Changes in Lognormal Shape Parameter Guide Design of Patient-Specific Radiochemotherapy Cocktails

Uptake of radiopharmaceuticals and chemotherapeutic drugs is nonuniform at the microscopic level. Their distributions are typically lognormal, suggesting that failure in chemotherapy and targeted radionuclide therapy may be attributable, in part, to the characteristics of this biologically ubiquitous distribution. The lognormal problem can be overcome by using cocktails of 2 or more agents, tailored such that at least 1 agent is strongly incorporated by every cell in the target population. Therefore, critical assessment of the tissue uptake of each cocktail component is warranted. Methods: Cellular incorporation of the a-particle–emitting radiochemical (210Po-citrate) and 2 anti-cancer drugs (daunomycin and doxorubicin) was determined using flow cytometry. The role of their lognormal distribution in clonogenic cell survival was evaluated. Results: The shape parameter of the lognormal distribution was found to be corre-lated to both intracellular agent concentration and cell survival. Although no difference emerged between the shape parameters for citrate within the first 2 logs of cell kill, those for daunomycin and doxorubicin changed significantly. Conclusion: Changes in the value of the lognormal shape parameter and slope of the cellular drug uptake curves can be used to rapidly screen radio-pharmaceuticals and other cytotoxic agents to formulate more effective cocktails for cancer therapy. Key Words: radiobiology/dosimetry; radionuclide therapy; dau-nomycin; doxorubicin; flow cytometry; lognormal; polonium-21