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Ovarian reticular cell sarcoma of the mouse (M5076) made resistant to cyclophosphamide
Abstract:
Resistance of mouse M5076 (M5) ovarian reticular cell sarcoma to cyclophosphamide (CTX) was obtained in vivo by repeated drug treatment followed by transplantation of the regrowing tumor. After 16 passages, we obtained an M5 subline resistant to CTX (M5-CTX-16R). Median survival times were approximately 29 and 39 days for M5 and M5-CTX-16R, respectively. Survival of M5-bearing mice given a single i.p. dose of 200 or 300 mg/kg was 160 and 168% of controls, respectively, whereas in M5-CTX-16R it ws 103 and 123%, respectively. The resistance was not reversible after 14 additional passages with no further CTX treatment. M5 and M5-CTX-16R appear similar in histological features, pattern of metastasis formation, and DNA content, as assessed by flow cytometry (hypotetraploid). Metastases of M5-CTX-16R were also resistant to CTX. Flow cytometry studies 12 and 24 hr after CTX treatment revealed a block in S and G2-M phases in both tumors. After 48 hr and at subsequent times, no cytokinetic pertubation was evident in M5-CTX-16R, whereas in M5 marked accumulation of cells in G2-M was observed at 48, 72, 96, and 120 hr. Cross-resistance was found between CTX, L-phenylalanine mustard, chlorambucil, and hexamethylmelamine. M5-CTX-16R was sensitive, but less so than M5, to cis-platinum, 1,3-bis(2-chloroethyl)-1-nitrosourea, and imidazole-4-carboxamide,5-(3,3-dimethyl-1-triazene). Adriamycin was equally active on M5 and M5-CTX-16R, while 4'-demethylepipodophyllotoxin-9-(4,6-O-ethylidine-beta-D-glucopyranoside) was inactive. This model appears to be suitable for studies on the mechanism of resistance to CTX and alkylating agents and for screening new, non-cross-resistant drugs.
Insights
This study developed a mouse ovarian sarcoma subline resistant to cyclophosphamide (CTX). The resistant model is valuable for investigating drug resistance mechanisms and screening new chemotherapy agents.
Area of Science:
- Oncology
- Pharmacology
- Cancer Research
Background:
- Mouse M5076 ovarian reticular cell sarcoma (M5) is a model for studying chemotherapy resistance.
- Acquired resistance to cyclophosphamide (CTX) is a significant clinical challenge in cancer treatment.
Purpose of the Study:
- To develop and characterize a CTX-resistant M5 subline (M5-CTX-16R) for studying drug resistance mechanisms.
- To evaluate the cross-resistance patterns of the M5-CTX-16R subline to various chemotherapeutic agents.
- To assess the suitability of this model for preclinical drug screening.
Main Methods:
- In vivo development of CTX resistance through serial drug treatment and tumor passage.
- Assessment of tumor growth, survival rates, and metastatic patterns in treated and control mice.
- Flow cytometry analysis to evaluate cell cycle kinetics and DNA content.
- In vitro and in vivo drug sensitivity testing against a panel of chemotherapeutic agents.
Main Results:
- A CTX-resistant M5 subline (M5-CTX-16R) was successfully established, exhibiting reduced sensitivity to CTX compared to the parental M5 line.
- M5-CTX-16R showed cross-resistance to other alkylating agents (L-phenylalanine mustard, chlorambucil, hexamethylmelamine) but retained sensitivity to platinum-based drugs and nitrosoureas, albeit reduced.
- The resistant subline displayed altered cell cycle kinetics following CTX treatment, with a transient block in S and G2-M phases.
- Histological features and metastatic patterns remained similar between M5 and M5-CTX-16R, suggesting resistance is not due to major phenotypic changes.
Conclusions:
- The M5-CTX-16R model provides a valuable tool for elucidating the mechanisms underlying acquired resistance to cyclophosphamide and related alkylating agents.
- This model can be utilized for screening novel anticancer drugs that are effective against CTX-resistant tumors.
- Understanding resistance patterns is crucial for optimizing chemotherapy strategies and developing more effective treatments for ovarian cancer.