Oncotelic Therapeutics Inc (OTLC)

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OXi4503 for Acute Myeloid Leukemia

 

OXi4503 (combretastatin A1-diphsphate; CA1P) is a novel investigational vascular disrupting agent (“VDA”) that has been shown to have a significant in vitro cytotoxic as well as chemo-sensitizing activity against human Acute Myeloid Leukemia (“AML”) cells. OXi4503 also exhibited in vivo anti-leukemic activity in xenografted mice with human AML.

 

OXi4503 employs a new, broader strategy against AML than currently exists for standard chemotherapy, as it provides a dual mechanism of action involving both anti-vascular effects and direct cytotoxicity to AML cells. Vascular and/or Bone marrow endothelial cells (“ECs”) appear to provide a protective effect for AML cells, keeping them dormant within the bone marrow. VDAs may target these ECs and reverse their chemo protective effect, providing a novel approach to the treatment of AML which may otherwise be resistant to other chemotherapeutic therapies. Preclinical data indicate that OXi4503 alone and in combination with traditional AML treatments such as cytarabine may provide significant benefit in eliminating AML cells. Results from two completed Phase I clinical trials demonstrated the clinical impact potential of OXi4503 against relapsed AML when it is alone or in combination with the standard chemotherapy drug cytarabine (“ARA-C”) can induce complete remissions in relapsed AML patients. Notably, OXi4503 showed single agent activity in a clinical Phase I trial and resulted in complete remission of a relapsed AML patient. Sustained complete remissions were also achieved in relapsed AML patients who were treated with OXi4503 in combination with ARA-C.

 

OXi4503 has received orphan designation for AML in both the United States (Designation No. 12-3824) and the European Union (Designation No. EU/3/15/1587 - EMA/OD/144/15). In 2017, the FDA has granted fast-track designation to OXi4503 for the treatment of relapsed/refractory AML. Oxi4503 met the qualifying criteria for the Fast Track designation since AML is a serious and life-threatening condition, and a large unmet medical need exists for additional treatment strategies for this disease.

 

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The Investigator-Sponsored trial (IST) UF OXi4503 AML MDS Ph 1 (UF4503), “A Phase 1 Clinical Trial of OXi4503 for Relapsed and Refractory AML and Myelodysplastic Syndromes (“MDS”) was designed to evaluate the safety profile and the maximum tolerated dose (“I”) as well as a recommended Phase 2 dose (RP2D) of OXi4503 in patients with recurrent/refractory (R/R) AML and MDS (ClinicalTrials.gov NCT01085656) (14, 50). The clinical single agent activity of OXi4503 was also assessed within the confines of a Phase 1 clinical trial setting. A total of 18 patients enrolled in the study from February 2011 to January 2016. The patients were predominantly male (78%) and the median age was 62.5 years. Of the 15 patients with AML, 4 (27%) had primary refractory AML, 2 (13%) were in first relapse, and 9 (60%) had refractory AML beyond CR1.

 

Eight patients (44%) completed at least one cycle of CA1P and were evaluable for efficacy assessments. Of the eight patients evaluable, one achieved morphologic remission with incomplete blood count recovery (“CRi”) after 1 cycle but came off study in cycle 2 due to fungal pneumonia. Three patients had stable disease after at least one cycle of CA1P. Three patients experienced progressive disease after 1 cycle of CA1P and were withdrawn from the study.

 

The Phase 1 dose-escalation combination of the Company sponsored study OX1222 (NCT02576301) was a Phase 1b dose escalation study of OXi4503 as a single agent and in combination with Cytarabine with subsequent combination Phase 2 cohorts for subjects with relapsed/refractory (R/R) AML and MDS. 29 subjects were treated with OXi4503 in combination with Cytarabine.

 

Of these 29 patients, one was evaluable for safety analysis, but no EFS/OS data or response data were available for activity evaluations. Of the 28 patients evaluable for EFS/OS outcome analyses, 26 had AML and 2 had MDS. For the 26 AML patients, there were 4 CRs. The CR responses were associated with prolonged overall survival substantially better the median OS time: One patient who became eligible for allogeneic PBSCT remains alive, free-of-leukemia at 720+ days. The overall survival times were 434 days, 521 days, 535 days and 720 days, respectively. The median OS time for the 4 patients who achieved a CR/CRi was 528 (95% CI: 434 - NA) days which was significantly better than the median OS time of 113 (95% CI: 77 - 172) days for the remaining 22 AML patients who did not achieve a CR (Log Rank = 11.8, P-value = 0.0006).

 

Three of the 4 CR/CRis were achieved in 1st relapse patients while one patient with CRi had failed 5 previous regimens, including 7:3, HiDAC, and PBSCT. Patients who achieved a CR/CRi went on to receive other treatments after receiving 4-6 cycles of OXi4503. The median OS for all 26 AML patients who received therapy was 119 (95% CI: 87 - 232) days. Patients who had rapidly progressive disease or developed toxicity could not get as many OXi4503 doses as patients who responded to their treatment favorably. The median OS time for 18 patients receiving 1-3 doses Of OXi4503 was 82 (95% CI: 66 - 135) days and these patients exhibited a worse survival outcome compared to 9 patients receiving 4-6 doses which was recorded at 434 (95% CI: 191 - NA) days (Log Rank = 12.3, P-value = 0.0004).