 25, 35, and 45 after transplantation. On day 53, they had minimal or undetectable numbers of CD45.2+ AML cells, and WBC counts were normal or slightly below normal.

At day 81—a month after stopping treatment—4 of the mice had detectable CD45.2+ AML cells in their blood. So they restarted treatment the next day. After 4 additional cycles, AML cells were undetectable in all 5 mice. At day 146—a month after stopping the second round of treatment—AML cells again became detectable in the blood.

The mice did not receive any additional treatment. One died at day 196, and 1 was killed at day 197 due to weight loss related to feeding difficulties (but this mouse did not show signs of AML).

The other 3 mice were “active and healthy” until they were killed at day 214. However, they had “high proportions” of CD45.2+ myeloid cells in their blood since day 183. And 2 of the mice had increased WBC counts from day 197.