Vinblastin and vincristin inhibit growth of cancer cells by

Options

A. Inducing contact inhibition
B. Arresting cell division through inhibition of spindle formation
C. Suppression of oncogenes
D. Activating protooncogenes

Answer

To solve the question about how vinblastine and vincristine inhibit the growth of cancer cells, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Role of Vinblastine and Vincristine**:
- Vinblastine and vincristine are alkaloids derived from the periwinkle plant (Catharanthus roseus) and are commonly used in chemotherapy to treat various types of cancer.

2. **Mechanism of Action**:
- These drugs primarily work by affecting the process of cell division, specifically during mitosis. They disrupt the normal function of the mitotic spindle, which is crucial for the separation of chromosomes during cell division.

3. **Inhibition of Spindle Formation**:
- Vinblastine and vincristine inhibit the polymerization of tubulin into microtubules, which are essential components of the spindle apparatus. Without proper spindle formation, cells cannot complete mitosis, leading to cell cycle arrest.

4. **Conclusion**:
- Given the options provided in the question, the correct answer is:
- **B. Arresting cell division through inhibition of spindle formation**. This is because the primary mechanism by which these drugs inhibit cancer cell growth is through their effect on the mitotic spindle.