Combination photoimmunotherapy and cisplatin: effects on human ovarian cancer ex vivo.
BACKGROUND
Patients with ovarian cancer that is clinically resistant to cisplatin-based chemotherapy have little hope of a cure of their disease. Photoimmunotherapy, which involves the antibody-targeted delivery of a nontoxic photosensitizer that is activated to a cytotoxic state with visible light, may offer a new treatment option. Photoimmunotherapy may be applied intraperitoneally to target disseminated tumor. We tested the hypothesis that this treatment in combination with cisplatin potentiates cytotoxicity in ovarian cancer cell lines and primary cultures of human tumors.


METHODS
Five human cancer cell lines (ovarian and breast) and 19 primary cultures were studied. The primary cultures were from solid and ascites tumor samples obtained from 14 patients with ovarian cancer who were undergoing primary surgery. The photosensitizer chlorin e(6) was conjugated to the F(ab')(2) fragment of the murine monoclonal antibody OC-125, which is directed against the antigen CA 125. Cytotoxicity was measured by the microculture tetrazolium assay. Treatments consisted of cisplatin alone, photoimmunotherapy alone, and photoimmunotherapy followed by cisplatin. The fractional product method was used to assess synergy in treatment effects. Ex vivo cultured human cells exhibiting 80% or greater survival at cisplatin concentrations of 10 microM for 24 hours were defined as cisplatin resistant for this study.


RESULTS
When all cell types (cisplatin sensitive and cisplatin resistant) were considered together, combination treatment yielded cytotoxicity that was, on average, 6.9 times (95% confidence interval = 1.86-11.94) greater than that of cisplatin alone (two-sided P =.023). Cisplatin-resistant cells showed a synergistic effect of the two treatments (two-sided P =.044), while cisplatin-sensitive cells showed an additive effect.


CONCLUSIONS
These ex vivo data suggest that platinum resistance in human ovarian cancer cells may be reversible by pretreatment with OC-125-targeted photoimmunotherapy. Further studies are required to confirm the efficacy of this approach in vivo.
Duska
L R
LR
Wellman Laboratories of Photomedicine and Vincent Memorial Obstetrics and Gynecology Service, Harvard Medical School, Massachusetts General Hospital, Boston 02114, USA.
Hamblin
M R
MR
Miller
J L
JL
Hasan
T
T
D000911:Antibodies, Monoclonal / Q000627:therapeutic use*; D000970:Antineoplastic Agents / Q000627:therapeutic use*; D001943:Breast Neoplasms / Q000628:therapy*; D018394:CA-125 Antigen / Q000276:immunology*; D002735:Chlorophyllides; D002945:Cisplatin / Q000627:therapeutic use*; D003131:Combined Modality Therapy; D019008:Drug Resistance, Neoplasm; D005260:Female; D019084:Fluorescent Antibody Technique, Indirect; D006801:Humans; D007167:Immunotherapy / Q000379:methods*; D010051:Ovarian Neoplasms / Q000628:therapy*; D017319:Photosensitizing Agents / Q000627:therapeutic use*; D010789:Phototherapy / Q000379:methods*; D011166:Porphyrins / Q000627:therapeutic use*; D016896:Treatment Outcome; D014407:Tumor Cells, Cultured
D000911:Antibodies, Monoclonal; D000970:Antineoplastic Agents; D018394:CA-125 Antigen; D002735:Chlorophyllides; D017319:Photosensitizing Agents; D011166:Porphyrins; C062985:phytochlorin; D002945:Cisplatin