Preliminary Metabolism of Lomustine in Dogs and Comparative Cytotoxicity of Lomustine and Its Major Metabolites in Canine Cells

L-LOP/LOPP for the treatment of canine gastrointestinal/hepatosplenic lymphoma

Canine gastrointestinal (GI) and hepatosplenic (HS) high-grade (large cell) lymphomas are uncommon forms of canine lymphomas, with a very poor response to chemotherapy and a very poor prognosis. Currently, there are no established effective chemotherapy protocols for canine GI/HS lymphomas. This case series aimed to retrospectively evaluate the efficacy of lomustine-based protocols L-LOP (L-asparaginase, lomustine, vincristine, and prednisolone) and L-LOPP (with the addition of procarbazine) for treatment of canine GI/HS lymphomas. Medical records of dogs with cytologically or histologically diagnosed lymphoma at CityU Veterinary Medical Centre from 2019 to 2022 were retrospectively reviewed. The L-LOP/LOPP treatment protocol was well tolerated with rare severe adverse events. Median progression-free survival for GI and HS lymphoma was 56 days (range, 10-274 days) and 57 days (range 8-135 days) respectively; while median survival time for GI and HS lymphoma was 93 days (range 10-325 days) and 210 days (range 8-240 days) respectively.

Phase I study of procaspase-activating compound-1 (PAC-1) in the treatment of advanced malignancies

BACKGROUND

Procaspase-3 (PC-3) is overexpressed in multiple tumour types and procaspase-activating compound 1 (PAC-1) directly activates PC-3 and induces apoptosis in cancer cells. This report describes the first-in-human, phase I study of PAC-1 assessing maximum tolerated dose, safety, and pharmacokinetics.

METHODS

Modified-Fibonacci dose-escalation 3 + 3 design was used. PAC-1 was administered orally at 7 dose levels (DL) on days 1-21 of a 28-day cycle. Dose-limiting toxicity (DLT) was assessed during the first two cycles of therapy, and pharmacokinetics analysis was conducted on days 1 and 21 of the first cycle. Neurologic and neurocognitive function (NNCF) tests were performed throughout the study.

RESULTS

Forty-eight patients were enrolled with 33 completing ≥2 cycles of therapy and evaluable for DLT. DL 7 (750 mg/day) was established as the recommended phase 2 dose, with grade 1 and 2 neurological adverse events noted, while NNCF testing showed stable neurologic and cognitive evaluations. PAC-1's t1/2 was 28.5 h after multi-dosing, and systemic drug exposures achieved predicted therapeutic concentrations. PAC-1 clinical activity was observed in patients with neuroendocrine tumour (NET) with 2/5 patients achieving durable partial response.

CONCLUSIONS

PAC-1 dose at 750 mg/day was recommended for phase 2 studies. Activity of PAC-1 in treatment-refractory NET warrants further investigation.

CLINICAL TRIAL REGISTRATION

Clinical Trials.gov: NCT02355535.

Biochemical, functional, and histopathologic characterization of lomustine-induced liver injury in dogs

OBJECTIVE

To characterize the biochemical, functional, and histopathologic changes associated with lomustine-induced liver injury in dogs.

ANIMALS

I0 healthy purpose-bred sexually intact female hounds.

PROCEDURES

Dogs were randomly assigned to receive lomustine (approx 75 mg/m², PO, q 21 d for 5 doses) alone (n = 5) or with prednisone (approx 1.5 mg/kg, PO, q 24 h for 12 weeks; 5). For each dog, a CBC, serum biochemical analysis, liver function testing, urinalysis, and ultrasonographic examination of the liver with acquisition of liver biopsy specimens were performed before and at predetermined times during and after lomustine administration. Results were compared between dogs that did and did not receive prednisone.

RESULTS

7 of the I0 dogs developed clinical signs of liver failure. For all dogs, serum alanine aminotransferase (ALT) and alkaline phosphatase (ALP) activities, bile acid concentrations, and liver histologic score increased and hepatic reduced glutathione content decreased over time. Peak serum ALT (r = 0.79) and ALP (r = 0.90) activities and bile acid concentration (r = 0.68) were positively correlated with the final histologic score. Prednisone did not appear to have a protective effect on histologic score.

CONCLUSIONS AND CLINICAL RELEVANCE

In dogs, liver enzyme activities, particularly ALT and ALP activities, should be closely monitored during lomustine treatment and acute increases in those activities may warrant discontinuation of lomustine to mitigate liver injury. Nonspecific ultrasonographic findings and abnormal increases in liver function tests were not detected until the onset of clinical liver failure. Glutathione depletion may have a role in lomustine-induced hepatopathy and warrants further investigation.

Procaspase-3 Overexpression in Cancer: A Paradoxical Observation with Therapeutic Potential

Many anticancer strategies rely on the promotion of apoptosis in cancer cells as a means to shrink tumors. Crucial for apoptotic function are executioner caspases, most notably caspase-3, that proteolyze a variety of proteins, inducing cell death. Paradoxically, overexpression of procaspase-3 (PC-3), the low-activity zymogen precursor to caspase-3, has been reported in a variety of cancer types. Until recently, this counterintuitive overexpression of a pro-apoptotic protein in cancer has been puzzling. Recent studies suggest subapoptotic caspase-3 activity may promote oncogenic transformation, a possible explanation for the enigmatic overexpression of PC-3. Herein, the overexpression of PC-3 in cancer and its mechanistic basis is reviewed; collectively, the data suggest the potential for exploitation of PC-3 overexpression with PC-3 activators as a targeted anticancer strategy.

Alkylation and Carbamylation Effects of Lomustine and Its Major Metabolites and MGMT Expression in Canine Cells

DNA Alkylation is thought to be the reason for the efficacy of lomustine while carbamylation has been implicated as the cause for the side effects seen with lomustine treatment such as hepatotoxicity. In the alkylation study we show that lomustine and its metabolites form similar levels of the DNA adducts N⁷ hydroxyethylguanine and O⁶ hydroxyethyldeoxyguanosine. In terms of carbamylation, lomustine showed greater extent of carbamylation in the canine hepatocytes and lymphoma cell lines. The DNA repair enzyme O⁶ methylguanine DNA methyltransferase (MGMT) causes resistance of tumor cells to bifunctional nitrosourea, like lomustine. There is no data available regarding MGMT expression/activity in canine cells or tissues. Our study shows that there is low MGMT activity in the canine lymphoid cell line 17-71 while the GL-1 cells did not show any detectable enzyme activity or mRNA expression. The MGMT enzyme activity measured in canine hepatocytes is about 250-350 fmol/mg protein as compared to about 90 fmol/mg protein in 17-71 cells. We also show that MGMT mRNA expression in 17-71 cells and canine hepatocytes positively correlates with its enzyme activity in these cells.